Climate Change Glossary

Climate change is a complex topic often using difficult and confusing words or phrases. The following terms have been gathered from many sources including the National Oceanic and Atmospheric Administration (NOAA), Intergovernmental Panel on Climate Change (IPCC), and others. Included are the most commonly referred to terms in climate change literature and news media.



The physiological adaptation to climatic variations.


See Adaptive capacity.



Adaptation assessment


Adaptation benefits


Adaptation costs


Adaptive capacity



Reduction in emissions by sources or enhancement of removals by sinks that is additional to any that would occur in the absence of a Joint Implementation or a Clean Development Mechanism project activity as defined in the Kyoto Protocol Articles on Joint Implementation and the Clean Development Mechanism. This definition may be further broadened to include financial, investment, and technology additionality. Under "financial additionality," the project activity funding shall be additional to existing Global Environmental Facility, other financial commitments of Parties included in Annex I, Official Development Assistance, and other systems of cooperation. Under "investment additionality," the value of the Emissions Reduction Unit/Certified Emission Reduction Unit shall significantly improve the financial and/or commercial viability of the project activity. Under "technology additionality," the technology used for the project activity shall be the best available for the circumstances of the host Party.

Adjustment time

See response time.


A collection of airborne solid or liquid particles, with a typical size between 0.01 and 10 mm that reside in the atmosphere for at least several hours. Aerosols may be of either natural or anthropogenic origin. Aerosols may influence climate in two ways: directly through scattering and absorbing radiation, and indirectly through acting as condensation nuclei for cloud dormation or modifying the optical properties and lifetime of clouds. See indirect aerosol effect.



Algal blooms





Alternative energy

Energy derived from non-fossil-fuel sources.

Ancillary Benefits

Complementary benefits of a climate policy including improvements in local air quality and reduced reliance of imported fossil fuels.



Resulting from or produced by human beings.


Anthropogenic emissions

Emissions of greenhouse gases, greenhouse gas precursors, and aerosols associated with human activities. These include burning of fossil fuels for energy, deforestation, and land-use changes that result in net increase in emissions.


Under an emissions trading scheme, permits to emit can initially either be given away for free, usually under a 'grandfathering' approach based on past emissions in a base year or an 'updating' approach based on the more recent emissions. The alternative is to auction permits in an initial market offering.




Arid regions

Ecosystems with less than 250 mm precipitation per year.



The gaseous envelop surrounding the Earth. The dry atmosphere consists almost entirely of nitrogen (78.1% volume mixingratio) and oxygen (20.9% volume mixing ratio), together with a number of trace gases, such as argon (0.93% volume mixingratio), helium, and radiatively active greenhouse gases such as carbon dioxide (0.035% volume mixing ratio) and ozone. In addition, the atmosphere contains water vapor, whose amount is highly variable but typically 1% volume mixing ratio. The atmosphere also contains clouds and aerosols.

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Black carbon




Boreal forest


Bottom-up models

A modeling approach that includes technological and engineering details in the analysis. See also top-down models.



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Capacity building

In the context of climate change, capacity building is a process of developing the technical skills and institutional capability in developing countries and economies in transition to enable them to participate in all aspects of adaptation to, mitigation of, and research on climate change, and the implementation of the Kyoto Mechanisms, etc.

Carbonaceous aerosol


Carbon credit

A permit that allows an entity to emit a specified amount of greenhouse gases. Also called emission permit. Buying a carbon credit is like building a credit reserve for later withdrawal of some type.

Carbon cycle

The term used to describe the flow of carbon (in various forms such as carbon dioxide) through the atmosphere, ocean, terrestrial biosphere, and lithosphere.

Carbon dioxide (CO2)


Carbon dioxide (CO2) fertilization

The enhancement of the growth of plants as a result of increased atmospheric carbon dioxide concentration. Depending on their mechanism of photosynthesis, certain types of plants are more sensitive to changes in atmospheric carbon dioxide concentration. In particular, plants that produce a three-carbon compound (C3)during photosynthesis-including most trees and agricultural crops such as rice, wheat, soybeans, potatoes, and vegetables-generally show a larger response than plants that produce a four-carbon compound (C4) during photosynthesis-mainly of tropical origin, including grasses and the agriculturally important crops maize, sugar cane, millet, and sorghum.

