IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Synthesis Report

Glossary R-Z


Radiative forcing

Radiative forcing is the change in the net, downward minus upward, irradiance (expressed in Watts per square metre, W/m2) at the tropopause due to a change in an external driver of climate change, such as, for example, a change in the concentration of carbon dioxide or the output of the Sun. Radiative forcing is computed with all tropospheric properties held fixed at their unperturbed values, and after allowing for stratospheric temperatures, if perturbed, to readjust to radiative-dynamical equilibrium. Radiative forcing is called instantaneous if no change in stratospheric temperature is accounted for. For the purposes of this report, radiative forcing is further defined as the change relative to the year 1750 and, unless otherwise noted, refers to a global and annual average value.


Planting of forests on lands that have previously contained forests but that have been converted to some other use. For a discussion of the term forest and related terms such as afforestation, reforestation and deforestation, see the IPCC Report on Land Use, Land-Use Change and Forestry (IPCC, 2000). See also the Report on Definitions and Methodological Options to Inventory Emissions from Direct Human-induced Degradation of Forests and Devegetation of Other Vegetation Types (IPCC, 2003)


A region is a territory characterised by specific geographical and climatological features. The climate of a region is affected by regional and local scale forcings like topography, land-use characteristics, lakes etc., as well as remote influences from other regions.


The ability of a social or ecological system to absorb disturbances while retaining the same basic structure and ways of functioning, the capacity for self-organisation, and the capacity to adapt to stress and change.


Retrofitting means to install new or modified parts or equipment, or undertake structural modifications, to existing infrastructure that were either not available or not considered necessary at the time of construction. The purpose of retrofitting in the context of climate change is generally to ensure that existing infrastructure meets new design specifications that may be required under altered climate conditions.


That part of precipitation that does not evaporate and is not transpired, but flows over the ground surface and returns to bodies of water. See Hydrological cycle



The accumulation of salts in soils.

Saltwater intrusion

Displacement of fresh surface water or groundwater by the advance of saltwater due to its greater density. This usually occurs in coastal and estuarine areas due to reducing land-based influence (e.g., either from reduced runoff and associated groundwater recharge, or from excessive water withdrawals from aquifers) or increasing marine influence (e.g., relative sea-level rise).


A plausible and often simplified description of how the future may develop, based on a coherent and internally consistent set of assumptions about driving forces and key relationships. Scenarios may be derived from projections, but are often based on additional information from other sources, sometimes combined with a narrative storyline. See also SRES scenarios; Climate scenario; Emission scenarios.

Sea-ice biome

The biome formed by all marine organisms living within or on the floating sea ice (frozen seawater) of the polar oceans.

Sea ice

Any form of ice found at sea that has originated from the freezing of sea water. Sea ice may be discontinuous pieces (ice floes) moved on the ocean surface by wind and currents (pack ice), or a motionless sheet attached to the coast (land-fast ice). Sea ice less than one year old is called first-year ice. Multi-year ice is sea ice that has survived at least one summer melt season.

Sea level change/sea level rise

Sea level can change, both globally and locally, due to (i) changes in the shape of the ocean basins, (ii) changes in the total mass of water and (iii) changes in water density. Factors leading to sea level rise under global warming include both increases in the total mass of water from the melting of land-based snow and ice, and changes in water density from an increase in ocean water temperatures and salinity changes. Relative sea level rise occurs where there is a local increase in the level of the ocean relative to the land, which might be due to ocean rise and/or land level subsidence.

See also Mean Sea Level, Thermal expansion.

Seasonally frozen ground

See Frozen ground


Sensitivity is the degree to which a system is affected, either adversely or beneficially, by climate variability or climate change. The effect may be direct (e.g., a change in crop yield in response to a change in the mean, range, or variability of temperature) or indirect (e.g., damages caused by an increase in the frequency of coastal flooding due to sea level rise).

This concept of sensitivity is not to be confused with climate sensitivity, which is defined separately above.


A trait marking one phenomenon or aspect as distinct from others; something singular, distinct, peculiar, uncommon or unusual.


Any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas or aerosol from the atmosphere.

Snow pack

A seasonal accumulation of slow-melting snow.

Soil temperature

The temperature of the ground near the surface (often within the first 10cm).

Solar activity

The Sun exhibits periods of high activity observed in numbers of sunspots, as well as radiative output, magnetic activity, and emission of high energy particles. These variations take place on a range of time-scales from millions of years to minutes

Solar radiation

Electromagnetic radiation emitted by the Sun. It is also referred to as short-wave radiation. Solar radiation has a distinctive range of wavelengths (spectrum) determined by the temperature of the Sun, peaking in visible wavelengths. See also Thermal infrared radiation, Total Solar Irradiance


Source mostly refers to any process, activity or mechanism that releases a greenhouse gas, an aerosol, or a precursor of a greenhouse gas or aerosol into the atmosphere. Source can also refer to e.g. an energy source.

