The process of adjustment to actual or expected climate and its effects. In human systems, adaptation seeks to moderate harm or exploit beneficial opportunities. In natural systems, human intervention may facilitate adjustment to expected climate and its effects.


A suspension of airborne solid or liquid particles, with a typical size between a few nanometres and 10 μm, that reside in the atmosphere for at least several hours. Many act as surfaces for water droplets and ice crystals to form on.


Albedo is a measure of how much of the sun’s energy is reflected by a surface. It is derived from the Latin word albus, meaning white. Albedo is measured as a percentage or fraction of the sun’s energy that is reflected away. Snow and ice tend to have a higher albedo than, for example, soil, forests and open water.


Resulting from or produced by human activities.

BECCS = Bio-Energy with Carbon Capture and Storage

Is the process of growing plants, crops or trees, harvesting them for energy generation and then capturing the carbon given off so it can be stored underground.

Biological pump

The process of transporting carbon from the ocean’s surface layers to the deep ocean by the primary production of marine phytoplankton, which converts dissolved inorganic carbon (DIC), mainly CO2, and nutrients into organic matter through photosynthesis.


The average weather, or more rigorously, 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 for averaging these variables is 30 years, as defined by the World Meteorological Organization. The relevant quantities are most often surface variables such as temperature, precipitation and wind.

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 some of its known properties. Climate models are applied as a research tool to study and simulate the climate, and for operational purposes, including monthly, seasonal and interannual climate predictions.

Climate Sensitivity

The amount of warming we can expect when carbon dioxide in the atmosphere reaches double what it was before the industrial revolution. There are two ways to express climate sensitivity: Transient Climate Response (TCR) is the warming at Earth’s surface we can expect at the point of doubling, while Equilibrium Climate Sensitivity (ECS) is the total amount of warming once the Earth has had time to adjust fully to the extra carbon dioxide.

Energy Budget

The Earth is a physical system with an energy budget that includes all gains of incoming energy and all losses of outgoing energy. The Earth’s energy budget is determined by measuring how much energy comes into the Earth system from the Sun, how much energy is lost to space, and accounting for the remainder on Earth and energy flows between the atmosphere and the ocean or land surface.

Emissions Scenario

A plausible representation of the future development of emissions of substances that potentially influence the earth’s energy budget (e.g., greenhouse gases, aerosols) and are based on a coherent and internally consistent set of assumptions about driving forces (such as demographic and socioeconomic development, technological change) and their key relationships.


An interaction in which a perturbation (change) in one climate quantity causes a change in a second, and the change in the second quantity ultimately leads to an additional change in the first. A negative feedback is one in which the initial perturbation is weakened by the changes it causes; a positive feedback is one in which the initial perturbation is increased. For example, melting ice can expose dark-coloured land. The dark-coloured land absorbs more heat than the white ice, leading to further warming and melting. This is positive feedback.


Forcing represents any external factor that influences global climate by heating or cooling the planet. They may be either natural or anthropogenic. Natural forcings include volcanic eruptions, solar variations and orbital forcing; the amount of solar energy reaching Earth changes with orbital parameters eccentricity, tilt and precession of the equinox. Anthropogenic forcing include changes in the composition of the atmosphere and land use change.


A broad set of methods and technologies that aim to deliberately alter the climate system in order to alleviate the impacts of climate change. Most, but not all, methods seek to either (1) reduce the amount of absorbed solar energy in the climate system (Solar Radiation Management) or (2) increase net carbon sinks from the atmosphere at a scale sufficiently large to alter climate (Carbon Dioxide Removal).

Greenhouse Gas

Atmospheric gases that absorb and emit radiation at specific wavelengths within the spectrum of radiation emitted by the Earth’s surface, the atmosphere, and by clouds.

Integrated Assessment Models

IAMs are computer models that analyse a broad range of data – e.g. physical, economic and social – to produce information that can be used to help decision-making. For climate research, specifically, IAMs are typically used to project future greenhouse gas emissions and climate impacts, and the benefits and costs of policy options that could be implemented to tackle them.

Internal variability

Variations in the mean state and other statistics (such as the occurrence of extremes) of the climate on all spatial and time scales beyond that of individual weather events, due to natural, unforced processes within the climate system. Because the climate systems has components with very different response times complex dependencies, the components are never in equilibrium and are constantly varying. An example of internal variability is El Niño, a warming cycle in the Pacific Ocean which has a big impact on the global climate, resulting from the interaction between atmosphere and ocean in the tropical Pacific.


A human intervention to reduce the sources or enhance the sinks of greenhouse gases.

Radiative forcings:

Radiative forcing is the difference between incoming and outgoing energy in the Earth’s climate. When increased greenhouse gases result in incoming energy being greater than outgoing energy, the planet will warm due to increased radiative forcing. Some forcings are positive while others, such as those from volcanoes or human-emitted aerosols, are negative.


The RCPs (Representative Concentration Pathways) are scenarios of future concentrations of greenhouse gases and other forcings. RCP8.5 is a scenario of “comparatively high greenhouse gas emissions“ brought about by rapid population growth, high energy demand, fossil fuel dominance and an absence of climate change policies. This “business as usual” scenario is the highest of the four RCPs and sees atmospheric CO2 rise to around 935ppm by 2100, equivalent to 1,370ppm once other forcings are included (in CO2e). The likely range of global temperatures by 2100 for RCP8.5 is 4.0-6.1C above pre-industrial levels.


Approach to reconstructing the past temporal and spatial characteristics of a climate variable from predictors. The predictors can be instrumental data if the reconstruction is used to infill missing data or proxy data if it is an indirect measure used to develop paleoclimate reconstructions.

Solubility pump

An important physicochemical process that transports dissolved inorganic carbon from the ocean’s surface to its interior. Because carbon dioxide is more soluble in colder water, and the thermohaline circulation of the oceans is driven by cold, dense water sinking at high latitudes, deep water contains more dissolved inorganic carbon.


The highly stratified region of the atmosphere above the troposphere extending from about 10 km (ranging from 9 km at high latitudes to 16 km in the tropics on average) to about 50 km altitude.

Tipping point

A hypothesized critical threshold when global or regional climate changes rapidly from one stable state to another stable state. The tipping point event may be irreversible.


The lowest part of the atmosphere, from the surface to about 10 km in altitude at mid-latitudes (ranging from 9 km at high latitudes to 16 km in the tropics on average), where clouds and weather phenomena occur. In the troposphere, temperatures generally decrease with height.

Turnover time

A measure of how long a component stays in a reservoir. It is the ratio of the mass M of a reservoir (e.g., a gaseous compound in the atmosphere) and the total rate of removal S from the reservoir: T = M/S. For each removal process, separate turnover times can be defined. In soil carbon biology, this is referred to as Mean Residence Time.


A state of incomplete knowledge that can result from a lack of information or from disagreement about what is known or even knowable. It may have many types of sources, from imprecision in the data to ambiguously defined concepts or terminology, or uncertain projections of human behaviour.


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