IPCC Glossary

The extent to which a policy or system change is evaluated unfavourably or favourably, or rejected or supported, by members of the general public (public acceptability) or politicians or governments (political acceptability).

Acceptability may vary from totally unacceptable/fully rejected to totally acceptable/fully supported; individuals may differ in how acceptable policies or system changes are believed to be.

See Access under Food Security

A change in functional or morphological traits occurring once or repeatedly (e.g., seasonally) during the lifetime of an individual organism in its natural environment.

Through acclimatisation, the individual maintains performance across a range of environmental conditions. For a clear differentiation between findings in laboratory and field studies, the term ‘acclimation’ is used in ecophysiology for the respective phenomena when observed in well-defined experimental settings. The term ‘(adaptive) plasticity’ characterises the generally limited scope of changes in phenotype that an individual can reach through the process of acclimatisation.

A Fund established under the Kyoto Protocol in 2001 and officially launched in 2007.

The Fund finances adaptation projects and programmes in developing countries that are Parties to the Kyoto Protocol. Financing comes mainly from sales of Certified Emissions Reductions (CERs) and a share of proceeds amounting to 2 % of the value of CERs issued each year for Clean Development Mechanism (CDM) projects. The Adaptation Fund can also receive funds from governments, the private sector, and individuals.

Human actions that directly or indirectly affect the risks of climate change impacts.

The gap between the current state of a system and a state that minimises adverse impacts from existing climate conditions and variability.

The difference between actually implemented adaptation and a societally set goal, determined largely by preferences related to tolerated climate change impacts and reflecting resource limitations and competing priorities (UNEP, 2014; UNEP, 2018).

The point at which an actor’s objectives (or system needs) cannot be secured from intolerable risks through adaptive actions.
• Hard adaptation limit – No adaptive actions are possible to avoid intolerable risks.
• Soft adaptation limit – Options may exist but are currently not available to avoid intolerable risks through adaptive action.

The circumstances requiring action to ensure the safety of populations and the security of assets in response to climate impacts.

Reduction of friction at the base of an ice sheet or glacier due to lubrication by meltwater.

This can allow the glacier or ice sheet to slide over its base. Meltwater may be produced by pressure-induced melting, friction or geothermal heat, or surface melt may drain to the base through holes in the ice.

A time period against which differences are calculated (e.g., expressed as anomalies relative to a baseline).

The baseline (or reference) isthe state against which change is measured.

A baseline period isthe period relative to which anomalies are computed. The baseline concentration of a trace gas is that measured at a location not influenced by local anthropogenic emissions.

See Reference Scenario

The community of organisms living on the bottom or in sediments of a body of water (such as an ocean, a river or a lake).

The ecological zone at the bottom of a body of water, including the sediment surface and some subsurface layers, is known as the benthic zone.

Relatively stable, carbon-rich material produced by heating biomass in an oxygen-limited environment.

Biochar is distinguished from charcoal by its application: biochar is used as a soil amendment with the intention to improve soil functions and to reduce greenhouse gas emissions from biomass that would otherwise decompose rapidly (IBI, 2018).

The EECO is a period of geological time that occurred about 53 to 49 million years ago, during the Eocene Epoch.

Continental positions at this time were somewhat different to present due to tectonic plate movements. Geological data indicate that the EECO was a period of relatively high atmospheric CO2 concentrations (about 1150–2500 ppmv) and relative warmth (global mean surface temperature was about 10–18 °C above the 1850–1900 reference), and polar ice sheets were absent.

The set of technical and institutional capacities to forecast, predict, and communicate timely and meaningful warning information to enable individuals, communities, managed ecosystems, and organisations threatened by a hazard to prepare to act promptly and appropriately to reduce the possibility of harm or loss.

Depending upon context, EWS may draw upon scientific and/or Indigenous knowledge, and other knowledge types. EWS are also considered for ecological applications, e.g., conservation, where the organisation itself is not threatened by hazard but the ecosystem under conservation is (e.g., coral bleaching alerts), in agriculture (e.g., warnings of heavy rainfall, drought, ground frost, and hailstorms) and in fisheries (e.g., warnings of storm, storm surge, and tsunamis).