Spatial and temporal scales

Climate may vary on a large range of spatial and temporal scales. Spatial scales may range from local (less than 100,000 km2), through regional (100,000 to 10 million km2) to continental (10 to 100 million km2). Temporal scales may range from seasonal to geological (up to hundreds of millions of years).

SRES scenarios

SRES scenarios are emission scenarios developed by Nakic4enovic4 and Swart (2000) and used, among others, as a basis for some of the climate projections used in the Fourth Assessment Report. The following terms are relevant for a better understanding of the structure and use of the set of SRES scenarios:

Scenario Family: Scenarios that have a similar demographic, societal, economic and technical-change storyline. Four scenario families comprise the SRES scenario set: A1, A2, B1 and B2.

Illustrative Scenario: A scenario that is illustrative for each of the six scenario groups reflected in the Summary for Policymakers of Nakic4enovic4 et al. (2000). They include four revised ‘scenario markers’ for the scenario groups A1B, A2, B1, B2, and two additional scenarios for the A1FI and A1T groups. All scenario groups are equally sound.

Marker Scenario: A scenario that was originally posted in draft form on the SRES website to represent a given scenario family. The choice of markers was based on which of the initial quantifications best reflected the storyline, and the features of specific models. Markers are no more likely than other scenarios, but are considered by the SRES writing team as illustrative of a particular storyline. They are included in revised form in Nakic4enovic4 and Swart (2000). These scenarios received the closest scrutiny of the entire writing team and via the SRES open process. Scenarios were also selected to illustrate the other two scenario groups.

Storyline: A narrative description of a scenario (or family of scenarios), highlighting the main scenario characteristics, relationships between key driving forces and the dynamics of their evolution.


Keeping constant the atmospheric concentrations of one or more greenhouse gases (e.g. carbon dioxide) or of a CO2-equivalent basket of greenhouse gases. Stabilisation analyses or scenarios address the stabilisation of the concentration of greenhouse gases in the atmosphere.


A person or an organisation that has a legitimate interest in a project or entity, or would be affected by a particular action or policy.


Set of rules or codes mandating or defining product performance (e.g., grades, dimensions, characteristics, test methods, and rules for use). Product, technology or performance standards establish minimum requirements for affected products or technologies. Standards impose reductions in greenhouse gas emissions associated with the manufacture or use of the products and/or application of the technology.

Storm surge

The temporary increase, at a particular locality, in the height of the sea due to extreme meteorological conditions (low atmospheric pressure and/or strong winds). The storm surge is defined as being the excess above the level expected from the tidal variation alone at that time and place.

Storm tracks

Originally, a term referring to the tracks of individual cyclonic weather systems, but now often generalised to refer to the regions where the main tracks of extratropical disturbances occur as sequences of low (cyclonic) and high (anticyclonic) pressure systems.


The highly stratified region of the atmosphere above the troposphere extending from about 10 km (ranging from 9 km in high latitudes to 16 km in the tropics on average) to about 50 km altitude.


Water flow within a river channel, for example expressed in m3/s. A synonym for river discharge.

Structural change

Changes, for example, in the relative share of Gross Domestic Product produced by the industrial, agricultural, or services sectors of an economy; or more generally, systems transformations whereby some components are either replaced or potentially substituted by other ones.

Sulphurhexafluoride (SF6)

One of the six greenhouse gases to be curbed under the Kyoto Protocol. It is largely used in heavy industry to insulate high-voltage equipment and to assist in the manufacturing of cable-cooling systems and semi-conductors.

Surface temperature

See Global surface temperature.

Sustainable Development (SD)

The concept of sustainable development was introduced in the World Conservation Strategy (IUCN 1980) and had its roots in the concept of a sustainable society and in the management of renewable resources. Adopted by the WCED in 1987 and by the Rio Conference in 1992 as a process of change in which the exploitation of resources, the direction of investments, the orientation of technological development, and institutional change are all in harmony and enhance both current and future potential to meet human needs and aspirations. SD integrates the political, social, economic and environmental dimensions.



