I. Climate Research, a Major Challenge

The Earth and the environment

Institutions and organizations: Who does what?

Agence nationale de la recherche (ANR): the French National Agency les rayonnements ionisants). It fulfils research and audit remits with for Research, a public-sector administrative establishment (set up in regard to nuclear and radiological risks. Drawing on over 30 years’ 2005 as a public-interest group), charged with funding research pro- experience with earthquakes, IRSN conducts research on earthquake jects, selected on scientific and economic criteria. hazards, with regard to nuclear installation safety and protection. Airparif: the air quality monitoring network for the Île-de-France Institut français de recherche pour l’exploitation de la mer (IFREMER): region (i.e. the region around Paris). the French Research Institute for the Use of Marine Resources, an Autorité de sûreté nucléaire (ASN): the French Nuclear Safety organization contributing, through its work and expertise, to know - Authority, an independent state administration set up to oversee civil ledge of the oceans and their resources, to the monitoring of nuclear activities, in France, under the aegis of the French Act of marine and coastal environments, and to the sustainable develop- 13 June 2006 on transparency and safety in nuclear matters. ASN ment of maritime activities. For these remits, IFREMER designs and monitors, on behalf of the French state, nuclear safety and radio- deploys instruments for observational, experimental, and monitoring protection, to ensure the protection of workers, patients, the popu- purposes, and runs the French oceanographic fleet, on behalf of the lation and the environment from nuclear activities-related hazards. scientific community as a whole, along with managing oceano graphic databases. Beijing Municipal Environmental Monitoring Center: the local authority establishment charged with air quality monitoring, in like man- Institut géographique national (IGN): the French National Geographical ner to Airparif in the Paris (France) region. Institute, a public-sector administrative establishment, having the Bureau de recherches géologiques et minières (BRGM): the French purpose of providing a description, in both geometric and physical Office of Geological and Mining Research, a public-sector establish- terms, of the surface of the French national territory and its land use. ment of industrial and commercial character, serving as reference One of its remits is the deployment and maintenance of geodetic and in the area of Earth sciences, with regard to resource management, leveling networks, related to the national geographical, planimetric and soil, and underground risk management. and altimetric coordinate reference system, and making available the corresponding information. Centre d’études techniques maritimes et fluviales (CETMEF): the French Center for Maritime and Waterways Technical Studies, char- Institute of Atmospheric Physics in Beijing: a laboratory coming ged, on behalf of all agencies of the French Ministry of Infrastructures, under the Chinese Academy of Sciences, concerned with scientific with developing and disseminating techniques, carrying out studies issues relating to the physicochemistry of the Earth’s atmosphere. and research, and providing engineering and audit services in the International Atomic Energy Authority (IAEA): an intergovernmen- areas of marine and waterway engineering and structures, marine tal agency, acting, under the aegis of the United Nations, for the pea- and waterway hydraulic phenomena, safety aids and systems, with ceful uses of nuclear power, and compliance with the Nonproliferation regard to maritime and inland navigation, transmissions, electronic Treaty. communications and satellite technologies. International Data Center (IDC): the body collecting the data coming Centre national d’études spatiales (CNES): the French National Space from stations set up under the Comprehensive Nuclear Test Ban Treaty Research Center, a public-sector establishment of industrial and (CTBT), and making these data available to the Treaty’s signatory commercial character, charged with implementing France’s space governments. policy. International Seismological Center (ISC): a nongovernmental orga- Centre national de la recherche scientifique (CNRS): a public-sec- nization, charged with the final collection, analysis and publication of tor establishment of scientific and technological character, carrying standard earthquake information from all around the world. out its research activity in all fields of knowledge. The National Institute International Water Management Institute: a nongovernmental orga- for the Sciences of the Universe (INSU: Institut national des scien- nization, based in Colombo (Sri Lanka), with a specialized remit to ces de l’Univers) has the remit of defining, developing and steering support water use policies, with regard to agriculture and water requi- national and international research efforts in the fields of astronomy, rements in developing countries. Earth and ocean sciences, and space science, carried out within CNRS and in public-sector educational establishments. Lamont–Doherty Earth Observatory: a research institute, bringing Columbia University: US private university, founded in 1754, in New together some 200 scientists, carrying out work to document the ori- York City, as King’s College, one of the eight member universities of gin, evolution and future of the Earth’s natural resources. the so-called Ivy League, and taking the lead, among US universities, Leosphere: a French company, set up in 2004, specializing in atmosphe- in terms of Nobel Prize winners. ric measurement equipment. European Commission: one of the key organs of the European Union, LI–COR (Corporation): a US corporation, specialist manufacturers of it oversees the implementation of the texts – directives and regula- environmental measuring instruments. tions – adopted by the Council, and has sole power to propose legis- Laboratoire des sciences du climat et de l’environnement (LSCE): lation. It has broad powers to steer common policies. In the area of the Climate and Environmental Sciences Laboratory is a joint science and technology, its instrument is the Framework Program CEA–CNRS–Versailles - Saint-Quentin-en-Yvelines University research for Research and Technological Development (FP6 covered the unit, formed in 1998 through merger of the Low Radioactivity Center years 2002–2006, while FP7 covers the years 2007–13). (CFR: Centre des faibles radioactivités), and Climate and Environmental Hamburg University: set up in 1919, this now ranks as the fifth lar- Modeling Laboratory (LMCE). Within the Pierre-Simon Laplace Institute gest university in Germany, with a roll of 40,000 students. Its research (IPSL), which brings together a number of laboratories, active in the work ranges across many scientific, and arts and humanities areas. fields of aeronomy, meteorology, oceanography and climate, LSCE Harvard University: US university, founded in 1636 in Cambridge carries out work along three directions: understanding of climate (Massachusetts), considered to be the oldest higher education esta- variability mechanisms on various timescales, investigation of bio- blishment in the United States. It has produced more than 40 Nobel geochemical cycles, geochronology and geomarker analysis. Prize winners, and claims first place in the worldwide academic ran- Météo France: the French national meteorological organization, a king of universities; it is also seen as the most richly endowed uni- public-sector establishment, charged with the prediction and inves- versity the world over. tigation of meteorological phenomena, and issuing meteorological Institut de physique du globe de Paris (IPGP): the Paris Physics of warnings. the Earth Institute is a higher education and research establishment, Pacific Tsunami Warning System (PTWS): this has been run under having as its remits the observation and study of natural phenomena, the aegis of UNESCO since 1968. The Pacific Tsunami Warning Center research, education and the dissemination of knowledge in the area (PTWC) is hosted by the United States, in Ewa Beach (Hawaii). This of physical Earth sciences. It plays a part in seismic, and volcanic risk was set up in 1949, following the tsunami that devastated Hawaiian prevention, and mitigation. coves, on 1 April 1946. Subsequent to the tsunami that was caused Institut de radioprotection et de sûreté nucléaire (IRSN): the French by an earthquake occurring in Chile, in 1960, the PTWC has been asso- Radioprotection and Nuclear Safety Institute, a public-sector esta- ciated to an international monitoring and warning network, charged blishment of industrial and commercial character, set up in 2002, as with the continuous monitoring of seismic activity, and sea level across a result of the merging of the erstwhile Nuclear Protection and Safety the Pacific Ocean, and keeping informed most of the countries around Institute (IPSN: Institut de protection et de sûreté nucléaire), and that ocean, along with Hawaii, Alaska, and the West Coast of the USA, Ionizing Radiation Protection Office (OPRI: Office de protection contre to prevent, and mitigate the effects of tsunamis.

2 CLEFS CEA - No.57 - WINTER 2008-2009 L. Hobbs/PhotoLink Predicting the future evolution of climate entails a better understanding of the processes involved in exchanges of matter, and energy between the atmosphere, the ocean, and the continental biosphere. The two latter compartments also play a crucial part in the carbon cycle, by absorbing more than half of the carbon dioxide released by human activities.

I. CLIMATE RESEARCH, A MAJOR CHALLENGE

Climate research has emerged, over less than 20 years, from its initial status, as one scientific field of enquiry among others, to rank as an essential instrument, if an understanding is to be gained, as to the future of the planet, and its denizens – and, possibly, to change its foreseeable course. What had stood as a hypothesis now attracts near-general consensus within the scientific community. With the Intergovernmental Panel on Climate Change (IPCC), an organization is now available, for policymakers – for the first time on such a scale – that is able to transpose, into the language they know, the synthesis of the research that has been done, and of the findings collected the world over. As part of that research, climate modeling, involving a coupling of the atmosphere, ocean, and vegetation, plays a crucial role. In their endeavor to determine what the climate will be, or may be like, in the future, modelers needs must adjust their tools to the timescale being considered. And the models obtained must be tuned and calibrated, by reference to what is known – in increasingly detailed fashion – of past climates. Geochronology and isotopic geochemistry prove to be of assistance, in this respect, in yielding a better understanding of the various mechanisms involved in climate variability, and setting events in a unified chronological framework. The issue raised by greenhouse gases – first and foremost, carbon dioxide – is the other main aspect of the matters researchers are concerned with, as they seek to gain an understanding of the Earth’s climate machinery. Here again, the validity of the models used is only as good as the quality and extent of the data that is fed into them, and used to check their predictions. In all of these areas, research workers at CEA are collaborating with their counterparts in other research organizations, mainly within the Climate and Environmental Sciences Laboratory (LSCE), jointly run with the French CNRS and Versailles–Saint-Quentin-en-Yvelines University, and in a structure bringing together a number of laboratories, the Pierre-Simon Laplace Environmental Science Institute. LSCE is indeed the heir to a Low-level Radioactivity Center, the name of which hints at the importance of nuclear techniques in climate and environmental research, not to mention the position nuclear energy itself is bound to take on, as an energy source virtually free of greenhouse gas emissions. Rising as it is to a global challenge, climate research also plays its part at the regional, and even local level, particularly at the scale of large urban conglomerations, accounting as these do for a growing proportion of the world’s population. It will thus prove useful to evaluate the impact that global climate changes and pollutant emissions may have, locally, on air quality.

CLEFS CEA - No.57 - WINTER 2008-2009 3 Climate research, a major challenge

Modeling climate means adjusting for timescales Global modeling of the Earth’s climate, over timescales that may extend to several billion years, entails, for researchers, a rigorous selection of the components and processes to be taken on board, in their models. This is the outcome of an ongoing tradeoff between complexity and the time interval covered, in order to adjust to the capabilities of the computation tools being used. PhotoLink

The atmosphere, hydrosphere, biosphere, volution of the Earth’s climate (see Focus A, Journey climate change thus also entails the drawing up of “glo- and cryosphere interact constantly, by way of Eto the center of the Earth, and the outer reaches bal” models, since such models cover the climate of the exchanges of matter of the atmosphere, p. 21) is evidenced by a variety of planet as a whole. The question thus arises: Which com- and energy. However, data types, making it possible to go back in time over ponents, and processes should these models take into the processes occurring several billion years. However, climate variations are account? Providing an answer to that query entails, first in them involve widely diverse response times. ascertained, over the past 4 billion years, or close enough, and foremost, considering the spatial and temporal The timescale considered by way of an ensemble of relatively indirect data. Indeed, scales involved. determines the number no actual “paleothermometer” is available, nor yet any of components that need to be taken on board “paleo-rain gauge,” such as might provide informa- A system involving many aspects in models. tion as to past climates. It is by way of a whole conca- tenation of deductions and analyses that scientists are The climate system comprises a number of compo- able to draw on physical properties (e.g. of oxygen and nents, interacting with one another. Moreover, these carbon isotopes), and transfer functions for distribu- components exhibit widely diverse response times. tions of fauna and flora, in order to assign, ultimately, This response time characterizes the interval requi- a climate value, along with an uncertainty range. red for one component to come back into equili- Obviously, the further back in time the climates being brium, subsequent to a perturbation. The fastest- looked into, the scarcer the data available. To overcome responding component is the atmosphere, involving such issues, as regards the reconstruction of climate a response time ranging from a few minutes to a few variables on the basis of indicators, and the conside- days, however the climate system includes far slower rable lack of homogeneity, across space and time, of such components, such as the lithosphere (see Focus A, indicators, numerical simulation provides another Journey to the center of the Earth, and the outer rea- approach to assess climate variations. Understanding ches of the atmosphere, p. 21). This indeed retains

4 CLEFS CEA - No.57 - WINTER 2008-2009 the memory of the ice sheets that covered, more than 20,000 years ago, the northern reaches of Europe, and North America. This is why, at the present time, the Earth’s crust is still rising, e.g. in Norway,(1) to keep the discussion to short timescales.

From atmospheric to climatic models

Weather forecasting, as carried out in meteorology, calls for the development of high-quality models of the atmosphere. This was achieved, as early as the 1960s, by meteorological centers, and acade- mia, with the development of three-dimensional atmospheric general circulation models (AGCMs). Such models make it possible to predict the evolution of weather over a few days. Such predictions are often excellent, as regards the evolution of surface temperatures. However, they may turn out a poorer performance with respect to local precipi- Bazoge/CEA P. tation distributions, in particular owing to the fact Assessing climate change over the 21st century, and beyond, may not be achieved by mere extrapolation from past climates. Modeling must be brought in. A climate model must that these models’ spatial resolution tends to stand take on board all of the components in the climate system, as determined by the timescale, at some 100 km, making for but a very sketchy adding in the perturbations arising from human activity, and set up an interaction between account of orography in mountain areas, but equally all of these components. due to the way cloud microphysics is addressed in terms of a highly rough-and-ready representation. How, then, are such shortcomings to be made good? e.g. from 400 km to 50 km; unfortunately, however, These models may be used at a higher resolution, computation times then swiftly become unmanage- by going for a smaller model mesh cell size across able. It is nonetheless feasible to “come down,” in the entire surface of the Earth, bringing it down terms of resolution, to a few tens of kilometers. Beyond this point, the physics of such models cea- (1) Continents sink, to a greater or a lesser extent, into the ses to be appropriate. One other method involves magma in the Earth’s mantle, depending on their weight, “zooming in,” i.e. reducing mesh cell sizes in a region and rise up again gradually, when that weight comes down, whether due to erosion, or the melting of large masses of ice. of interest, bringing it down to 50 km – obviously, This is known as isostatic equilibrium. the model’s cell size will be increased in consequence

“Zoomed” modeling to assist paleontologists 1

Using an atmospheric general circula- (Laurentide) Ice Sheet, covering the nor- sapiens, who had settled in regions to tion model (AGCM) zoomed over the thern Atlantic with icebergs, drifting the north, from crossing the Ebro River. Iberian Peninsula, modelers were able across and melting off present-day This accounts for why Neanderthal to show that, 39,000 years ago, at the Portugal, the climate in central and (Homo sapiens neanderthalensis) camp- time of an abrupt cooling of the North southern Spain became considerably sites survived far later in southern Atlantic, corresponding to the breakup “aridified.” This change in climate and Spain than anywhere else in Western of part of the North American environment prevented Homo sapiens Europe (see Figure).

before Aurignacian Figure. (modern humans) 42° N ca 36,500 years ago Left, simulated tree cover, before, and during 39° N the swift cooling that occurred Mousterian 39,000 years ago 36° N (Neanderthals) up to (Heinrich event H4). 9° W 6° W 3° W 0° 3° E ca 30,000 years ago Its disappearance, to be replaced by grass cover, 0 0.05 0.100.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 is consistent with the halt in the during advance of Homo environmental conditions shielding the sapiens sapiens into 42° N peninsula from being overrun by modern southern and central Spain, and the humans (Homo sapiens sapiens) persistence of 39° N > survival of Homo sapiens neanderthalen- Neanderthal sis for the duration of this cold event, extinc- (Homo sapiens 36° N tion being delayed. neanderthalensis) 9° W 6° W 3° W 0° 3° E campsites. LSCE

CLEFS CEA - No.57 - WINTER 2008-2009 5 Climate research, a major challenge

Timescale determines what processes are involved

Should the timescale be extended from the order of the week to that of the year, a second component must be brought in: the ocean. Indeed, the two fluids that transport energy and moisture from the equator to the poles are the atmosphere, and the ocean (see Figure 1). As early as the 1980s, oceanic general circulation models (OGCMs) were used to complement AGCMs, and the two types of model were coupled (see Box 2). Keeping to that timescale, up to time intervals of 100 years, a third component required taking into account, the biosphere, this interacting both with solar radiation (its presence modifying the albedo), and the water cycle. Such models, whether highly simplified, or incorporating numerous plant functional types (PFTs),(2) have been produced and Philippe Bigard/goodshoot.com coupled to the atmospheric, and oceanic components. Vegetation is a major component in the climate system. It plays a radiative role, Over timescales that are longer still, ranging from first of all, since a surface covered with vegetation absorbs solar radiation far more than would bare ground; and it plays a crucial part in the water cycle, absorbing as it does about 1,000 years to 100,000 years or so, one crucial water for its growth, and releasing it through evapotranspiration. component that must be taken into account, if an understanding is to be gained of climate during the in the antipodal region (see Box 1). If questions are Quaternary period (i.e. over the past 2 million years to be answered as to the impact of climate change or so), is the cryosphere. Three-dimensional thermo- in a given region, in this case on scales of the order mechanical models, featuring 50-km spatial resolu- of 1 kilometer, the strategy involves coupling the tions, have been draw up. Coupled to climate models, global model with a regional model, appropriate these make it possible, on the one hand, to predict for kilometer scales, but requiring boundary condi- the evolution of ice sheets, and, on the other hand, tions to be set, as provided by the general circula- to evaluate cryosphere–climate feedbacks. In parti- tion model (GCM). Such strategies are currently cular, as an ice sheet melts, it injects large amounts undergoing intensive development. Indeed, adap- of fresh water at the oceans’ surface, which may result, ting and refining the climate change scenarios deve- by bringing down surface water density, in inhibiting loped under the aegis of the Intergovernmental the sinking of such waters to deeper levels. Over the Panel on Climate Change (IPCC: see Box The IPCC: past million years, climate has alternated between For what purpose? How does it work? p. 10) at regio- short interglacial periods and extended glacial phases . nal level, to measure the impact involved, has become a priority. Such regions may include, e.g., a moun- (2) The characteristics of the various pollen types are far tain region, the aim being to determine the levels too numerous for these to be individually represented in models. of snowfall at winter resorts, or coastal regions, for Consequently, pollens exhibiting common characteristics are subsumed together into a number of categories, known as “plant the purposes of evaluating the impact of rising sea functional types” (PFTs). As a rule, the number of PFTs used levels… in models ranges from 5 to 15.

South Pole equator North Pole South Pole equator North Pole 6 80 60 4 northward transport total )

2 40 W)

20 15 2 0 oceanic - 20 0 - 40

- 60 2 atmospheric - 80 radiation budget (W/m radiation - 100 (10 transport energy 4 southward transport - 120 - 140 6 90° S 60° S 30° S 0° 30° N 60° N 90° N 90° S 60° S 30° S 0° 30° N 60° N 90° N latitude latitude

Figure 1. Left, the radiation budget, i.e. the balance between the energy received from the Sun, and energy reemitted into space, as a function of latitude. This curve is the outcome of the ERBE (Earth Radiation Budget Experiment) satellite measurement campaigns. Right, the balance of energy transport by the atmosphere, and oceans. Total transport is measured by satellite (ERBE campaigns). Ocean transport is derived from meteorological data. Atmospheric transport is obtained from the difference. This energy transport is considerable.

6 CLEFS CEA - No.57 - WINTER 2008-2009 An instance of ocean–atmosphere coupling: the onset of glaciation 2

Understanding how climate switched that summertime insolation, at high alti- radiative forcing involved is so weak that from interglacial conditions, similar to tudes in the Northern Hemisphere, would the atmosphere, by itself, is insufficient those we experience, to glacial condi- be lower (astronomical theory of climate), to amplify it. New simulations taking the tions – when snow accumulates, to form allowing snow that had fallen in winter- ocean and vegetation into account ultimately huge ice sheets – is a chal- time to persist through the summer. For (AOVGCMs) were able to reproduce the lenge for climate modelers. Very early that purpose, they initially used purely transition, by simulating permanent snow on, in the 1980s, they sought to repro- atmospheric models (AGCMs); this howe- at the locations where ice sheets did duce this transition, ascribed to the fact ver proved to be a failure. Indeed, the indeed start developing (see Figure).

800 Figure. When selecting the 700 Canadian Arctic 600 Archipelago as study region, as corresponding 500 115,000 years to the locus of ice cover 400 initiation, it should be noted that whereas, in 300 present current conditions (red 200 line), the snow melts, such

snow thickness (cm) thickness snow 100 is not the case when the 0 onset of glaciation, 600 660 720 780 840 900 960 1,020 1,080 115,000 years ago, is simulated using a coupled months LSCE model (OAGCM).

During these cold phases, the Earth supports, rather the lithosphere tends to modify climate, and the car- than two ice sheets as is the case at present (Antarctica, bon cycle (see Figure 3). Plate tectonics has a direct Greenland), four ice sheets. The two former sheets effect on climate, related to the shifting of continents are supplemented by the Laurentide Ice Sheet, across from tropical to temperate regions. This impact was North America, and the Fennoscandian Ice Sheet, identified from the outset by German meteorologist covering Northern Europe. Quite recently, such cou- and astronomer Alfred Wegener, in his work, pub - pled models have made it possible to reproduce the lished in 1924, coauthored with German climato logist last glacial–interglacial cycle (see Figure 2), i.e. the Wladimir Köppen, Die Klimate der geologischen Vorzeit. Earth’s climate over the past 130,000 years. One further effect, evidenced by teams from the French Further still, on timescales of 10 million years or so, Climate and Environmental Sciences Laboratory the process that then stands out as fundamental is (LSCE: Laboratoire des sciences du climat et de plate tectonics (see Focus D, Plate tectonics and l’environnement), and the Geological Mechanisms earthquakes, p. 90). The slow jig of continents across and Transfers Laboratory (LMTG: Laboratoire des

Figure 2. Reconstruction of the thickness (in m) and extent of the main Northern a b c Hemisphere ice sheets during the last climate cycle. Six key periods are shown: a) 110,000 years BP (before present) (presence of an initial significant ice sheet in North America); b) 75,000 years BP (prior to formation of the Fennoscandian Ice Sheet); c) 60,000 years BP (after the formation of an initial significant ice sheet in Northern Europe); d) 30,000 years BP (prior to d e f renewed ice sheet growth); e) 20,000 years BP (last glacial maximum); 1 10 100 500 1,000 1,500 2,000 3,000 4,000 5,000 (m) f) 0 year (present time –

LSCE preindustrial).