Carbon footprint

The amount of carbon an entity of any type (e.g., person, group, vehicle, event, building, corporation) emits into the atmosphere.

Carbon market:

A system for buying, selling and trading carbon credits. The regulatory carbon market is based on government regulations such as international Kyoto accords, or recent legislation in California. A voluntary carbon market refers to systems for trading carbon offsets as opposed to carbon credits

Carbon neutral


Carbon offset

Paying to plant new trees or investing in "green" technologies such as solar and wind power. Often these payments are a monetary donation to an environmental fund and/or endowment.

Carbon sink

Anything sequestering carbon such as trees and other vegetation, forests, oceans and grasslands.


Carbon source

Anything emitting carbon into the atmosphere including forest fires, car exhaust, factories, livestock.

Carbon tax

A tax on energy sources which emit carbon dioxide into the atmosphere.


An area that collects and drains rainwater.

Chlorofluorocarbons (CFCs)

Greenhouse gases covered under the 1987 Montreal Protocol and used for refrigeration, air conditioning, packaging, insulation, solvents, or aerosol propellants. Since they are not destroyed in the lower atmosphere, CFCs drift into the upper atmosphere where, given suitable conditions, they break down ozone. These gases are being replaced by other compounds, including hydrochlorofluorocarbons and hydrofluorocarbons, which are greenhouse gases covered under the Kyoto Protocol.


Climate in a narrow sense is usually defined as the "average weather" or more rigorously as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These relevant quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.

Climate change




Climate feedback


Climate model (hierarchy)

A numerical representation of the climate system based on the physical, chemical, and biological properties of its components, their interactions and feedback processes, and accounting for all or some of its known properties. The climate system can be represented by models of varying complexity-that is, for anyone component or combination of components a "hierarchy" of models can be identified, differing in such aspects as the number of spatial dimensions, the extent to which physical, chemical or biological processes are explicitly represented, or the level at which empirical parametrizations are involved. Coupled atmosphere/ocean/sea-ice general circulation models (AOGCMs) provide a comprehensive representation of the climate system. There is an evolution towards more complex models with active chemistry and biology. Climate models are applied, as a research tool, to study and simulate the climate, but also for operational purposes, including monthly, seasonal, and interannual climate predictions.

Climate prediction

A climate prediction or climate forecast is the result of an attempt to produce a most likely description or estimate of the actual evolution of the climate in the future (e.g., at seasonal, interannual, or long-term time-scales). See also climate projection and climate scenario.

Climate projection

A projection of the response of the climate system to emission or concentration scenarios of greenhouse gases and aerosols, or radiative forcing scenarios, often based upon simulations by climate models. Climate projections are distinguished from climate predictions in order to emphasize that climate projections depend upon the emission/concentration/radiative forcing scenario used, which are based on assumptions, concerning, for example, futures CIO-economic and technological developments that may or may not be realized, and are therefore subject to substantial uncertainty.

Climate scenario


Climate system



Climate variability



The benefits of policies that are implemented for various reason sat the same time-including climate change mitigation-acknowledging that most policies designed to address greenhouse gas mitigation also have other, often at least equally important, rationales (e.g., related to objectives of development, sustainability, and equity). The term co-impact is also used in a more generic sense to cover both the positive and negative sides of the benefits. See also ancillary benefits.


The use of waste heat from electric generation, such as exhaust from gas turbines, for either industrial purposes or district heating.

Coping range


Coral bleaching




A criterion that specifies that a technology or measure delivers a good or service at equal or lower cost than current practice, or the least-cost alternative for the achievement of a given target.


The component of the climate system consisting of all snow, ice, and permafrost on and beneath the surface of the earth and ocean. See also glacier and ice sheet.

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Deepwater formation



Conversion of forest to non-forest.

Deposit-refund system

Combines a deposit or fee (tax) on a commodity with a refund or rebate (subsidy) for implementation of a specified action.


An ecosystem with less than 100 mm precipitation per year.



Detection and attribution


Disturbance regime


Diurnal temperature range

The difference between the maximum and minimum temperature during a day.