The time-mean (or representative) energy exchanges within the climate system (including energy energy exchanges at the surface and top-of-atmosphere).

This also includes horizontal ocean and atmospheric heat transports.

The product of global mean surface air temperature (GSAT) change and the net feedback parameter (i.e.

sum of all feedbacks), which determines the net top-of-atmosphere radiative flux that opposes a change in radiative forcing. Units: W m^-2.

A coupled atmosphere–ocean general circulation model (AOGCM) in which a representation of the carbon cycle is included, allowing for interactive calculation of atmospheric carbon dioxide (CO2) or compatible emissions.

Additional components (e.g., atmospheric chemistry, ice sheets, dynamic vegetation, nitrogen cycle, but also urban or crop models) may be included.

From Wikipedia The East Asian Monsoon is a monsoonal flow that carries moist air from the Indian Ocean and Pacific Ocean to East Asia. It affects approximately one-third of the global population, influencing the climate of Japan, the Korean Peninsula, Taiwan, China, the Philippines and Mainland Southeast Asia but most significantly Vietnam. It is driven by temperature differences between the East Asian continent and the Pacific Ocean.

An El Niño event in which sea surface temperature anomalies are largest in the eastern tropical Pacific.

The portion of the technical potential for which the social benefits exceed the social costs, taking into account a social discount rate and the value of externalities.

From Wikipedia

A functional unit consisting of living organisms, their non-living environment and the interactions within and between them.

The components included in a given ecosystem and its spatial boundaries depend on the purpose for which the ecosystem is defined: in some cases they are relatively sharp, while in others they are diffuse. Ecosystem boundaries can change over time. Ecosystems are nested within other ecosystems, and their scale can range from very small to the entire biosphere. In the current era, most ecosystems either contain people as key organisms or are influenced by the effects of human activities in their environment.

The use of ecosystem management activities to increase the resilience and reduce the vulnerability of people and ecosystems to climate change (Campbell et al., 2009).

From Wikipedia Ecosystem-based adaptation (EBA) encompasses a broad set of approaches to adapt to climate change. They all involve the management of ecosystems and their services to reduce the vulnerability of human communities to the impacts of climate change.

Ecosystem health is a metaphor used to describe the condition of an ecosystem, by analogy with human health.

Note that there is no universally accepted benchmark for a healthy ecosystem. Rather, the apparent health status of an ecosystem is judged on the ecosystem’s resilience to change, with details depending upon which metrics are employed in judging it and which societal aspirations are driving the assessment (following IPBES 2019).

Ecological processes or functions having monetary or non-monetary value to individuals or society at large.

These are frequently classified as (1) supporting services such as productivity or biodiversity maintenance, (2) provisioning services such as food or fibre, (3) regulating services such as climate regulation or carbon sequestration, and (4) cultural services such as tourism or spiritual and aesthetic appreciation.

The final radiative forcing (or effect) from the aerosol perturbation, including the adjustments to the initial change in droplet or crystal formation rate. These adjustments include changes in the strength of convection, precipitation efficiency, cloud fraction, lifetime or water content of clouds, and the formation or suppression of clouds in remote areas due to altered circulations.

The final radiative forcing (or effect) from the aerosol perturbation, including adjustments to the initial change in radiation. These adjustments include changes in cloud caused by the impact of the radiative heating on convective or larger-scale atmospheric circulations, traditionally known as semi-direct aerosol forcing (or effect).

The term El Niño was initially used to describe a warm-water current that periodically flows along the coast of Ecuador and Peru, disrupting the local fishery.

It has since become identified with warming of the tropical Pacific Ocean east of the dateline. This oceanic event is associated with a fluctuation of a global-scale tropical and subtropical surface pressure pattern called the Southern Oscillation. This coupled atmosphere–ocean phenomenon, with preferred time scales of two to about seven years, is known as the El Niño–Southern Oscillation (ENSO). The warm and cold phases of ENSO are called El Niño and La Niña, respectively. ENSO is often measured by the surface pressure anomaly difference between Tahiti and Darwin and/or the sea surface temperatures in the central and eastern equatorial Pacific. This phenomenon has a 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 through global teleconnections. See Section AIV.2.3 in Annex IV of the AR6 WGI report.