CLEFS CEA - No.57 - WINTER 2008-2009 7 Climate research, a major challenge

mécanismes et transferts en géologie), in Toulouse CO2, and turn acid. These in turn cause alterations (France), is more indirect, and concerns the in soils, and, by way of the river systems, transport carbon cycle. Indeed, when a major conti- that carbon to the oceans, where it falls in sediments nental landmass is situated in tropical on the sea floor. On the other hand, if the continen- regions, precipitations are intense, and tal landmass is situated at high latitudes, atmosphe- ~ 250 Ma weathering stands at a maximum: ric CO2 drawdown through precipitation and soil large quantities of atmospheric weathering is lower, and atmospheric CO2 levels thus carbon dioxide (CO2) are stabilize at higher values. Thus, when continents lie thus transported to the at lower latitudes, atmospheric CO2 tends to come ocean. Precipitations down, and conversely. CO2 then acts as a thermal incorporate some of regulator. Another aspect of plate tectonics relates not ~ 120 Ma the atmospheric to the horizontal process of continental drift, but Figure 3. rather to the vertical deformations (uplift – i.e. the The breakup of slow buildup – of mountain ranges), modifying the Pangea atmospheric circulation and climate (see Box 3). supercontinent. Continental drift, but equally the uplift of ~ 95 Ma The need to bring forward a suite mountain ranges (the Himalayas in northern of climate models India and Tibet, the East LSCE African Rift, the Andes) While the timescale governs the number of compo- extensively modified both ~ 68 Ma nents that need to be taken on board, one further atmospheric and ocean aspect concerns the models’ complexity. Indeed a dynamics, along with the carbon cycle, by way of changes in weathering. These long-term Simulation of the “East Side Story” scenario, 3 modifications of the face of the Earth are the first and the East African Rift uplift factors that should be taken into account, in order The engaging narrative told by French paleontolo- Rift uplift was accompanied by quite considerable to reconstruct climate on the million-year (Ma) gist and paleoanthropologist Yves Coppens – when aridification in East Africa, and a reduction in woo- scale. he accounts for the bipedal posture, along with the ded areas. existence of hominids(1) solely to the east of the East (2) African Rift by the fact that the uplift of that moun- (1) Hominids constitute a family of species, bringing tain range resulted in a drying out of East Africa, together most great primates, e.g. humans, chimpanzees, to such an extent that trees disappeared – has been bonobos or gorillas, together with a number of extinct dealt a blow by the discovery of Toumaï,(3) well to species, whether standing as ancestors of the human line, the west of the Rift Valley… Be that as it may, cli- or otherwise. mate modeling does make it possible to check (2) The East African Rift Valley extends from the south of what impact that uplift did have on climate. By cou- the Red Sea (to the north) to the Zambezi (south), being more than 9,500 km in length, 40–60 km wide, with a pling the climate model with a vegetation model, depth of several hundred to several thousand meters. it is thus feasible to evaluate environmental chan- (3) A hominid 6–7 million years old, the oldest known ges. A model zoomed over Africa was thus used representative of the human line, standing close to the last (see Figure). This indeed shows that the East African common ancestors of both chimpanzees and humans.

40° N 40° N

20° N 20° N

0° 0°

20° S 20° S

40° S 40° S 20° W0° 20° E 40° E 20° W0° 20° E 40° E ■ tropical rainforest ■ arboreal savanna ■ herbaceous savanna ■ steppe-like ■ desert-like Pierre Sepulchre/LSCE Pierre

Figure. The climate model is coupled to a biome (vegetation) model. Left, present-day vegetation; right, vegetation in the absence of the East African Rift System.

8 CLEFS CEA - No.57 - WINTER 2008-2009 Climate in the next century 4

When the issue is that of modeling future climate change, e.g. for the 21st century, the uncertainty inherent in the model 6.0 A2 A1B itself is compounded by that attaching to B1 CO emission scenarios. As pointed out 5.0 2 constant concentrations, Figure. above, the general circulation models year 2000 levels Multi-model averages (GCMs) used for that purpose are of such 4.0 20th century of surface warming complexity, and feature such a fine-mes- (relative to 1980–1999) hed spatial resolution that only a certain 3.0 for IPCC scenarios A2, A1B, number of trajectories (scenarios) may and B1, as set out in the 2.0 IPCC Special Report on be investigated. Intercomparisons, whe- Emission Scenarios (SRES), reby all of the models involved simulate shown as continuations 21st-century climate for the same sce- 1.0 of the 20th-century narios, have been carried out. The Figure simulations. The purple global surface warming (°C) surface global sets out the results obtained. The models 0 line corresponds are of the coupled ocean–atmosphere to the case where -1.0 concentrations would model type. No dynamic vegetation, che- be kept at 2000 levels. mistry, or aerosols are involved, nor is 1900 2000 2100 there any modeling of the cryosphere. year These components will be included in A2: very heterogeneous world, continuously increasing global population, per capita economic subsequent scenarios. All of these growth and technological change are more fragmented and slower than in other storylines. models do, nonetheless, their diversity A1B: rapid economic growth, global population that peaks in mid-century and declines thereafter, notwithstanding, show an increase in glo- and rapid introduction of new and more efficient technologies, with a balance across all energy bal temperature, in the 2–6 °C range. sources. Such increases are considerable, bea- B1: convergent world with global population that peaks in mid-century and declines thereafter, and ring in mind that the difference between with the introduction of clean and resource-efficient technologies. a glacial and an interglacial state stands (See http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf, page 18).

at a mere 4 °C. IPCC

three-dimensional general circulation model – taking in the atmosphere, ocean, and vegetation – may not, even using the most powerful computers, be integrated over more than a few centuries. Such is the practice, for instance, as regards the climate of the future, in work carried out for the IPCC (see Box 4). IPCC scenarios allow a number of possible evolutions to be considered, with respect to CO2 emissions, using highly sophisticated models, covering not only the ocean–atmosphere–vegetation, but equally more rapid processes, such as chemistry, and aerosols. The level of complexity arrived at is such that only a few 100-year (21st-century) paths (scenarios) are analyzed. Consequently, if longer time - scales are to be explored, complexity needs must be set aside, and simpler models must be brought in (Earth models of intermediate complexity [EMICs], box models…). Climate modeling thus also needs to be “polymorphous.” Depending on the kind of issue being addressed, it is indispensable that the appropriate tools be available. Thus, development of a range of models and couplings has enabled LSCE to investigate equally the first glaciations on Earth, some 2 billion years ago, the climate prevailing when hominids emerged, 7 million years ago, or the irre- versible melting of the Greenland Ice Sheet, according to a variety of anthropic scenarios. CEA-IPEV Present-day ice sheets, Antarctica and Greenland, account for some 77% of the Earth’s Gilles Ramstein freshwater reserves, corresponding to 70 m in terms of sea level. Antarctica alone holds 90% > of the ice present on Earth. The models that have been developed compute changes in ice Climate and Environmental Sciences sheet geometry in response to a given climate change, and allow the rise in sea level Laboratory/Pierre-Simon Laplace Institute to be evaluated, with regard to a given global warming. Coupled with climate models, Joint CEA–CNRS–UVSQ Research Unit they afford the ability to investigate not only the part played by the polar ice caps in the climate system, but equally to simulate their interaction with the ocean, and atmosphere, Physical Sciences Division over timescales ranging from a few tens to several hundred thousand years. CEA Saclay Center (Orme des Merisiers) Shown here: the Antarctic landscape.

CLEFS CEA - No.57 - WINTER 2008-2009 9 Climate research, a major challenge

The IPCC: For what purpose? How does it work?

review purposes. The final draft of the report, together with the summary for policymakers, some 15 pages long or so, are again submitted for scrutiny by the scientific community, but equally by representatives from member governments of WMO or UNEP. To give an idea of what this involves, to draw up the last Working Group I Assessment Report, no fewer than thirty thousand comments were sent in by scientists, and governments. The authors of the report are duty bound to respond to every one of these comments. “Editors” are charged with overseeing this review process. Finally, the summary for policymakers is submitted for approval by government representatives, meeting in plenary

IPCC – photo Jerry Meehl IPCC – photo session. This general assembly mee- Summaries for policymakers are submitted for approval by government representatives ting brings together representatives at plenary sessions. These documents are discussed line by line, until unanimous agreement from member governments, obser- is achieved. vers from nongovernmental organiza- Establishment, and remits limiting greenhouse gas emissions, and tions, and the two scientists appoin- generally of mitigating climate change. ted as co-chairs of the IPCC working In 1988, the World Meteorological These three main working groups are group, joined by the coordinating lead Organization (WMO) and the United complemented by more specific task authors of the report. Over a week, Nations Environment Program (UNEP) groups, concerned with national green- extending at times into and through established the Intergovernmental Panel house gas inventories, or certain tech- the night, the document is scrutinized on Climate Change (IPCC), its remit being nical topics (carbon sequestration, air line by line, until unanimous agree- to assess, in impartial fashion, interna- transport, the ozone layer…). ment can be reached. It is at the out- tionally available scientific, technical, come of this trial that a consensus is and socio–economic information on cli- A unique operating mode said to emerge between scientists, and mate change.(1) The IPCC published its governments. Since the IPCC was esta- first Assessment Report in 1990. Since The IPCC’s work is carried out on a blished, all assessment reports have then, every 5–6 years or so, the IPCC has scientific basis, however it also invol- been so adopted in plenary session, by issued assessment reports, which stand ves interaction between scientists, all 192 member governments repre- as a reference for scientists, and poli- and government officials. Typically, sented in the IPCC General Assembly. cymakers the world over. The latest such an IPCC cycle progresses as follows. report, the Fourth Assessment Report, Government representatives vote, in Consensus, and transparency was released in 2007. plenary session, to give the go-ahead The IPCC is set up around three wor- for a report, and decide how it should This consensual approach has, on king groups, each one of which brings be organized (i.e. the number of groups occasion, been criticized by “climate together hundreds of specialists. involved), along with electing the IPCC skeptics,” i.e. by those who question Working Group I (WG I) surveys the cur- Chairman, and chairpersons of the the reality of climate change, or the rent state of scientific research in the various working groups, as well as set- origin assigned to it, namely human field of climate change. In effect, WG I ting a deadline for the report. The activity. Their argument goes as fol- assesses the entire ensemble of data chairs of the various groups call on lows: in science, there is no such thing on observed climate change, and fin- experts to take part in a number of as a consensus, no single-minded dings from climate modeling, for the scoping meetings, to finalize a basic orthodoxy; on the contrary, there is a 20th and 21st centuries. Working Group II outline structure for the report. constant thrashing out of competing (WG II) is concerned with the impacts Authors are then selected for the va- ideas, and an ongoing questioning of of climate change on a variety of sec- rious chapters, from the international established findings. This is quite true tors (water, ecosystems, agriculture, scientific community. These authors – and the work of IPCC is fully conso- health…), and the options for adapting subsequently meet every six months, nant with this conception. Over two to this. Finally, Working Group III (WG III) over a period of two years, to produce years, the co-chairs of each working investigates the ways and means of the report. Successive interims group, together with the authors they drafts of the report are made availa- steer, survey all of the extant know - (1) See http://www.ipcc.ch/. ble to the scientific community, for ledge in the area they are concerned

10 CLEFS CEA - No.57 - WINTER 2008-2009 with. They do so in completely trans - parent fashion. Not only are the drafts of the chapters posted on the web, but so likewise are the points made by the many reviewers, along with the authors’ responses to these re- marks. Uncertainties, and unresolved controversies are clearly set out in the copious assessment reports. Only the summary for policymakers, some 15 pages long, is discussed in plenary session – not the technical summary, about 50 pages in length, or the full report, about 1,000 pages in length, both mainly intended for scientists. The purpose of that plenary session is to come out with a document, the summary for policymakers, that will carry the seal of approval of the scientists who drew it up, and of the member governments who will be its joint signatories. This should thus be writ- ten in a language understandable by, IPCC – photo Odd-Steinar Tollefsen Odd-Steinar IPCC – photo and unambiguous for, nonscientists. The IPCC and former United States Vice-President Al Gore were awarded the Nobel Peace Member governments suggest textual Prize in 2007. They were jointly awarded the Prize for their efforts to build up and disseminate amendments, chiefly with respect to greater knowledge about man-made climate change, and to lay the foundations for the form, the content, i.e. the scientific measures that are needed to counteract such change. import, as a rule never being queried by government representatives. In any dations for the measures that are nee- Fourth Assessment Report were relea- event, the co-chairs steering the ded to counteract such change.” sed in 2007, before the Conference of report secure the agreement of the Indeed, the IPCC’s First Assessment the Parties to the UNFCCC, meeting authors in charge of the relevant chap- Report, published in 1990, led the in Bali (Indonesia), and provide a fra- ter, for the passage discussed, prior United Nations General Assembly to mework for the ongoing international to agreeing to any amendment to the draw up a Framework Convention on negotiations on the follow-up to be summary. Climate Change (UNFCCC), which given to the Kyoto Protocol, which will came into force in 1994. The Second expire in 2012. A Fifth Assessment Report Assessment Report, issued in 1995, pro- At the IPCC’s plenary session, held in scheduled for 2013–2014 vided the evidence that served as the Budapest (Hungary) in April 2008, it basis for negotiations on the Kyoto was decided to draw up a Fifth The IPCC’s strength lies, on the one Protocol,(2) under the aegis of the Assessment Report. This is due to be hand, in its extensive reports, which UNFCCC. The Third Assessment Report, published in 6 years’ time. At the same stand as a valuable source of infor- published in 2001, confirmed the role time, effective initiatives should be set mation for the scientific community, of human activities as regards the war- in train, on an international basis, for and, on the other hand, in the sum- ming observed over the latter half of the purposes of adapting to the conse- mary for policymakers, which, owing the 20th century. It predicted, in par- quences of future climate change, but to its mode of approval in plenary ses- ticular, a steepening of the process, to equally, most crucially, in order to sion, fully commits member govern- result in an average global warming effect a reduction in greenhouse gas ments. Governments are unable to by several degrees, between 1990 and emissions: this indeed is the only sus- claim they lack the relevant informa- 2100. Finally, the conclusions of the tainable way of limiting the scale of tion: they have given their approval to that climate change. (2) Kyoto Protocol: one of the three it. The policy initiatives required to curb international treaties serving as the basis climate change are thus thereafter up for international climate governance. > Pierre Friedlingstein to them. The Protocol sets out a timetable for Climate and Environmental reductions in emissions of the six greenhouse It is this two-pronged approach which gases deemed to form the main cause of such Sciences Laboratory/ earned IPCC members the Nobel climate warming as has been observed over Pierre-Simon Laplace Institute Peace Prize award, in 2007, “for their the past 50 years. It entails absolute emission Joint CEA–CNRS–UVSQ efforts to build up and disseminate reduction commitments for 38 industrialized Research Unit countries, and calls for a global reduction by greater knowledge about man-made 5.2% of carbon dioxide emissions by 2012, Physical Sciences Division climate change, and to lay the foun- relative to 1990 levels. Saclay Center (Orme des Merisiers)

CLEFS CEA - No.57 - WINTER 2008-2009 11 Climate research, a major challenge

The contributions of geochronology to our knowledge of climate For the purposes of reconstructing climate evolution, for a given period, and setting events in a global chronological framework, the use of climate archives entails switching between highly diverse dating methods. Radioactivity measurements, involving a variety of techniques, often play a central part in this process. P. Stroppa/CEA P.

General view of the ARTEMIS accelerator he Earth’s climate undergoes natural change, this Geochronology has the chief purpose of bringing mass spectrometer, set up at CEA’s Saclay Tinvolving time constants that range from several the evolution of the Earth, and hence of climate, Center, which allows the hundred million years to one season. As early as the into a unified spatio-temporal framework. It fur- carbon-14 dating of 19th century, geologists had adduced evidence as to ther stands as a valuable aid for the purposes of cli- samples up to around 50,000 years. Using the the existence of glacial and interglacial periods in mate change prediction, since it makes it possible (1) various dating methods past ages, by identifying huge moraine deposits to compare the various theories put forward as to available, all of the across the northern reaches of the American and the causes and mechanisms of past climate varia- information extracted European continents. However, these climate chan- tions. Building up this global chronological frame- from climate archives may be pieced together, ges still had to be dated, characterizing as they do work is anything but straightforward, since this relies as the pieces of a jigsaw the Pleistocene, an epoch in the Quaternary period on a wide range of dating methods, and cross-dating puzzle, each extending over some 1.8 million years. This became on this basis, which allows the validity to be tested, corroborating the others, to reconstruct climate feasible with the discovery and development of pre- of the ages obtained for one and the same event. evolution for a given cise measurement methods for radioactivity, and the One further difficulty also arises, owing to the period. development of ever deeper-going sedimentary rock core-sampling methods, be it on the continental land- (1) Moraine: an accumulation of debris, transported by a mass, in the ocean, or in ice sheets, in order to “go glacier, or an ice sheet, and deposited, as the ice melts, as a rule back” in time. at one and the same altitude, building up rocky mounds.

12 CLEFS CEA - No.57 - WINTER 2008-2009 The Calypso core-sampling device, on board the Marion-Dufresne research vessel. The development of ever deeper-going sediment core-sampling methods makes it possible to go further back in terms of

Aurélie Van Toer-LSCE/CEA-CNRS-UVSQ Van Aurélie timescale.

diversity of datable materials, ranging as they do from inorganic crystals – quartz, feldspar, calcite, or aragonite(2) – to biogenic remains, such as shells, foraminiferal tests (skeletons), or plants.

Suitable dating techniques for the Pleistocene

The dating methods used for the study of the Pleistocene paleoclimate are, as a rule, classed into two groups: absolute dating methods, these including radioactivity measurement methods in the broad sense, and relative dating methods. The latter rely on the correlation of physicochemical or biological 100 μm signals that stand out as characteristic, at the global or regional scale, in sedimentary archives. In prac- and H. Leclaire-LSCE/CEA-CNRS-UVSQ L. Froget tice, each method benefits from the advances achie- Globorotalia menardii fimbriata, a species of planktonic foraminifera, present in surface ocean waters. Foraminifera ved for every other one of its counterparts. live, and die in oceanic waters. Their shells are found in Radioactivity-based methods are used to address the marine sediments. dating of point events, located within relatively short geological periods, whether identifiable on a global scale, or otherwise. Such age determinations provide Measurement of natural radioactivity a chronological framework for the building up of Over time, radioactive atoms decay, yielding stable relative timescales. nuclides, or nuclides that are likewise radioactive, these decaying in turn to yield further nuclides, and Counting with dendrochronology so on. Decay half-lives vary, depending on the nuclide Absolute ages, or calendar ages, are obtained through involved, and this allows climate variability to be ascer- the direct counting of annual formations. Such tained over a number of distinct timescales. Natural counting is used on annual tree growth rings, in radioactive nuclides have been present on Earth since dendrochronology, or is applied to annual, bi-sea- the planet was formed, e.g. uranium-238 (238U), sonal, or varved(3) deposits, in lacustrine or marine uranium-235 (235U), and thorium-232 (232Th), or sediments, or to yearly snow deposits. potassium-40 (40K); while others are constantly being generated by the effects of cosmic radiation on nuclei in the upper atmosphere, e.g. carbon-14 (14C), and (2) Calcium carbonate (CaCO3), the major constituent of limestone, chalk, marble, but equally of the shells of marine beryllium-10 (10Be), such nuclides therefore being lifeforms, and snails, naturally crystallizes into two main known as cosmogenic isotopes. forms: aragonite, and calcite. The potassium–argon (K–Ar) and argon–argon (3) Varve (from the Swedish varv, meaning “layer,” varvig, (Ar–Ar) methods are suitable for potassium-rich “layered, striated”): a lacustrine sediment, consisting of alternately fine- and coarse-grained deposits, settling minerals, in volcanic rocks in particular, and allow at glacier heads. dating events to within accuracies of 0.5–1%.

CLEFS CEA - No.57 - WINTER 2008-2009 13 Climate research, a major challenge LSCE P. Stroppa/CEA Stroppa/CEA P.

The principle of carbon-14 (radiocarbon) dating relies on the fact that, in any living organism, the ratio of 14C content over 12C content is the same as that for atmospheric carbon dioxide. At death, exchanges stop. Carbon-14 ceases to be renewed, and its radioactivity decays, with a half-life of 5,730 years. From measurement of 14C activity in the sample, its age may be derived. The accelerator mass spectrometry method affords the advantage of using just a few hundred micrograms carbon in an analysis. Samples, e.g. foraminifera, are subjected to chemical treatment, to extract the carbon, which is then purified in CO2 form. This carbon dioxide is subsequently reduced, to be transformed into graphite. Shown here, the positioning of CO2 ampoules in the reduction bench of the ARTEMIS installation. At top left, a graphite target (around 1 mm in diameter).

Techniques based on the decay series of uranium, and undistinguishable from atmospheric nitrogen-14 its daughter products, involve large numbers of radio- (14N/N ~ 0.99). Moreover, atmospheric 14C content nuclides, of diverse half-lives. These methods are has varied over time, owing to fluctuations affecting used, typically, for the dating of Pleistocene materials, solar activity, the Earth’s magnetic field, residence to within accuracies of about 1%. They are applied time, and carbon-14 exchanges occurring between to corals, which record variations in sea level, and the various carbon reservoirs. Ages, as measured by physicochemical changes in the oceanic water mass, way of carbon-14 dating, thus involve a difference, and to stalagmites, these forming archives of ther- or offset, with respect to absolute ages. Cross-dating, mal, and rainfall conditions. Other nuclides, e.g. i.e. the comparison of 14C measurements with dendro- lead-210 (210Pb), or radium-226 (226Ra) make it pos- chronological ages, or with ages obtained with other sible to date more recent events, owing to their half- radionuclides, chiefly with the pair 230Th–U, makes lives, standing at 22 years, and 1,600 years respecti- it possible to arrive at a precise quantitative estimate vely. These are appropriate for inorganic, and biogenic of that offset, i.e. a calibration. This method, which minerals, as well as for organic remains. These tech- earned US chemist Willard Frank Libby the Nobel niques rely on measurement of the initial radionu- Prize in Chemistry, in 1960, allows dating up to around clides, and their daughter products, which is ruled 50,000 years, to accuracies ranging from about 0.5% out as regards the carbon-14 (radiocarbon) method. to 2% or so, depending on sample age, samples taken Indeed, this nuclide decays, with a half-life of 5,730 from oceanic environments – e.g. foraminifera, corals, years, to yield nitrogen-14 (14N), the latter being quite shells – and continental environments – inorganic, and biogenic crystals (calcite, aragonite), and organic remains (seeds, wood, chars, insects). Age determinations based on natural radioactivity have been complemented by radioactive time markers. Indeed, certain nuclides were injected in large amounts into the atmosphere, during nuclear tests carried out in the early 1960s, e.g. 14C, cesium-137 Corals stand as valuable (137Cs) – half-life: 30 years – or tritium – half-life: climate archives, 12 years – or as a result of the Chernobyl (Ukraine) since they record 137 variations in sea level, accident, in 1986, as regards Cs. and physicochemical changes in oceanic water (4) The splitting into two fragments (fission) of the uranium- masses. They may be 238 nucleus releases energy, chiefly taking the form of kinetic dated, in particular, energy. The fragments are ejected across the material, by the 14C and 230Th–U generating regions of intensive damage, known as fission

methods. Norbert Frank-LSCE/CEA-CNRS-UVSQ tracks.