A carbon tax is a levy on the carbon content of fossil fuels. Because virtually all of the carbon in fossil fuels is ultimately emitted as carbon dioxide, a carbon tax is equivalent to an emission tax on each unit of CO2-equivalent emissions. An energy tax - a levy on the energy content of fuels - reduces demand for energy and so reduces carbon dioxide emissions from fossil fuel use. An eco-tax is designed to influence human behaviour (specifically economic behaviour) to follow an ecologically benign path. An international carbon/emission/energy tax is a tax imposed on specified sources in participating countries by an international agreement. A harmonised tax commits participating countries to impose a tax at a common rate on the same sources. A tax credit is a reduction of tax in order to stimulate purchasing of or investment in a certain product, like GHG emission reducing technologies. A carbon charge is the same as a carbon tax.

Technological change

Mostly considered as technological improvement, i.e. more or better goods and services can be provided from a given amount of resources (production factors). Economic models distinguish autonomous (exogenous), endogenous and induced technological change. Autonomous (exogenous) technological change is imposed from outside the model, usually in the form of a time trend affecting energy demand or world output growth. Endogenous technological change is the outcome of economic activity within the model, i.e. the choice of technologies is included within the model and affects energy demand and/or economic growth. Induced technological change implies endogenous technological change but adds further changes induced by policies and measures, such as carbon taxes triggering R&D efforts.


The practical application of knowledge to achieve particular tasks that employs both technical artefacts (hardware, equipment) and (social) information (‘software’, know-how for production and use of artefacts).

Technology transfer

The exchange of knowledge, hardware and associated software, money and goods among stakeholders that leads to the spreading of technology for adaptation or mitigation The term encompasses both diffusion of technologies and technological cooperation across and within countries.

Thermal expansion

In connection with sea-level rise, this refers to the increase in volume (and decrease in density) that results from warming water. A warming of the ocean leads to an expansion of the ocean volume and hence an increase in sea level. See Sea level change.

Thermal infrared radiation

Radiation emitted by the Earth’s surface, the atmosphere and the clouds. It is also known as terrestrial or longwave radiation, and is to be distinguished from the near-infrared radiation that is part of the solar spectrum. Infrared radiation, in general, has a distinctive range of wavelengths (spectrum) longer than the wavelength of the red colour in the visible part of the spectrum. The spectrum of thermal infrared radiation is practically distinct from that of shortwave or solar radiation because of the difference in temperature between the Sun and the Earth-atmosphere system.

Tide gauge

A device at a coastal location (and some deep sea locations) that continuously measures the level of the sea with respect to the adjacent land. Time averaging of the sea level so recorded gives the observed secular changes of the relative sea level. See Sea level change/sea level rise.

Top-down models

Top-down model apply macroeconomic theory, econometric and optimization techniques to aggregate economic variables. Using historical data on consumption, prices, incomes, and factor costs, top-down models assess final demand for goods and services, and supply from main sectors, like the energy sector, transportation, agriculture, and industry. Some top-down models incorporate technology data, narrowing the gap to bottom-up models.

Total Solar Irradiance (TSI)

The amount of solar radiation received outside the Earth’s atmosphere on a surface normal to the incident radiation, and at the Earth’s mean distance from the sun. Reliable measurements of solar radiation can only be made from space and the precise record extends back only to 1978. The generally accepted value is 1,368 Watts per square meter (W m-2) with an accuracy of about 0.2%. Variations of a few tenths of a percent are common, usually associated with the passage of sunspots across the solar disk. The solar cycle variation of TSI is on the order of 0.1%. Source: AMS, 2000.

Tradable permit

A tradable permit is an economic policy instrument under which rights to discharge pollution – in this case an amount of greenhouse gas emissions – can be exchanged through either a free or a controlled permit-market. An emission permit is a non-transferable or tradable entitlement allocated by a government to a legal entity (company or other emitter) to emit a specified amount of a substance.


The boundary between the troposphere and the stratosphere.


The lowest part of the atmosphere from the surface to about 10 km in altitude in mid-latitudes (ranging from 9 km in high latitudes to 16 km in the tropics on average), where clouds and weather phenomena occur. In the troposphere, temperatures generally decrease with height.



An expression of the degree to which a value (e.g., the future state of the climate system) is unknown. Uncertainty can result from lack of information or from disagreement about what is known or even knowable. It may have many types of sources, from quantifiable errors in the data to ambiguously defined concepts or terminology, or uncertain projections of human behaviour. Uncertainty can therefore be represented by quantitative measures, for example, a range of values calculated by various models, or by qualitative statements, for example, reflecting the judgement of a team of experts (see Moss and Schneider, 2000; Manning et al., 2004). See also Likelihood; Confidence.

