Climate science
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Here is a glossary of key vocabulary related to climate change.

 - A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z


                           - A -

  • Adaptation

The process of adjusting to current or expected climate change impacts. In human systems, the aim of adaptation is to reduce risks, increase resilience or seize on beneficial opportunities. In natural systems, human intervention may facilitate adjustments to expected climate change impacts.

  • Afforestation

The establishment of a forest through tree planting or seeding on land that has lacked forest cover for a very long time or has never been forested.

  • Agroecology

A type of sustainable farming that applies ecological concepts and principals in agriculture.

  • Agroforestry

A method of using agricultural land combining trees and crops or animal husbandry.

  • Albedo

Meaning “whiteness”, albedo is the reflective power of an object or surface. For instance, ice and fresh snow have a high albedo, ranging from 40% to 80%. This means that they reflect 40% to 80% of the incoming sunlight. The ocean is darker, with an albedo of less than 10%. 

  • Anthropogenic emissions

Greenhouse gases emitted by human activities.

                           - B -

  • Biodiversity

Biodiversity first refers to the variety of species (flora and fauna) that live on Earth or in a particular ecosystem. More precisely, we distinguish between three levels of biodiversity: intraspecific biodiversity (differences between members of the same species), interspecific biodiversity (differences between species) and ecosystem diversity (the environment and species that live in it).

  • Biodiversity hotspot

Region of the world where the level of biodiversity is significantly highly threatened by human habitation. Biodiversity hotspots contain often local and specific (endemic) and high biodiversity. Biodiversity hotspots are commonly found in tropical regions. 

  • Biomass

​​​​​​​Organic matter used as a fuel, especially in a power station for the generation of electricity.

  • Biome

​​​​​​​​​​​​​​The ensemble of flora and fauna in a specific region.


  • Blue carbon

Carbon dioxide (CO2) removed from the atmosphere by world’s coastal ecosystems (such as mangroves, salt marshes, seagrasses and algae). Aquatic plants grow, accumulate CO2 that is then bury as organic matter (OM) in the soil. 

  • Browning

Browning is a systematic decrease in vegetation growth or the death of vegetation that results in a loss of productivity over a period of time.

                           - C -

  • Calving

The breaking off or detachment of a glacier, ice sheet or an iceberg.

  • Carbonic acid (H2CO3)

This acid is formed when carbon dioxide dissolves in water, causing an increase in the acidity of the water.

  • Carbon cycle

Carbon is a chemical element which can be found in many molecules, in living beings as well as in non-living materials. Carbon is stored in huge amounts in what are called “reservoirs” on Earth – the most important being the ocean and the soil. But the carbon in these reservoirs does not stay there forever; it moves between reservoirs: these movements are called “flows”. The natural flows are perfectly balanced, leading to a carbon cycle.

  • Carbon dioxide (CO2)

A gas produced by the combustion of carbon (for example: fossil fuels). It is also produced by living organisms through respiration. CO2 contributes to the greenhouse effect and ocean acidification.

  • Carbon fertilisation

Carbon fertilisation is also known as carbon dioxide fertilisation. It is the phenomenon by which the increase of carbon dioxide in the atmosphere increases the rate of photosynthesis in plants.

  • Carbon footprint

A carbon footprint (in CO2-eq) is defined as the total amount of greenhouse gases produced directly or indirectly by human activities. It can be calculated for an individual, a particular event or an organisation.

  • Carbon sequestration

Long term storage of carbon dioxide (CO2) – or other forms of carbon – to mitigate climate change, by slowing down atmospheric and marine accumulation of greenhouse gases. 

  • Carbon sink

This is a natural reservoir that stores carbon-containing chemical compounds accumulated over time. Carbon sinks help reduce the amount of atmospheric CO2. Natural sinks are soil – the largest carbon store – and part of the biosphere via photosynthesis by terrestrial plants and marine phytoplankton and algae, a process that incorporates atmospheric CO2 into sugars, using solar energy.

  • Cascading effects

Inevitable and sometimes unforeseen chain of events due to an act affecting part of the climate system. These cascading effects are often negative.

  • Climate

An average pattern of weather conditions – such as temperature, precipitation, humidity, wind, air pressure – for a particular region over a long period of time (months, years, decades, centuries or more).

  • Climate change

Climate change refers to several global phenomena, for example: changes in temperature, precipitation, extreme events, sea level rise and ocean acidification. The term is most used to describe the current human-induced climate change that started around 1850 due to an increase in the global average temperature. The term “global warming” is also used.