14 CLEFS CEA - No.57 - WINTER 2008-2009 Putting radionuclide decay to advantage Likewise, the polarity, and intensity of the Earth’s Radiogenic methods rely on physical defects left magnetic field have varied over time. Investigation inside minerals, such as the fission tracks genera- of these parameters, using volcanic rocks, dated by ted by recoil nuclei,(4) as uranium-238 decays. This means of the K–Ar and Ar–Ar methods, has allo- technique essentially yields information as to the wed a reference, “standard” chronology to be drawn thermal history of the rocks examined, its domain up, covering the past 100 million years (geomagne- of applicability covering volcanic glasses, these for- tic polarity timescale [GPTS]). During the ming unique regional time markers, serving to link Pleistocene, the Jaramillo (~ 1.8 million years), and the various sedimentary archives together. This Brunhes–Matuyama (760,000 years) polarity rever- category of dating methods further includes opti- sals occurred, as well as polarity excursions – shor- cally-stimulated luminescence (OSL), and ther- ter-lived instabilities – e.g. the Blake Event (115,000 mally-stimulated luminescence (thermolumines- years), and Laschamp (41,000 years) and Mono Lake cence [TL]) methods, these involving dosimetry (~ 30,000 years) excursions. Variations in magnetic of the internal, and external radiation crystals have field intensity are recorded in continuous fashion been subjected to naturally, owing to the presence in marine sediments, and the similar patterns of of radioactive nuclides (238U, 232Th, 40K), held in a such variations at global, or regional scales has allo- given crystal, and its environment. Such lumines- wed reference chronostratigraphic curves to be cence techniques may be applied to quartz and drawn up, extending back up to about 800,000 years, feldspar crystals included in volcanic rocks, marine through the identification, and dating of magnetic sediments, dune formations, and glacial loess(5) field reversals, and excursions. In like manner, archeo- formations. They are theoretically suitable for the magnetism, which involves measuring the remanent Pleistocene, and feature accuracies of around 5% magnetization of objects known in a historically on average. defined setting, offers a dating method for objects from the past 2,000 years. Sapropel formations, in Correlation of similar signals the Mediterranean environment – i.e. sediments rich Relative chronology methods rely on the correlation in organic materials – as also volcanic eruption pro- of sedimentary rock series, exhibiting common phy- ducts, or tephras, further provide time markers, ser- sical, chemical, or biological characteristics, such ving to build up a unified chronological framework. as may be identified in regional, or global contexts. Thus, variations in the isotopic composition of oxygen, in carbonates of marine, or continental provenance, or of CO2 trapped in the air bubbles held in ice exhibit, on a global scale, quasi-periodical oscillations, ascribed to changes in the Earth’s insolation over time. This indeed varies, as a function of the Earth’s orbital parameters,(6) the planet’s orbit varying over 100,000-year cycles (eccentricity), and likewise the tilt of its axis of rotation, owing to changes in obliquity (40,000 years), and precession (23,000- and 19,000-year quasi-periods). Variations in insolation may be computed quite precisely for past times, and long-term climate variations may thus be dated by way of their correlation with astronomical insolation cycles. This correlation method, also known as orbital tuning, has allowed sedimentary series to be dated, over the past 25 million years, Bazoge/CEA P. with accuracies of the order of a few percent. Measurement of the remanent magnetization of a marine sediment sample. Sediments acquire a remanent magnetization when, as they are deposited, microparticles in them, (5) Loess: a friable, detrital sedimentary rock, originating, in exhibiting a magnetic moment, statistically align with the ambient magnetic field. the Pleistocene, in the accumulation on the ground, in a cold, Sediments may thus yield information as to the direction, and intensity of the Earth’s magnetic dry climate, of silts transported by wind from source areas field in the past. (alluvial deposits, glaciofluvial deposits, coastal and estuarial sediments, arid regions), subjected to eolian (wind) erosion. Loess chiefly consists of detrital quartz and calcium carbonate. (6) The Earth’s orbital parameters determine its position in space, relative to the Sun. The Earth is subjected to attraction from the Sun, but equally from the other planets in the Solar System, resulting in perturbations to its motion. Three types of alteration have an impact on the Earth’s position relative to the Sun: the elliptical orbit followed by the Earth varies in shape (eccentricity); the Earth’s axis of rotation is tilted, relative to the perpendicular to the ecliptic (the plane containing the Earth’s orbit, and the Sun), by an angle that varies from 22° to 25° (obliquity); the axis of rotation is subjected to a slow motion (precession), whereby it sweeps out a cone, about the Scanning electron microscopy perpendicular to the ecliptic, of half apex angle equal to image of volcanic glasses, obliquity (presently 23° 27´), with the apex at the center of the sampled in a tephra. Such Earth. This results in turn in the positions of the equinoxes, time markers contribute to and solstices, gradually shifting along the ellipse of the Earth’s the building up of a global 100 μm orbit, relative to the perihelion (where insolation is strongest). LSCE/CEA-CNRS-UVSQ chronological framework.

CLEFS CEA - No.57 - WINTER 2008-2009 15 Climate research, a major challenge

and Nicholas John Shackleton demonstrated, in 1976, the existence of astronomical cycles, on the basis of isotopic variations in the oxygen from foraminifera, taken from South Pacific core samples, exhibiting periodicities of 106,000, 43,000, 24,000, and 19,000 years. The chronology established for these variations relied on ages obtained through carbon- 14, Th–U, and K–Ar methods, the K–Ar age determination dating the Brunhes–Matuyama magnetic field polarity reversal at around 700,000 years. Geochronology further contributed to a change in our understanding of the working of the global ocean circulation loop, or conveyor, this referring to the formation of deep waters in the North Atlantic Ocean, their travel to the Pacific, and ultimate return, as surface waters, to the North Atlantic. Rapid climate fluctuations punctuate the last glacial period, and degla- ciation, including such cold events as the Younger Dryas, and Heinrich events, or the hot/cold alter-

Michel Fontugne-LSCE/CEA-CNRS-UVSQ nations of the Dansgaard–Oeschger events. These were accounted for by an either “on” or “off” mode Varved deposits are preserved in sediments owing to the near-absence of oxygen, and consequently of burrowing organisms, at the bottom of the lakes, or ocean basins of deepwater formation in the North Atlantic, the where they are found. Each varve comprises two laminae: one light in color, deposited in “off” mode having the effect of restricting heat trans- summertime, the other of blackish hue, in wintertime, the deposition rhythm being an fers in the ocean, and exchanges between the ocean annual one. Light-colored laminae form in summertime, when sedimentation is most intensive, owing to high rates of glacial meltwater flow, feeding into the lake. Counting and atmosphere at high latitudes. This scenario was such laminae in proglacial lakes (i.e. lakes formed in front of a receding glacier) allows disproved, in particular through precise measure- dating sediments up to 13,000 years or so. By combining such counting with carbon-14 ments of atmospheric 14C content, during deglacia- dating of pollens, seeds, or insect remains held in these sediments, it thus becomes 14 possible to estimate the offset between carbon-14 ages, and absolute ages. Shown here, tion, obtained by cross-dating of C ages, and abso- a core sample of varved sediments taken from Lake Perespilno, in Poland. lute ages derived from the counting of annual varved sediment deposits from the Cariaco Basin (7) (Venezuela). Atmospheric CO2 is transferred to A better understanding of climate deep oceanic layers by way of the ocean circulation, mechanisms and, owing to the low abundance of 14C 14 –14 14 ( C/C~10 ), atmospheric CO2 content is highly The astronomical theory of climate, as formulated sensitive to the deepwater formation rate. During in the 19th century by French mathematician Joseph- the Younger Dryas cold climate event, which lasted Alphonse Adhémar, and subsequently developed, in about 1,200 calendar years, atmospheric 14C content particular, by way of the insolation computations rose initially, during the first 200 years, consonant carried out by Serb mathematician and astronomer with a model attributing this to a reduction in North Milutin Milankovitch, in the years 1920–40, was long Atlantic deepwater formation. On the other hand, rejected by the scientific community. Initial evidence such a scheme could not account for the fall in 14C, in favor of this theory came from the 230Th–U dating as found for the following 1,000 years, in a cold cli- of samples of coral reefs, from coral terraces in the mate context. Synchronization of oxygen isotopic island of Barbados (West Indies: Lesser Antilles). As compositions, through measurement of methane early as 1968, US paleo-oceanographer Wallace Smith held in Greenland, and Antarctic ice,(8) showed that Broecker and his coworkers had shown that the ages the abrupt climate changes observed equally in the of three high-sea-level episodes, due to the melting Northern, and Southern hemispheres involved a of ice sheets 80,000 years, 100,000 years, and phase opposition. When Antarctica was warmer, 120,000 years ago, matched ages of insolation maxi- Greenland would be cold, and vice-versa. Analyzing mums in the Northern Hemisphere. The theory finally these two findings, Wallace Smith Broecker sugges- gained acceptance when James D. Hays, John Imbrie, ted, in 1998, a “thermal bipolar seesaw” model of North–South heat transfer: warm periods in Antarctica were the expression of deepwater forma- (7) K. A. HUGHEN, M. G. L. BAILLIE, E. BARD, J. W. BECK, C. J. H. BERTRAND, P. G. BLACKWELL, C. E. BUCK, tion in the Southern Ocean, thus making for a reduc- G. S. BURR, K. B. CUTLER, P. E. DAMON, R. L. EDWARDS, tion in atmospheric 14C content. In the Northern R. G. FAIRBANKS, M. FRIEDRICH, T. P. GUILDERSON, Hemisphere, a cold climate, modulated by the sup- B. KROMER, F. G. MCCORMAC, S. W. MANNING, C. BRONK RAMSEY, P. J. REIMER, R. W. REIMER, pression of deepwater formation in the North Atlantic, S. REMMELE, J. R. SOUTHON, M. STUIVER, would dominate, over the same time interval. S. TALAMO, F. W. TAYLOR, J. vAN DER PLICHT and C. E. WEYHENMEYER, “Marine04 Marine radiocarbon age calibration, 0–26 cal kyr BP”, Radiocarbon 46, 2004, > Martine Paterne pp. 1059–1086. Climate and Environmental Sciences (8) T. BLUNIER, J. CHAPPELLAZ, J. SCHWANDER, Laboratory/Pierre-Simon Laplace Institute A. DÄLLENBACH, B. STAUFFER, T. F. STOCKER, Joint CEA–CNRS–UVSQ Research Unit D. RAYNAUD, J. JOUZEL, H. B. CLAUSEN, C. U. HAMMER Physical Sciences Division and S. J. JOHNSEN, “Asynchrony of Antarctic and Greenland climate change during the last glacial period”, Nature 394, CEA Saclay Center (Gif-sur-Yvette) 1998, pp. 739–743.

16 CLEFS CEA - No.57 - WINTER 2008-2009 Isotopic geochemistry, the thermometer for past climates For the purposes of reconstructing past climate changes, analysis of the isotopic composition of polar ices and marine sediments – providing as they do veritable natural archives – allows valuable information to be obtained, as to temperature variations and ocean circulation across geological ages. Standing as it does as an essential tool, isotopic geochemistry plays a major part, as regards gaining an understanding of climate mechanisms. L. Froget and H. Leclaire-LSCE/CEA-CNRS-UVSQ and H. Leclaire-LSCE/CEA-CNRS-UVSQ L. Froget

Living foraminifera (left), and foraminiferal shells (right). When a foraminifer dies, only the carbonate shell, or test, settles as sediment, being preserved in marine sediments. It is such foraminiferal tests that are sorted and analyzed using mass spectrometry, to reconstruct the variations in

F. Lombard-LSCE/CEA-CNRS-UVSQ Lombard-LSCE/CEA-CNRS-UVSQ F. oxygen isotopic composition.

hanges in the climate have been much in the news, The geochemistry of the stable isotopes of oxygen and Cover the past few years, with winters bereft of snow carbon plays a leading part in this respect. The isoto- following heatwave-stricken summers, and the mani- pes of oxygen will be more particularly considered, in fold climate upheavals feeding into media controver- the following pages. sies. In order to understand what mechanisms rule the Earth’s climate, and to provide a setting, across time, Oxygen isotopes as climate indicators for the climate events we experience, scientists analyze meteorological records obtained by satellites or ground Oxygen is present in the air we breathe, or the water measurements. However, the time interval so covered, that is around us, in the form of a number of isotopes spanning some 150 years as it does, as far as meteoro- of mass number 16, 17, or 18, respectively, depending logical networks are concerned, does not allow the on the number of neutrons in the nucleus. These iso- investigation of mechanisms involving longer time topes have identical chemical properties, however they constants. do differ in terms of the physical properties related to In this respect, paleoclimatology affords the ability to their mass. The ratio 18O/16O, on Earth, for any sub- go back in time, over several tens, hundreds, thousands, stance containing oxygen, will stand close to 0.2%, or even millions of years. It is investigations of this kind however this does not remain strictly constant. For that have made it possible to evidence the high varia- instance, that isotopic ratio, for a given water mass, will bility of climate, over time, involving as this has, over depend on evaporation–precipitation processes. Indeed, a few thousand years, alternations between warm per- the lighter isotope evaporates more readily than the iods, such as that in which Neolithic agriculture was heavier one, which, on the other hand, condenses more able to develop, and glacial periods, during which the readily into raindrops. The isotopic composition, for high latitudes in the Northern Hemisphere were cove- ice obtained from polar or tropical core drillings, makes red by thick ice sheets. How, on the other hand, does it possible to monitor, over time, the evolution of the one set about reconstructing the climates of the past? physical processes affecting the water cycle. As a fur-

CLEFS CEA - No.57 - WINTER 2008-2009 17 Climate research, a major challenge

on that of the water in which the carbonate precipitated. The physical measurement thus involves conver- ting the calcium carbonate into carbon dioxide (CO2), for which the isotopic composition of oxygen will be measured. It was owing to the pioneering work of US chemist Harold Clayton Urey, in 1947, that isotopic paleoclimatology was able to develop. This undoubtedly played a major part in the understanding that was gained, of natural climate mechanisms involving the ocean, the atmosphere, the cryosphere and the biosphere. Two instances of findings obtained at the French Climate and Environmental Sciences Laboratory (LSCE: Laboratoire des sciences du climat et de l’environnement) will be presented in detail in the following paragraphs.

C. Morel/Our Polar Heritage Polar C. Morel/Our Understanding the impact of iceberg

As the ocean’s water evaporates at low latitudes, a cloud may form. Light isotopes discharges on ocean circulation (i.e. water molecules containing 16O) evaporate more readily than heavy isotopes. As the cloud moves from the equator towards the poles, it releases rain on a number of Investigations carried out with marine sediments, occasions (precipitation). Heavy isotopes, such as 18O, condense more readily into and polar ices have shown that climate in the last raindrops. The cloud thus becomes depleted in heavy isotopes all along its travel. The glacial period, specifically between 60,000 and 10,000 snow falling on the poles will thus be very “light,” as it is depleted in 18O. This heavy isotope, on the other hand, is to be found in the oceans, particularly during glacial years ago, was punctuated by extremely cold epi- periods. Shown here, a Greenland landscape. sodes, quite rapid on geological timescales, that had an impact at least on a hemisphere-wide scale. Such ther example, a living organism with a calcium car- events, known as Heinrich events, are due to mas- bonate (CaCO3) shell draws from seawater the bicar- sive iceberg discharge (calving) into the North bonate ions and calcium ions it needs to build its shell. Atlantic, between 40° N and 60° N approximately Now, carbonate ions containing heavy isotopes of (see Figure 1). The record of these episodes, in oxygen (18O) do not precipitate at the same rate as marine sediments, takes the form of layers rich in ions containing light isotopes (16O), and the difference pebbles of various sizes, and of all kinds, in petro- in precipitation rate, between light- and heavy-isotope graphic terms, encompassed by sediment that is, ions, is all the larger, the lower the water temperature. as a rule, rich in carbonate microorganic remains. Isotopic composition, in a calcium carbonate of bio- Such iceberg discharges had the effect, through the logical origin, thus acts as a thermometer for the water huge input of fresh water they released as they mel- in which it developed. It should be emphasized, howe- ted, of slowing down the transport of warm, salty ver, that this isotopic composition is also dependent waters from low to high latitudes, by way of the North Atlantic Drift, and bringing about a cooling of North Atlantic surface waters. Marine sediment core samples have allowed the isotopic impact of a Heinrich event on surface waters to be mapped, and to quantify its influence, in terms of temperature and salinity. Surface water temperatures fell, on average, by 2–4 °C during such discharges, while the salinity of these waters fell by 0.5‰. This combined drop in temperature and salinity altered surface water density, thus impacting ocean circulation on a much wider scale than in the sole North Atlantic. While isotopic geochemistry did yield information as to the amplitude of the drop in salinity, the duration of these events and their intensity, in terms of Gas-source mass the volume of ice involved, was still far from accu- spectrometer used to 3 measure the isotopic rately estimated (from 0.1 million km to composition of oxygen 10 million km3, over 10 years, or more than in foraminifera. 1,000 years). Numerical simulation of water iso- Calcium carbonate foraminiferal shells are tope transport, in iceberg discharge experiments, converted into carbon made it possible to provide some answers to these dioxide, and it is on this queries as to the duration and intensity of such dis- that the isotopic analysis is carried out. Shown charges. Now, these two parameters are fundamental, here, a close-up view of if the thermohaline circulation response thresholds the glass vials, inside are to be quantified in a freshwater discharge situa- which the reaction tion. For that purpose, researchers at LSCE used an between calcium carbonate and acid Earth model of intermediate complexity (EMIC)

takes place. Bazoge/CEA P. to mimic an iceberg discharge that occurred

18 CLEFS CEA - No.57 - WINTER 2008-2009 The analysis of polar ice cores and marine sediment core samples has evidenced cold, very rapid climate events occurring during the last glacial period. These are due to massive iceberg discharges, which brought huge quantities of freshwater into the North Atlantic, bringing about a strong perturbation in ocean

C. Morel/Our Polar Heritage Polar C. Morel/Our circulation.

40,000 years ago, modifying its duration and intensity, and determined which simulations most clo- 70° N sely matched the data yielded by marine sediment measurements.(1) The best analogy between the numerical experiments and isotopic data was obtained for an iceberg discharge duration of 8 °C 200 ± 100 years, and a freshwater flux of around 60° N 0.25·106 m3/s, i.e. a total of 1.5 million km3 of ice, melting of which will have resulted in a rise in sea level by about 3 m. The extreme abruptness of this 50° N event was unexpected, considering its huge impact on global climate. 40° N Understanding possible mechanisms of glacial ice sheet destabilization 30° N a More closely matching as it did the climate expe- 80° W 60° W 40° W 20° W 0° rienced at the present time, the last interglacial pe - riod, prior to our own – occurring between 129,000 70° N and 118,000 years ago – has yielded much illumi- nating information. Geological archives, be they of marine, glacial, or continental provenance, have served to show that air, and ocean surface temperatures, during that period, were on average some 2–5 °C 60° N warmer than those prevailing in our own interglacial period, known as the Holocene. The sea level stood some 4–6 m higher than the present level, owing in particular to the partial melting of conti- 50° N nental ice sheets present over Greenland and West Antarctica. Ice sheets do not all exhibit identical 8 °C sensitivity to changes in temperature: in the Arctic 40° N region, the last interglacial was sufficiently warm to bring about a reduction, by about 50%, in the 30° N b size of the Greenland Ice Sheet. On the other hand, 80° W 60° W 40° W 20° W 0° in Antarctica, air temperature is very low, and the LSCE/CEA-CNRS-UVSQ West Antarctic Ice Sheet, the base of which lies 600 m Figure 1. below sea level, is far more sensitive to the tem- The mechanisms involved in Heinrich events. Shown at a, temperature during a glacial period, prior to the discharge event. At b, impact of an iceberg discharge on surface water (1) D. ROCHE, D. PAILLARD and E. CORTIJO, “Constraints temperatures. A reversion to normal conditions is found to occur, once the iceberg meltwater on the duration and freshwater release of Heinrich event 4 has disappeared. Arrows correspond to the North Atlantic Drift, in undisturbed (red), through isotope modelling”, Nature 432, 2004, pp. 379–382. and disturbed mode (orange); dotted lines correspond to the 8 °C isotherm.