United Nations Framework Convention on Climate Change (UNFCCC)

The Convention was adopted on 9 May 1992 in New York and signed at the 1992 Earth Summit in Rio de Janeiro by more than 150 countries and the European Community. Its ultimate objective is the “stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”. It contains commitments for all Parties. Under the Convention, Parties included in Annex I (all OECD member countries in the year 1990 and countries with economies in transition) aim to return greenhouse gas emissions not controlled by the Montreal Protocol to 1990 levels by the year 2000. The Convention entered in force in March 1994. See Kyoto Protocol.


The addition of a substance of concern to a reservoir. The uptake of carbon containing substances, in particular carbon dioxide, is often called (carbon) sequestration.


The conversion of land from a natural state or managed natural state (such as agriculture) to cities; a process driven by net rural-to-urban migration through which an increasing percentage of the population in any nation or region come to live in settlements that are defined as urban centres.



An organism, such as an insect, that transmits a pathogen from one host to another.

Voluntary action

Informal programmes, self-commitments and declarations, where the parties (individual companies or groups of companies) entering into the action set their own targets and often do their own monitoring and reporting.

Voluntary agreement

An agreement between a government authority and one or more private parties to achieve environmental objectives or to improve environmental performance beyond compliance to regulated obligations. Not all voluntary agreements are truly voluntary; some include rewards and/or penalties associated with joining or achieving commitments.


Vulnerability is the degree to which a system is susceptible to, and unable to cope with, adverse effects of climate change, including climate variability and extremes. Vulnerability is a function of the character, magnitude, and rate of climate change and variation to which a system is exposed, its sensitivity, and its adaptive capacity.


Water consumption

Amount of extracted water irretrievably lost during its use (by evaporation and goods production). Water consumption is equal to water withdrawal minus return flow.

Water stress

A country is water stressed if the available freshwater supply relative to water withdrawals acts as an important constraint on development. In global-scale assessments, basins with water stress are often defined as having a per capita water availability below 1,000 m3/yr (based on long-term average runoff). Withdrawals exceeding 20% of renewable water supply have also been used as an indicator of water stress. A crop is water stressed if soil available water, and thus actual evapotranspiration, is less than potential evapotranspiration demands.



See Plankton


Glossaries of the contributions of Working Groups I, II and III to the IPCC Fourth Assessment Report.

AMS, 2000: AMS Glossary of Meteorology, 2nd Ed. American Meteorological Society, Boston, MA, http://amsglossary.allenpress.com/glossary/browse.

Cleveland C.J. and C. Morris, 2006: Dictionary of Energy, Elsevier, Amsterdam, 502p

Heim, R.R., 2002: A Review of Twentieth-Century Drought Indices Used in the United States. Bull. Am. Meteorol. Soc., 83, 1149–1165

IPCC, 1996: Climate Change 1995: The Science of Climate Change. Contribution of Working Group I to the Second Assessment Report of the Intergovernmental Panel on Climate Change [Houghton., J.T., et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 572 pp.

IPCC, 2000: Land Use, Land-Use Change, and Forestry. Special Report of the Intergovernmental Panel on Climate Change [Watson, R.T., et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 377 pp.

IPCC, 2003: Definitions and Methodological Options to Inventory Emissions from Direct Human-Induced Degradation of Forests and Devegetation of Other Vegetation Types [Penman, J., et al. (eds.)]. The Institute for Global Environmental Strategies (IGES), Japan , 32 pp.

IUCN, 1980: The World Conservation Strategy: living resource conservation for sustainable development, Gland, Switzerland, IUCN/UNEP/WWF.

Manning, M., et al., 2004: IPCC Workshop on Describing Scientific Uncertainties in Climate Change to Support Analysis of Risk of Options. Workshop Report. Intergovernmental Panel on Climate Change, Geneva.

Moss, R., and S. Schneider, 2000: Uncertainties in the IPCC TAR: Recommendations to Lead Authors for More Consistent Assessment and Reporting.  In: IPCC Supporting Material:  Guidance Papers on Cross Cutting Issues in the Third Assessment Report of the IPCC.  [Pachauri, R., T. Taniguchi, and K. Tanaka (eds.)]. Intergovernmental Panel on Climate Change, Geneva, pp. 33–51.

Nakic4enovic4, N., and R. Swart (eds.), 2000: Special Report on Emissions Scenarios. A Special Report of Working Group III of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 599 pp.

Van Everdingen, R. (ed.): 1998. Multi-Language Glossary of Permafrost and Related Ground-Ice Terms, revised May 2005. National Snow and Ice Data Center/World Data Center for Glaciology, Boulder, CO, http://nsidc.org/fgdc/glossary/.