  • Climate justice

This term is used to acknowledge the social and political dimensions of the challenges associated with climate change, rather than considering only their environmental dimension. It relates the differences observed between those more responsible for climate change and those more affected by its consequences, to the notion of justice (in particular, social and environmental justice).

  • Climate-resilient pathways

Climate-resilient pathways are trajectories of development that combine mitigation and adaptation to aim for sustainable human development and help avoiding dangerous interference with the climate system. 

  • Climate zones

Areas with distinct climates that can be classified using different parameters, such as temperature, precipitation, etc.

  • Coastal ecosystems

Coastal ecosystems are created where land and ocean meet. The resulting mixture of freshwater and seawater creates unique environments and ecosystems with distinct structures and diversity. They include saltmarshes, mangroves, seagrass meadows, estuaries and bays. 

  • Coastal erosion

A phenomenon whereby material (sand and rock) is removed from the coast, leading to loss of land. This can be exacerbated by climate change (especially by sea level rise or an increase in precipitation).

  • CO2 uptake

All the processes that contribute to the removal of CO2 from the atmosphere. CO2 can be removed by biological processes such as ocean or land photosynthesis or by physical processes such as carbon absorption in seawater.

  • Complex system

A system (such as the climate system) regulated by many factors that interact with and influence each other: for example the atmosphere, the ocean, the cryosphere, land and the biosphere, in the case of the climate system.

  • Compound event

An event that has more than one possible outcomes. 

  • Continental ice

All the ice on land. Continental ice is formed by the accumulation and compaction of snow over a long period of time.

  • Cryosphere

The places on or beneath the Earth’s surface (including the ocean) that contain snow and ice (continental ice, sea ice and permafrost).

                           - D -

  • Displacement

Transfer of groups of people from one place of leaving to another. This movement can be temporary or permanent. People are moved away from a place that had became dangerous or that cannot sustain the concerned population due to climate change effects; to a safer place. 

  • Deforestation

Destruction of a forest, often with the aim of turning it into agricultural land.

  • Desertification

Land degradation in arid or semi-arid areas by human or climatic actions.

  • Drought

A drought is an event of prolonged shortages in the water supply. A drought can last for months or years, or may be declared after as few as fifteen days.

  • Dryland

Drylands are ecosystems characterised by a lack of water. They include cultivated lands, scrublands, shrublands, grasslands, savannas, semi-deserts and true deserts.

  • Dust storms

Masses of sand and dust raised by the wind in very dry areas such as deserts.

                           - E -

  • Eco-anxiety

Climate change can generate different feelings and emotions; some may leave us feeling helpless or hopeless. This is called “eco-anxiety”.

  • Ecoregion

See Biome.

  • Ecosystem

The totality of living beings in a given environment, plus the environment itself. In an ecosystem, everything is interconnected and interdependent.

  • Ecosystem services

Humans can directly or indirectly benefit from ecosystems, which provide them with services. They are grouped into four categories: provisioning, regulating, supporting and cultural. For example, ecosystems produce oxygen (through photosynthesis) and food, and they provide us with raw materials. Ecosystems also preserve soil fertility, fertilise plants and protect coasts.

  • Emission pathways

Emission pathways refers to the modelled trahectories of global anthropogenic GHG emissions for the future following different scenarios possible (here for instance, we focus on the RCP2.6 and the RCP8.5).

  • Equity

Justice, fairness: when the same opportunities are given to all – education, health, rights etc. In a climate change context, equity is about fairness in sharing the burden and opportunities of climate change impacts.

  • Evapotranspiration

The process by which water is transferred from the land to the atmosphere by evaporation, either from the soil and other surfaces, or by transpiration from plants.

  • Exposure

How much a population is exposed to a certain climate hazard due, for example, to its geographic location. Example: lowlying lands are more exposed to sea level rise than mountain regions.

  • Extreme events

Unusual events that can have a high negative impact on humans and nature, for example tornadoes, storm surges, landslides, droughts and heatwaves.

                           - F -

  • Feedback loop

A feedback loop is a cycle in which some outputs of a process can exacerbate or attenuate one or more of its own causes.

  • Fermentation

Fermentation is a chemical reaction that happens naturally in some plants and animal substances. It needs the presence of very small living organisms, such as bacteria, fungi or yeast, to occur. This phenomenon is also used for human activities and can produce methane, lactic acid (in yogurts) and alcohol (in wine or beer).

