both the surface winds and associated precipitation. Montane

The biogeographic zone made up of relatively moist, cool upland slopes below the sub-alpine zone that is characterised by the presence of mixed deciduous at lower and coniferous evergreen forests at higher elevations.


Rate of occurrence of disease or other health disorders within a population, taking account of the age-specific morbidity rates. Morbidity indicators include chronic disease incidence/prevalence, rates of hospitalisation, primary care consultations, disability-days (i.e., days of absence from work), and prevalence of symptoms.


The form and structure of an organism or land-form, or any of its parts.


Rate of occurrence of death within a population; calculation of mortality takes account of age-specific death rates, and can thus yield measures of life expectancy and the extent of premature death.

Net biome production (NBP)

Net biome production is the net ecosystem production (NEP) minus carbon losses resulting from disturbances such as fire or insect defoliation.

Net ecosystem production (NEP)

Net ecosystem production is the difference between net primary production (NPP) and heterotrophic respiration (mostly decomposition of dead organic matter) of that ecosystem over the same area (see also net biome production (NBP).

Net primary production (NPP)

Net primary production is the gross primary production minus autotrophic respiration, i.e., the sum of metabolic processes for plant growth and maintenance, over the same area.

Nitrogen oxides (NOx)

Any of several oxides of nitrogen.

No regrets policy

A policy that would generate net social and/or economic benefits irrespective of whether or not anthropogenic climate change occurs.


A process is called 'non-linear' when there is no simple proportional relation between cause and effect.

Non-market impacts

Impacts that affect ecosystems or human welfare, but that are not easily expressed in monetary terms, e.g., an increased risk of premature death, or increases in the number of people at risk of hunger. See also market impacts.

Normalised difference vegetation index (NDVI)

A satellite-based remotely sensed measure of the 'greenness' of the vegetation cover.

North Atlantic Oscillation (NAO)

The North Atlantic Oscillation (NAO) consists of opposing variations of barometric pressure near Iceland and near the Azores. It is the dominant mode of winter climate variability in the North Atlantic region.

Ocean acidification

Increased concentrations of CO2 in sea water causing a measurable increase in acidity (i.e., a reduction in ocean pH). This may lead to reduced calcification rates of calcifying organisms such as corals, molluscs, algae and crustacea.

Ombrotrophic bog

An acidic peat-accumulating wetland that is rainwater (instead of groundwater) fed and thus particularly poor in nutrients.

Opportunity costs

The cost of an economic activity forgone through the choice of another activity.


The triatomic form of oxygen (O3), 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, tro-pospheric ozone can be harmful to many living organisms. Tro-pospheric ozone acts as a greenhouse gas. In the stratosphere, ozone is created by the interaction between solar ultraviolet radiation and molecular oxygen (O2). Depletion of stratospheric ozone, due to chemical reactions that may be enhanced by climate change, results in an increased ground-level flux of ultraviolet (UV) B radiation.

Paludification he process of transforming land into a wetland such as a marsh, a swamp or a bog.


Very small solid exhaust particles emitted during the combustion of fossil and biomass fuels. Particulates may consist of a wide variety of substances. Of greatest concern for health are partic-ulates of less than or equal to 10 nm in diameter, usually designated as PM10.


Peat is formed from dead plants, typically Sphagnum mosses, which are only partially decomposed due to the permanent submergence in water and the presence of conserving substances such as humic acids.


Typically a wetland such as a mire slowly accumulating peat.

Pelagic community

The community of organisms living in the open waters of a river, a lake or an ocean (in contrast to benthic communities living on or near the bottom of a water body).


Perennially frozen ground that occurs where the temperature remains below 0°C for several years.


The study of natural phenomena that recur periodically (e.g., development stages, migration) and their relation to climate and seasonal changes.

Photochemical smog

A mix of photochemical oxidant air pollutants produced by the reaction of sunlight with primary air pollutants, especially hydrocarbons.


The synthesis by plants, algae and some bacteria of sugar from sunlight, carbon dioxide and water, with oxygen as the waste product. See also carbon dioxide fertilisation, C3 plants and C4 plants.


Of, relating to, or employing a description of nature or natural phenomena.


The plant forms of plankton. Phytoplankton are the dominant plants in the sea, and are the basis of the entire marine food web. These single-celled organisms are the principal agents of pho-tosynthetic carbon fixation in the ocean. See also zooplankton.


