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1.5°C pathway
See Pathways
Acceptability of policy or system change
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.
Adaptation
In human systems, the process of adjustment to actual or expected climate and its effects, in order to
moderate harm or exploit beneficial opportunities. In natural systems, the process of adjustment
to actual climate and its effects; human intervention may facilitate adjustment to expected climate and
its effects.
See also Adaptation options, Adaptive capacity, and Maladaptive actions (Maladaptation)
Adaptation limits
The change in climate where adaptation is unable to prevent damaging impacts and further risk. Soft
limits occur when additional adaptation may be possible if constraints are able to be overcome. Hard
limits occur when no additional adaptation is possible.
Incremental adaptation
Adaptation that maintains the essence and integrity of a system or process at a given scale (Park et al.
2012). In some cases, incremental adaptation can accrue to result in transformational adaptation (Tàbara
et al. 2019; Termeer et al. 2017). Incremental adaptations to change in climate are understood as
extensions of actions and behaviours that already reduce the losses or enhance the benefits of natural
variations in extreme weather / climate events.
Transformational adaptation
Adaptation that changes the fundamental attributes of a social-ecological system in anticipation of
climate change and its impacts.
Adaptation options
The array of strategies and measures that are available and appropriate for addressing adaptation. They
include a wide range of actions that can be categorised as structural, institutional, ecological or
behavioural.
Adaptation pathways
See Pathways
Adaptive capacity
The ability of systems, institutions, humans and other organisms to adjust to potential damage, to take
advantage of opportunities, or to respond to consequences (MA 2005).
Adaptive governance
See Governance
Additionality
The property of being additional. Mitigation is additional if the greenhouse gas emission reductions or
removals would not have occurred in the absence of the associated policy intervention or activity. [Note:
Additionality is one of several key criteria used to ensure the environmental integrity of Offsets (in
climate change mitigation)]
See also Greenhouse gas emission metric
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Adverse side-effect
A negative effect that a policy or measure aimed at one objective has on another objective, thereby
potentially reducing the net benefit to society or the environment.
See also Co-benefits, Risk, and Trade-off
Aerosol
A suspension of airborne solid or liquid particles, with typical diameters between a few nanometres and
a few micrometres and atmospheric lifetimes of up to several days in the troposphere and up to years in
the stratosphere. The term aerosol, which includes both the particles and the suspending gas, is often
used in this report in its plural form to mean ‘aerosol particles’. Aerosols may be of either natural or
anthropogenic origin in the troposphere; stratospheric aerosol mostly stems from volcanic eruptions.
Aerosols can cause an effective radiative forcing directly through scattering and absorbing radiation
(aerosol–radiation interaction), and indirectly by acting as cloud condensation nuclei or ice nucleating
particles that affect the properties of clouds (aerosol–cloud interaction), and upon deposition on snow-
or ice-covered surfaces. Atmospheric aerosols may be emitted as primary particulate matter, and form
within the atmosphere from gaseous precursors (secondary production). The main classes of aerosol
chemical composition are sea salt, organic carbon, black carbon (BC), mineral species (mainly desert
dust), sulphate, nitrate and ammonium.
See also Short-lived climate forcers (SLCFs)
Afforestation
Conversion to forest of land that historically has not contained forests. [Note: For a discussion of the
term forest and related terms such as afforestation, reforestation and deforestation, see the 2006 IPCC
Guidelines for National Greenhouse Gas Inventories and their 2019 Refinement, and information
provided by the United Nations Framework Convention on Climate Change (IPCC 2006, 2019;
UNFCCC 2021a,b).]
See also Deforestation, Reducing Emissions from Deforestation and Forest Degradation (REDD+),
Reforestation, Anthropogenic Removals, and Carbon dioxide removal (CDR)
Agreement
In this report, the degree of agreement within the scientific body of knowledge on a particular finding
is assessed based on multiple lines of evidence (e.g., mechanistic understanding, theory, data, models,
expert judgement) and expressed qualitatively (Mastrandrea et al. 2010).
