TREE-1098; No of Pages 4 Opinion Systematic long-term observations of the global carbon cycle R.J. Scholes1, P.M.S. Monteiro2,3, C.L. Sabine4 and J.G. Canadell5 1 CSIR Natural Resources and Environment, PO Box 395, Pretoria 0001, South Africa 2 Africa Centre for Climate and Earth Systems Science (ACCESS), CSIR, PO Box 320, Stellenbosch, 7599, South Africa 3 Department of Oceanography, University of Cape Town, Rondebosch 7700, South Africa 4 NOAA Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, USA 5 Global Carbon Project, CSIRO Marine and Atmospheric Research, Canberra, ACT 2601, Australia Imagine a meeting convened to avert a global financial the Global Atmosphere Watch (24 stations in the global crisis where none of the finance ministers had access to network) and the National Oceanic and Atmospheric reliable information on changes in the stock market, Administration (NOAA) Global Monitoring Directorate national gross domestic product or international trade Flask Network (112 locations; Table 1). The differences flows. It is hardly conceivable. Yet the infinitely more in the observed CO2 concentrations within the network at a existence-threatening planetary social and ecological given time, together with atmospheric transport models, are crisis we refer to as ‘global change’ (comprising the used to infer the locations and magnitudes of anthropogenic linked issues of biogeochemical, climate, biotic and and natural sources and sinks of carbon [5]. At first, this human system change) is in an analogous situation. approach was only able to discriminate between broad Our information on the profound and accelerating latitudinal belts (‘boreal,’ ‘temperate’ and ‘tropical’ in the changes currently depends to an unacceptable degree Northern and Southern Hemispheres), but a larger and on serendipity, individual passion, redirected funding better-distributed set of observations, plus the addition of and the largely uncoordinated efforts of a few nations. other model constraints such as isotopes, elemental ratios The thesis of this paper is that navigation of the very and the seasonality of ocean and land production derived narrow ‘safe passages’ that lie ahead requires a com- from satellite observations, now permits such estimates to prehensive and systematic approach to Earth obser- be constrained into large regions by longitude as well [6]. vations, supported by a globally coordinated long- A second invaluable data set that arose largely out of term funding mechanism. We developed the argument the determination of a few individuals and has now grown based on observations of the carbon cycle, because the into a series of internationally coordinated initiatives are issues there are compelling and easily demonstrated, the observations of carbon dioxide partial pressure but we believe the conclusions also to be true for many (pCO2) in the surface ocean. Whereas large-scale spatial other types of observations relating to the state and and seasonal patterns in atmospheric CO2 can span a management of the biosphere. range of 10 matm in an average year, large-scale pat- terns in the surface ocean can easily span 200 matm. For Luck and persistence many years, surface ocean pCO2 measurements have The observation that triggered much of our contemporary been made on research vessels as they traversed the concern regarding global climate change is the record of global oceans. The first global picture of surface pCO2 atmospheric carbon dioxide concentration (CO2) collected distributions required 250 000 measurements collected at Mauna Loa since 1957 by Charles Keeling. Only the over 40 years to properly characterise the patterns of dogged persistence of Keeling ensured the continuity of spatial variability [7]. This work showed that whereas this data set over a period of 30 years [1]. The precise and average surface ocean pCO2 values are slightly lower continuous measurements unequivocally demonstrated than atmospheric, leading to a net uptake of CO2 from the accelerating rise in the concentration of this major the atmosphere to the ocean, there are large regions like greenhouse gas. The subtleties of the seasonal cycle and its the equatorial Pacific Ocean that are significant sources interannual variation revealed crucial details of the global of CO2 back to the atmosphere [8]. It also showed the carbon cycle – such as the sensitivity to climate. The crucial role of certain regions such as the Southern addition of carbon isotope analyses and the simultaneous Ocean, and revealed the effect of nutrient limitation on measurement of the ratio of oxygen to nitrogen permitted net carbon uptake by marine ecosystems [7,9]. the development of global carbon budgets based entirely on The latest surface ocean pCO2 