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Economic potential

Economic potential is the portion of technological potential for greenhouse gas emissions reductions or energy efficiency improvements that could be achieved cost-effectively through the creation of markets, reduction of market failures, or increased financial and technological transfers. The achievement of economic potential requires additional policies and measures to break down market barriers. See also market potential, socio-economic potential, and technological potential.



Ecosystem services

Ecological processes or functions that have value to individuals or society.


El Niño Southern Oscillation (ENSO)

El Niño, in its original sense, is a warmwater current that periodically flows along the coast of Ecuador and Peru, disrupting the local fishery. This oceanic event is associated with a fluctuation of theintertropical surface pressure pattern and circulation in the Indian and Pacific Oceans, called the Southern Oscillation. This coupled atmosphere-ocean phenomenon is collectively known as El Niño Southern Oscillation, or ENSO. During an El Niño event, the prevailing trade winds weaken and the equatorial countercurrent strengthens, causing warm surface waters in the Indonesian area to flow eastward to overlie the cold waters of the Peru current. This event has great impact on the wind, sea surface temperature, and precipitation patterns in the tropical Pacific. It has climatic effects throughout the Pacific region and in many other parts of the world. The opposite of an El Niño event is called La Niña.


In the climate change context, emissions refer to the release of greenhouse gases and/or their precursors and aerosols into the atmosphere over a specified area and period of time.

Emissions permit

An emissions permit is the non-transferable or tradable allocation of entitlements by an administrative authority (intergovernmental organization, central or local government agency) to a regional (country, sub-national) or a sectoral (an individual firm) entity to emit a specified amount of a substance.

Emissions quota


Emissions Reduction Unit (ERU)

Equal to 1 tonne (metric ton) of carbon dioxide emissions reduced or sequestered arising from a Joint Implementation (defined in Article 6 of the Kyoto Protocol) project calculated using Global Warming Potential. See also Certified Emission Reduction Unit and emissions trading.

Emissions tax

Levy imposed by a government on each unit of CO2-equivalent emissions by a source subject to the tax. Since virtually all of the carbon in fossil fuels is ultimately emitted as carbon dioxide, a levy on the carbon content of fossil fuels-a carbon tax-is equivalent to an emissions tax for emissions caused by fossilfuel combustion. 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 ecotax is designated for the purpose of influencing human behavior (specifically economic behavior) to follow an ecologically benign path. International emissions/carbon/energy tax is a tax imposed on specified sources in participating countries by an international agency. The revenue is distributed or used as specified by participating countries or the international agency.

Emissions trading

A market-based approach to achieving environmental objectives that allows, those reducing greenhouse gas emissions below what is required, to use or trade the excess reductions to offset emissions at another source inside or outside the country. In general, trading can occur at the intracompany, domestic, and international levels.

Energy efficiency

Ratio of energy output of a conversion process or of a system to its energy input.

Energy intensity

Energy intensity is the ratio of energy consumption to economic or physical output. At the national level, energy intensity is the ratio of total domestic primary energy consumption or final energy consumption to Gross Domestic Product or physical output.


Energy service

The application of useful energy to tasks desired by the consumer such as transportation, a warm room, or light.

Energy transformation

The change from one form of energy, such as the energy embodied in fossil fuels, to another, such as electricity.

Environmentally Sound Technologies (ESTs)

Technologies that protect the environment, are less polluting, use all resources in a more sustainable manner, recycle more of their wastes and products, and handle residual wastes in a more acceptable manner than the technologies for which they were substitutes and are compatible with nationally determined socio-economic, cultural, and environmental priorities. ESTs in this report imply mitigation and adaptation technologies, hard and soft technologies.

Equivalent CO2 (carbon dioxide)

The concentration of carbon dioxide that would cause the same amount of radiative forcing as a given mixture of carbon dioxide and other greenhouse gases.



Eustatic sea-level change

A change in global average sea level brought about by an alteration to the volume of the world ocean. This may be caused by changes in water density or in the total mass of water. In discussions of changes on geological time scales, this term sometimes also includes changes in global average sea level caused by an alteration to the shape of the ocean basins. In this report, the term is not used in that sense.


The process by which a liquid becomes a gas.