Microscopic aquatic organisms that drift or swim weakly. See also phytoplankton and zooplankton.

Plant functional type (PFT)

An idealised vegetation class typically used in dynamic global vegetation models (DGVM).


Areas of permanently unfrozen sea water resulting from warmer local water currents in otherwise sea-ice covered oceans. They are biological hotspots, since they serve as breathing holes or refuges for marine mammals such as whales and seals, and fish-hunting birds.

Population system

An ecological system (not ecosystem) determined by the dynamics of a particular vagile species that typically cuts across several ecological communities and even entire biomes. An example is migratory birds that seasonally inhabit forests as well as grasslands and visit wetlands on their migratory routes.

Potential production

Estimated crop productivity under non-limiting soil, nutrient and water conditions.


See industrial revolution.

Primary production

All forms of production accomplished by plants, also called primary producers. See GPP, NPP, NEP and NBP.


The potential evolution of a quality or set of quantities, often computed with the aid of a model. Projections are distinguished from predictions in order to emphasise that projections involve assumptions - concerning, for example, future socio-economic and technological developments, that may or may not be realised - and are therefore subject to substantial uncertainty. See also climate projection and climate prediction.


Planktonic, small marine snails with swimming organs resembling wings.

Pure rate of time preference

The degree to which consumption now is preferred to consumption one year later, with prices and incomes held constant, which is one component of the discount rate.

Radiative forcing

Radiative forcing is the change in the net vertical irradiance (expressed in Watts per square metre; Wm-2) at the tropopause due to an internal or external change in the forcing of the climate system, such as a change in the concentration of CO2 or the output of the Sun.


Unmanaged grasslands, shrublands, savannas and tundra. Recalcitrant

Recalcitrant organic material or recalcitrant carbon stocks resist decomposition.

Reference scenario

See baseline/reference.


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 Special Report on Land Use, Land-Use Change, and Forestry (IPCC, 2000).

Reid's paradox

This refers to the apparent contradiction between inferences of high plant migration rates as suggested in the palaeo-record (particularly after the last Ice Age), and the low potential rates of migration that can be inferred through studying the seed dispersal of the plants involved, e.g., in wind-tunnel experiments.


The transfer of a portion of primary insurance risks to a secondary tier of insurers (reinsurers); essentially 'insurance for insurers'.

Relative sea-level rise

See sea-level rise.


A component of the climate system, other than the atmosphere, that has the capacity to store, accumulate or release a substance of concern (e.g., carbon or a greenhouse gas). Oceans, soils, and forests are examples of carbon reservoirs. 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 or water supply.


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.


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


Relating to or living or located on the bank of a natural watercourse (such as a river) or sometimes of a lake or a tidewater.

River discharge

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


That part of precipitation that does not evaporate and is not transpired.


The accumulation of salts in soils. Salt-water intrusion / encroachment

Displacement of fresh surface water or groundwater by the advance of salt water 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).


Tropical or sub-tropical grassland or woodland biomes with scattered shrubs, individual trees or a very open canopy of trees, all characterised by a dry (arid, semi-arid or semi-humid) climate.


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 climate (change) scenario, emissions scenario and SRES.

Sea-ice biome

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

Sea-level rise

An increase in the mean level of the ocean. Eustatic sea-level rise is a change in global average sea level brought about by an increase in the volume of the world ocean. 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. In areas subject to rapid land-level uplift, relative sea level can fall.

Sea wall

A human-made wall or embankment along a shore to prevent wave erosion.

Semi-arid regions

Regions of moderately low rainfall, which are not highly productive and are usually classified as rangelands. 'Moderately low' is widely accepted as between 100 and 250 mm precipitation per year. See also arid region.


Sensitivity is the degree to which a system is affected, either adversely or beneficially, by climate variability or 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).


See carbon sequestration.


Cultivation, development and care of forests. Sink

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

Snow water equivalent

The equivalent volume/mass of water that would be produced if a particular body of snow or ice was melted.


A seasonal accumulation of slow-melting snow.

Social cost of carbon

The value of the climate change impacts from 1 tonne of carbon emitted today as CO2, aggregated over time and discounted back to the present day; sometimes also expressed as value per tonne of carbon dioxide.

Socio-economic scenarios

Scenarios concerning future conditions in terms of population, Gross Domestic Product and other socio-economic factors relevant to understanding the implications of climate change. See SRES (source: Chapter 6).

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