Wavelength, frequency or energy range of all electromagnetic radiation.

In terms of solar radiation, the spectral irradiance is the power arriving at the Earth per unit area, per unit wavelength.

Characteristic of many regions where mountains are located, in which past and/or future surface air temperature changes vary neither uniformly nor linearly with elevation.

In many cases, warming is enhanced within or above a certain elevation range.

The total emissions [water use, land use] generated [used] in the production of goods and services regardless of the location and timing of those emissions [water use, land use] in the production process.

This includes emissions [water use, land use] within the country used to produce goods or services for the country’s own use, but also includes the emissions [water use, land use] related to the production of such goods or services in other countries that are then consumed in another country through imports. Such emissions [water, land] are termed ‘embodied’ or ‘embedded’ emissions, or in some cases, (particularly with water) as ‘virtual water use’ (Davis and Caldeira, 2010; Allan, 2005; MacDonald et al., 2015).

Emergence of a climate change signal or trend refers to when a change in climate (the ‘signal’) becomes larger than the amplitude of natural or internal variations (defining the ‘noise’), This concept is often expressed as a ‘signal-to-noise’ ratio and emergence occurs at a defined threshold of this ratio (e.g., S/N > 1 or 2).

Emergence can refer to changes relative to a historical or modern baseline (usually at least 20 years long) and can also be expressed in terms of time (time of emergence) or in terms of a global warming level. Emergence is also used to refer to a time when we can expect to see a response to reducing greenhouse gas (GHG) emissions (emergence with respect to mitigation). Emergence can be estimated using observations and/or model simulations.

A set of modelled emission and socio-economic scenarios collected in a database.

The scenarios can come from a single multi-model study with systematic variation of harmonised scenario designs (structured ensemble) or from multiple studies in the literature (unstructured ensemble). Depending on the scope of the ensemble, variation of the results across the scenarios in the ensemble give an indication of the spread of results in the literature (unstructured ensemble), or an estimate of uncertainties due to different modelling structures and methodologies (structured ensemble).

Modelled trajectories of global anthropogenic emissions over the 21st century.

Reproducing the behaviour of complex, process-based models (namely, Earth system models, ESMs) via simpler approaches, using either emulators or simple climate models (SCMs).

The computational efficiency of emulating approaches opens new analytical possibilities given that ESMs take a lot of computational resources for each simulation.

A broad class of heavily parametrized models (’simple climate models’), statistical methods like neural networks, genetic algorithms or other artificial intelligence approaches, designed to reproduce the responses of more complex, process-based Earth system models (ESMs).

The main application of emulators is to extrapolate insights from ESMs and observational constraints to a larger set of emission scenarios.

Conditions that enhance the feasibility of adaptation and mitigation options.

Enabling conditions include finance, technological innovation, strengthening policy instruments, institutional capacity, multi-level governance, and changes in human behaviour and lifestyles.

The difference between the total incoming and total outgoing energy.

If this balance is positive, warming occurs; if it is negative, cooling occurs. Averaged over the globe and over long time periods, this balance must be zero. Because the climate system derives virtually all its energy from the Sun, zero balance implies that, globally, the absorbed solar radiation, that is, incoming solar radiation minus reflected solar radiation at the top of the atmosphere and outgoing longwave radiation emitted by the climate system are equal.

An energy balance model is a simplified climate model that is typically used as an emulator of climate to analyse the energy budget of the Earth to compute changes in the climate.

In its simplest form, there is no explicit spatial dimension, and the model then provides an estimate of the changes in globally averaged temperature computed from the changes in radiation. This zero-dimensional energy balance model can be extended to a one-dimensional or two-dimensional model if changes to the energy budget with respect to latitude, or both latitude and longitude, are explicitly considered.