CLEFS CEA - No.57 - WINTER 2008-2009 19 Climate research, a major challenge

of available marine sediment core samples, from all heat oceans around the world, allowed an isotopic dif- transfer to the ference to be evidenced between animal shells for- atmosphere med in modern deepwater and those from the last interglacial. This difference is quite small, since, converted into temperature values, it corresponds to about 0.3–0.5 °C, depending on the ocean basin. Pacific Atlantic Ocean In this case again, coupled use of models of inter- Ocean warm surface mediate complexity and isotopic data made it pos- current sible to account for the warming of Atlantic deepwater during the last interglacial. Indeed, the orbital Indian Ocean parameters governing the amount and distribution of the energy the Earth receives from the Sun have

deep, cold salty not remained constant over time. 125,000 years ago, current summers were warmer than present-day summers, whereas greenhouse gas concentrations were similar to the values found for the preindustrial heat transfer to the atmosphere Holocene. The model yields a satisfactory simula- Yuvanoé/CEA tion of an ocean that was globally warmer, The deep circulation, known as thermohaline circulation, generated by differences in 125,000 years ago, than it is at present. Changes in density between water masses. In the Norwegian Sea, but equally around Antarctica, waters become very cold. A fraction of the water freezes up (at around –1.8 °C), forming sea water temperature, at a depth of 500 m, in the ice (ice shelves), and sheds its salt, thus increasing salinity in the liquid water. This results Southern Ocean, as simulated by the model, indi- in very salty, very cold – and hence very dense – water, which sinks to the bottom of the cate a warming of around 0.1–0.5 °C. This may seem ocean. This water then travels along an extended circuit, close to the bottom of the world’s oceans. As cold, deep waters rise up again, through diffusion into warmer masses, small, however the consequences of such warming or through wind-driven processes near certain coastlines, or in the equatorial region, these should not be taken lightly. Indeed, satellite obser- waters rise again to the surface, where they heat up. They are taken over by surface vations show that the rate of retreat, for glaciers circulation, and ultimately returned to the regions of deepwater formation, at the end of a emanating from the Antarctic Ice Sheet, increases circuit that may take 1,000 years. (IPCC, Third Assessment Report, 2001.) by 1 m/year for every rise by 0.1 °C in the temperature of the seawater bathing them. The West perature of the seawater that bathes it, than it is to Antarctic Ice Sheet is thus peculiarly vulnerable to air temperature. Ascertaining the evolution of deep- small changes in temperature. water temperatures, during the last interglacial, is thus a key to understanding the possible destabili- An increasingly sophisticated tool zation mechanisms affecting the West Antarctic Ice Sheet.(2) Here again, the isotopic tool proves to be With the increased precisions achieved by measu- of prime importance. Highly precise investigation ring equipment, it is now becoming feasible to measure very slight isotopic effects, affecting the 17O isotope of oxygen, in air bubbles trapped in ice cores, (2) J.-C. DUPLESSY, D. ROCHE and M. KAGEYAMA, and derive from this the past evolution of the bio- “The deep ocean during the last interglacial period”, Science 316 (5821), 2007, pp. 89–91. sphere. In carbonates, it is now feasible to measure more complex isotopic combinations: thus, measurement of equilibrium concentrations, for the species involved in the following reaction:

13 16 2- 12 18 16 2- 13 18 16 2- 12 16 2- C O3 + C O O2 ↔ C O O2 + C O3

should allow a direct determination to be made of the temperature of the waters in which these carbonates precipitated, even as the 18O/16O ratio is equally dependent on the water’s 18O content. All of these ongoing developments, being carried forward at LSCE, are opening up new prospects for the understanding of climate phenomena. Over the past 50 years, isotopic geochemistry has evidenced its potential, for the purposes of identifying and quantifying environmental changes, particularly with respect to the study of past climates. Isotopic geochemistry still has much to offer. LSCE P. Bazoge/CEA P. > Elsa Cortijo The basement core-sample storeroom, sited at Gif-sur-Yvette, near Paris (France), holds the collection of marine sediment samples taken from all oceans, around the world. These Climate and Environmental Sciences sediments contain many organisms, which recorded the conditions prevailing in their Laboratory/Pierre-Simon Laplace Institute environment, as they developed. The isotopic composition of foraminiferal shells found Joint CEA–CNRS–UVSQ Research Unit in such samples yields information as to the climate prevailing during the foraminifers’ Physical Sciences Division lifetime. Bottom left, a marine sediment core sample from the North Atlantic. It has been cut into segments 1.50 m long, which, when stacked, make it possible to go back in time, CNRS (Gif-sur-Yvette) across geological timescales.

20 CLEFS CEA - No.57 - WINTER 2008-2009 FOCUS A Journey to the center of the Earth, and the outer reaches of the atmosphere

he Earth is a solid, rotating sphere, Twith a mean diameter of 12,750 km, surrounded by a gaseous envelope, the atmosphere. About 71% of its surface is covered with water, the remainder consisting in continents, and islands, of variegated relief, and very unevenly distributed.

The Earth’s internal structure Formed some 4.57 billion years ago, through the accretion of meteorites, the Earth consists in a succession of envelopes, of diverse thicknesses and compositions, the main envelopes comprising, from the surface to the planet’s center: the lithosphere, the mantle and the core (see Figure 1). These layers were identified through investigations on the propagation StockTrek of seismic waves, traveling through and The Earth is covered with water over some 71% of its surface. across the globe in all directions, this determination being based on the fact that the velocity of a seismic wave changes abruptly, in a major way, as it crosses into a new medium. This method made it possible to ascertain the state of matter, at depths that are beyond human reach. 9 The lithosphere (0–100 km), i.e. the glo- 10 be’s superficial shell, is divided into a number of rigid segments, the tectonic plates, which move across the viscous material in the underlying region, in the upper mantle, 11 known as the asthenosphere, and are in constant motion. Comprising as it does the 8 Earth’s crust, and part of the upper mantle, 6 the lithosphere’s depth varies, from 100 km 1 under the oceans, to 300 km under the continents. The continental crust, which is 7 solid, and mainly granitic,(1) though in pla- ces overlain by sedimentary rocks,(2) has a 5 depth standing, on average, at 30 km under continents, which may reach 100 km under mountain ranges. The oceanic crust, like- 4 Skip to page 22 2 3 (1) Granite: a dense, magmatic rock consisting of crystals visible to the naked eye, mainly quartz (silica [SiO2]), micas (minerals chiefly consisting of aluminum silicate, and potassium), alkali 1 continental crust 5 outer core 9 Gutenberg discontinuity feldspars (KAlSi3O8), and sodium plagioclases 2 oceanic crust 6 inner core 10 Mohoroviˇcic´ discontinuity (NaAlSi3O8). 3 upper mantle 7 lithosphere 11 Lehmann discontinuity (2) Sedimentary rocks: rocks arising from the 4 lower mantle 8 asthenosphere accumulation, and compacting of debris of mineral provenance (degradation of other rocks), StockTrek or of organic origin (animal or vegetal remains, Figure 1. fossils), or from chemical precipitation. The Earth’s internal structure.

CLEFS CEA - No.57 - WINTER 2008-2009 21 Climate research, a major challenge

FOCUS A StockTrek

Lava flow in Hawaii. Magma wells up from the Earth’s interior, and flows out in the form of lava.

22 CLEFS CEA - No.57 - WINTER 2008-2009 at the planet’s surface owing to the green- gas volume (ppmv) house effect it generates (see Focus C, nitrogen (N ) 780,840 (78.084%) Greenhouse gases and aerosols at the cen- 2 oxygen (O ) 209,460 (20.946%) ter of the climate change debate, p. 66). 2 argon (Ar) 9,340 (0.934%) Table. Indeed, in the absence of any atmosphere, Composition of the carbon dioxide (CO2) 382 (0.038 2%) surface temperature would stand at around atmosphere, in the neon (Ne) 18.18 –18 °C, rather than the 15 °C observed. vicinity of the Earth’s helium (He) 5.24 surface. Atmospheric air consists in a mixture of methane (CH ) 1.745 In thermodynamic gases (see Table), holding suspended par- 4 krypton (Kr) 1.14 terms, atmospheric air ticles, both liquid (water droplets…), and is treated as a mixture hydrogen (H2) 0.55 solid (ice crystals, dust particles, salt crys- of two gases: dry air nitrous oxide (N2O) 0.30 and water vapor. tals…), with most of its mass lying close to Greenhouse gases ozone (O3)0.04 the Earth’s surface. At sea level, atmosphe- appear in purple. CO2 water vapor (H2O) from 1% (in polar regions) ric pressure stands at 1,013.25 hPa. Gas to 4% (in equatorial regions) concentrations stood (highly variable) at 280 ppmv in 1800, molecules become rarified, and disperse 345 ppmv in 1998. at higher altitude, and pressure falls off. The atmosphere is thus ever less dense as altitude increases, until it finishes by “blen- ding into” outer space. 100 The atmosphere comprises a number of thermosphere layers, within each of which temperature varies differently, as a function of altitude: mesopause 80 the troposphere, the stratosphere, the mesosphere and the thermosphere (see Figure 2). In the troposphere (from the Earth’s surface 60 mesosphere to 8 km over the poles, 15 km at the equator), temperature declines swiftly with alti- stratopause

tude, at a rate of about 6.4 °C per kilometer. altitude (km) Temperature varies, on average, from 20 °C 40 at ground level to –60 °C at the upper boun- ozone layer stratosphere dary of this region. As this layer holds 80–90% Figure 2. of the total air mass, and virtually all of the 20 The layers in the water vapor, pressure and density are highest tropopause atmosphere. Their troposphere in this region. It is in this region that most boundaries are determined on the basis meteorological phenomena (cloud forma- 0 - 100 - 80 - 60 - 40 - 20 0 20 of discontinuities in temperature variations, tion, rain…) take place, together with the hori- temperature (°C) zontal and vertical motions of the atmosphere as a function of altitude. (thermal convection, winds). In the topmost layer of the troposphere, known as the tropopause, temperature undergoes an inversion, and begins to rise. The height of this region varies, from the poles to the equator, but equally according to the seasons. In the stratosphere (from 8–15 km to 50 km), temperature stays constant over the first few kilometers, then rises slowly, and far more swiftly thereafter, increasing with altitude up to 0 °C. This region contains, at an altitude of around 25 km, a large part of the ozone layer. Ozone is produced through the effects of solar radiation on oxygen molecules. The ozone layer acts as a protective shield, by absorbing the Sun’s ultraviolet radiation, resulting in the layer heating up. It is in the stratosphere that short-wavelength light rays undergo scattering over the air’s constituent Most meteorological molecules – hence the sky’s blue color in phenomena take place in the troposphere, the daytime – and it is host to violent winds, racing region where pressure

Skip to page 24 StockTrek and density are highest.

CLEFS CEA - No.57 - WINTER 2008-2009 23 Climate research, a major challenge

FOCUS A

air, yielding ions and free electrons. This layer exhibits the property of reflecting radio waves. A fraction of the energy radiated by a radio transmitter is absorbed by the ionized air, the remaining fraction being reflected downwards, thus allowing communications to be set up between various points on the Earth’s surface, which, in some cases, may be far distant from one another. It is in the ionosphere that auroras occur. Lying at an altitude of 60–70 km, the neutropause stands as the boundary between the ionosphere and the neutro- sphere, which is the lower region of the atmosphere, where electron concentration remains insignificant. In the exosphere (from 350–800 km to 50,000 km), the region extending beyond the ionosphere, the laws of gas physics cease to be applicable. Molecules disperse, and become rarified as altitude increases. The lighter, more agitated molecules may then escape the Earth’s attraction, and be StockTrek lost forever, ultimately, to interstellar space. The stratosphere holds a major part of the ozone layer, which acts as a protective shield It is in this layer that most satellites are against the Sun’s harmful radiations. placed into orbit. At an altitude of around 2,000 km, ions Page 23 cont'd account for the greater part of the parti- at velocities of up to 200–300 km/h. In the cles present. They form the magneto- top layer of the stratosphere, known as the sphere, where the Earth’s magnetism stratopause, temperature begins to decline takes over from gravitation. This region, again. chiefly holding protons as it does, is also In the mesosphere (from 50 km to 80 km), known as the protonosphere (or proto- temperature decreases swiftly with alti- sphere). The magnetosphere acts as a tude, down to –80 °C. This is the coldest shield, protecting the Earth’s surface from layer of the atmosphere, and it is as a rule the harmful effects of the solar wind. in this region that meteorites burn up as In like manner, if the criterion used is that they enter the atmosphere. In the top layer of the air’s changing composition along a of the mesosphere, known as the meso- vertical direction, the atmosphere may be pause, temperature begins to rise again. divided into two regions: the homosphere In the thermosphere (from 80 km to (from the Earth’s surface to an altitude of 350–800 km), temperature again increa- 80 km), within which the composition of ses with altitude, rising well above 1,000 °C. dry air undergoes little variation, and the This heating up is due to the strong absorp- heterosphere, extending above it. The level tion, by oxygen, of ultraviolet radiation emit- above which air composition alters signi- ted by the Sun. In this region, while tem- ficantly is known as the homopause. peratures are high, density is extremely low, and the prevailing pressure is very low. Oxygen molecules break up into two oxygen atoms. The upper boundary of this layer is known as the thermopause. Aside from temperature, other criteria

C. Morel/Our Polar Heritage Polar C. Morel/Our may serve to define distinct layers in the Polar auroras – here an aurora borealis atmosphere. (Northern lights) – are caused by the The ionosphere, a region coterminous with interaction between solar wind particles the thermosphere, is characterized by a and the upper atmosphere. They occur in the high concentration of electrically charged ionosphere, a region characterized by a high concentration of electrically charged particles. There, solar energy is so strong particles. that it “breaks up” the molecules in the

24 CLEFS CEA - No.57 - WINTER 2008-2009 Long-term monitoring of atmospheric CO2 Models as a whole – atmospheric models in particular – are dependent, in terms of validity, on the amount and quality of the measurement data fed into them. This proves to be all the truer as regards the long-term monitoring of carbon dioxide concentrations, since factors of signal interference abound. Which is why ever higher-performance networks are being developed, internationally.

Connecting and setting up the sampling lines on the sampling heads, for all the measuring instruments at the Ivittuut site, on the western coast of Greenland. The scientific purpose of the mission, which extended from 1 August 2007 to 20 September 2007, was to set up two automated continuous measurement instruments: one for CO2, the other for atmospheric oxygen. The measurements will enable scientists at LSCE to set better constraints on North Atlantic carbon balances, and achieve a better understanding of the part played by that ocean in the global

C.Morel/Our Polar Heritage Polar C.Morel/Our carbon cycle.

ystematic measurement of atmospheric CO2 was up a new CO2 monitoring station in South Greenland. Sinitiated, in 1957, by US scientist Charles David At such a time, it is opportune to ask a number of (1) Keeling, with support coming under the International questions: How has the CO2 measurement network Geophysical Year.(2) 50 years later, taking advantage of developed over the past half century? What have we (3) the International Polar Year (IPY), France’s Climate learned about the CO2 cycle from atmospheric mea- and Environmental Sciences Laboratory (LSCE: surements? What are the goals set for the coming years? Laboratoire des sciences du climat et de l’environne- It is these queries we aim to answer, by providing an ment), together with the Institute for Research on the overview of the CO2 monitoring network. Fundamental Laws of the Universe (IRFU: Institut de recherche sur les lois fondamentales de l’Univers) set The first steps in the systematic observation of atmospheric CO2 (1) Keeling (Charles David): US scientist (1928–2005) whose measurements of carbon dioxide, made at Mauna Loa In 1957, Charles David Keeling set himself the goal of Observatory, alerted the world community determining the atmosphere’s average CO content to the anthropogenic contribution to the greenhouse effect 2 and climate warming. and of identifying the processes governing this. At the (2) International Geophysical Year (IGY): an ensemble of time, measurements had already been carried out, at research programs, coordinated on a worldwide scale, carried specific locations, in particular in Scandinavia, where, out from July 1957 to December 1958, at a time of maximum as early as 1954, a measurement network, comprising solar activity, for the purposes of improving our knowledge of the Earth’s physical properties and the interactions between some 15 sites, had been set up. In view of the widely the Sun and our planet. fluctuating readings obtained, from one station to the (3) International Polar Year (IPY): an ensemble of research other, but equally from one day to the next, the scien- programs, internationally coordinated (March 2007–March tists running the project felt, at the time, that it would 2009), for the purposes of achieving major advances in our not prove feasible to arrive at a reliable estimate of knowledge of the polar regions, where some of the answers are to be found, regarding issues of world concern, atmospheric CO2 content, and its long-term variabi- as to the evolution of the environment. lity, through measurements of this kind. The records

CLEFS CEA - No.57 - WINTER 2008-2009 25 Climate research, a major challenge

plant respiration. This choice, of building stations to house advanced instruments in Antarctica, or on top of Mauna Loa (Hawaii), a 3,400-m high volcano in the middle of the Pacific Ocean, was anything but an easy option. However, at the outcome of that initiative, after careful screening to discount certain CO2 spikes associated to Hawaiian volcanic emissions, or diesel engine exhaust at the South Pole base, Keeling obtained records that turned out to be remarkably stable. These enabled him to provide, for the first time, an estimate of the CO2 content of our atmosphere, as standing, at the time, at 315 ppm. Carried out as it was over a full year, at these two remote sites, this high-precision measurement campaign yielded a great deal of information as to the global carbon cycle. It allowed, in particular, a seasonal cycle of 5–6 ppm amplitude to be detected at Mauna Loa, which was not found in the Southern Hemisphere, further warranting that it be attributed to carbon exchanges with vegetation – a finding achieved through comple- 13 mentary measurements of the CO2 isotope. There is Checking, prior a decrease in atmospheric CO2 content in spring and to carrying out tests, the sampling head fitted summer, owing to carbon uptake from plants and their to the sample flask photosynthesis reactions. Conversely, plant and soil carrying case, at the microorganism respiration causes an increase in Ivittuut site (western coast of Greenland). atmospheric CO2 concentration in fall and winter. In

In the foreground, Heritage Polar C. Morel/Our an equilibrium carbon cycle, the two mechanisms can- sample flasks. cel each other out, and CO2 concentration remains sta- obtained by Charles David Keeling were soon to prove ble over the long term. However, as early as the end them wrong. of 1958, the high-precision monitoring of CO2 in Two factors account for this difference in outcome bet- Antarctica already evidenced a disequilibrium in the ween the two programs. The first one stems from the carbon cycle, by showing up a rise of some 0.8 ppm fact that Keeling tweaked his measuring instrument annually. (an infrared absorption spectrophotometer) to Following on this, France’s contribution to atmosphe- achieve hitherto unequalled levels of precision ric CO2 monitoring started in 1981, on Amsterdam (±0.3 ppm). The second factor lay in his decision to Island (just 58 km2), lying in the midst of the Indian set up his stations at remote sites, away from sources Ocean and coming under the French Southern and of CO2 emissions, whether due to human activities or Antarctic Lands. At that time, the international

Amsterdam Island Mace Head

440 440

420 420

(ppm) 400 400 2

CO 380 380

360 360 Jan. Feb. Mar. Apr. May June Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June Jul. Aug. Sep. Oct. Nov. Dec.

Puy de Dôme Gif-sur-Yvette

440 440

420 420

(ppm) 400 400 2

CO 380 380

360 360 Jan. Feb. Mar. Apr. May June Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June Jul. Aug. Sep. Oct. Nov. Dec.

Figure 1. Daily CO2 averages, as measured, in 2005, at four RAMCES observatories, located in very diverse environments: one remote background site, away from any source of pollution (Amsterdam Island); an Irish coastal site (Mace Head); a site in a rural environment, on top of the Puy de Dôme (south-central France); and a suburban site, at Gif-sur-Yvette (near Paris, France).

26 CLEFS CEA - No.57 - WINTER 2008-2009 measurement network comprised 10 observatories, carrying out continuous CO2 measurements, com- 460 plemented by about 15 sites where air samples would Amsterdam Island be taken, on a weekly basis. The latter procedure allows 440 Mace Head for the monitoring of CO2 trends, while calling for only Puy de Dôme 420 slight local logistical resources – samples being analy- Gif-sur-Yvette zed by central laboratories, including LSCE, which was Biscarosse 400 established in 1996. (ppm) Hanle In the early 1980s, all new sites were being set up on 2 islands, coastlines, or mountaintops – the aim, at the CO 380 time, being that of characterizing the North–South 360 CO2 gradient for the “background” atmosphere, i.e. the atmosphere away from local contamination sour- 340 ces, these generating high short-term variability (see 3 -6

Figure 1). With respect to CO2, the findings then sho- Southern Oscillation wed that sources of signal interference originate both -4 in human activities and vegetation, and that such sour-

2 Index ces exhibit strong variation over a span of a few hours -2 or a few kilometers. As measurement sites were selec- 0 buildup rate

ted on the basis of their representative character, at a 2 (ppm/year) 1 large scale, with regard to CO2 emissions, the obser- CO 2 vation network thus failed, for far too long, to cover continental areas. 0 4 1980 1985 1990 1995 2000 2005 Quantifying and monitoring carbon sinks Figure 2. We owe most of our knowledge of the global carbon Top: monitoring of atmospheric CO2 at RAMCES observatories. cycle to extended time series of measurements, i.e. Bottom: CO2 buildup rate at Amsterdam Island (red) and Southern Oscillation Index (SOI) (black dots), this being a measure of the monthly variation in the difference in standardized series over time intervals longer than 20 years, rea- sea-level pressure between Tahiti and Darwin. A persistently negative SOI value is an indicator dings from such series being available for 20 stations, of an El Niño episode. sited with regard to the background atmosphere. These measurements make it possible, in particular, A number of processes may account for such a large- to monitor the rate of CO2 buildup in the atmosphere. scale variation in atmospheric CO2 concentrations. Bearing in mind that, since 1800, 350 Gt C (billions Consequently, the issue arises of how the respective of tonnes carbon) have been released into the atmo- contributions should be evaluated from carbon sinks sphere through fossil energy combustion and defo- and sources – of anthropogenic and natural prove- restation, average atmospheric CO2 concentrations, nance. Aside from models designed to take into at the present time, should stand close to 450 ppm. account vegetation and the ocean, which do yield Now, the average CO2 concentration is found to stand some initial answers, the empirical approach allows at 385 ppm. This finding shows that natural reser- other atmospheric molecules (CO, O2, H2…) to be voirs (the ocean, the continental biosphere) act as measured, along with the various isotopic ratios for 13 12 14 12 16 18 carbon sinks, absorbing more than half of the CO2 CO2 ( C/ C, C/ C, O/ O). These various tra- emitted by human activities. cers monitor exchanges of CO2 in varying propor- On average, only 45% of CO2 emissions accumulate tions, depending on the process involved. For instance, in the atmosphere. This quantity, known as the a CO2 source due to combustion (fires, heating, atmospheric fraction, varies markedly from one year transportation…) will involve a concomitant emis- to the next, even though anthropogenic CO2 emission of CO, whereas plant CO2 respiration releases sions are rising regularly, evidencing no sharply defi- no CO. Likewise, a continental carbon sink will cause ned surge or downturn. This high interannual varia- an increased atmospheric 13C/12C ratio (since vege- 12 bility found for the rate of atmospheric CO2 buildup tation preferentially takes up C), whereas an ocea- may thus only be accounted for by variability in the nic carbon sink will cause virtually no change in the exchanges with oceans and the continental biosphere. 13C/12C ratio. Through the simultaneous measure- For instance, analysis of the measurements obtained ment of a number of atmospheric tracers at obser- on Amsterdam Island show high buildup rates for the vatories, it thus becomes feasible to quantify the respec- years 1983, 1987, 1988, 1995, 1998, and 2002. These tive contributions from carbon sources and sinks. periods match those of oceanic–climatic perturba- Thus, the monitoring of atmospheric CO2 shows that tions caused by the El Niño coastal current (see carbon sinks absorb, on average, 55% of anthropo- Figure 2). They are characterized by large-scale alte- genic emissions, while the measurement of further rations in wind regimes and precipitations, resulting tracers allows a distribution to be arrived at for the in anomalous temperatures, droughts and fires. respective contributions from the oceanic sink (~ 25%) Atmospheric measurements show that the climate and the continental sink (~ 30%). Be that as it may, upheavals due to the successive impacts of the El Niño it should also be noted that recent atmospheric and current bring about a temporary reduction in car- oceanographic measurements would seem to point bon uptake by natural sinks, a greater fraction of the to saturation mechanisms affecting the oceanic car- emissions of human origin thus remaining in the bon sink, in regions such as the Subantarctic Indian atmosphere. Ocean and North Atlantic Ocean.