External cost

Used to define the costs arising from any human activity, when the agent responsible for the activity does not take full account of the impacts on others of his or her actions. Equally, when the impacts are positive and not accounted for in the actions of the agent responsible they are referred to as external benefits. Emissions of particulate pollution from a power station affect the health of people in the vicinity, but this is not often considered, or is given inadequate weight, in private decision making and there is no market for such impacts. Such a phenomenon is referred to as an "externality," and the costs it imposes are referred to as the external costs.

Extreme weather event


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Final energy

Energy supplied that is available to the consumer to be converted into usable energy (e.g., electricity at the wall outlet).

Food insecurity




Fossil CO2 (carbon dioxide) emissions

Emissions of carbon dioxide resulting from the combustion of fuels from fossil carbon deposits such as oil, natural gas, and coal.

Fossil fuels

Carbon-based fuels from fossil carbon deposits, including coal, oil, and natural gas.

Fuel switching

Policy designed to reduce carbon dioxide emissions by switching to lower carbon-content fuels, such as from coal to natural gas.

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General circulation



Efforts to stabilize the climate system by directly managing the energy balance of the Earth, thereby overcoming the enhanced greenhouse effect.



Global surface temperature

The global surface temperature is the area-weighted global average of (i) the sea surface temperature over the oceans (i.e., the sub-surface bulk temperature in the first few meters of the ocean), and (ii) the surface air temperature over land at 1.5 m above the ground.

Global Warming Potential (GWP)


Greenhouse effect


Greenhouse gas

Greenhouse gases are those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of infrared radiation emitted by the Earth's surface, the atmosphere, and clouds. This property causes the greenhouse effect. Water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and ozone (O3) are the primary greenhouse gases in the Earth's atmosphere. Moreover there are a number of entirely human-made greenhouse gases in the atmosphere, such as the halocarbons and other chlorine- and bromine-containing substances, dealt with under the Montreal Protocol. Besides CO2, N2O, and CH4, the Kyoto Protocol deals with the greenhouse gases sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).

Groundwater recharge


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The particular environment or place where an organism or species tend to live; a more locally circumscribed portion of the total environment.

Heat island



Heterotrophic respiration


Hydrofluorocarbons (HFCs)

Among the six greenhouse gases to be curbed under the Kyoto Protocol. They are produced commercially as a substitute for chlorofluorocarbons. HFCs largely are used in refrigeration and semiconductor manufacturing. Their Global Warming Potentials range from 1,300 to 11,700.


The component of the climate system composed of liquid surface and subterranean water, such as oceans, seas, rivers, freshwater lakes, underground water, etc.

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Ice cap

A dome shaped ice mass covering a highland area that is considerably smaller in extent than an ice sheet.

Ice sheet


Ice shelf


(Climate) Impact assessment


(Climate) Impacts

Consequences of climate change on natural and human systems. Depending on the consideration of adaptation, one can distinguish between potential impacts and residual impacts. Potential impacts: All impacts that may occur given a projected change in climate, without considering adaptation. Residual impacts: The impacts of climate change that would occur after adaptation. See also aggregate impacts, market impacts, and non-market impacts.



Implementation refers to the actions (legislation or regulations, judicial decrees, or other actions) that governments take to translate international accords into domestic law and policy. It includes those events and activities that occur after the issuing of authoritative public policy directives, which include the effort to administer and the substantive impacts on people and events. It is important to distinguish between the legal implementation of international commitments (in national law) and the effective implementation (measures that induce changes in the behavior of target groups).

Compliance is a matter of whether and to what extent countries do adhere to the provisions of the accord. Compliance focuses on not only whether implementing measures are in effect, but also on whether there is compliance with the implementing actions. Compliance measures the degree to which the actors whose behavior is targeted by the agreement, whether they are local government units, corporations, organizations, or individuals, conform to the implementing measures and obligations.

Introduced species


Invasive species

An introduced species that invades natural habitats.

Isostatic land movements

Isostasy refers to the way in which the lithosphere and mantle respond to changes in surface loads. When the loading of the lithosphere is changed by alterations in land ice mass, ocean mass, sedimentation, erosion, or mountain building, vertical isostatic adjustment results, in order to balance the new load.

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La Niña

See El Niño Southern Oscillation.