  • Food system

The food system includes every step that our food goes through, from farm to fork: food production, processing, storage, distribution, consumption and recycling.

  • Food web

A food web is a representation of the “prey–predator” relationship in an ecosystem. It is a web rather than a chain, meaning that an organism may eat several species and a species may be eaten by multiple organisms.

                           - G -

  • Glacier

A large mass of ice on land that slowly moves downhill.

  • Global warming

See Climate Change.

  • Global warming potential (GWP)

The term Global Warming Potential is used to compare the “power” of a gas to warm the atmosphere and the duration of its effect. By definition, CO2 has a global warming potential of 1 regardless of the time period used. CO2 remains in the atmosphere for a century. CH4 is estimated to have a GWP of 28-36 over 100 years, meaning it absorbs much more energy than CO2. Nevertheless, it “only” remains in the atmosphere about a decade on average. The net effect of the shorter lifetime and higher energy absorption is reflected in the GWP. N2O has a GWP 265-298 times that of CO2 for a 100-year timescale.

  • Greenhouse effect

Solar radiation crosses the atmosphere, is absorbed by the Earth’s surface and warms it. The absorbed solar radiation is transformed into infrared radiation (heat). Some of this infrared radiation is trapped on its escape towards space by greenhouse gases in the atmosphere and is sent back towards the Earth’s surface – heating it up even more. This is called the greenhouse effect.​​​​​​​

  • Greenhouse gas

Greenhouse gases cause the greenhouse effect. They include water vapour, carbon dioxide, methane, nitrous oxide and ozone.

  • Greening

Greening is an observed increase in vegetation productivity over a certain period of time. Trees, shrubs, herbaceous plants and ground cover vegetation are taken into account.

                           - H -

  • Heat island effect

An urban area has a higher average temperature than its rural surroundings owing to the greater absorption, retention and generation of heat by its buildings, pavements and human activities.

  • Heat sink

In the context of climate change, a heat sink is a body – for example a forest or the ocean – that absorbs heat from a warmer body – such as the atmosphere. This results in cooling of the warmer body. The most important heat sink in the climate system is the ocean which, so far, has absorbed over 90% of the heat that has resulted from global warming.

  • Heatwave

A period of abnormally hot weather with high daytime temperatures and no or little cooling down at night. A heatwave can last up to several weeks.

                           - I -

  • Ice sheet

A very large and thick layer of ice on a continent.

  • Indigenous local knowledge

Indigenous communities often live a lifestyle based on a complex and important relationship with their direct environment, with low impact on it and on the climate. Their local knowledge of nature management and agriculture is important to adapt and mitigate climate change.

  • Industrial Revolution

The historical period between 1760 and the 1840s. It has marked the transition from agricultural to industrial societies. The Industrial Revolution started in Europe and the United States and led to a rapid development of productivity, technologies and science, and therefore to population growth.

  • Infrared radiation

Infrared radiation is the invisible part of light we can feel as heat. It plays a key role in the greenhouse effect.

  • Invasive species

Species that is not native to a specific location and has the tendency to spread to a degree that ca cause damage to the environment, human economy or human health. A lot of factors can help the spreading of invasive species such as the increase of the intensity of global commercial fluxes. 

                           - J -

                           - K -

                           - L -

  • Land degradation

Temporary or permanent decline in quality of soil, vegetation, water resources or wildlife – or the deterioration of the economic productivity of the land, such as the ability to farm the land.

  • Landslide

A mass of rock and earth moving suddenly and quickly down a steep slope. 

                           - M -

  • Marine currents

A flow of water through the ocean. Warm and cold currents redistribute heat around the globe.

  • Marine heatwave

Period of time of minimum 5 days when seawater temperatures exceed a seasonally based maximum temperature (minimum, an exceeding average 2°C).

  • Migration

See the definition of displacement. 

  • Mitigation

Human intervention to reduce global warming by reducing GHG emissions or by enhancing GHG sinks.

                           - N -

  • Natural variability

Variations in the climate system that are not related to human activities (for example, alternation of glacial and interglacial eras).

                           - O -

  • Ocean acidification

Increase in the acidity of seawater, caused by CO2 from the atmosphere dissolving in the ocean’s surface water. When CO2 reacts with water, the water becomes more acidic.

                           - P -

  • Permafrost

Soil, rock or sediment that is permanently frozen (for at least two consecutive years).