CLEFS CEA - No.57 - WINTER 2008-2009 27 Climate research, a major challenge

Apart from drawing up a global balance for the carbon cycle, the atmospheric measurement network now seeks to quantify the intensity and equally the evolution of carbon sources and sinks at the regional scale. For researchers, this sets a challenge involving manifold stakes. A scientific stake, first of all, since identifying the ecosystems or the ocean basins responsible for the absorption of anthropogenic CO2 will allow an understanding to be gained of the processes involved, and thus make for easier prediction of their evolution and vulnerability with respect to future climate changes. And a socio–economic stake C. Morel/Our Polar Heritage Polar C. Morel/Our also, insofar as the deployment of strategies to curb Connecting the air line to the atmospheric oxygen measuring greenhouse gas emissions will call for strategies to device. verify emission balances for these gases, e.g. on the scale of a country such as France. European Union, further participants include the Max Planck Institute for Biogeochemistry (MPI–BGC)(7) and France’s LSCE. The growth of the atmospheric CO2 measurement network The European measurement network exhibits the peculiar feature of being both relatively dense on the Currently, the atmospheric CO2 monitoring network ground and highly heterogeneous. This is due to the comprises some 50 observatories carrying out mea- fact that many institutes contribute to it, each one surements on a continuous basis, together with however with a single measuring site – the strongest 60 dedicated air sampling sites, samples being taken contribution coming from the Atmospheric on a weekly basis for analysis in a central laboratory Greenhouse Compound Measurement Network (see Figure 3). The chief players in this measurement (RAMCES: Réseau atmosphérique de mesure des network include the Earth System Research Laboratory composés à effet de serre)(8) developed by LSCE (see of the US National Oceanic and Atmospheric Figure 4). In terms of measurement precision, this Administration (ESRL/NOAA),(4) Australia’s CSIRO international network aims to sustain, over the long Marine and Atmospheric Research, coming under term, a comparability level of 0.1 ppm (0.025%) bet- the Commonwealth Scientific and Industrial Research ween stations. Achieving this entails carrying forward, Organization (CMAR/CSIRO)(5) and Japan’s National and expanding the intercomparison programs set up Institute for Environmental Studies.(6) For the between the main institutes charged with running the network, but equally keeping stations equipped (4) The Earth System Research Laboratory (ESRL) is with high-performance instrumentation. For the a US laboratory based in Boulder (Colorado), working on the understanding of the Earth’s climate, and its evolution, within the National Oceanic and Atmospheric Administration (7) The Max Planck Institute for Biogeochemistry (MPI–BGC) (NOAA), the US federal agency charged with research is a German, Jena-based laboratory carrying out research on the oceans and atmosphere. chiefly concerned with the biogeochemical cycle of carbon. (5) CSIRO Marine and Atmospheric Research (CMAR) (8) The Atmospheric Greenhouse Compound Measurement is an Australian research agency working on climate changes Network (RAMCES: Réseau atmosphérique de mesure des and their impacts within the Commonwealth Scientific and composés à effet de serre) is a network of atmospheric Industrial Research Organization (CSIRO), the Australian observatories set up to address two main goals: first, to gain an national government scientific research organization. understanding of the main greenhouse gas cycles, and the part (6) The National Institute for Environmental Studies was set they play in the climate system; while the second goal is to up as the research department of the Japanese government quantify the carbon balance for a major region, together with Environment Agency (now the Japanese Ministry of the its variability, with a view to the verification of greenhouse gas Environment). emission control or reduction policies.

Figure 3. World atmospheric CO2 monitoring network. Blue dots show continuous measurement sites, red dots weekly

sampling sites. Anglia of East A.C. Manning, University

28 CLEFS CEA - No.57 - WINTER 2008-2009 Griffin

Mace Head 55° N Ivittuut 60° N Mace Head

Hanle 30° N Ile Grande 50° N Gif-sur-Yvette

Traînou Lamto 0° Orleans

observatory Biscarrosse planned observatory Puy de Dôme 45° N Réunion Island tall tower 30° S air sampling airborne measurements Amsterdam Island 10° W Pic du Midi Begur 5° W 60° W 0° 60° E 120° E 0° 5° E

Figure 4. The Atmospheric Greenhouse Compound Measurement Network (RAMCES: Réseau atmosphérique de mesure des composés à effet de serre). purposes of carrying out high-precision measurements, most observatories use infrared absorption spectrophotometers, as employed by Charles David Keeling at Mauna Loa. A few sites are fitted with gas chromatographs. Currently, no commercial measuring instrument can guarantee the required precision of 0.1 ppm. Consequently, all the analytical devices deployed at the various sites are based on commercial sensors, optimized however in research laboratories. Thus, LSCE, working in collaboration with IRFU, has developed a CO2 measuring instrument dubbed Caribou.(9) Featuring an infrared absorption analyzer, put on the market by LI–COR corporation, this instrument has the ability to effect the continuous measurement of CO2 concentration in air, with a reproducibility level of about 0.01 ppm. Improving the instrument’s performance, by a factor higher than

10, entailed highly precise stabilization of the abso- O. Cloué lute pressure (to within less than 0.05 mbar) and RAMCES measurement temperature (less than 0.01 °C) of the gas being site at Hanle (Ladakh, India), analyzed. From 2005 to 2007, four automated, where Caribou instruments remotely operable Caribou stations were construc- are deployed. ted and deployed: in France (at Traînou and Biscarosse), in the Himalayas (Hanle) and in Greenland (Ivittuut). The two French stations may serve to illustrate the evolution, in recent years, of the greenhouse gas monitoring network, which is now also looking at continental areas. This was an indispensable development, if an understanding was to be gained of the part played by the continental biosphere, though a development, at the same time, that involved analyzing signals subject to strong perturbation from CO2 sources localized within a radius of a few

(9) Caribou is a self-standing CO2 measurement instrument, suitable for remote operation, constructed around a RAMCES measurement site commercial catalytic analyzer, featuring improved precision at Biscarosse (southwestern through accurate control of physical parameters such as France), where Caribou

temperature and pressure. CEA/DR instruments are deployed.

CLEFS CEA - No.57 - WINTER 2008-2009 29 Climate research, a major challenge

kilometers around the instruments – which does raise issues, the aim being that of obtaining signals representative of a spatial scale coextensive at least with one French administrative region. To achieve this, researchers opted to set up their instruments on mountaintops, such as the Puy de Dôme (in central France), or atop telecommunications towers, e.g. the tower at Traînou, which is 180 m high. In the latter case, the instruments are set up at the base of the tower, while air is sampled at the top, to mini- mize the influence of local sources, confined as this is to surface layers. In order to characterize the manner in which CO2 is transported over longer distances, regular airborne measurements complement the findings from this ground network.

Prospects for the observation network

Within two years, two satellites should be circling the Earth to carry out measurements of CO2 concentration, vertically integrated (i.e. yielding the mean CO2 value between the ground surface and the upper atmosphere), with a precision of around 1%. On the other hand, however valuable this satellite contribution may prove, it will be inadequate with regard to the regional breakdown of carbon fluxes. CEA/DR Indeed, at the scale of a country such as France, the The CO2 measurement instrument dubbed Caribou. drawing up of carbon balances may only be contem- plated by way of a combination of spaceborne, air- red by LSCE, will necessarily play an essential part. borne and ground measurements. Setting up a high- Initiated in April 2008, this project seeks to develop precision ground-based network is thus a requisite, and coordinate the greenhouse gas measurement net- if only in order to validate satellite measurements and work across Europe. Ultimately, ICOS will comprise guarantee the integrity of long-term monitoring. about 30 stations, fitted with instruments providing In this respect, the European Integrated Carbon a capability to measure both greenhouse gases, and Observation System (ICOS) infrastructure,(10) stee- meteorological parameters. All of these stations will be connected, first of all, to a European calibration (10) The Integrated Carbon Observation System (ICOS) is a center, to ensure a direct connection with interna- European research infrastructure deploying a measurement network to monitor greenhouse gas concentrations, and tional measurement programs, and subsequently to biospheric CO2 fluxes, at about 20 sites across Europe. a data center, intended to ensure near-real-time distribution of the readings subject to standardized quality control. ICOS instruments will also be installed in stations in undersampled areas, e.g. Africa, Siberia or India. Thus, at the present time, there is but one measuring station in India, this being set up, in 2005, at Hanle, under the aegis of a French–Indian research program. By the end of 2008, LSCE will have built a new center at Lamto, in the Ivory Coast. With the ICOS project, a greenhouse gas observation network is being deployed that is unique the world over, in terms of density, and the consistency of measurement techniques and quality control. The data set it will provide should bring LSCE and the European community to the forefront of the research effort on regionalization of CO2 fluxes, as of other greenhouse gas fluxes (CH4, N2O).

> Michel Ramonet Climate and Environmental Sciences Laboratory (LSCE)/Pierre-Simon Laplace Institute Physical Sciences Division CEA Saclay Center (Orme des Merisiers) Making the final line > Olivier Cloué connections (air, Institute for Research on the Fundamental Laws calibration standard) on of the Universe (IRFU) the Caribou, a continuous Physical Sciences Division CO2 measurement

instrument. Heritage Polar C. Morel/Our CEA Saclay Center

30 CLEFS CEA - No.57 - WINTER 2008-2009 The evolution of air quality under the impact of global changes

While greenhouse gases emitted by human activities are having a decisive impact on global climate changes, on the other hand, other pollutants – gases, and aerosols – determine air quality and impact health. From the global through to the regional or local scale, changes in pollutant emissions and in the climate will result in a marked alteration in the air we breathe.

Campaign in the equatorial Atlantic Ocean, on board the Meteor research vessel, to measure emissions of trace gases (CO, volatile organic compounds)

CEA/DR by the ocean.

s a consequence of the development of space tech- undergoes oxidation, as indeed all volatile organic Anology in the 1960s, observation of the Earth from compounds, from the hydroxyl (OH) radical, this outer space has brought about a real awareness of the being chiefly yielded by interaction of ozone with water global environment and its fragility. Indeed, pollutants, vapor, in the presence of ultraviolet radiation. gases and aerosols, released since the onset of the By their presence, these major greenhouse gases bring industrial age by human activities are disturbing the about a perturbation in the climate by trapping energy composition of a layer of atmospheric fluid that is radiated from the Earth. Not one of these gases has any extremely thin, at the scale of the planet (10–100 kilo- direct effect on health or the environment on Earth. meters), each of these constituents then embarking on On the other hand, many other gases, or aerosols, relea- its own specific evolution. For instance, the concen- sed by human activities, or arising from the chemical tration of carbon dioxide, which is chemically inert, transformation of compounds so released, do impact has increased by 30% over 150 years, even though health and living ecosystems across the surface of the vegetation and the oceans reabsorb close to half of all planet: these are the pollutants which determine air emissions. Nitrous oxide released by agricultural acti- quality. This category includes small-particle aerosols vities shows a similar increase. Over the same period, (particulate matter with a diameter of less than methane concentration has seen a threefold increase. 10 microns, known as PM 10), which may be primary This, of course, is not a chemically inert gas, since it aerosols (i.e. directly emitted, as e.g. soot), or secondary

CLEFS CEA - No.57 - WINTER 2008-2009 31 Climate research, a major challenge

aerosols, e.g. nitrates, or sulfates. This category fur- out by the Paris district air quality organization, ther includes oxidizing pollutants yielded by photo- Airparif, its influence is felt over a few hundred chemical processes, e.g. ozone. Any control and reduc- meters.(1) Further out, concentrations become more tion policy, as regards pollutant emissions, thus needs homogeneous, and are chiefly influenced by emissions must meet a multiplicity of constraints which may only at the regional scale. Concentrations depend, in that be taken on board in integrated fashion. The challenge case, on proximity to a large city, or major industrial lies in not hindering economic development while centers, and population density. In Europe, regions protecting the climate and air quality to the best of our experiencing the heaviest emissions are the Benelux abilities. countries and the Po basin, in northern Italy, owing to population density. The evolution of regional air The factors involved in changes quality is then dependent on regional, national, or in air quality even European policies, as regards curbing pollutant emissions. Such evolutions are much slower, invol- Two factors will contribute, in the decades to come, ving timescales ranging from several years to a decade. to alterations in air quality, at any given location: chan- Emission reductions associated to a technological ges in pollutant emissions, and changes in the climate. innovation, e.g. the oxidation catalyst fitted to certain As regards pollutant emissions and the proximate envi- vehicles (the catalytic converter), may only be felt after ronment, the impact of these factors may be evaluated over the short term. For instance, air quality in the (1) The full findings from this survey, carried out by Airparif, vicinity of a highway changes quite swiftly, depending may be accessed at the site: on traffic conditions. According to a survey carried http://www.airparif.asso.fr/airparif/pdf/Rapbagn.pdf.

surface ozone concentration (ppb) – July surface ozone difference (ppb) – July CLE scenario CLE scenario

ppbv

- 20.0 - 15.0 - 10.0 - 7.5 - 5.0 - 4.0 - 3.0 - 2.0 - 1.0 0.0 1.0 2.0 3.0 4.0 5.0 7.5 10.0 15.0 20.0

surface ozone difference (ppb) – July surface ozone difference (ppb) – July

Figure 1. Top left: average surface ozone concentration (in ppb), across the planet, in 2001, as simulated by the LMDz–INCA model, developed at the Pierre-Simon Laplace Institute. Top right: difference with average concentrations as predicted for 2030, at constant meteorological conditions, if global emissions conform to a scenario governed by strict implementation of current legislation. Bottom left: difference obtained for the more optimistic scenario, involving emission reductions compatible with available technologies. Bottom right: difference obtained taking as an assumption the IPCC’s pessimistic A2 scenario [taken from S. Szopa et al. (2006).

32 CLEFS CEA - No.57 - WINTER 2008-2009 some 20 years or so, this being the pace of automo- tive fleet turnover. Thus, due to such early measures, nitrogen oxide emissions from road traffic, in France, have declined by half, since 1990. The same may not be said of other sectors of activity. Another, aggravating factor is superimposed on this situation. It may occur that pollutants are transported from one continent to another. Indeed, it frequently happens that layers of aerosols are found in the atmosphere over Europe, coming from fires in North America, or from Russia, after traveling around the Earth. Such products are added to pollutants emitted locally, or in regional proximity. While, to date, air quality has chiefly undergone changes that were depen- CEA/DR dent on the various emissions involved, in future years, Pollutant transport at the regional, continental, or global this will also be influenced by climate change. scale, investigated by means of models integrating both chemistry and transport. Such models allow a prediction to be made, in particular, of the evolution of atmospheric The evolution of global air quality composition under the impact of changes in emissions and climate change. The composition of the global atmosphere, as regards reactive gases and aerosols, liable to impact air qua- these simulations, the same values are used, for meteo- lity, has considerably altered, over the past century, rological variables – namely, those for the year 2001 as a result of increased pollutant emissions. Globally, – for the purposes of simulating ozone concentra- emissions of nitrogen oxides as of volatile organic tions for 2030, as for 2001. Now, climate change indu- compounds (VOCs) have increased, from the onset ces a multiplicity of effects, some of them contradic- of the industrial age through to the 1980s, a trend tory, meaning any prediction exercise concerning the initially arising in developed regions. Thus, the glo- end of the 21st century is fraught with difficulties. bal concentration of tropospheric ozone has increa- Rising temperature will, in all likelihood, be conco- sed more than threefold since the 19th century. While mitant with increased atmospheric water vapor the evolution of aerosol emissions during the 20th concentrations, resulting in a drop in ozone concen- century is as yet imperfectly known, it would appear trations. This decline should prove significant in tro- highly likely that industrial emissions and use of coal pical and equatorial regions. On the other hand, in as a source of energy have generated, through to the southern temperate regions, owing to pollutant gas end of the 20th century, large concentrations of aero- emissions, increasingly dry conditions, together with sols in the atmosphere. At the present time, such emis- anticyclonic stagnation, will make for a photoche- sions have declined, or are in the process of declining, mically induced rise in ground-level ozone contents. in Europe and North America. On the other hand, Higher temperatures should also result in increased they are rising steeply in emerging countries, in Asia natural emissions of certain chemical compounds. in particular. For instance, isoprene, a reactive hydrocarbon pro- The evolution, in future years, of global emissions, duced by certain trees, including Northern European and the associated changes in air quality remain highly white oaks, increases markedly with temperature, thus uncertain. A study, carried out at the French Climate favoring photochemical ozone formation. Nitrogen and Environmental Sciences Laboratory (LSCE:

Laboratoire des sciences du climat et de l’environ- 0 1 nement), arrived at a number of estimates, as to the 2 4 differences in concentrations arising between 2001 6 9 12 and 2030 (see Figure 1). These findings were obtai- 36 ned using the simulation model developed by the Pierre-Simon Laplace Institute (LMDz–INCA),(2) which allows computation, at the same time, of oxidation chemistry and pollutant transport, at the global scale. This model will be used for the forthcoming simulations to be carried out by the Intergovernmental Panel on Climate Change (IPCC), for prediction purposes, for its future climate scenarios. According to the most likely scenario, the so-called “Current Legislation” (CLE) scenario, ozone concentrations rise markedly, due to emissions generated in Asia Figure 2. (particularly in India and China), while trends remain Map of reductions in life expectancy, in months, as estimated contrasted over Europe. These findings do not take by the International Institute for Applied Systems Analysis (IIASA), due to atmospheric pollution from fine particulate into account climate change-related effects, since, in matter (particle size of less than 2.5 microns). The European average, for this estimated life expectancy reduction, is (2) INCA (Interaction chimie–aérosols) is a model of higher than 8 months. Figure taken from the report for the chemistry–aerosol interactions and emissions. It is coupled European Commission’s Clean Air for Europe (CAFE) program with the LMDz general circulation model, which allows [M. Amann et al., CAFE Scenario Analysis Report No. 6: A final the interactive simulation of long-lived greenhouse gases set of scenarios for the Clean Air for Europe (CAFE) programme; (CO2, CH4, N2O). available at http://www.iiasa.ac.at/rains/cafe.html].

CLEFS CEA - No.57 - WINTER 2008-2009 33 Climate research, a major challenge

quate knowledge. Indeed, the computing power that 90 would be required, in order to take on board, in sufficiently detailed fashion, these phenomena, in cli- 90th centile mate prediction models, still falls well short of what 80 Figure 3. is needed. Median and 90th centile daily maximums of ozone concentration (ppb), for 70 The evolution of air quality in Europe every summer, computed over a set of 34 stations In Europe, it is now acknowledged that air quality providing homogeneous 60 data (i.e. involving no is impacting health. According to current estima- median major missing period), tes, fine particulate matter contributes to a reduc- from 1994 to 2004 (ppb) concentration tion in life expectancy by more than 8 months (full circles), and a 50 further set (61 stations) on average, or even 15 months in some regions, providing homogeneous e.g. Benelux (see Figure 2). On the basis of this fin- data from 1995 to 2004 40 ding, pollutant emission reduction targets have been (open squares). 1990 1995 2000 2005 set and taken up in the form of European Union Taken from R. Vautard year et al. (2007). Directives. For instance, France is planning to bring down its nitrogen oxide emissions by about 40% between 2000 and 2010. The targets adopted by the oxides arising from combustion, but equally genera- other European states being similar, pollutant ted by lightning discharges, will likewise increase in concentrations, as a whole, are showing a down- tropical regions, due to enhanced convection. ward trend in Europe. Rather spectacular drops in Increasingly dry conditions in regions such as the the concentration of primary compounds have even Mediterranean should promote eolian erosion, with been found in Paris, with a recorded falloff in nitro- a resulting higher inorganic fraction in aerosol par- gen oxides by 40% between 1990 and 2007. The ticulates (particularly due to dust, or sand entrain- evolution of maximum ozone concentrations over ment). One further consequence of such heightened Europe (see Figure 3), as characterized by the 90th drought conditions is an increased vulnerability of centile of concentration, on an annual basis, as forests to fires, a higher frequency of which would observed at several tens of sites, is downward: by about cause the atmosphere to be laden with carbon dioxide 5 ppb (7%) between 1997 and 2005, this including, and monoxide, and carbonaceous particles (soot), however, an “accident” in 2003, due to the excep- resulting in a degradation of air quality. Although this tional heatwave in that year. However, in spite of process is known but inadequately, a changing fre- the abnormal character of the conditions observed quency of stratospheric ozone intrusions into the during that summer, maximum ozone concentra- troposphere may act as a further factor in the evolutions still remained lower than, or comparable to, tion of air quality. Finally, anthropic changes in land those found in the summers of 1990 and 1994. This use also impact agriculture-related emissions and may be due to the fact that ozone concentrations affect the deposition of such pollutants as ozone onto are subject to contradictory influences. Indeed, plant surfaces: a falloff in ozone deposition results in owing to the effect of emission reductions in Europe, increased ozone concentration in the atmosphere. high values are coming down. However, rising glo- At the present time, it is still far from easy to quan- bal emissions of ozone precursors do tend to push tify the net impact of all of these phenomena, of which up the “background” concentrations present in the knowledge remains fragmentary. Issues raised by pre- atmosphere. Thus, a number of European sites evi- dictions of the evolution of global atmospheric com- dence, at the same time, declining maximum and position are not solely those stemming from inade- rising minimum values; the median values, as

ppbv - 10.0 - 7.5 - 5.0 - 4.0 - 3.0 - 2.0 - 1.0 - 0.1 0.1 1.0 2.0 3.0 4.0 5.0 7.5 10.0

Figure 4. Left, differences in ozone concentrations, between 2030 and 2001, as estimated according to a scenario involving implementation of current legislation, at the global, and European scale. Center, with changes in global emissions, though not in European emissions. At right, with changes in European emissions only. Taken from S. Szopa et al. (2006).