climatology compiles over observations (as opposed to inferences), with known con- 3 million measurements collected using bottle and under- fidence ranges [2–4]. way samples from research ships, continuous underway Comparable measurements of atmospheric composition measurements on voluntary observing ships (VOS), and are now collected in many places worldwide, through autonomous systems on moored buoys [10]. Coordination and intercalibration are just as crucial for ocean pCO2 Corresponding author: Scholes, R.J. ([email protected]). as it is for atmospheric CO2 measurements. The exchange 0169-5347/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2009.03.006 Available online xxxxxx 1 TREE-1098; No of Pages 4 Opinion Trends in Ecology and Evolution Vol.xxx No.x Table 1. Key carbon observation networks and activities mentioned in the text Network or activity Description Web address Global Atmosphere Watch Atmospheric chemistry part of the Global Climate http://www.wmo.int/pages/prog/arep/gaw/gaw_ Observing System home_en.html Global Flask Network Places taking monthly air samples for analysis by NOAA http://www.esrl.noaa.gov/gmd/ccgg/flask.html International Ocean Carbon Coordinates measurements of the C cycle in the oceans http://www.ioccp.org Coordination Project Fluxnet Network of terrestrial C flux sites http://www.fluxnet.ornl.gov Global Carbon Project Project of the Earth System Science partnership to do http://www.globalcarbonproject.org coordinated research on the C cycle Orbital Carbon Observatory Example of space-based carbon observations http://www.oco.jpl.nasa.gov Carbon Dioxide Information Data centre for C-related data sets http://cdiac.ornl.gov Analysis Center of seawater standards from the Scripps Institute of Ocean- What is the value of a carbon observation system? ography [11] and primary gas standards by NOAA plays an Monitoring changes in carbon fluxes and pool sizes is essential role here. essential for tracking human-induced climate change In the examples given above, the power of the obser- and predicting the future trajectories of the human-car- vations resides in their collective geographical coverage, not bon-climate system. Currently, 55–65% of all anthropo- in the value of any single measurement: a clear argument for genic carbon dioxide emissions are removed from the consistent methods, standards and data sharing. However, atmosphere by natural sinks. But the strength of these in both cases, large regional uncertainties remain owing to sinks is influenced by the rate of emissions and the chan- sparse coverage, most notably on tropical land and in the ging climate [17]. Steering human efforts toward atmos- Southern Ocean [12–14]. This is so because measurements pheric CO2 stabilisation requires detailed knowledge in remote locations are expensive to collect, and sampling regarding both the natural fluxes and human pertur- priorities tend to be dictated by national interest rather than bations of the carbon cycle. the need to achieve balanced global coverage. A global carbon observatory would consolidate infor- There is no direct terrestrial equivalent of the atmos- mation on both anthropogenic emissions and natural pheric and oceanic data sets described above. The reasons fluxes. With an appropriate temporal and spatial resol- are a combination of political and ecological realities. ution, the system would be able to resolve the contributions Politically, the land is carved up into nearly 200 sovereign of individual processes and regions critical to the under- states, which are not always forthcoming with obser- standing of possible future trajectories. vations pertaining to their soil and forest resources (in Such a system would need to include close monitoring of much the same way as they are often reluctant to share the carbon pools on land and in the oceans most likely to fisheries resource data in their continental waters). The change [18]. Major vulnerable pools include carbon in measurement methods applied in different countries are tropical forests, the Southern Ocean deep waters, frozen often somewhat incompatible. On the ecological side, ter- soils, peatlands (both at high latitude and in the tropics) restrial carbon stocks and fluxes can vary by orders of and methane hydrates in permafrost and on continental magnitude over distances of tens of meters, requiring a shelves. dense and well-distributed observation system for accurate A carbon observatory would also enable the monitoring and unbiased estimates. and verification of emissions and removals of carbon by The absence of systematic terrestrial carbon obser- human-induced activities at national and subnational vations is the main reason why, until relatively recently, scales. Many billions of dollars are