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Equilibrium response

The steady state response of the climate system (or a climate model) to an imposed radiative forcing.

Equivalent CO2

The concentration of CO2 that would cause the same amount of radiative forcing as the given mixture of CO2 and other greenhouse gases.

External impacts/externalities

Impacts generated by climate change (or some other environmental change) that cannot be evaluated by a competitive market because of a lack of information and or the inability to act on that information.

Falsifiability rule

Science today recognizes that there is no way to prove the absolute truth of any hypothesis or model, since it is always possible that a different explanation might account for the same observations. In this sense, even the most well established physical laws are "conditional". Hence, with scientific methodology it is never possible to prove conclusively that a hypothesis is true, it is only possible to prove that it is false.

Feedback

When one variable in a system triggers changes in a second variable that in turn ultimately affects the original variable; a positive feedback intensifies the effect, and a negative feedback reduces the effect.

Flux adjustment

To avoid the problem of a coupled atmosphere-ocean general circulation model drifting into some unrealistic climatic state (e.g., excessively warm temperatures in the tropical Pacific ocean), adjustment terms can be applied to the fluxes of beat and precipitation (and sometimes the surface stresses resulting from the effect of the wind on the ocean surface) before being imposed on the model ocean.

Fossil fuel reserves

The quantity of a fossil fuel that is known to exist, based on geological and engineering evidence, and that can be recovered under current economic conditions and operating capabilities.

Fossil fuel resources

The quantity of fossil fuel that is thought to exist and that may be recoverable based on an explicit scenario for future economic conditions and operating capabilities.

GDP

Gross Domestic Product. The value of all goods and services produced (or consumed) within a nation's borders.

Greenhouse gas

A gas that absorbs radiation at specific wavelengths within the spectrum of radiation (infrared radiation) emitted by the

Earth's surface and by clouds. The gas in turn emits infrared radiation from a level where the temperature is colder than the surface. The net effect is a local trapping of part of the absorbed energy and a tendency to warm the planetary surface. Water vapour (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH) and ozone (03) are the primary greenhouse gases in the Earth's atmosphere.

Halocarbons

Compounds containing either chlorine, bromine or fluorine and carbon. Such compounds can act as powerful greenhouse gases (q.v) in the atmosphere. The chlorine and bromine containing halocarbons are also involved in the depletion of the ozone layer.

Infrared radiation

Radiation emitted by the Earth's surface, the atmosphere and by clouds. Also known as terrestrial and long-wave radiation. Infrared radiation has a distinctive spectrum (ie., range of wavelengths) governed by the temperature of the Earth-atmosphere system. The spectrum of infrared radiation is practically distinct from that of solar (q.v.) or short-wave radiation because of the difference in temperature between the Sun and the Earthatmosphere system.

Integrated assessment

A method of analysis that combines results and models from the physical, biological, economic and social sciences, and the interactions between these components, in a consistent framework, to project the consequences of climate change and the policy responses to it.

Lifetime

In general, lifetime denotes the average length of time that an atom or molecule spends in a given reservoir, such as the atmosphere or oceans. It is not to be confused with the response time of a perturbation in concentration. CO2 has no single lifetime.

Marginal cost

The cost on one additional unit of effort. In terms of reducing emissions, it represents the cost of reducing emissions by one more unit.

Marine blosphere

A collective term for all living marine organisms.

Market damages

The value of damages generated by climate change (or some other environmental change) and evaluated based on information available to and usable by a competitive market.

Mitigation marginal cost function

The relation between the total quantity of emissions reduced and the marginal cost of the last unit reduced. The marginal cost of mitigation generally increases with the total quantity of emissions reduced.

Nitrogen fertilization

Enhancement of plant growth through the deposition of nitrogen compounds. In IPCC reports, this typically refers to fertilization from anthropogenic sources of nitrogen such as, man-made fertilizers and nitrogen oxides released from burning of fossil fuels.