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 its atmosphere. Solar radiation is the dominant source of energy into the Earth system. Incoming solar energy may be scattered and reflected by clouds and aerosols or absorbed in the atmosphere. The transmitted radiation is then either absorbed or reflected at the Earth’s surface. The average albedo of the Earth is about 0.3, which means that 30% of the incident solar energy is reflected into space, while 70% is absorbed by the Earth. Radiant solar or shortwave energy is transformed into sensible heat, latent energy (involving different water states), potential energy, and kinetic energy before being emitted as infrared radiation. With the average surface temperature of the Earth of about 15°C (288 K), the main outgoing energy flux is in the infrared part of the spectrum.

The ratio of output or useful energy or energy services or other useful physical outputs obtained from a system, conversion process, transmission or storage activity to the input of energy (measured as kWh kWh^-1, tonnes kWh^-1 or any other physical measure of useful output like tonne-km transported).

Energy efficiency is often described by energy intensity.

The goal of a given country, or the global community as a whole, to maintain an adequate, stable and predictable energy supply.

Measures encompass safeguarding the sufficiency of energy resources to meet national energy demand at competitive and stable prices and the resilience of the energy supply; enabling development and deployment of technologies; building sufficient infrastructure to generate, store and transmit energy supplies and ensuring enforceable contracts of delivery.

A proposed method to increase the natural rate of removal of carbon dioxide (CO2) from the atmosphere using silicate and carbonate rocks.

The active surface area of these minerals is increased by grinding, before they are actively added to soil, beaches or the open ocean.

A collection of comparable datasets that reflect variations within the bounds of one or more sources of uncertainty, and that when averaged can provide a more robust estimate of underlying behaviour.

Ensemble techniques are used by the observational, reanalysis and modelling communities.

A natural part of the digestion process in ruminant animal species (domesticated and wild), such as cattle, buffalo, sheep, goats, antelope, etc.

Microorganisms (bacteria, archaea, fungi, protozoa and viruses) present in the fore-stomach (reticulorumen or rumen) breakdown plant biomass to produce substrates that can be used by the animal for energy and growth with methane produced as a by-product. Fermentation end-products such as hydrogen, carbon dioxide, formate and methyl-containing compounds are important substrates for the production of methane by the rumen’s methane-forming archaea (known as methanogens).

An equilibrium climate experiment is a climate model experiment in which the model is allowed to fully adjust to a change in radiative forcing.

Such experiments provide information on the difference between the initial and final states of the model, but not on the time-dependent response. If the forcing is allowed to evolve gradually according to a prescribed emissions scenario, the time-dependent response of a climate model may be analysed. Such an experiment is called a transient climate experiment.

The equilibrium (steady state) change in the surface temperature following a doubling of the atmospheric carbon dioxide (CO2) concentration from pre-industrial conditions.

The spatially averaged boundary at a given moment, usually chosen as the seasonal mass budget minimum at the end of summer, between the region on a glacier where there is a net annual loss of ice mass (ablation area) and that where there is a net annual gain (accumulation area).

The altitude of this boundary is referred to as equilibrium line altitude (ELA).

The principle of being fair and impartial, and a basis for understanding how the impacts and responses to climate change, including costs and benefits, are distributed in and by society in more or less equal ways.

Often aligned with ideas of equality, fairness and justice and applied with respect to equity in the responsibility for, and distribution of, climate impacts and policies across society, generations and gender, and in the sense of who participates and controls the processes of decision-making.

The amount of carbon dioxide (CO2) emission that would have an equivalent effect on a specified key measure of climate change, over a specified time horizon, as an emitted amount of another greenhouse gas (GHG) or a mixture of other GHGs.

For a mix of GHGs it is obtained by summing the CO2-equivalent emissions of each gas. There are various ways and time horizons to compute such equivalent emissions (see greenhouse gas emission metric). CO2-equivalent emissions are commonly used to compare emissions of different GHGs, but should not be taken to imply that these emissions have an equivalent effect across all key measures of climate change.

Ethics involves questions of justice and value.

Justice is concerned with right and wrong, equity and fairness, and, in general, with the rights to which people and living beings are entitled. Value is a matter of worth, benefit or good.

Relational well-being concept based on the premise that experiencing life purpose, challenges and growth leads to flourishing, self-realisation, personal expression, and full functioning (Niemiec 2014; Lamb and Steinberger 2017).

