Glossary of Climate Related Terminologies

The glossary is also available in: French, Arabic, Portugues, Kiswhahili, and Hausa.


Adjustment in natural or human systems to a new or changing environment. Adaptation to climate change refers to adjustment in natural or human systems in response to actual or expected climatic stimuli and effects, which moderates harm or exploits beneficial opportunities.

Adaptation assessment:

The practice of identifying options to adapt to climate change and evaluating them in terms of criteria such as availability, benefits, costs, effectiveness, efficiency, and feasibility.


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 influence climate directly through scattering and absorbing radiation and/or indirectly through acting as condensation nuclei for cloud formation or modifying the optical properties and lifetime of clouds.


The gaseous envelop surrounding the Earth. The dry atmosphere consists almost entirely of nitrogen (78.1% volume mixing ratio) and oxygen (20.9% volume mixing ratio), together with a number of trace gases, such as argon (0.93% volume mixing ratio), 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.


The numbers and relative abundances of different genes (genetic diversity), species, and ecosystems (communities) in a particular area.


The part of the Earth system comprising all ecosystems and living organisms in the atmosphere, on land (terrestrial biosphere), or in the oceans (marine biosphere), including derived dead organic matter such as litter, soil organic matter, and oceanic detritus.


An area that collects and drains rainwater to the same source.

Climate change:

Climate change refers to a statistically significant variation in either the mean state of the climate (or in its variability), persisting for an extended period, typically decades or longer.

Climate feedback:

An interaction mechanism between processes in the climate system. Normally, the result of the first process triggers changes in a second process that in turn influences (intensifies or reduces) the initial one.

Climate Impact assessment:

The practice of identifying and evaluating the detrimental and beneficial consequences of climate change on natural and human systems. Such systems may be simplified into sectors such as agriculture, health, water, food and security, etc.

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 may occur given a projected change in climate, without considering adaptation. Residual impacts on the other hand refer to the impacts of climate change that would occur after adaptation.

Climate model:

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.

Climate prediction:

A climate prediction (also called 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. The prediction can be at seasonal, inter-annual or long-term time-scales.

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), and is often based upon simulations by climate models. Climate projections are based on assumptions concerning future developments that may or may not be realized in an area.

Climate scenario:

A plausible and often simplified representation of the future climate, based on an internally consistent set of climatological relationships that has been constructed for explicit use in investigating the potential consequences of anthropogenic climate change. The scenarios are constructed from Climate projections and are often used as input to impact models.


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 defined by the World Meteorological Organization (WMO) is 30 years.


The phenomenon that exists when precipitation is significantly reduced below normal recorded levels, thereby causing serious hydrological imbalances that adversely affect land resource production systems.

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.

El Niño Southern Oscillation (ENSO):

A coupled atmosphere-ocean phenomenon associated with a fluctuation of the inter-tropical surface pressure patterns, and circulation in the Indian and Pacific Oceans. 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. The 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.

Emissions scenario:

A plausible representation of the future development of emissions of substances that are potentially radioactively active (e.g., greenhouse gases, aerosols), based on a coherent and internally consistent set of assumptions about driving forces (such as demographic and socio-economic development, technological change) and their key relationships.


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.


With regard to human health, endemic refers to the prevalence of a disease in a population or geographical area at all times.


Occurring suddenly in numbers clearly in excess of normal expectancy said especially of infectious diseases but applied also to any disease, injury, or other health-related event occurring in such outbreaks.


The process by which a body of water becomes rich in dissolved nutrients with a seasonal deficiency in dissolved oxygen.

Extreme weather event:

An extreme weather event is an event that is rare within its statistical reference distribution at a particular place. An extreme weather event would normally be as rare as (or rarer than) the 10th or 90th percentile. An extreme climate event is an average of a number of weather events over a certain period of time, normally an average which is itself extreme.

Food insecurity:

A situation that exists when people lack secure access to sufficient amounts of safe and nutritious food for normal growth and development, and thus an active and healthy life. It may be caused by the unavailability of food, insufficient purchasing power, inappropriate distribution, or inadequate use of food at the household level. Food insecurity may be chronic, seasonal, or transitory.

General Circulation Model (GCM):

Mathematical model of the general circulation of a planetary atmosphere or ocean. They are normally, based on the Navier–Stokes equations, with thermodynamic terms for various energy sources. These equations are the basis for complex computer programs commonly used for simulating the atmosphere or ocean of the Earth.

