Appendix I Glossary Editor: A.P.M. Baede A → indicates that the following term is also contained in this Glossary. Adjustment time centrimetric precision. Altimetry has the advantage of being a See: →Lifetime; see also: →Response time. measurement relative to a geocentric reference frame, rather than relative to land level as for a →tide gauge, and of affording quasi- Aerosols global coverage. A collection of airborne solid or liquid particles, with a typical size between 0.01 and 10 µm and residing in the atmosphere for Anthropogenic at least several hours. Aerosols may be of either natural or Resulting from or produced by human beings. anthropogenic origin. Aerosols may influence climate in two ways: directly through scattering and absorbing radiation, and Atmosphere indirectly through acting as condensation nuclei for cloud The gaseous envelope surrounding the Earth. The dry formation or modifying the optical properties and lifetime of atmosphere consists almost entirely of nitrogen (78.1% volume clouds. See: →Indirect aerosol effect. mixing ratio) and oxygen (20.9% volume mixing ratio), The term has also come to be associated, erroneously, with together with a number of trace gases, such as argon (0.93% the propellant used in “aerosol sprays”. volume mixing ratio), helium, and radiatively active →greenhouse gases such as →carbon dioxide (0.035% volume Afforestation mixing ratio), and ozone. In addition the atmosphere contains Planting of new forests on lands that historically have not water vapour, whose amount is highly variable but typically 1% contained forests. For a discussion of the term →forest and volume mixing ratio. The atmosphere also contains clouds and related terms such as afforestation, →reforestation, and →aerosols. →deforestation: see the IPCC Report on Land Use, Land-Use Change and Forestry (IPCC, 2000). Attribution See: →Detection and attribution. Albedo The fraction of solar radiation reflected by a surface or object, Autotrophic respiration often expressed as a percentage. Snow covered surfaces have a →Respiration by photosynthetic organisms (plants). high albedo; the albedo of soils ranges from high to low; vegeta- tion covered surfaces and oceans have a low albedo. The Earth’s Biomass albedo varies mainly through varying cloudiness, snow, ice, leaf The total mass of living organisms in a given area or volume; area and land cover changes. recently dead plant material is often included as dead biomass. Altimetry Biosphere (terrestrial and marine) A technique for the measurement of the elevation of the sea, land The part of the Earth system comprising all →ecosystems and or ice surface. For example, the height of the sea surface (with living organisms, in the atmosphere, on land (terrestrial respect to the centre of the Earth or, more conventionally, with biosphere) or in the oceans (marine biosphere), including derived respect to a standard “ellipsoid of revolution”) can be measured dead organic matter, such as litter, soil organic matter and oceanic from space by current state-of-the-art radar altimetry with detritus. 788 Appendix I Black carbon either the mean state of the climate or in its variability, persisting Operationally defined species based on measurement of light for an extended period (typically decades or longer). Climate absorption and chemical reactivity and/or thermal stability; change may be due to natural internal processes or external consists of soot, charcoal, and/or possible light-absorbing refrac- forcings, or to persistent anthropogenic changes in the composi- tory organic matter. (Source: Charlson and Heintzenberg, 1995, tion of the atmosphere or in land use. p. 401.) Note that the →Framework Convention on Climate Change (UNFCCC), in its Article 1, defines “climate change” as: “a Burden change of climate which is attributed directly or indirectly to The total mass of a gaseous substance of concern in the human activity that alters the composition of the global atmosphere. atmosphere and which is in addition to natural climate variability observed over comparable time periods”. The Carbonaceous aerosol UNFCCC thus makes a distinction between “climate change” Aerosol consisting predominantly of organic substances and attributable to human activities altering the atmospheric various forms of →black carbon. (Source: Charlson and composition, and “climate variability” attributable to natural Heintzenberg, 1995, p. 401.) causes. See also: →Climate variability. Carbon cycle The term used to describe the flow of carbon (in various forms, Climate feedback e.g. as carbon dioxide) through the atmosphere, ocean, terrestrial An interaction mechanism between processes in the →climate →biosphere and lithosphere. system is called a climate