Over-enrichment of water by nutrients such as nitrogen and phosphorus.

It is one of the leading causes of water quality impairment. The two most acute symptoms of eutrophication are hypoxia (or oxygen depletion) and harmful algal blooms.

Data and information used in the scientific process to establish findings.

In this report, the degree of evidence reflects the amount, quality and consistency of scientific/technical information on which the Lead Authors are basing their findings.

Capacity of energy flows to perform useful work.

Exergy is a quality (versatility) indicator of energy flows which ranges from low (e.g., low-temperature heat, biomass) to high (e.g., electricity). Exergy efficiency describes how much useful work can be performed by a particular energy flow in relation to the thermodynamic maximum possible. It can be determined for all energy flows and energy conversion steps, also including alternative service delivery systems. (Grubler et al., 2012).

External forcing refers to a forcing agent outside the climate system causing a change in the climate system.

Volcanic eruptions, solar variations and changes in Earth’s orbit, as well as anthropogenic changes in the composition of the atmosphere or in land use are external forcings.

Externalities arise from a human activity, when agents responsible for the activity do not take full account of the activity’s impact on others’ production and consumption possibilities, and no compensation exists for such impacts.

When the impact is negative, they are external costs. When positive they are referred to as external benefits.

A population, species or more inclusive taxonomic group has gone extinct when all its individuals have died.

A species may go extinct locally (population extinction), regionally (e.g., extinction of all populations in a country, continent or ocean) or globally (IPBES, 2019).

The disappearance of a species from an area, sometimes also referred to as local extinction.

Its use implies that the species still occurs elsewhere.

Any cyclonic-scale storm that is not a tropical cyclone.

Usually refers to a mid- or high-latitude migratory storm system formed in regions of large horizontal temperature variations. Sometimes called extratropical storm or extratropical low.

Extratropical jets are wind maxima in the upper troposphere marking zones of baroclinic instability.

Anomalies in the position of these jets are often associated with storms, blocking, and weather extremes.

An extreme/heavy precipitation event is an event that is of very high magnitude with a very rare occurrence at a particular place.

Types of extreme precipitation may vary depending on its duration, hourly, daily or multi-days (e.g., 5 days), though all of them qualitatively represent high magnitude. The intensity of such events may be defined with a block maxima approach such as annual maxima or with peaks over threshold approach, such as rainfall above the 95th or 99th percentile at a particular place.

The occurrence of an exceptionally low or high local sea-surface height, arising from (a combination of) short term phenomena (e.g., storm surges, tides and waves).

Relative sea level changes affect extreme sea levels directly by shifting the mean water levels and indirectly by modulating the propagation of tides, waves and/or surges due to increased water depth. In addition, extreme sea levels can be influenced by changes in the frequency, tracks or strength of weather systems and storms, or due to anthropogenically induced changes such as the modification of coastlines or dredging. In turn, changes in any or all of the contributions to extreme sea levels may lead to long term relative sea-level changes. Alternate expressions for ESL may be used depending on the processes resolved.

Extreme still water level (ESWL) refers to the combined contribution of relative sea level change, tides and storm surges. Wind-waves also contribute to coastal sea level via three processes: infragravity waves (lower frequency gravity waves generated by wind waves), wave setup (time-mean sea-level elevation due to wave energy dissipation) and swash (vertical displacement up the shore-face induced by individual waves). Extreme total water level (ETWL) is the ESWL plus wave setup. When considering coastal impacts, swash is also important, and extreme coastal water level (ECWL) is used.

Bright patches on the Sun.

The area covered by faculae is greater during periods of high solar activity.

In this report, feasibility refers to the potential for a mitigation or adaptation option to be implemented.

Factors influencing feasibility are context-dependent, temporally dynamic and may vary between different groups and actors. Feasibility depends on geophysical, environmental-ecological, technological, economic, socio-cultural and institutional factors that enable or constrain the implementation of an option. The feasibility of options may change when different options are combined, and increase when enabling conditions are strengthened.

Aerosol optical depth due to aerosol particles smaller than 1 µm in radius.