Land use


Land-use change

A change in the use or management of land by humans, which may lead to a change in land cover. Land cover and land-use change may have an impact on the albedo, evapotranspiration, sources, and sinks of greenhouse gases, or other properties of the climate system, and may thus have an impact on climate, locally or globally.




Leapfrogging (or technological leapfrogging) refers to the opportunities in developing countries to bypass several stages of technology development, historically observed in industrialized countries, and apply the most advanced presently available technologies in the energy and other economic sectors, through investments in technological development and capacity building.


The upper layer of the solid Earth, both continental and oceanic, which is composed of all crustal rocks and the cold, mainly elastic, part of the uppermost mantle. Volcanic activity, although part of the lithosphere, is not considered as part of the climate system, but acts as an external forcing factor.

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Mean Sea Level (MSL)

Mean Sea Level is normally defined as the average relative sea level over a period, such as a month or a year, long enough to average out transients such as waves. See also sea-level rise.

Methane (CH4)

A hydrocarbon that is a greenhouse gas produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and oil, coal production, and incomplete fossil-fuel combustion. Methane is one of the six greenhouse gases to be mitigated under the Kyoto Protocol.

Methane recovery

Method by which methane emissions (e.g., from coal mines or waste sites) are captured and then reused either as a fuel or for some other economic purpose (e.g., reinjection in oil or gas reserves).



Mitigative capacity

The social, political, and economic structures and conditions that are required for effective mitigation.


Mixed layer


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Net carbon dioxide emissions

Difference between sources and sinks of carbon dioxide in a given period and specific area or region.

Nitrogen fertilization

Enhancement of plant growth through the addition of nitrogen compounds.

Nitrogen oxides (NOx)

Any of several oxides of nitrogen.


Nitrous oxide (N2O)

A powerful greenhouse gas emitted through soil cultivation practices, especially the use of commercial and organic fertilizers, fossil-fuel combustion, nitric acid production, and biomass burning. One of the six greenhouse gases to be curbed under the Kyoto Protocol.


Non-point-source pollution



North Atlantic Oscillation (NAO)

The North Atlantic Oscillation consists of opposing variations of barometric pressure near Iceland and near the Azores. On average, a westerly current, between the Icelandic low pressure area and the Azores high pressure area, carries cyclones with their associated frontal systems towards Europe. However, the pressure difference between Iceland and the Azores fluctuates on time scales of days to decades, and can be reversed at times. It is the dominant mode of winter climate variability in the North Atlantic region, ranging from central North America to Europe.

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Ocean conveyor belt


Organic aerosol

Aerosol particles consisting predominantly of organic compounds, mainly C, H, and O, and lesser amounts of other elements.

Ozone (O3)

Ozone, the triatomic form of oxygen (O3), is a gaseous atmospheric constituent. In the troposphere it is created both naturally and by photochemical reactions involving gases resulting from human activities (photochemical "smog"). In high concentrations, tropospheric ozone can be harmful to a wide-range of living organisms. Tropospheric ozone acts as a greenhouse gas. In the stratosphere, ozone is created by the interaction between solar ultraviolet radiation and molecular oxygen (O2). Stratospheric ozone plays a decisive role in the stratospheric radiative balance. Its concentration is highest in the ozone layer. Depletion of stratospheric ozone, due to chemical reactions that may be enhanced by climate change, results in an increased ground-level flux of ultraviolet-B radiation. See also Montreal Protocol and ozone layer.

Ozone layer


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The process by which plants take carbon dioxide (CO2) from the air (or bicarbonate in water) to build carbohydrates, releasing oxygen (O2) in the process. There are several pathways of photosynthesis with different responses to atmospheric CO2 concentrations. See also carbon dioxide fertilization.







Point-source pollution

Pollution resulting from any confined, discrete source, such as a pipe, ditch, tunnel, well, container, concentrated animalfeeding operation, or floating craft. See also non-point-source pollution.

Positive Feedback

A process that results in an amplification of the response of a system to an external influence. For example, increased atmospheric water vapor in response to global warming would be a positive feedback on warming, because water vapor is a GHG.


Post-glacial rebound

The vertical movement of the continents and sea floor following the disappearance and shrinking of ice sheets-for example, since the Last Glacial Maximum (21 thousand years before the present). The rebound is an isostatic land movement.