34 CLEFS CEA - No.57 - WINTER 2008-2009 illustrated (see Figure 3), exhibit no particular trend. LSCE has estimated the evolution in ozone concentrations, subject to these twin effects, by simula- 56° ting, separately and simultaneously, differences in 54° predicted global, and European emissions, between 360 2001 and 2030, while using the meteorological condi- 52° 300 tions for 2001, for all of the cases considered. The 240 50° 220 findings evidence highly contrasted differences 200 180 48° between 2001 and 2030 (see Figure 4). 170 As is the case at the global scale, climate change will 160 also impact air quality in Europe, where average tem- 46° 150 140 peratures have been rising, over several decades, at 44° 130 a pace at least as strong as that predicted by IPCC 120 42° 110 Figure 5. 100 90 Surface ozone concentrations (in µg·m–3: divide by 2 to obtain 40° 80 ppb values), as simulated by the model, for 8 August 2003, at 70 14:00 h UTC, with stations indicated by open circles when 38° 60 –3 concentration is not higher than 180 µg•m , full circles if 40 higher than 180 µg·m–3. Taken from R. Vautard et al., 36° 20 “Simulation of ozone during the August 2003 heat wave and 0 emission control scenarios”, Atmospheric Environment 39, 2005, - 10°- 8° - 6° - 4° - 2° 0° 2° 4° 6° 8° 10° 12° 14° 16° 18° 20° 22° pp. 2957–2967.

a MODIS b ref c fire 2003-08-03 2003-08-03 2003-08-03 58° 58° 56° 1.2 56° 56° 1.00 54° 1.1 54° 54° 0.80 52° 1.0 52° 52° 0.70 50° 0.9 50° 50° 0.60 48° 0.8 0.7 48° 48° 0.50 46° 0.6 46° 46° 0.40 44° 0.5 44° 44° 0.30 42° 0.4 42° 42° 0.20 40° 0.3 40° 40° 0.2 0.15 38° 38° 38° 0.1 0.10 36° 36° 36° 0.0 0.00 - 10° - 6° - 2° 2° 6° 10° 14° 18° 22° - 14° - 10° - 6° - 2° 2° 6° 10° 14° 18° 22° - 14° - 10° - 6° - 2° 2° 6° 10° 14° 18° 22° 2003-08-04 2003-08-04 2003-08-04 58° 58° 56° 1.2 56° 56° 1.00 54° 1.1 54° 54° 0.80 52° 1.0 52° 52° 0.70 50° 0.9 50° 50° 0.60 48° 0.8 0.7 48° 48° 0.50 46° 0.6 46° 46° 0.40 44° 0.5 44° 44° 0.30 42° 0.4 42° 42° 0.20 40° 0.3 40° 40° 0.2 0.15 38° 38° 38° 0.1 0.10 36° 36° 36° 0,0 0.00 - 10° - 6° - 2° 2° 6° 10° 14° 18° 22° - 14° - 10° - 6° - 2° 2° 6° 10° 14° 18° 22° - 14° - 10° - 6° - 2° 2° 6° 10° 14° 18° 22°

2003-08-05 2003-08-05 2003-08-05 58° 58° 56° 1.2 56° 56° 1.00 54° 1.1 54° 54° 0.80 52° 1.0 52° 52° 0.70 50° 0.9 50° 50° 0.60 48° 0.8 0.7 48° 48° 0.50 46° 0.6 46° 46° 0.40 44° 0.5 44° 44° 0.30 42° 0.4 42° 42° 0.20 40° 0.3 40° 40° 0.2 0.15 38° 38° 38° 0.1 0.10 36° 36° 36° 0.0 0.00 - 10° - 6° - 2° 2° 6° 10° 14° 18° 22° - 14° - 10° - 6° - 2° 2° 6° 10° 14° 18° 22° - 14° - 10° - 6° - 2° 2° 6° 10° 14° 18° 22°

Figure 6. Geographical distribution of aerosol optical thickness at 500 nm over Europe, 3–5 August 2003; A (left-hand column) as established from MODIS satellite data, and simulated with the CHIMERE model; B (middle column) without, and C (right-hand column) with emissions due to fires. Taken from Vautard et al. (2007).

CLEFS CEA - No.57 - WINTER 2008-2009 35 Climate research, a major challenge

10,000 10,000 9,000 9,000 CO CO 8,000 benzene 8,000 benzene 7,000 7,000 6,000 6,000 5,000 5,000 4,000 4,000 3,000 3,000 2,000 2,000 CO (ppb) – benzene (ppt) CO (ppb) – benzene (ppt) 1,000 1,000 0 0 08/16/04 08/17/04 08/18/04 08/19/04 08/20/04 08/21/04 08/22/04 08/23/04 09/18/05 09/19/05 09/20/05 09/21/05 09/22/05 09/23/05 09/24/05 09/25/05

Figure 7. Evolution, over one models. The last decade was characterized by the 2003, forest fires in southern Europe laid waste a week, of benzene and occurrence of several very hot summers. In 2003, an considerable area, releasing into the atmosphere large carbon monoxide concentrations, at the unprecedented heatwave affected all Europe, France quantities of pollutants, in particular carbonaceous center of Beijing (left), in particular. In 2006, Central Europe was most stron- aerosols, which subsequently dispersed across the and at the center of Paris gly affected, and, in 2007, South-East Europe. An continent. The plume from fires in Portugal was (right). Taken from V. Gros et al. (2007). increased heatwave frequency is one component in found to have reached northern Europe, as confir- the predicted overall set of consequences of climate med by observations from the MODIS satellite, and change, in Europe. Thus, the summer of 2003 is now numerical simulations (see Figure 6). seen as the prototype for the summers that will be Emissions, land use, and many other factors will, in experienced by Europeans in the second half of the all likelihood, have undergone some changes, a few 21st century. It will thus prove particularly illumi- decades from now. Nevertheless, analysis of the conse- nating to investigate the impact of the 2003 heat- quences of the 2003 heatwave has made it possible wave on air quality. to show that, during extreme events of this type, epi- One of the prime characteristics of the ozone concen- sodes of atmospheric stagnation may be anticipated, trations observed during the first half of the month resulting in a marked, large-scale degradation of air of August 2003 resides in the spatial and temporal quality. extent of the high values found. The stagnation of air masses over Europe enabled a buildup to occur, Air quality in emerging megacities day after day, of photochemically produced pollutants. For 8 August 2003, the simulation carried out The most severe public health issues related to with the air quality model (CHIMERE) developed atmospheric pollution will probably not arise in by the Pierre-Simon Laplace Institute shows the ozone Europe. Indeed, the share of world urban popu- concentrations, together with an indication of the lation is forever rising, particularly in emerging concentrations found at a number of stations in countries. This population concentrates pollutant Europe (see Figure 5). The extent of the pollution emissions in a number of megacities that is increa- cloud spreads well beyond national boundaries, and sing at the same pace. These urban conglomera- only measures to ensure emission reductions, taken tions of over 10 million inhabitants, numbering at the European scale, and several days ahead, would 8 in 1950, 41 in 2000, could reach the 59 mark by have allowed such concentrations to be brought down 2015. Hence the importance attached to determi- significantly. ning the concentration levels and chemical com- The consequences of the heatwaves anticipated in position found in these emerging urban centers, the context of climate change, in Europe, are not markedly different as they are from their western confined to large-scale photochemical pollution. In counterparts. For that reason, a team at LSCE is dedicating part of its activity to campaigns on the ground to determine these properties. For instance, the Beijing city center is subjected to benzene and carbon monoxide concentrations that are 5–10 FOR FURTHER INFORMATION times higher than what is found for the Paris city V. GROS, J. SCIARE and T. YU, “Air quality measurements in megacities: focus on center (see Figure 7). Major health impacts from gaseous organic and particulate pollutants and comparison between two contrasted atmospheric pollution cannot fail to occur in these cities, Paris and Beijing”, Comptes rendus geosciences 339, 2007, pp. 764–774. new megacities. S. SZOPA, D. A. HAUGLUSTAINE, R. VAUTARD, L. MENUT, “Future global tropospheric ozone changes and impact on European air quality”, Geophys. Res. Lett. 33, 2006, L14805, > Robert Vautard doi: 10.1029/2006GL025860. Climate and Environmental Sciences Laboratory R. VAUTARD, M. BEEKMANN, J. DESPLATS, A. HODZIC, S. MOREL, “Air quality in Europe (LSCE)/Pierre-Simon Laplace Institute during the summer of 2003 as a prototype of air quality in a warmer climate”, Physical Sciences Division Comptes rendus geosciences 339, 2007, pp. 747–763. CEA Saclay Center (Orme des Merisiers)

36 CLEFS CEA - No.57 - WINTER 2008-2009 FOCUS A Journey to the center of the Earth, and the outer reaches of the atmosphere

Lava flow in Hawaii. Magma wells up from the Earth’s interior, and flows out in the form of lava.

Page 21 cont'd wise solid, and chiefly consisting of basal- mantle is not liquid, as might be inferred tallization of the outer core. The prevailing tic rocks, is relatively thin (with a thickness from the lava flows involved in some vol- pressure keeps it in a solid state, with a of around 6–8 km). The Earth’s crust canic eruptions, however it is less “hard” density of about 13, in spite of a tempera- accounts for some 1.5% of the Earth’s than the other layers. It exhibits the pro- ture standing higher than 5,000 °C. The volume. The upper, solid part of the mantle, perties of an elastic solid. The mantle, with transition region between the outer and consisting of peridotites,(3) also exhibits a temperature higher than 1,200 °C, inner core is known as the Lehmann dis- varying depth, according to whether it lies accounts for about 84% of the Earth’s continuity. The core accounts for about 15% under an ocean or a continent. The transi- volume. The transition region between the of the Earth’s volume. tion region between crust and mantle, dis- mantle and the Earth’s core was located, Within the planet’s core, radioactive ele- covered in 1909 by Croatian geophysicist in 1912, at a depth of 2,900 km, by German ments (potassium, uranium, thorium) and seismologist Andrija Mohorovicˇic´, is seismologist Beno Gutenberg, and is conse- decay, yielding considerable heat. This pro- known as the Mohorovicˇic´ discontinuity, or quently known as the Gutenberg dis - vides the various layers in the Earth’s struc- Moho. continuity. ture with the energy required to sustain the The upper mantle (100–670 km), chiefly The outer core (2,900–5,100 km) essen- motions affecting them, while allowing mol- consisting of peridotites, is more viscous tially consists of iron (to about 80%), ten rocks (magma) to rise up from the than the lower mantle (670–2,900 km), nickel, and a few lighter elements. This Earth’s interior. Part of the magma solidi- essentially composed of perovskites,(4) as metallic core, the fluidity of which was fies as it comes into contact with the Earth’s the prevailing physical constraints in that determined, in 1926, by British geophysi- crust, which is cooler, whereas a fraction region make it partly liquid. The lower cist and astronomer Harold Jeffreys, exhi- breaks out at the surface, in lava form. bits a viscosity close to that of water, an (3) Peridotite: a rock formed as a result average temperature of 4,000 °C, and a The Earth’s atmosphere of the slow cooling of magma, consisting of density of 10. The convective motions ari- The gaseous envelope surrounding the grains visible to the naked eye. It chiefly consists sing in this huge mass of molten metal, lin- Earth, held close to the planet’s surface of olivine, pyroxene, and hornblende (a hydrated 7– ked to the Earth’s rotation, are the proces- as it is by gravity, the atmosphere is mineral, characterized by the [Si4O11(OH)] anion). ses that give rise to the Earth’s magnetic indispensable to life. It contains the air (4) Perovskite: named after Russian mineralogist field. we breathe, shields all lifeforms from the L. A. Perovskii, this refers broadly to a crystal The inner core (5,100–6,378 km) was dis- Sun’s harmful radiations through its ozone structure common to many oxides, of general covered in 1936 by Danish seismologist Inge layer, stands as a major component in the formula ABO3. Perovskites exhibit a variety of electrical, and magnetic properties, depending Lehmann. Essentially metallic in compo- water cycle, and markedly contributes to on the nature of A, and B. sition, it has formed owing to gradual crys- making the average temperature milder, at the planet’s surface owing to the green- gas volume (ppmv) house effect it generates (see Focus C, nitrogen (N ) 780,840 (78.084%) Greenhouse gases and aerosols at the cen- 2 oxygen (O ) 209,460 (20.946%) ter of the climate change debate, p. 66). 2 argon (Ar) 9,340 (0.934%) Table. Indeed, in the absence of any atmosphere, Composition of the carbon dioxide (CO2) 382 (0.038 2%) surface temperature would stand at around atmosphere, in the neon (Ne) 18.18 –18 °C, rather than the 15 °C observed. vicinity of the Earth’s helium (He) 5.24 surface. Atmospheric air consists in a mixture of methane (CH ) 1.745 In thermodynamic gases (see Table), holding suspended par- 4 krypton (Kr) 1.14 terms, atmospheric air ticles, both liquid (water droplets…), and is treated as a mixture hydrogen (H2) 0.55 solid (ice crystals, dust particles, salt crys- of two gases: dry air nitrous oxide (N2O) 0.30 and water vapor. tals…), with most of its mass lying close to Greenhouse gases ozone (O3)0.04 the Earth’s surface. At sea level, atmosphe- appear in purple. CO2 water vapor (H2O) from 1% (in polar regions) ric pressure stands at 1,013.25 hPa. Gas to 4% (in equatorial regions) concentrations stood (highly variable) at 280 ppmv in 1800, molecules become rarified, and disperse 345 ppmv in 1998. at higher altitude, and pressure falls off. The atmosphere is thus ever less dense as altitude increases, until it finishes by “blen- ding into” outer space. 100 The atmosphere comprises a number of thermosphere layers, within each of which temperature varies differently, as a function of altitude: mesopause 80 the troposphere, the stratosphere, the mesosphere and the thermosphere (see Figure 2). In the troposphere (from the Earth’s surface 60 mesosphere to 8 km over the poles, 15 km at the equator), temperature declines swiftly with alti- stratopause

Skip to page 24 StockTrek and density are highest. FOCUS A

hether of natural or anthropic pro- Wvenance, substances found in the solvent extraction environment call for the use of analyti- ion exchangers cal methods that are flexible – the aim extraction coprecipitation being both to detect, and identify extre- volatilization electrodeposition membrane technologies mely diverse compounds – and highly sensitive. They further entail the imple- acid leaching liquid mentation of rigorous procedures, ope- calcination gas solid-phase sorption rating step by step. alkaline melting solid inorganic analysis Rigorous preparation sample of samples collection Standing as a fundamental step in the solid-phase sorption organic microextraction analytical process, the pretreatment of solid analysis condensation samples involves either preconcentra- gas ting substances occurring with too low liquid a content to allow direct detection, or separating them from an overly complex extraction extraction – liquid–liquid extraction matrix. If research workers spend nearly – solvent extraction – solvent extraction – supercritical fluid extraction 60% of the time required, for an overall – solid-phase extraction – HP, HT extraction solid-phase microextraction analysis, on this preliminary step, it is – matrix solid-phase dispersion (MSPD)… because, according to a number of stu- sorption… dies, it accounts for nearly 30% of errors in findings. Presently, these same Figure 1. research workers have developed a Examples of pretreatment techniques for environmental samples gamut of fast, economical, automated, reliable techniques, for the purposes of means of an absorbent polymer, coating ves allowing a solution of the substance treating samples, depending on their a (magnetic) stir bar, impelled inside the being investigated to percolate through nature, or the concentration being sample. Based as it is on the same prin- a column, packed with adsorbent mate- considered: ciple as SPME, this technique allows the rials: the constituents, each traveling at • Solid-phase extraction (SPE) allows extraction of greater quantities of ana- different rates, become partitioned into the isolation of chemicals present in a lytes, and thus makes for increased sen- distinct regions, or bands, which can sim- liquid (e.g. water), through use of an sitivity. ply be considered separately, for analy- absorbent polymer, conditioned as a rule • Solvent extraction – this as a rule invol- tical purposes. in filtration cartridge form. This proves ving a volatile solvent, sparingly soluble • Liquid chromatography (LC), or high- highly effective for the purposes of pre- in water (a light alkane, ethyl acetate…) performance liquid chromatography concentrating traces, in highly dilute – allows the extraction of molecules from (HPLC) relies on the separation of the media, or purifying samples. aqueous media. Solvent–water separa- substances present in a mixture through • Fiber-supported solid-phase micro- tion is effected simply, through settling. their introduction into, and subsequent extraction (SPME) is used to extract che- • Preparative ion chromatography, which differential migration along, a separa- micals present in a gas, or a liquid (e.g. relies on the interaction, in an aqueous tion column (chromatographic column) air, or water), this being effected by medium, of ion species with ion- through which an eluting liquid (e.g. a means of an absorbent polymer, coating exchange resins, allows the extraction mixture of water and methanol) advan- a glass fiber a few millimeters long, pla- of inorganic substances (ions) occurring ces. Thereafter, a sequence of physico- ced in contact with the sample. As SPME in trace form, from a complex environ- chemical interactions between the requires neither solvents, nor any spe- mental matrix. substances subject to analysis, and the cific equipment, it thus proves simple to two separation phases (the stationary deploy. This is an innovative technique, Separation for selection purposes phase, and the mobile, eluent phase) seeing increasing use for the purposes Used nowadays for the purposes of iden- allows the constituents to be separated of air quality monitoring, or the analysis tifying, or titrating, the chemical com- out. Coupling the chromatographic sepa- of organic micropollutants in water. pounds in a mixture, chromatography ration module with specific detectors • Stir-bar sorptive extraction (SBSE) sees was invented, in 1906, by Russian bota- (mass spectrometer, UV–visible absorp- broader employment, for the purposes nist Mikhail Tsvet (1872–1919), who was tion spectrometer…) results in a variety of extracting chemicals present in a liquid seeking to separate out various plant pig- of analytical instrumental setups (water). Such extraction is effected by ments. Nowadays, the technique invol- (HPLC–MS, HPLC–UV…). C.Dupont/CEA

In the analytical chemistry laboratory. Separation, and purification of actinide traces in environmental samples, as preliminary steps for mass spectrometry measurements.

• Capillary electrophoresis (CE), as indeed the substances, due to entrainment by a Radiation spectrometry all electrophoretic separation methods, carrier gas (e.g. helium). Chromatographic Radiation spectrometry relies on the inter- is used to separate electrically charged columns, nowadays, chiefly involve action of electromagnetic radiation with particles (ions), through their differential capillary tubes, 30–100 m long, internally matter. It makes use of processes as migration under the influence of an coated with an appropriate polymer, with diverse as emission, absorption, fluores- electric field. Each species migrates at a regard to the substances subjected to ana- cence, and diffusion, whether involving specific rate, which is a function of its lysis. A detection system, located at the visible, or nonvisible radiation. Whether charge-to-size ratio. As regards, more column outlet, measures the signals emit- in the atomic, or molecular state, every specifically, capillary electrophoresis, as ted by the various constituents, allowing substance exhibits a characteristic spec- its name implies, the separation support their identification, and quantification (e.g. trum, whether the spectrum considered medium is a capillary, filled with a speci- GC–MS). be an emission, or an absorption spec- fic liquid medium (the electrolyte), • Ion chromatography (IC) relies on the trum (or indeed a diffusion, or fluores- and immersed at either end in electrolyte application of the various liquid chroma- cence spectrum); it is thus sufficient to reservoirs, connected by way of a tography methods to the analysis of orga- recognize the occurrence of that spec- high-voltage generator. The sample is nic, or inorganic ions (whether anions, or trum, to have evidence of the presence of inserted into the electrolyte flow, and the cations). the corresponding substance. sample’s constituent species migrate • Atomic absorption spectrometry relies at their respective specific rates, these Analysis to gain knowledge on the principle whereby atoms may being dependent, as a whole, both on To determine a sample’s composition, absorb photons of a certain wavelength the distance between the injection, researchers can draw on the full range, (characteristic of the element subject to and detection points, and migration and variety of spectrometric methods, i.e. analysis). The number of photons absor- time. methods of spectral analysis allowing the bed being related to the number of atoms • Gas chromatography (GC) allows the material’s composition, and structure to absorbing them, the element’s concen- separation of volatile, or semivolatile sub- be ascertained. Such methods may be tration may thus be derived from such a stances from a complex mixture. This grouped into two categories: radiation measurement. relies on the introduction of the mixture, spectrometry, and mass spectrometry, this • Emission spectrometry is based on the by vaporization, into a separation column in turn being subdivided, as a rule, into characteristic photon emission yielded by (chromatographic column), and subse- atomic spectrometry, and molecular spec- atoms excited by an energy input. Such quent differential migration (elution) of trometry. Continued p. 54 FOCUS B

Continued from p. 53 energy may be provided by means e.g. of X-radiation, the material then reemitting pulse), allowing the elimination of unwan- an inductively coupled argon plasma energy, in the form, in particular, of ted, short-lived fluorescence signals. source; this allows the measurement of secondary X-rays; analysis of the spec- Current developments involving this tech- elemental content (copper, lead, tin, trum allows the sample’s elemental com- nique concern speciation (i.e. the deter- arsenic, nickel…), however without yiel- position to be derived, in both qualitative mination of chemical species), and ding any information as to the chemical and quantitative terms. remote measurement via optical fiber in form in which these elements occur in • UV–visible absorption spectrometry the nuclear industry, and for environ- the sample. relies on the absorption of light by mat- mental analysis. • Glow-discharge spectrometry (GD- ter. This technique chiefly allows the mea- • Raman scattering spectrometry is OES) involves the process of cathodic surement of chemical species concen- employed to ascertain a sample’s che- sputtering of the sample undergoing ana- trations in aqueous solutions, or solutions mical structure, and molecular compo- lysis, this being positioned in a source of other types. sition, by placing it under laser radiation, operating on the cathode-ray tube prin- • Infrared (IR) spectrometry allows, by and analyzing the scattered light emis- ciple. The elements sputtered into the way of the molecular absorption of IR sion. This is a nondestructive method, glow discharge lamp are then identified radiation, the determination of the che- complementing infrared spectroscopy. from their light emission spectra. The mical bonds making up a molecule, Raman spectroscopy is a local measu- glow-discharge source may also be com- and thus makes it possible to build up rement technique: by focusing the laser bined with a mass spectrometer. structural hypotheses. Since IR spectra beam onto a small region in the medium, • Laser-induced breakdown spectros- can prove highly complex, they may thus that medium’s properties may be pro- copy (LIBS) is an optical emission spec- be seen as a veritable molecular ID docu- bed, over a volume of a few cubic microns. troscopy technique, making use of the ment. This is known as micro-Raman spec- interaction of a pulsed laser beam with • Time-resolved laser-induced fluores- troscopy. a material, resulting in the latter’s vapo- cence (TRLIF) is an ultrasensitive analy- • Nuclear magnetic resonance (NMR) rization, in plasma form. The ejected exci- tical technique, used for the determina- spectrometry involves a principle relying ted atoms, and ions, as they relax, emit tion of certain actinides, and lanthanides, on the spin alignment that occurs in cer- a UV, and visible spectrum made of lines, which are fluorescent in solution. Its prin- tain atomic nuclei, under the influence the wavelengths of which allow the iden- ciple relies on excitation, carried out by of an intense magnetic field. These nuclei tification, and quantification of the ele- means of a pulsed laser, and subsequent may then interact with radio waves, emit- ments present in the sample. time resolution of the fluorescence signal ting signals that allow the molecular • X-ray fluorescence spectrometry (by setting a measurement time gate, at structure of the compounds present to involves bombarding the material with a few microseconds’ delay after the laser be identified. C.Dupont/CEA

Preparing samples, for the purposes of radiological analysis. Environmental samples undergoing treatment: chromatography, for the purposes of extracting radionuclides. tiply charged ions to be obtained, these being particularly advantageous for the purposes of characterizing macromole- cules. This method further makes it possible to achieve a “soft” ionization, yielding mainly molecular ions. • Desorption electrospray ionization (DESI) relies on the use of a nebulized solvent, containing molecules in an excited electronic state, which transfer their energy to the substances being investigated, resulting in their ionization, and desorption from a solid sample, or a liquid sample deposited onto a substrate.