The climate response pattern in space and/or time to a specific forcing is commonly referred to as a fingerprint.

The spatial patterns of sea level response to melting of glaciers or ice sheets (or other changes in surface loading) are also referred to as fingerprints. Fingerprints are used to detect the presence of this response in observations and are typically estimated using forced climate model simulations.

Weather conditions conducive to triggering and sustaining wildfires, usually based on a set of indicators and combinations of indicators including temperature, soil moisture, humidity, and wind.

Fire weather does not include the presence or absence of fuel load.

Snow that has survived at least one ablation season but has not been transformed to glacier ice.

Its pore space is at least partially interconnected, allowing air and water to circulate. Firn densities typically are 400–830 kg m^–3.

The suitability of a model (or other resource, such as a dataset or method) for a particular task, such as quantifying the contribution of increased greenhouse gas concentrations to recent changes in global mean surface temperature or projecting changes in drought frequency in a region under a given scenario.

Assessment of a model’s fitness-for-purpose can be informed both by how the model represents relevant physical processes and by how it scores on relevant performance metrics.

Strategies of governance at various levels, which prioritise the use of social learning and rapid feedback mechanisms in planning and policymaking, often through incremental, experimental and iterative management processes.

The overflowing of the normal confines of a stream or other water body, or the accumulation of water over areas that are not normally submerged.

Floods can be caused by unusually heavy rain, for example, during storms and cyclones. Floods include river (fluvial) floods, flash floods, urban floods, rain (pluvial) floods, sewer floods, coastal floods, and glacial lake outburst floods (GLOFs).

Illnesses transmitted through the consumption of unsafe or contaminated food.

That contamination can come from a variety of sources, including contaminated water (adapted from UNEP, 2018).

‘The decrease in quantity or quality of food’.

Food waste is part of food loss and refers to discarding or alternative (non-food) use of food that is safe and nutritious for human consumption along the entire food supply chain, from primary production to end household consumer level. Food waste is recognised as a distinct part of food loss because the drivers that generate it and the solutions to it are different from those of food losses (FAO, 2015).

A situation that exists when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life.

The four pillars of food security are: access; availability; stability; and utilisation. The nutritional dimension is integral to the concept of food security (FAO, 2009,2018).

All the elements (environment, people, inputs, processes, infrastructures, institutions, etc.) and activities that relate to the production, processing, distribution, preparation and consumption of food, and the output of these activities, including socio-economic and environmental outcomes (HLPE, 2017).

[Note: Whilst there is a global food system (encompassing the totality of global production and consumption), each location’s food system is unique, being defined by that place’s mix of food produced locally, nationally, regionally or globally.]

Single-celled, sand-sized marine organisms (protists) that possess a hard test mainly composed of agglutinated walls (detrital grains glued together with organic cement) or calcium carbonate (predominantly calcite).

They are used to reconstruct a range of (paleo)environmental variables such as salinity, temperature, oxygenation, oxygen isotope composition and organic and nutrient flux.

Radiative forcing is the change in the net, downward minus upward, radiative flux (expressed in W m2 ) at the tropopause or top of atmosphere due to a change in an driver of climate change, such as a change in the concentration of carbon dioxide or the output of the Sun.

The traditional radiative forcing is computed with all tropospheric properties held fixed at their unperturbed values, and after allowing for stratospheric temperatures, if perturbed, to readjust to radiative-dynamical equilibrium. Radiative forcing is called instantaneous if no change in stratospheric temperature is accounted for. The radiative forcing once rapid adjustments are accounted for is termed the effective radiative forcing. Radiative forcing is not to be confused with cloud radiative forcing, which describes an
unrelated measure of the impact of clouds on the radiative flux at the top of the atmosphere.

A vegetation type dominated by trees.

Many definitions of the term forest are in use throughout the world, reflecting wide differences in biogeophysical conditions, social structure and economics. [Note: For a discussion of the term forest in the context of National GHG inventories, see the 2006 IPCC Guidelines for National GHG Inventories and their 2019 Refinement, and information provided by the United Nations Framework Convention on Climate Change (IPCC 2006, 2019; UNFCCC, 2021a, b).]