feedback, when the result of an initial process triggers changes in a second process that in turn Carbon dioxide (CO2) influences the initial one. A positive feedback intensifies the A naturally occurring gas, also a by-product of burning fossil original process, and a negative feedback reduces it. fuels and →biomass, as well as →land-use changes and other industrial processes. It is the principal anthropogenic Climate model (hierarchy) →greenhouse gas that affects the earth’s radiative balance. It is A numerical representation of the →climate system based on the the reference gas against which other greenhouse gases are physical, chemical and biological properties of its components, measured and therefore has a →Global Warming Potential of 1. their interactions and feedback processes, and accounting for all or some of its known properties. The climate system can be Carbon dioxide (CO2) fertilisation represented by models of varying complexity, i.e. for any one The enhancement of the growth of plants as a result of increased component or combination of components a hierarchy of models atmospheric CO2 concentration. Depending on their mechanism can be identified, differing in such aspects as the number of of →photosynthesis, certain types of plants are more sensitive to spatial dimensions, the extent to which physical, chemical or → changes in atmospheric CO2 concentratioin. In particular, C3 biological processes are explicitly represented, or the level at → plants generally show a larger response to CO2 than C4 plants. which empirical →parametrizations are involved. Coupled atmosphere/ocean/sea-ice General Circulation Models Charcoal (AOGCMs) provide a comprehensive representation of the Material resulting from charring of biomass, usually retaining climate system. There is an evolution towards more complex some of the microscopic texture typical of plant tissues; models with active chemistry and biology. chemically it consists mainly of carbon with a disturbed graphitic Climate models are applied, as a research tool, to study and structure, with lesser amounts of oxygen and hydrogen. See: simulate the climate, but also for operational purposes, including →Black carbon; Soot particles. (Source: Charlson and monthly, seasonal and interannual →climate predictions. Heintzenberg, 1995, p. 402.) Climate prediction Climate A climate prediction or climate forecast is the result of an Climate in a narrow sense is usually defined as the “average attempt to produce a most likely description or estimate of the weather”, or more rigorously, as the statistical description in actual evolution of the climate in the future, e.g. at seasonal, terms of the mean and variability of relevant quantities over a interannual or long-term time scales. See also: →Climate period of time ranging from months to thousands or millions of projection and →Climate (change) scenario. years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most Climate projection often surface variables such as temperature, precipitation, and A →projection of the response of the climate system to wind. Climate in a wider sense is the state, including a statistical →emission or concentration scenarios of greenhouse gases and description, of the →climate system. aerosols, or →radiative forcing scenarios, often based upon simulations by →climate models. Climate projections are distin- Climate change guished from →climate predictions in order to emphasise that Climate change refers to a statistically significant variation in climate projections depend upon the emission/concentration/ Appendix I 789 radiative forcing scenario used, which are based on assumptions, CO2 fertilisation → concerning, e.g., future socio-economic and technological See Carbon dioxide (CO2) fertilisation developments, that may or may not be realised, and are therefore subject to substantial uncertainty. Cooling degree days The integral over a day of the temperature above 18°C (e.g. a Climate scenario day with an average temperature of 20°C counts as 2 cooling A plausible and often simplified representation of the future degree days). See also: →Heating degree days. climate, based on an internally consistent set of climatological relationships, that has been constructed for explicit use in Cryosphere investigating the potential consequences of anthropogenic The component of the →climate system consisting of all snow, →climate change, often serving as input to impact models. ice and permafrost on and beneath the surface of the earth and →Climate projections often serve as the raw material for ocean. See: →Glacier; →Ice sheet. constructing climate scenarios, but climate scenarios usually require additional information such as about the observed C3 plants current climate.