Primary energy



Private cost

Categories of costs influencing an individual's decision making are referred to as private costs. See also social cost and total cost.

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Radiative Forcing

The term radiative forcing refers to changes in the energy balance of the earth-atmosphere system in response to a change in factors such as greenhouse gases, land-use change, or solar radiation. The climate system inherently attempts to balance incoming (e.g., light) and outgoing (e.g. heat) radiation. Positive radiative forcings increase the temperature of the lower atmosphere, which in turn increases temperatures at the Earth's surface. Negative radiative forcings cool the lower atmosphere. Radiative forcing is most commonly measured in units of watts per square meter (W/m2).


Unimproved grasslands, shrublands, savannahs, and tundra.




Rapid climate change


Rebound effect

Occurs because, for example, an improvement in motor efficiency lowers the cost per kilometer driven; it has the perverse effect of encouraging more trips.



Relative sea level

Sea level measured by a tide gauge with respect to the land upon which it is situated. See also Mean Sea Level.


(Relative) Sea level secular change

Long-term changes in relative sea level caused by either eustatic changes (e.g., brought about by thermal expansion) or changes in vertical land movements.


Energy sources that are, within a short time frame relative to the Earth's natural cycles, sustainable, and include non-carbon technologies such as solar energy, hydropower, and wind, as well as carbon-neutral technologies such as biomass.

Renewable Energy

Energy obtained from sources such as geothermal, wind, photovoltaic, solar, and biomass.

Revenue Recycling

If permits are auctioned, this gives considerable sums of money to be recycled back into the economy, either through a lump sum payment of offsetting other taxes. If the existing taxes that are correspondingly reduced were very inefficient, this allows this allows the possibility of both environmental and economic benefits from the trading system, commonly called the 'double dividend.'

Research, development, and demonstration

Scientific and/or technical research and development of new production processes or products, coupled with analysis and measures that provide information to potential users regarding the application of the new product or process; demonstration tests; and feasibility of applying these products processes via pilot plants and other pre-commercial applications.


Refer to those occurrences that are identified and measured as economically and technically recoverable with current technologies and prices. See also resources.


A component of the climate system, other than the atmosphere, which has the capacity to store, accumulate, or release a substance of concern (e.g., carbon, a greenhouse gas, or a precursor). Oceans, soils, and forests are examples of reservoirs of carbon. Pool is an equivalent term (note that the definition of pool often includes the atmosphere). The absolute quantity of substance of concerns, held within a reservoir at a specified time, is called the stock. The term also means an artificial or natural storage place for water, such as a lake, pond, or aquifer, from which the water may be withdrawn for such purposes as irrigation, water supply, or irrigation.


Amount of change a system can undergo without changing state.

Resource base

Resource base includes both reserves and resources.



Resources are those occurrences with less certain geological and/or economic characteristics, but which are considered potentially recoverable with foreseeable technological and economic developments.



The process whereby living organisms converts organic matter to carbon dioxide, releasing energy and consuming oxygen.

Response time

The response time or adjustment time is the time needed for the climate system or its components to re-equilibrate to a new state, following a forcing resulting from external and internal processes or feedbacks. It is very different for various components of the climate system. The response time of the troposphere is relatively short, from days to weeks, whereas the stratosphere comes into equilibrium on a time scale of typically a few months. Due to their large heat capacity, the oceans have a much longer response time, typically decades, but up to centuries or millennia. The response time of the strongly coupled surface-troposphere system is, therefore, slow compared to that of the stratosphere, and mainly determined by the oceans. The biosphere may respond fast (e.g., to droughts), but also very slowly to imposed changes. See lifetime for a different definition of response time pertinent to the rate of processes affecting the concentration of trace gases.



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The accumulation of salts in soils.

Saltwater intrusion/encroachment

Displacement of fresh surfacewater or groundwater by the advance of saltwater due to its greater density, usually in coastal and estuarine areas.


Sea-level rise




Semi-arid regions

Ecosystems that have more than 250 mm precipitation per year but are not highly productive; usually classified as rangelands.