General circulation:

The large scale motions of the atmosphere and the ocean as a consequence of differential heating on a rotating Earth, aiming to restore the energy balance of the system through transport of heat and momentum.

Global surface temperature:

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

Global Warming Potential (GWP):

An index, describing the radiative characteristics of well-mixed greenhouse gases, that represents the combined effect of the differing times these gases remain in the atmosphere and their relative effectiveness in absorbing outgoing infrared radiation. This index approximates the time-integrated warming effect of a unit mass of a given greenhouse gas in today’s atmosphere, relative to that of carbon dioxide.

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 of the gases causes the greenhouse effect.


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

Indigenous peoples:

People whose ancestors inhabited a place when persons from another culture or ethnic background arrived on the scene and dominated them through conquest, settlement, or other means and who today live more in conformity with their own social, economic, and cultural customs and traditions than those of the country of which they now form a part.

Infrared radiation:

Radiation emitted by the Earth’s surface, the atmosphere and clouds. It is also known as terrestrial or long-wave radiation. Infrared radiation has a distinctive range of wavelengths (also called spectrum) longer than the wavelength of the red color in the visible part of the spectrum.

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 evaluate the status and the consequences of environmental change and the policy responses to it.

Land use:

The total of arrangements, activities, and inputs undertaken in a certain land cover type, normally by humans. Can also be construed as the social and economic purposes for which land is managed, e.g. grazing, timber extraction, and conservation.

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.


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.


An anthropogenic intervention to reduce the sources or enhance the sinks of greenhouse gases. Climate change mitigation can thus be construed as the anthropogenic interventions that stress on reducing the effects of climate change.

Mitigative capacity:

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


Wind in the general atmospheric circulation typified by a seasonal persistent wind direction and by a pronounced change in direction from one season to the next.

Net carbon dioxide emissions:

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

Ozone layer:

The stratosphere contains a layer in which the concentration of ozone is greatest. This is called the ozone layer. The layer extends from about 12 to 40 km. The ozone concentration reaches a maximum between about 20 and 25 km. This layer is being depleted by human emissions of chlorine and bromine compounds.


Gaseous tri-atomic form of oxygen (O3), created in the troposphere from both natural process and by photochemical reactions involving gases resulting from human activities (photochemical “smog”). 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.


Used in climate models to refer to the technique of representing processes, that cannot be explicitly resolved at the spatial or temporal resolution of the model (sub-grid scale processes), by relationships between the area- or time-averaged effect of such sub-grid-scale processes and the larger scale flow.

Rapid climate change:

The non-linearity of the climate system may lead to rapid climate change, sometimes called abrupt events or even surprises. Some such abrupt events may be imaginable, such as a dramatic reorganization of the thermohaline circulation, rapid deglaciation, or massive melting of permafrost leading to fast changes in the carbon cycle. Others may be truly unexpected, as a consequence of a strong, rapidly changing, forcing of a non-linear system.


Amount of change a system can undergo without changing its state.


A plausible and often simplified description of how the future may develop based on a coherent and internally consistent set of assumptions about key driving forces (e.g., rate of technology change, market prices) and relationships. Scenarios are neither predictions nor forecasts and sometimes may be based on a “narrative storyline.” Scenarios may be derived from projections, but are often based on additional information from other sources.


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


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.

Surface runoff:

The water that travels over the soil surface to the nearest surface stream; runoff of a drainage basin that has not passed beneath the surface since precipitation.


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 behavior. Uncertainty can therefore be represented by quantitative measures (e.g., a range of values calculated by various models) or by qualitative statements (e.g., reflecting the judgment of a team of experts).


The degree to which a system is susceptible to, or 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 variation to which a system is exposed, its sensitivity, and its adaptive capacity.

Water stress:

A country is water-stressed if the available freshwater supply relative to water withdrawals acts as an important constraint on development. Withdrawals exceeding 20% of renewable water supply has been used as an indicator of water stress.

Water-use efficiency:

Carbon gain in photosynthesis per unit water lost in evapotranspiration. It can be expressed on a short-term basis as the ratio of photosynthetic carbon gain per unit transpirational water loss, or on a seasonal basis as the ratio of net primary production or agricultural yield to the amount of available water.