The upper limit of the closed upper montane forest or forest at high latitudes.

It is less elevated or less poleward than the tree line.

The release of greenhouse gases that occur during the exploration, processing and delivery of fossil fuels to the point of final use.

This excludes greenhouse gas emissions from fuel combustion for the production of useful heat or power. It encompasses venting, flaring, and leaks.

The large-scale motions of the atmosphere and the ocean as a consequence of differential heating on a rotating Earth.

General circulation contributes to the energy balance of the system through transport of heat and momentum.

A numerical representation of the atmosphere–ocean–sea ice system based on the physical, chemical and biological properties of its components, their interactions and feedback processes.

General circulation models are used for weather forecasts, seasonal to decadal prediction, and climate projections. They are the basis of the more complex Earth system models (ESMs).

The change in local mean sea surface height with respect to the terrestrial reference frame; it is the sea level change observed with instruments from space.

The equipotential surface having the same geopotential at each latitude and longitude around the world (geodesists denote this potential W0) that best approximates the mean sea level.

It is the surface of reference for measurement of altitude. In practice, several variations of definitions of the geoid exist depending on the way the permanent tide (the zero-frequency gravitational tide due to the Sun and Moon) is considered in geodetic studies.

A wind or current that is in balance with the horizontal pressure gradient and the Coriolis force, and thus is outside of the influence of friction.

Thus, the wind or current is directly parallel to isobars and its speed is proportional to the horizontal pressure gradient.

Accessible thermal energy stored in the Earth’s interior, in both rock and trapped steam or liquid water (hydrothermal resources), which may be used to generate electric energy in a thermal power plant, or to supply heat to any process requiring it.

The main sources of geothermal energy are the residual energy available from planet formation and the energy continuously generated from radionuclide decay.

A statistical measure of dispersion in a distribution and degree of mathematical measure of inequality.

For example, it can be used for measuring inequality in income, wealth, carbon emissions, and access to well-being defining services. The dimensionless GINI coefficient ranges between 0 (absolute equality) and 1 (absolute inequality).

The ongoing changes in gravity, rotation and viscoelastic solid Earth deformation (GRD) in response to past changes in the distribution of ice and water on Earth’s surface.

On a time scale of decades to tens of millennia following mass redistribution, Earth’s mantle flows viscously as it evolves toward isostatic equilibrium, causing solid Earth movement and geoid changes, which can result in regional-to-local sea level variations.

A period characterized by the establishment of expanded ice sheets and glaciers, and associated with global mean sea level (GMSL) substantially lower than present; generally coincides with even-numbered marine isotope stages.

Glacial intervals were interrupted by interglacial intervals. The Last Glacial Maximum (LGM) is a specific interval within the most recent glaciation, when ice sheets were near their global maximum volume (Clark et al., 2009; Gowan et al., 2021) and GMSL was nearly at its lowest level (Lambeck et al., 2014; Yokoyama et al., 2018). Local or regional glacial maxima may be diachronous, for example ranging from about 29,000 years ago and 16,000 years ago. For purposes of global synthesis, IPCC AR6 adopts a practical chronostratigraphic definition of LGM of 23,000–19,000 years BP (before 1950; chronozone level 1 of Mix et al., 2001). For modelling purposes, LGM is defined by the model time step nearest to the centre of this interval, 21,000 years ago (Kageyama et al., 2017).

A perennial mass of ice, and possibly firn and snow, originating on the land surface by accumulation and compaction of snow and showing evidence of past or present flow.

A glacier typically gains mass by accumulation of snow and loses mass by ablation. Land ice masses of continental size (>50,000 km2) are referred to as ice sheets (Cogley et al., 2011).

The Global Environment Facility, established in 1991, helps developing countries fund projects and programmes that protect the global environment.

GEF grants support projects related to biodiversity, climate change, international waters, land degradation, the ozone (O3) layer, and persistent organic pollutants.

A collective term for the group of partially halogenated organic species, which includes the chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), halons, methyl chloride and methyl bromide.

Many of the halocarbons have large global warming potentials. The chlorine and bromine-containing halocarbons are also involved in the depletion of the ozone layer.