The process of increasing the carbon content of a carbon reservoir other than the atmosphere. Biological approaches to sequestration include direct removal of carbon dioxide from the atmosphere through land-use change, afforestation, reforestation, and practices that enhance soil carbon in agriculture. Physical approaches include separation and disposal of carbon dioxide from flue gases or from processing fossil fuels to produce hydrogen- and carbon dioxide-rich fractions and long term storage in underground in depleted oil and gas reservoirs, coal seams, and saline aquifers. See also uptake.





Development and care of forests.



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



A seasonal accumulation of slow-melting snow.

Social cost

The social cost of an activity includes the value of all the resources used in its provision. Some of these are priced and others are not. Non-priced resources are referred to as externalities. It is the sum of the costs of these externalities and the priced resources that makes up the social cost. See also private cost and total cost.

Soil moisture


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. See also solar cycle.

Solar ("11 year") cycle


Solar radiation

Radiation emitted by the Sun. It is also referred to as shortwave radiation. Solar radiation has a distinctive range of wavelengths (spectrum) determined by the temperature of the Sun.

Soot particles

Particles formed during the quenching of gases at the outer edge of flames of organic vapors, consisting predominantly of carbon, with lesser amounts of oxygen and hydrogen present as carboxyl and phenolic groups and exhibiting an imperfect graphitic structure (Charlson and Heintzenberg, 1995). See also black carbon.



Southern Oscillation

See El Niño Southern Oscillation.

Spill-over effect

The economic effects of domestic or sectoral mitigation measures on other countries or sectors. In this report, no assessment is made on environmental spillover effects. Spillover effects can be positive or negative and include effects on trade, carbon leakage, transfer, and diffusion of environmentally sound technology and other issues.


The achievement of stabilization of atmospheric concentrations of one or more greenhouse gases (e.g., carbon dioxide or a CO2-equivalent basket of greenhouse gases).


Stabilization analysis

In this report, this refers to analyses or scenarios that address the stabilization of the concentration of greenhouse gases.




Set of rules or codes mandating or defining product performance (e.g., grades, dimensions, characteristics, test methods, and rules for use). International product and/or technology or performance standards establish minimum requirements for affected products and/or technologies in countries where they are adopted. The standards reduce greenhouse gas emissions associated with the manufacture or use of the products and/or application of the technology. See also regulatory measures.

Stimuli (climate-related)


Storm surge






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.






Direct payment from the government to an entity, or a tax reduction to that entity, for implementing a practice the government wishes to encourage. Greenhouse gas emissions can be reduced by lowering existing subsidies that have the effect of raising emissions, such as subsidies to fossil-fuel use, or by providing subsidies for practices that reduce emissions or enhance sinks (e.g., for insulation of buildings or planting trees).





Surface runoff


Sustainable development


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Technology transfer

The broad set of processes that cover the exchange of knowledge, money, and goods among different stakeholders that lead to the spreading of technology for adapting to or mitigating climate change. As a generic concept, the term is used to encompass both diffusion of technologies and technological cooperation across and within countries.

Thermal erosion


Thermal expansion



Thermohaline circulation


Time scale

Characteristic time for a process to be expressed.

Top-down models

The terms "top" and "bottom" are shorthand for aggregate and disaggregated models. The top-down label derives from how modelers applied macro-economic theory and econometric techniques to historical data on consumption, prices, incomes, and factor costs to model final demand for goods and services, and supply from main sectors, like the energy sector, transportation, agriculture, and industry. Therefore, top-down models evaluate the system from aggregate economic variables, as compared to bottom-up models that consider technological options or project specific climate change mitigation policies. Some technology data were, however, integrated into top-down analysis and so the distinction is not that clear-cut.


The boundary between the troposphere and the stratosphere.





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Ultraviolet (UV)-B radiation





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. See also sequestration.






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Value added

The net output of a sector after adding up all outputs and subtracting intermediate inputs.



Worth, desirability, or utility based on individual preferences. The total value of any resource is the sum of the values of the different individuals involved in the use of the resource. The values, which are the foundation of the estimation of costs, are measured in terms of the willingness to pay (WTP) by individuals to receive the resource or by the willingness of individuals to accept payment (WTA) to part with the resource.






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Water stress


Water-use efficiency


Water withdrawal

Amount of water extracted from water bodies.

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Credit: (2010) Climate Change Glossary. Retrieved February 2, 2010, from

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