  • Permaculture

Development of an agricultural ecosystem intended to be sustainable and self-sufficient.

  • pH

pH is a measure of acidity and alkalinity of a solution on a scale in which 7 represents neutrality. A lower value indicates a more acidic solution whereas a higher value indicates a more alkaline solution.

  • Photosynthesis

When they are exposed to light, plants are able to use this light, in addition to carbon dioxide, water and minerals, to produce their own organic matter and to grow. This process is called photosynthesis.

  • Primary production

Primary production is the process by which a primary producer (a cell or an organism) produces its own organic matter using mineral materials. For example, photosynthetic living beings only use water, CO2 and light to grow.

                           - Q -

                           - R -

  • Reforestation

The planting of forests on lands that have previously contained forests but have since been converted for some other use.

  • Relocation

See the definition of displacement. 

  • Resettlement 

See the definition of displacement. 

  • Runoff

The draining away of water or snow from the surface of an area of land, a building or a structure. 

                           - S -

  • Sea ice

Frozen seawater that floats on the ocean’s surface.

  • Sea level rise

Because of climate change, the global mean sea level has increased by about 15 cm from 1900 to 2018. The current rate of increase is between 3 and 4 mm / yr. The sea level is projected to rise by a further 20cm to over one metre by the end of this century, depending on how much greenhouse gases we emit.

  • Sea surface temperature

The average water temperature at a depth range from 1mm to 20 meters, according to the type of measurement.  

  • Shared socio-economic pathways (SSPs)

Scenarios of projected socioeconomic global changes up to 2100. They are used to derive greenhouse gas emissions scenarios with different climate policies. There are up to 5 SSPs:

  • SPP1: sustainability low mitigation and adaptation challenges 
  • SSP2: middle of the road intermediate challenges
  • SSP3: regional rivalry high mitigation and adaptation challenges
  • SSP4: inequality adaptation challenges dominate
  • SSP5: fossil-fueled development mitigation challenges dominate

SSPs were used to help produce the IPCC 6th assessment report on global warming due. 

  • Soil degradation

Soil degradation means the loss of arable land, and can be a consequence of water erosion, coastal erosion, wind erosion, salinity, loss of organic matter, fertility decline, soil acidity, etc.

  • Storm surge

Local rising of the sea as a result of wind and atmospheric pressure changes due to a storm. 

  • Stratification

Layers of seawater masses with different properties: difference of salinity, oxygenation, density and/or temperature. Water of the ocean will then not mix leading to anoxia and lack of nutrients (the water is depleted in O2 and/or in nutrients, which has dramatic consequences on the marine wildlife).

  • Sustainable development

Development that meets the needs of the present generations without compromising the ability of future generations to meet their own needs.

  • Sustainable Development Goals (SDGs)

Universal calls to action to end global poverty, protect the planet and ensure that all people enjoy peace and prosperity by 2030. There are 17 different Sustainable development goals adopted by all United Nations Member States in 2015 : (1) no poverty, (2) zero hunger, (3) good health and well-being, (4) quality education, (5) gender quality, (6) clean water and sanitation, (7) affordable and clean energy, (8) decent work and economic growth, (9) industry, innovation and infrastructure, (10) reduced inequalities, (11) sustainable cities and communities, (12) responsible consumption and production, (13) climate action, (14) life below water, (15) life on land, (16) peace, justice and strong institutions and (17) partnerships for the goals. 

                           - T -

  • Thermal expansion

An increase in volume as a result of rising temperature. With regard to climate change: when the ocean gets warmer, it expands and occupies more space. 

  • Thermal inertia

A property of matter characterising the speed with which it approaches the temperature of its surrounding. The slower it does, the higher the thermal inertia.

  • Tipping point

The point at which a series of small changes or incidents becomes significant enough to cause a larger, more important change.  

  • Transformation

An adaptation that changes the fundamental attributes of a system in response to climate and its effects. 

                           - U -

                           - V -

  • Vulnerability

Sensitivity of a population when exposed to climate change hazards and its consequences. Example: a low-lying region with coastal protection infrastructures and resources is less vulnerable to sea level rise than a low-lying region with no coastal protection infrastructures and few economical resources.

                           - W -

  • Weather

The state of the atmosphere at a particular time and place. To define it, many variables such as temperature, precipitation, cloudiness or wind are taken into account.

  • Wildfire

A fire that is burning strongly and out of control on an area of grass in the countryside.

                           - X -

                           - Y -

                           - Z -

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