With respect to inorganic mass spectrometry, numerous combinations are likewise to be found, however the ionization

CEA/DR sources involve higher energies than is Coupled liquid chromatography–inductively coupled plasma mass spectrometer (ICP–MS). the case in organic mass spectrometry, so as to ensure complete sample atomi- • Atom-trap trace analysis (ATTA) is a tech- Organic mass spectrometry involves many zation. nique involving magneto-optical trapping ways of combining the various ionization • Inductively coupled plasma is an extre- of “cold” atoms, enabling the detection of sources, and the various analyzers avai- mely energetic atomization and ionization single atoms, and the quantification of iso- lable. Certain sources are more widely source, which, when combined with a mass topic ratios for a few thousand atoms. A used than others. spectrometer – in inductively coupled complex technique, ATTA currently ranks • The electron impact ion source, relying plasma mass spectrometry (ICP–MS) – as one of the most sensitive, and most on the bombardment of molecules by a ranks as one of the most sensitive ele- selective techniques available. beam of electrons (usually with an energy mental analysis techniques. It allows, in of 70 eV), and the generation of positively particular, measurement of plutonium at Mass spectrometry charged ions. lower than femtogram levels. Mass spectrometry and ion-mobility spec- • The chemical ionization source relies on • Secondary ion mass spectrometry (SIMS), trometry stand as an ensemble of analy- negative ionization, by electron capture, involving the bombardment of a solid sam- tical techniques, allowing the detection, involving low-energy (1–2 eV) electrons, ple by an ion beam, allows the finescale but equally the precise identification either yielded by the primary ionization of a rea- characterization of its surface, thus pro- of elements (inorganic mass spectrome- gent gas (methane, ammonia…) that is viding the ability to analyze e.g. micro- try), or of a variety of molecules (organic, subjected to electron bombardment. meter-scale particles, containing minute or molecular mass spectrometry). In the • Atmospheric-pressure chemical ioniza- quantities of a given element. This latter case, the molecules’ chemical struc- tion (APCI), whereby liquid samples first technique also enables to carry out depth ture may be characterized by fragmen- undergo nebulization (transformation into profiling and elemental or isotopic ting them, or by measuring, with great a droplet aerosol), by means of a jet of air, mappings. precision, their molecular masses. For or nitrogen. Heating then ensures the • Thermal ionization mass spectrometry that purpose, a mass spectrometer com- desolvation of the compounds present. (TIMS) involves coupling a source effec- prises, first of all, a sample introduction These are then chemically ionized, at ting the atomization, and ionization of sam- system, involving either direct introduc- atmospheric pressure: as a rule, the ples, deposited onto a surface brought to tion (solid, liquid, or gaseous samples), mobile, vaporized phase acts as the ioni- a very high temperature, with a mass spec- or indirect introduction (i.e. coupled with zation gas, and electrons are obtained by trometer. This technique allows the mea- a separation technique, e.g. chromato- way of corona discharges at the electrode. surement, with outstanding precision, of graphy, or capillary electrophoresis). It APCI is a technique that is analogous to elemental isotopic ratios, as well as ele- further includes an ionization source, to chemical ionization (CI): it likewise invol- ment concentrations, through the use of effect element atomization, and ioniza- ves gas-phase ion–molecule reactions, at tracers. tion (or to effect molecule vaporization, atmospheric pressure however. • Ion mobility spectrometry (IMS), a gas- and ionization), a mass analyzer, this sepa- • The electrospray ionization (ESI) source phase chemical analysis technique, invol- rating ions according to their mass-to- generates ions from a liquid solution, by ves applying an electric field to molecu- charge (m/z) ratio, and, finally, one or more subjecting this solution to vaporization, les held in a gas stream. Ionization is detectors. and nebulization, in the presence of an usually effected by a light source (ultra- Many methods are available, for the intense electrostatic field. As is the case violet radiation), or a radioactive (alpha- purposes of ionizing atoms, or mole- with APCI, the advantage afforded by this or beta-emission) source. cules. ionization technique is that it allows mul- Continued p. 56 FOCUS B

Continued from p. 55 C.Dupont/CEA Thermal ionization mass spectrometer, allowing the very-high-precision analysis of uranium, and plutonium isotopes.

• Resonance ionization mass spectro- • The quadrupole ion trap relies on trap- transform, the very precise determina- metry (RIMS), a highly selective ele- ping ions in a specified spatial region, tion of the mass-to-charge ratio for mental analysis technique (owing to the through the action of a complex elec- every ion. ability to achieve perfect elemental trostatic field, and sequentially direc- • The Orbitrap involves forcing ions, selectivity at the ionization stage), is ting the ions to a detector, according to under the influence of a complex magne- used for the purpose of avoiding nume- their mass-to-charge ratio. tic field, to orbit around, and oscillate rous chemical separation operations. • The time-of-flight spectrometer seeks along, an electrode shaped somewhat The principle involves subjecting a to measure the velocity of ions introdu- like a fusiform muscle. The angular, and mixture of atoms in vapor phase to ced, in controlled manner, into a spa- oscillation frequencies for each of these laser “irradiation,” to excite, and subse - tial region subjected to an electric field, ions are measured by electromagnetic quently selectively ionize, only those the time required for ions to travel a interrogation, allowing, by way of the atoms involving electronic transitions given distance then being related to their Fourier transform, the very precise corresponding to the laser wavelength. mass-to-charge ratio. determination of the mass-to-charge Use of a mass-dispersion system • The magnetic-sector analyzer involves ratio for every ion. (magnetic analyzer, time-of-flight spec- constraining ions to follow a specific path • The ion-mobility spectrometer relies trometer) allows a twofold selectivity – (depending on their mass-to-charge on measuring the displacement velo- both elemental, and isotopic – to be ratio), chiefly under the influence of a city of ions subjected to the accelera- achieved. perfectly controlled magnetic field, prior ting effect of an electric field, and the to arriving at a detector, which ensures retarding effect of a gas, at atmosphe- Ion separation is effected by means of their detection, and quantification. ric pressure. Measurement of ion transit analyzers, which differ in terms of the • Ion cyclotron resonance (ICR) makes times, from the injection area to the ion technology involved, and which may be it possible to keep ions within a spatial detector, allows the ions’ chemical coupled together, for the purposes of region where an intense magnetic field nature to be determined (more or less determining molecular structures. prevails, and inside which each ion fol- accurately, depending on the precision • The quadrupole analyzer involves for- lows a circular path, with characteris- of the time measurements). cing ions to travel through a complex tics (radius) that are dependent on its electrostatic field, along metal rods, the mass-to-charge ratio. The angular fre- In every one of the cases outlined above, ions passing through this spatial region, quency, for each of these ions, is mea- a detector ultimately converts the ions or otherwise, depending on their mass- sured by electromagnetic interrogation, into an electric signal, which is ampli- to-charge ratio. and this allows, by way of the Fourier fied prior to IT processing. FOCUS C Greenhouse gases and aerosols at the center of the climate change debate Photolink

Solar radiation is reflected back into space by atmospheric air, white clouds, the Earth’s surface, particularly in the Arctic and Antarctic regions.

n 1824, French mathematician Joseph IFourier had already surmised that the reflected solar incoming solar outgoing longwave (IR) gases present in the Earth’s atmosphere radiation: 107 W/m2 radiation: 342 W/m2 radiation: 235 W/m2 contribute to global warming. Thus, it is to him that we owe the first theory of the 107 342 greenhouse effect. However, it was not atmospheric before 1864 that Irish physicist John Tyndall reflected by clouds, 235 window identified water vapor, and carbon dioxide aerosols and atmospheric gases (CO ) as the chief agents of that atmosphe- 40 2 30 ric phenomenon, and it was not before 1896 77 emitted by 67 atmosphere 165 that Swedish physical chemist Svante absorbed by Arrhenius put forward the account of the atmosphere greenhouse process that is still currently recognized. gases latent 78 24 heat The greenhouse effect, a natural

phenomenonl reflected by 350 It is from gardening parlance that the surface 168 40

greenhouse effect draws its name – green- 30 390 324 houses being enclosed spaces, featuring absorbed by evapo - surface absorbed walls that are transparent, to let through surface thermals transpiration radiation by surface Yuvanoé/CEA and trap in solar radiation, so as to raise Figure 1. the temperature to the requisite level for Energy fluxes within the climate system (IPCC diagram). seedlings. In near space, the greater part (about 60%) of solar radiation passes right hue, such as the Arctic and Antarctic it back into the atmosphere, where water through the atmosphere, which is transpa- regions. This latter property is referred to vapor and various gases, including carbon rent to it, the presence of clouds not- as the albedo. dioxide, absorb that radiation, standing as withstanding, and heats up the planet’s As for the radiation not so reflected, some a barrier that prevents that energy from surface. Subsequently, 28% of that radia- 20% is absorbed by the atmosphere, and passing directly from the Earth’s surface tion is reflected back into space, by 51% by the Earth’s surface, directly contri- into outer space, this having a twofold atmospheric air, white clouds, the Earth’s buting to warming it. This heat is not fully consequence. The result is a net warming surface – particularly by regions whiter in retained by the Earth. It reemits some of of the atmosphere, and reemission of that radiation, in all directions, in particular back radiative forcing (Wm-2) again to the Earth’s surface (see Figure 1).

In the absence of that complement of heat, 3 warming the planet’s surface temperature would go down to –18 °C. It is this energy flow, within halocarbons the climate system, that is referred to as 2 N2O aerosols the greenhouse effect. This is a natural phe- CH4 nomenon, and a well regulated one, since fossil fuels 1 tropospheric (black carbon: mineral dust aviation- the energy the Earth receives is broadly equal CO2 ozone direct effect) (direct effect) induced solar to that emitted by the Earth into space. contrails cirrus However, should an imbalance arise, the 0 planet then proceeds to build up, or release the stored energy it holds, thus causing chan- stratospheric fossil fuels ozone (organic carbon: land use ges in temperature (see Figure 2). -1 sulfates direct effect) biomass (albedo) (direct burning Artificial disturbance effect) (direct effect) -2 of a natural phenomenon tropospheric aerosols cooling Most greenhouse gases occur naturally. Such (indirect effect) is the case, in particular, of water vapor, high medium low very low which is generated by evaporation arising level of scientific understanding throughout the water cycle. This accounts all contributions to modifications in the amount of energy received, or emitted by the Earth in the form for about 0.4% of the atmosphere’s compo- of radiation are referred to as radiative forcing (IPCC graph) sition (down to 0.1% over Siberia, 5% however over equatorial oceanic regions), stan- Figure 2. Changes in radiative forcing between 1750 and 2000. ding as an agent in the natural greenhouse effect, of which it causes some 60%, while rage surface temperature, on Earth, accoun- up, in varying proportion, depending on the

CO2 stands as the cause of about 35%. While ting for 60% of the increase found for the season (minimum concentrations occurring most greenhouse gases turn out to be of total greenhouse effect, over the past cen- at the end of wintertime), or the time of day natural provenance, on the other hand the tury. Such alarming outcomes may be (night/day). In the atmosphere, ozone occurs Intergovernmental Panel on Climate Change accounted for by an inability of oceanic photo- at two levels: (IPCC) showed, as early as 1995, that the synthesis to counterbalance, at this stage, ● first, in the stratosphere, where it forms rise in emissions of such gases was indeed the releases that may be attributed to human a protective layer around the Earth, filtering due to anthropic activities. Indeed, unpre- activities. part of the ultraviolet radiation emitted by cedented demographic expansion (the the Sun, thus shielding lifeforms on Earth, world’s population has soared from 1.7 billion Methane (CH4) whether humans, or microorganisms, or to 6 billion over 100 years), compounded by Accounting as it does for 1% of the increase marine phytoplankton. This protective layer activities stemming from the industrial revo- in the Earth’s surface temperature, and 20% is currently under threat, owing to pollution lution, has resulted in increased production, of the increase in the total greenhouse effect, from releases of chlorofluorocarbons (CFCs), and consumption, inescapably going hand atmospheric concentration of this gas rose highly harmful gaseous compounds, occur- in hand with concomitant emissions, and from 750 ppb in 1750 to 1,745 ppb in 1998, ring in pesticides, cosmetics, aerosols… pollution, involving a heavy environmental i.e. an increase of 150%. While about half of which are the cause of the “hole” in the ozone impact. The increased atmospheric green- all methane emissions originate in the natu- layer. In 1998, world production of CFCs stood house gas content due to such releases now ral environment (e.g. from swamps, estua- at 800,000 tonnes, i.e. about 100 grams per ranks as the chief cause in the current imba- ries), the other half does arise from human person on Earth. The “hole” in the ozone lance in exchanges of energy between the activities (rice agriculture, direct releases layer is the outcome of complex reactions Earth, and outer space. into the atmosphere, digestive processes in from ultraviolet radiation on CFCs, resulting Of the gases that stand out, as contributors humans, and animals, fossil fuel mining…). in the release of chlorine, this acting as a to such an increase in the greenhouse effect, catalyst for the reaction destroying ozone to mention should be made of: Nitrous oxide (N2O) yield oxygen. To give an idea of its size, the Whether of natural (soils, oceans) or anthro- “hole” in the ozone layer may spread out

Carbon dioxide, or carbon gas (CO2) pic provenance (nitrogen fertilizers, biomass over an area as large as North America, and Concentration of this gas in the atmosphere burning, cattle farming, industry…), this gas across a depth equal to the elevation of Mount has increased by 31%, between 1750 contributes by 17% to the increase in green- Everest; and 2006, rising from 280 ppm to 381 ppm, house effect. Its concentration in the atmo- ● second, ozone is found in the troposphere, and is growing at a rate of 0.4% per annum, sphere rose from 270 ppb in 1750 to 314 ppb i.e. in the atmosphere close to the ground, i.e. by an average annual increase of 1.5 ppm. in 1998. and thus in the air breathed by living

Over the past few years, a steeper CO2 organisms. Above certain concentrations, increase has been evidenced, with an annual Ozone (O3) this gas stands as a hazardous pollutant. In growth rate of 1.9 ppm, since 2000. CO2 is Generated as it is mainly over the equator, large conglomerations, ozone arises from responsible for some 39% of the rise in ave- ozone diffuses to the poles, over which it builds Followed p. 68 FOCUS C

Followed from p. 67 aerosols may turn up at great distances from their point of production – as in the case of sand particles from the Sahara Desert, coming down onto vehicles in Europe. They may even reach the stratosphere, as happened after the eruption of Mount Pinatubo (Indonesia), when volcanic dust stayed in the stratosphere for 3 years, causing a fall in global temperature by one half-degree, for two years. On the other hand, humans, through their activities, also contribute to aerosol generation. Transportation, deforestation, industry, agriculture all yield dust. However, by far the greater part of anthropic dust production arises from the use of fossil and biomass fuels. Burning such fuels, by yiel-

ding sulfur dioxide (SO2), thus causes acid

© 1999 EyeWire, Inc. © 1999 EyeWire, rain and sulfate aerosols. Activities stemming from the industrial revolution have resulted in increased production, These aerosols have effects that run coun- going hand in hand with emissions and pollution, involving a heavy environmental impact. ter to those of greenhouse gases, in that they intercept part of the Sun’s energy rea- reactions between nitrogen oxides relea- uses cannot absorb as much carbon as a ching the Earth. This is complemented by sed in exhaust gases from motor vehicles, mature forest, rising releases of chloro- the indirect impact of aerosols on climate. or uncombusted hydrocarbons, and the fluorocarbons… Thus, they may act as water vapor conden- oxygen in the air. If meteorological condi- sation nuclei, in cloud formation, with a fur- tions are appropriate (as occurs in anti- The specific issue of aerosols ther incidence of aerosol concentration, cyclonic conditions), ozone removal slows Aerosols consist of fine particles suspen- influencing droplet size, and thus droplet down, resulting in respiratory diseases in ded in the atmosphere. Of natural prove- in-cloud residence time. Another occur- frail persons, which has led to the setting nance, these aerosols originate in the ocean rence, due to aerosols absorbing the Earth’s up of air monitoring systems. (sea salt, yielded by the evaporation of sea own surface radiation, is an aerosol- To sum up, the increase in atmospheric spray, sulfates arising from the oxidation induced local warming of the atmosphere, greenhouse gas content may be compa- of sulfur compounds released by plank- altering its vertical stability; or, by way of red to the effects of installing double gla- ton…), or continental landmasses (eolian complex chemical reactions, aerosols may zing in a horticultural greenhouse: if inputs erosion, soot arising from forest or bush influence greenhouse gas concentrations. of solar radiation stay constant, in the fires, volcanic ashes and sulfates…). Readily In some cases, they may also have an greenhouse, temperature inevitably rises. transported as they are by air currents, effect on photosynthesis, by providing an Of course, these various gases do not all have the same warming potential. Thus, the impact of 1 kilogram methane on the greenhouse effect turns out to be 23 times

higher than that of 1 kilogram CO2. The difference is calculated by way of the global warming potentials (GWPs) for these substances, with carbon dioxide as the reference (a substance’s GWP is the factor by which the mass of that gas must be

multiplied, to obtain the mass of CO2 that would make an equal impact on the greenhouse effect). The lifetime of greenhouse gases in the atmosphere likewise varies, from 12 years for methane to 100 years for carbon dioxide. Of anthropic activities resulting in higher greenhouse gas concentrations, mention may be made, in particular, of the massive use of fossil

fuels (coal, petroleum products, natural C. Sherburne/PhotoLink gas), deforestation for the purposes of Aerosols, i.e. fine airborne particles, are generated, in particular, by the ocean, or by forest cultivation and cattle grazing, which land or bush fires, but equally by volcanic eruptions. essential input of nutrients for phytoplankton in the open ocean, or for the Amazonian rainforest.

The impacts of imbalance According to the models drawn up by cli- matologists, the Earth’s average temperature should rise by 2 °C over the coming century, on the assumption of a doubling in atmospheric greenhouse gas concentrations. Such global warming will not be without its effects on the planet itself, as investigations carried out by paleoclimato- logists have shown that, in past times, a variation by only a few degrees was enough to result in major changes across the face of the Earth. Among the chief consequences of global war- Digital Vision Ltd. Digital ming, a rise in sea levels must be anticipa- Among the chief consequences of global warming, a rise in sea levels must be anticipated ted, which, according to medium-range hypo- (estimated at 50 cm over the coming century), due to the melting of part of the polar ice sheets theses, should reach 50 cm over the coming and ocean warming. century. Owing to the melting of part of the polar ice sheets, and ocean warming, the loss of land area could be by as much as 6% number of world conferences. In 1992, the sions. In the meantime, another conference in the Netherlands, 17% in Bangladesh, thus United Nations Framework Convention on was held, in Buenos Aires (Argentina), in threatening nearly 92 million people living Climate Change (UNFCCC), signed in Rio de 1998. This made it possible to set out com- in coastal areas. In France, areas such as the Janeiro (Brazil) – and adopted by 178 sta- pliance rules, and guidelines, along with delta of the Rhone River, in the south, would tes, and the European Union – set out a num- detailing specifics for the general provi- doubtless be affected. On top of such chan- ber of goals, the objective being a “stabili- sions carried in the Kyoto Protocol: emis- ges affecting landscapes comes a serious zation of greenhouse gas concentrations in sions trading mechanism, sanctions, spe- threat of famine, particularly in South, East, the atmosphere at a level that would pre- cifying best practice recommendations… and Southeastern Asia, as well as in the tro- vent dangerous anthropogenic interference Concurrently, a Conference of the Parties pical regions of Latin America. Hand in hand with the climate system” (article 2). (COP) meets annually, to discuss climate with more intense, longer-lasting heatwave Concurrently, the convention required deve- issues. The 2009 COP meeting is to be held episodes, public health-related risks will loped countries to adopt policies and mea- in Copenhagen (Denmark). This will stand rise, with an expected increase in cardio- sures aimed at returning, individually or as a major milestone, the aim being to arrive vascular diseases, or swifter transmission jointly, to their 1990 levels their emissions at a worldwide agreement on CO2 reduc- of diseases such as malaria, yellow fever, or of carbon dioxide and other greenhouse tions for the period beginning in 2012, when various types of encephalitis. As regards gases. the Kyoto Protocol expires. changes in climate, experts tend to antici- However, by 1997, governments deemed pate increased frequencies, and durations the commitments made under the UNFCCC France: a special case for floods, and droughts. For instance, in were proving inadequate. Now assembling With emissions levels standing at 1.7 tonne France, in the event of a 2 °C rise in average in Kyoto (Japan), they decided, rather than carbon per year, per capita, in 1995, France temperature, wintertime precipitations would to commit to a stabilization of emissions, ranks as one of the developed countries least increase by 20%, while summertime preci- to agree on quantitative greenhouse gas contributing to the greenhouse effect. This pitations would fall by 15%. Changes affec- emission reduction targets, and timetables: result is due, first of all, to the energy conser- ting oceanic currents should also play a major a reduction of 10%, below 1990 levels, by vation policy set in place after the first oil part. Thus, a slowing down in the Gulf Stream 2012, i.e., for industrialized countries, an crisis, together with the use of nuclear energy current, in the North Atlantic Ocean, could aggregate reduction in emissions by 5.2%. for electrical power production. It is further result in a marked falling off in temperatu- This outcome was made possible through due to the adoption of a national climate res across Western Europe, whereas tem- the European Union’s positive attitude, and change mitigation program. This program peratures would rise around the rest of the its commitment to ensuring significant provides for a number of measures, aimed planet. results. Nevertheless, such a percentage at achieving reductions in emissions of car- is still quite small, compared to the 25% bon dioxide, methane, and nitrous oxide, in International action to mitigate increase in emissions recorded since 1999 such sectors as construction (more strin- climate change – the more so since the United States did gent thermal regulations), industry (tax Climate change and changes in the global not ratify the Kyoto Protocol, while other, incentives to promote energy conservation), environment have spurred an international developing countries such as China or India, or transport (provisions to reduce vehicle reaction, along with the organization of a have been increasing their pollutant emis- energy consumption). FOCUS D Plate tectonics and earthquakes

he Earth’s crust, i.e. the superficial, In 1915, German meteorologist and astro- is this due, conversely, to a hot upwelling Toutermost portion of our planet, enve- nomer Alfred Wegener published his hypo- of the mantle, “thrusting” against the sur- lops the deeper layers, namely the mantle, thesis of continental drift. It was not before face, and causing the opposite, cold edge and the core (see Focus A, Journey to the 1967, however, that this took on a forma- of the plate to go under? Or to the effect of center of the Earth, and the outer reaches lized form. The theory was initially known a stress of a more mechanical nature, such of the atmosphere, p. 21). Its thickness is as seafloor spreading, subsequently as as the weight of the subducting crust slab, augmented by that of the uppermost part plate tectonics. This describes the motions pulling the plate with it, or the weight of of the mantle, together with which it forms of these plates, moving as they do – either the young crust pushing it along? the lithosphere, a mosaic comprising a drawing apart (Arabia is thus moving away Be that as it may, these motions form the dozen rigid plates (the so-called lithosphe- from Africa), or coming together – at a rate counterpart, at the surface, of the process ric plates), including 7 major plates, and of a few centimeters per year. The source of convection taking place within the 5 minor plates (see Figure 1). With a thick- of the force setting the plates in motion is mantle. This process is powered by heat ness varying from about 10 to 100 kilome- still a matter for debate: is this due to a (temperature stands at some 1,300 °C, at ters, these plates move across the under- subduction movement, initiated at the (cold) a depth of 100 km), coming from radioac- lying, more plastic part of the mantle, the edge of a plate, resulting in a (hot) upwel- tive decay of rocks in the Earth’s core, to asthenosphere. ling of the mantle at the opposite edge? Or wit potassium, uranium, and thorium. Convection is one of the three mechanisms through which cooling of the Earth takes 7 place, by removing heat at its surface – 2 along with heat conduction, and radiative transfer. Some regions in the mantle thus become hotter, and consequently less 14 dense, and rise through buoyancy. The 7 material cools at the surface (thus removing the heat generated inside the planet), 11 becoming cooler, and consequently den- 13 6 10 12 1 ser (and at the same time more “brittle”), causing it to sink again. This “conveyor belt” 1 process leads to the emergence of relati- 3 9 vely stable regions, in areas where matter 8 is rising (ridges), or sinking (subduction 5 zones), matter being displaced across the surface of the mantle, from the former to 4 15 the latter areas. The Earth produces magma both along the rising, and sinking currents.