"No-regrets" mitigation options

"No-regrets" mitigation options are those whose benefits, such as reduced energy costs and reduced emissions of local/regional pollutants, equal or exceed their cost to society, excluding the benefits of climate change mitigation. They are sometimes known as "measures worth doing anyway".

Non-market damages

Damages generated by climate change (or some other environmental change) and that cannot be evaluated by a competitive market because of a lack of information and/or the inability to act on that information.

Optimal control rate

The rate of intervention at which the net present value of the marginal costs of the intervention, equals the net present value of the marginal benefits of the intervention.

Parametrize (parametrization)

In climate modelling, this term refers to the technique of representing processes that cannot be explicitly resolved at the resolution of the model (sub-grid scale processes) by relationships between the area averaged effect of such sub-grid scale processes and the larger scale flow.

Photosynthesis

The metabolic process by which plants take CO2 from the air (or water) to build plant material, releasing O2 in the process.

Portfolio analysis

The mix of actions available to policy makers to reduce emissions or adapt to climate change.

Precautionary principal

Avoiding a solution that is irreversible, because the assumptions on which the solution is based may prove incorrect, in favour of a seemingly inferior solution that can be reversed.

Radiative damping

An imposed positive radiative forcing (q.v.) on the Earth-atmosphere system (e.g., through the addition of greenhouse gases) represents an energy surplus. The temperature of the surface and lower atmosphere will then increase and in turn increase the amount of infrared radiation being emitted to space, thus a new energy balance will be established. The amount that emissions of infrared radiation to space increase for a given increase in temperature is known as the radiative damping.

Radiative forcing

A simple measure of the importance of a potential climate change mechanism. Radiative forcing is the perturbation to the

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energy balance of the Earth-atmosphere system (in W m-2) following, for example, a change in the concentration of carbon dioxide or a change in the output of the Sun; the climate system responds to the radiative forcing so as to re-establish the energy balance. A positive radiative forcing tends to warm the surface and a negative radiative forcing tends to cool the surface. The radiative forcing is normally quoted as a global and annual mean value. A more precise definition of radiative forcing, as used in IPCC reports, is the perturbation of the energy balance of the surface-troposphere system, after allowing for the stratosphere to re-adjust to a state of global mean radiative equilibrium (see Chapter 4 of IPCC94). Sometimes called "climate forcing".

Respiration

The metabolic process by which organisms meet their internal energy needs and release CO2.

Soil moisture

Water stored in or at the continental surface and available for evaporation. In IPCC (1990) a single store (or “bucket”) was commonly used in climate models. Today's models which incorporate canopy and soil processes view soil moisture as the amount held in excess of plant “wilting point".

Solar luminosity

A measure of the brightness of (ie., the amount of solar radiation (q.v.) being emitted by) the Sun.

Solar radiation

Radiation emitted by the Sun. Also known as short-wave radiation. Solar radiation has a distinctive spectrum (i.e., range of wavelengths) governed by the temperature of the Sun. The spectrum of solar radiation is practically distinct from that of infrared (q.v.) or terrestrial radiation because of the difference in temperature between the Sun and the Earth-atmosphere system.

Spatial scales

Continental 10-100 million square kilometres (km2).
Regional 100 thousand- 10 million km2.
Local less than 100 thousand km2.

Spin-up

"Spin-up" is a technique used to initialize an AOGCM. At present it is not possible to diagnose accurately the state of the coupled atmosphere-ocean system and therefore it is not possible to prescribe observed starting conditions for an experiment with an AOGCM. Instead, the atmosphere and ocean components of the model are run separately, forced with "observed" boundary conditions, followed perhaps by a further period of "spin-up" when the atmosphere and ocean are coupled together, until the AOGCM is near to a steady state.

Stratosphere

The highly stratified and stable region of the atmosphere above the troposphere (q.v.) extending from about 10 km to about 50 km.

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