Yuvanoé/CEA The motions driving the displacement of Figure 1. tectonic plates are found to be of several The Earth’s outermost layer is subdivided into a number of rigid plates, slowly moving across the types. Divergence (spreading), whereby two underlying viscous material in the asthenosphere, while rubbing one against the other. Certain plates may in turn be subdivided into several plates, involving smaller relative motions. plates move apart, allows the mantle wel- ling up between them to replenish the ocea- plate average velocity nic lithosphere. The divergent interplate 1 Pacific Plate 10 cm/year northwestward boundary corresponds to a ridge, which at 2 Eurasian Plate 1 cm/year eastward the same time is a region of intense vol- 3 African Plate 2 cm/year northward canic activity. Convergence involves two 4 Antarctic Plate rotating about itself plates drawing together, resulting in three 5 Australian Plate 6 cm/year northeastward types of boundary. In subduction, one of 6 Indian Plate 6 cm/year northward the plates (as a rule the denser one, in 7 North American Plate 1 cm/year westward most cases oceanic crust) dips under the 8 South American Plate 1 cm/year northward continental crust. The area around 9 Nazca Plate 7 cm/year eastward the island of Sumatra, for instance, is thus 10 Philippine Plate 8 cm/year westward a subduction zone, where the dense 11 Arabian Plate 3 cm/year northeastward Indian–Australian Plate plunges under the 12 Cocos Plate 5 cm/year northeastward less dense Eurasian Plate, at an average 13 Caribbean Plate 1 cm/year northeastward rate of about 5 cm per year. The collision 14 Juan de Fuca Plate 2.8 cm/year northeastward of continental plates, on the other hand, is 15 Scotia Plate 3.6 cm/year westward the cause of mountain range formation, Canada Asia Japan Mexico continental United States Europe Asia North American Plate crust Africa Himalayas India fault San Andreas Fault island oceanic Pacific Plate oceanic arc crust crust continental continental oceanic lithosphere crust lithosphere crust crust old oceanic crust asthenosphere asthenosphere asthenosphere Yuvanoé/CEA

Figure 2. At left, an instance of transform boundary. The Pacific Plate and the North American Plate are slipping past each other, on either side of the San Andreas Fault, which is the source of Californian earthquakes. Middle, an instance of subduction. The formation of volcanic island arcs, extending from Japan to the Kuril Islands, and the Aleutians, is due to the fact that the Pacific Plate is plunging under the Eurasian Plate. At right, an instance of collision. The formation of the Himalayas is the result of the contest between the Indian Plate, and the Eurasian Plate, which overlap and undergo uplift. e.g. the uplift of the Himalayas, at the compression axes lie in the horizontal as hotspots). These hotspots are thought boundary between the Indian, and plane). Plate motions, classically moni- to be the surface manifestation of convec- Eurasian Plates (see Figure 2). Finally, tored by means of conventional instru- ting blobs of material, less dense than the obduction, or overthrusting, involves the ments (theodolites, distance meters), are mantle as a whole, rising straight through transport of a section of oceanic litho- increasingly tracked by way of satellite the latter. Such hotspots – the largest ones sphere on top of a continent (no conver- resources, namely the Global Positioning are located under the islands of Hawaii gence process of this type is currently System (GPS), which proves particularly (USA) and La Réunion (France) – scarcely active). Another kind of interaction invol- well suited to the requirements of defor- move relative to one another, while pla- ves friction between plates: transcurrence, mation measurements, across a given tes “ride past” above them. or transform boundaries, where two pla- region (see GPS measurement of defor- tes slip horizontally past each other (see mation: a method for the investigation of Volcanoes and earthquakes as Figure 2). large-scale tectonic motions, p. 95). markers of deep motions inside In effect, the three main families of faults It is along interplate boundaries that most the planet are associated, respectively, to these inter- earthquakes, and volcanoes arise, as a Volcanoes may be of the effusive, or explo- action types: normal faults (divergent, consequence of the selfsame deep phe- sive type, or a combination of the two. The extensional); reverse faults (convergent, nomena. A certain number of volcanoes former let molten rock stream out of their compressional); and strike–slip faults are found to arise, however, right at the crater(s), and often occur as chains of (transcurrent: both the extension, and center of plates (these locations are known Skip to page 92 CNRS Photothèque/Hervé Philip CNRS Photothèque/Hervé StockTrek

The Pacific Plate is dotted with volcanic Damage caused by the earthquake occurring in Spitak (Armenia), on 7 December 1988. islands, such as Hawaii, where volcanoes This earthquake, of magnitude 6.2, resulted in a death toll of about 25,000. The violent release numbered among the most active, the world of strains, accumulating as plates move, scraping against one another, induces a concomitant, over, are to be found. more or less abrupt, ground motion. FOCUS D

Page 91 cont'd volcanoes, especially under the sea. The face and a depth of around 700 km. The second type involves volcanoes that hold epicenter is the point on the surface lying in the rising pressure of imprisoned gases, vertically above the earthquake focus: this, until they “spring the plug;” these form as a rule, is the point where the shock expe- alignments, and occur on islands, and conti- rienced at the surface is strongest. Seismic nents. High-frequency, low-amplitude seis- waves propagate at velocities ranging from primary waves (P waves) mic noise (tremors) arises as a precursor 2 km/s to 14 km/s, with a longitudinal of eruptions. Some 3,500 volcanoes have motion (P waves, this standing for pres- been active over the past 10,000 years. sure, or primary waves), or transverse Plate motions, as they edge one against motion (S waves, standing for shear, or the other, cause deformations in the Earth’s secondary waves). P waves (6–14 km/s) act crust, and a buildup of strains. When such by compression, as in a coil spring, parti- strains exceed the crust’s mechanical cles being displaced along the direction of secondary waves (S waves) strength, weaker, more brittle zones fail. wave propagation, whether in solids, liquids, An earthquake is the violent release of such or gases. S waves (3–7 km/s) are shear accumulated strains, involving more or less waves, displacing particles perpendi- abrupt ground motion (from a few milli- cularly to the direction of propagation: meters, to several tens of meters) along these waves only travel through solids (see the faults. Figure 3). Love waves (L waves) Most earthquakes are of natural origin – Velocity, for both types of waves, varies as the Earth experiences more than one a function of the density of the medium they million seismic shocks every year, some travel through. The “softer” that medium 140,000 being of a magnitude greater is, the slower waves travel. Such wave than 3,(1) while some may be due to motions phenomena are subject to physical laws, of volcanic origin – however seismic events e.g. reflection, or refraction. It should be Rayleigh waves (R waves) may also be induced by human activities, added that these waves do not all travel at

e.g. dam reservoir impounding, or hydro- the same velocity, depending on the Yuvanoé/CEA carbon extraction from oil fields. Further, medium they are traveling through. Further, Figure 3. events such as mining or quarrying blasts, as a P wave reaches a transition zone, e.g. The various types of seismic wave. P wave propagation is parallel to the ground or nuclear tests, particularly underground the mantle–core interface, a small part of displacement induced, the ground being tests, likewise set off seismic waves, very its energy is converted into S waves, making alternately dilated, and compressed. similar to those generated by natural for more complicated interpretation of seis- In the case of S waves, rocks undergo shearing, events. mograph records. Seismologists therefore and evidence distortion, due to vibrations perpendicular to wave propagation. Regions involving intense seismic activity label waves by different letters, according L waves and R waves propagate along include mid-ocean ridges, subduction to their provenance (see Table). the Earth’s surface, and prove the most highly zones, areas around faults along which destructive types. plates are slipping past each other (e.g. the P wave S wave San Andreas Fault, in California [USA]), and traveled. That work thus contributed to mantle P S Earth’s inter- regions where collisions between conti- outer core K enhancing knowledge of the nents are taking place. inner core I J nal structure, making it possible, presently, The release of strains, as the earthquake to model correctly the wave paths invol- occurs, gives rise to elastic vibrations, Table. ved. Nowadays, methods such as seismic known as seismic waves, propagating in A PKP wave, for instance, is a P wave tomography further assist in improving reemerging at the surface, where it is detected all directions, across the Earth and through after it has passed through the liquid outer models, in particular by taking on board water, from the point of initial rupture of core. three-dimensional structures. the Earth’s crust – the focus (or hypocen- ter) – lying somewhere between the sur- Complementing these so-called body Seismic monitoring: location, waves, surface waves – L waves (Love magnitude, intensity, seismic (1) Currently, seismologists use magnitudes such waves, causing a horizontal displacement), moment… as moment magnitude, for the purposes of and R waves (Rayleigh waves, which are Detecting a seismic event involves detec- estimating the size of very strong earthquakes. This magnitude, noted Mw, introduced in 1977 slower, and induce both horizontal and ver- ting the waves generated by it, by means by Hiroo Kanamori, from the California Institute tical displacement) – involving much lar- of two types of facilities, appropriate for the of Technology, is defined by the relation ger amplitudes, propagate only through propagation medium. Ground motions, even log Mo = 1.5 Mw + 9.1 (where Mo stands for the seismic moment, expressed in newton–meters). the crust, which is a less homogeneous low-amplitude motions, are detected, both Information directed to the public at large medium than the mantle (see Figure 3). at close, and long distances, by seismic usually refers to the Richter magnitude It is through the painstaking effort initia- stations, fitted with seismographs, i.e. devi- (open-scale magnitude), as established by ted in the last century in seismological ces allowing the measurement of even the Charles Francis Richter, in California, in 1935, initially defined for the purposes of quantifying observatories, that tables could be drawn most minute ground motions, in all three the size of local earthquakes. up, relating propagation time and distance dimensions, and yielding their characteristics, in terms of displacement, velocity, several stations, the site of the epicenter Historically, this was based on the mea- or acceleration. may be geometrically located, at the inter- surement – in well-defined conditions – Hydroacoustic waves, generated by under- section of the corresponding circles (see of wave amplitudes, corrected for atte- sea explosions, or explosions set off under- Figure 4). Current numerical methods deal nuation effects from the soils traversed. ground close to a sea, or ocean, are detec- with the problem globally, by treating it as This is a logarithmic scale, energy being ted by hydroacoustic stations, comprising an inverse problem, involving unknowns multiplied by a factor 30 for every increase submerged receptors, and coastal seis- that are brought together into a 4-dimen- by one unit! Over time, this definition was mic stations. Networking such stations sional vector x (latitude, longitude, depth, found to be incomplete, leading to a num- around the globe (in particular in and event origin time), and data subsumed ber of other definitions being put forward.(1) around a region that needs to be monito- under a vector t covering the various mea- Magnitude should not be confused with red) makes it possible to determine pre- surements (e.g. wave arrival times). The earthquake intensity, this characterizing, cisely the geographic location of the earth- direct problem, as noted by vector t(x), on the other hand, the effects felt by human quake focus, and to issue an alert call, if involves computing, from x, the theoreti- beings, and the amount of damage obser- required. Indeed, while precursor signs cal values associated to the data involved. ved at a particular location, subsequent do exist (variations in the local magnetic Solving the inverse problem involves fin- to the event.(2) The largest earthquake to field, heightened groundwater circulation, ding the vector x0 that minimizes the dif- have occurred since 1900 took place in reductions in rock resistivity, slight ground ferences between t, and t(x0). Chile, in 1960, with a magnitude of 9.5. surface deformations), it is not feasible to The characterization of an earthquake However, the earthquake taking the lar- predict earthquakes. does not end with its geographical loca- Skip to page 94 The first methods used for the purposes tion. Describing the source poses a more of locating seismic events, on the basis of complex problem. (2) In France, as in most European countries, the intensity scale adopted is the EMS–98 scale the arrival times of the various wave trains, Magnitude is a representation of the elas- (European Macroseismic Scale, as established were based on geometric principles. For tic energy released by the earthquake. in 1998), which features 12 degrees. distances lower than 1,200 km, propagation times, for P waves and for S waves, are proportional, as a first approximation, seismic quiescence first P wave first S wave to the distances traveled by these waves. The difference between the two times of arrival is thus itself, in turn, proportional to distance, this allowing the source to be located on a circle, centered on the station. By repeating this analysis, across

1 minute 6 minutes

station3 Darwin

epicenter

station1 Kuala Lumpur

station2 Calcutta Yuvanoé/CEA C. Dupont/CEA

The short-period seismic detector allows Figure 4. measurement of ground motions involving The triangulation method has long been used for the purposes of locating a seismic event. The periods shorter than 2 seconds. It is time difference between arrivals of P waves, and S waves allows the distance of the detector particularly suitable for the purposes of from the epicenter to be derived. On the basis of a number of seismic stations, each yielding a studying body waves generated by nearby value for distance, the epicenter is located at the intersection of the circles centered on each earthquakes. station, of radius equal to the distance found at that station. FOCUS D

Page 93 cont'd gest toll in lives (some 250,000 casual- Division (DAM). LDG, based at Bruyères- behalf of a scientific interest group, brin- ties) was the Tangshan earthquake, in le-Châtel (Essonne département, near ging together CNRS/INSU, CEA, BRGM, China, in 1976, with a magnitude of 7.5. Paris), seeks to detect, and identify, in IRSN, IPGP, the Civil Engineers Central The earthquake that affected Sichuan real time, every seismic event, while Laboratory (LCPC: Laboratoire central Province (southwestern China) on 12 May advancing knowledge of the Earth’s des Ponts et chaussées), and a number 2008, with a magnitude of 7.9, caused at motions. The ensemble of data collected of universities – has the remit of provi- least 90,000 casualties. One and the same makes it possible to draw up a catalog of ding the scientific, and technological earthquake, of a given magnitude, as defi- seismicity, a reference serving as the basis community with data, allowing an ned by the energy released at its focus, for the seismic zoning of mainland France, understanding to be gained of phenomena will be experienced at varying intensity which was revised in 2007, for the imple- related to ground motion during earth- levels, depending on focus depth, distance mentation of the European Eurocode 8 quakes, and arrive at estimates of such from the epicenter, and the local charac- (EC 8) seismic design standard, due to motion, in future earthquakes. The high teristics of the observation location. supplant existing French seismic design sensitivity achieved makes it possible to The concept of seismic moment was intro- regulations (PS92, PS–MI) from 2010. investigate scaling laws, and nonlinearity duced, fairly recently, in an endeavor to Finally, the French Permanent Acce- phenomena. RAP should thus assist in provide a description of an earthquake in lerometer Network (RAP: Réseau accé- the determination of reference spectra, mechanical terms: the value of the seis- lérométrique permanent) – comprising allowing structural dimensioning to be mic moment is obtained by multiplying more than one hundred stations, run on carried out. an elastic constant by the average slip generated at a fault, and the area of that fault. This is complemented by the description of the rupture mechanism involved, specifying the parameters of the fault along which the rupture propagated (direction, length, depth…), the sections that have failed, their displacement, and rupture velocity, on the basis of wave recordings made by a number of detectors. Nowadays, data from stations are directly transmitted via satellite to an analysis center, where every event is studied. Networks with a global coverage, such as the US World-Wide Standardized Seismograph Network (WWSSN), or Incorporated Research Institutions for Seismology (IRIS), or France’s Géoscope,

chiefly bring together equipment C. Dupont/CEA recording all the components of ground DASE’s geophysical signals analysis room. In this room, all signals are centralized, as they are motion, across a wide band of frequen- detected by monitoring stations set up all around the world. Analysis of these signals makes it cies. At the European level, the possible to alert instantly government agencies, in the event of a strong earthquake, a nuclear test, or exceptional events. European–Mediterranean Seismological Center (EMSC) gathers all the findings from more than 80 institutions, in some 60 countries (from Iceland to the Arabian Peninsula, and from Morocco to Russia). In France, alongside the National Seismic Monitoring Network (RéNaSS: Réseau national de surveillance sismique), head- quarted in Strasbourg, which covers all Tests carried out on vibrating tables, of mainland France, the global monito- in CEA’s Tamaris ring remit is entrusted to CEA, more pre- laboratory – shown cisely to the Detection and Geophysics here, a test involving a structure Laboratory (LDG: Laboratoire de détec- of about 20 tonnes – tion et de géophysique), coming under have contributed the Environmental Assessment and to the drawing up Monitoring Department (DASE: Dépar- of European seismic engineering tement analyse, surveillance, environne- standards for

ment), part of CEA’s Military Applications S. Poupin/CEA buildings. FOCUS E How does a tsunami arise, and propagate? he initiating event, for a tsunami, is a Tsudden geological event (submarine earthquake, volcanic eruption, cliff failure…), disturbing the initially quiescent ocean (see Figure). This phenomenon is quite distinct and separate from tsunami-like occurren- ces, due to meteorological causes. Close to the source, the ocean begins to oscillate, being brought back to equilibrium by gravity, this generating a train of waves, invol- a b ving wavelengths of up to 40–300 km, propagating in all directions. Barely perceptible oceanic continental plate subduction in the high sea (involving as they do ampli- zone plate tudes ranging from a few centimeters to several tens of centimeters), these waves undergo amplification as the seafloor rises closer to the surface, i.e. near shores, tsunami velocity then slowing down to a few tens of kilometers per hour, compared with 500–1,000 km/h in the deep ocean. Owing to the conservation of energy, as wavelength shortens, wave amplitude rises: a wave less c d than 1 meter high in the deep ocean may rise up, in excess of several tens of meters at the coastline. This is where the tsunami results in the sea overflowing, causing inundations that may penetrate far inland, in some cases. For a submarine earthquake to cause a tsunami, it must occur at shallow depth (less than 50 km), and involve a magnitude of 6.5 at least. Above a magnitude of 8, an earthquake can generate a potentially destruc- e f tive, ocean-wide tsunami. Host as it was to 5 major tsunamis during the 20th century, the Pacific region was already well identi- Yuvanoé/CEA fied as a risk area, before the occurrence, Figure. A situation involving a subduction zone, where an oceanic plate is slipping under a continental plate on 26 December 2004, off the northwestern (a). In a strong earthquake, the overthrusting continental plate is abruptly uplifted by several tip of the Indonesian island of Sumatra, in meters, pushing upward the overlying volume of water (b). The surface bulge (c) begins to propagate the Indian Ocean, of the largest event to have in all directions (d). Subsequently, the wave train increases in intensity (e). As the seafloor rises closer to the surface, near the shore, the waves slow down, even as they gain in amplitude (f). arisen in that region, since the setting up of They may reach distant coastlines, thousands of kilometers away, where inundations may affect worldwide seismic networks, with a magni- locations at up to several meters elevation, in extreme cases. tude estimated at 9.2. The fault involved rup- tured over a length close to 1,500 km. Rupture No destructive tsunamis have occurred there, lution of the ocean’s level to be monitored duration was more than 9 minutes, the rup- since the 1956 event in the Aegean Sea, invol- over time. Satellites, including e.g. the ture causing displacements of as much as ving waves rising up to 10 m on the Greek French–US JASON satellites, likewise pro- 15 m. More than 500 aftershocks(1) were coastline. In the Atlantic Ocean, the last major vide precise measurements of ocean sur- detected in the hours that followed. The tsu- tsunami is the one that devastated Lisbon face levels, however they are of no use for nami inundated coasts over distances of (Portugal), in 1755. tsunami warning purposes. For major tsu- several kilometers, across relief that was Aside from strictly seismic detection resour- namis, as e.g. the 2004 event, inversion of very flat in the main, up to an elevation (runup) ces, specific resources are deployed, for the the altimetry data thus obtained makes it of 20–30 m; it ultimately caused about purposes of characterizing tsunamis. possible to provide a description of the tsu- 280,000 casualties. In the Mediterranean, Monitoring stations provide, in real time, nami source. The ensemble of marigraph, tsunamis are a more infrequent occurrence. sea level measurements (marigraphs set and satellite data may thus be subjected to up on the coastline, which monitor sea level, inversion, to determine the tsunami source, (1) Earthquakes of smaller intensity, and yield marigrams; or offshore tsuna- using an approach comparable to that imple- following the largest (the so-called main shock) in a sequence of earthquakes located within meters, linked to pressure sensors posi- mented by seismologists, to determine a proximate zone. tioned on the sea floor), allowing the evo- earthquake sources from seismograms.