See also Confidence, Likelihood, and Uncertainty
Agriculture, Forestry and Other Land Use (AFOLU)
In the context of national greenhouse gas (GHG) inventories under the United Nations Convention on
Climate Change (UNFCCC), AFOLU is the sum of the GHG inventory sectors Agriculture and Land
Use, Land-Use Change and Forestry (LULUCF); see the 2006 IPCC Guidelines for National GHG
Inventories for details. Given the difference in estimating the ‘anthropogenic’ carbon dioxide (CO2)
removals between countries and the global modelling community, the land-related net GHG emissions
from global models included in this report are not necessarily directly comparable with LULUCF
estimates in national GHG Inventories.
See also Land use, Land-use change and forestry (LULUCF) and Land-use change (LUC)
Agroecology
‘The science and practice of applying ecological concepts, principles and knowledge (i.e., the
interactions of, and explanations for, the diversity, abundance and activities of organisms) to the study,
design and management of sustainable agroecosystems. It includes the roles of human beings as a
central organism in agroecology by way of social and economic processes in farming systems.
Agroecology examines the roles and interactions among all relevant biophysical, technical and
socioeconomic components of farming systems and their surrounding landscapes.’ (IPBES 2019)
Air pollution
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Degradation of air quality with negative effects on human health or the natural or built environment due
to the introduction, by natural processes or human activity, into the atmosphere of substances (gases,
aerosols) which have a direct (primary pollutants) or indirect (secondary pollutants) harmful effect.
See also Short-lived climate forcers (SLCFs)
Albedo
The proportion of sunlight (solar radiation) reflected by a surface or object, often expressed as a
percentage. Clouds, snow and ice usually have high albedo; soil surfaces cover the albedo range from
high to low; vegetation in the dry season and/or in arid zones can have high albedo, whereas
photosynthetically active vegetation and the ocean have low albedo. The Earth’s planetary albedo
changes mainly through changes in cloudiness and of snow, ice, leaf area and land cover.
Anomaly
The deviation of a variable from its value averaged over a reference period.
Anthropogenic
Resulting from or produced by human activities.
Anthropogenic emissions
Emissions of greenhouse gases (GHGs), precursors of GHGs and aerosols caused by human activities.
These activities include the burning of fossil fuels, deforestation, land use and land use changes
(LULUC), livestock production, fertilisation, waste management, and industrial processes.
See also Anthropogenic and Anthropogenic removals
Anthropogenic removals
The withdrawal of greenhouse gases (GHGs) from the atmosphere as a result of deliberate human
activities. These include enhancing biological sinks of CO2 and using chemical engineering to achieve
long term removal and storage. Carbon capture and storage (CCS), which alone does not remove CO2
from the atmosphere, can help reduce atmospheric CO2 from industrial and energy-related sources if it
is combined with bioenergy production (BECCS), or if CO2 is captured from the air directly and stored
(DACCS). [Note: In the 2006 IPCC Guidelines for national GHG Inventories (IPCC 2006), which are
used in reporting of emissions to the UNFCCC, ‘anthropogenic’ land-related GHG fluxes are defined
as all those occurring on ‘managed land’, i.e., ‘where human interventions and practices have been
applied to perform production, ecological or social functions’. However, some removals (e.g., removals
associated with CO2 fertilisation and N deposition) are not considered as ‘anthropogenic’, or are referred
to as ‘indirect’ anthropogenic effects, in some of the scientific literature assessed in this report. As a
consequence, the land-related net GHG emission estimates from global models included in this report
are not necessarily directly comparable with LULUCF estimates in national GHG Inventories.]
See also Carbon dioxide removal (CDR), Afforestation, Biochar, Enhanced weathering, Ocean
alkalinisation/Ocean alkalinity enhancement, Reforestation, and Soil carbon sequestration (SCS)
Atmosphere
The gaseous envelope surrounding the Earth, divided into five layers – the troposphere which contains
half of the Earth’s atmosphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere,
which is the outer limit of the atmosphere. 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
(GHGs) such as carbon dioxide (CO2) (0.04% volume mixing ratio), methane (CH4), nitrous oxide
(N2O) and ozone (O3). In addition, the atmosphere contains the GHG water vapour (H2O), whose
concentrations are highly variable (0-5% volume mixing ratio) as the sources (evapotranspiration) and
sinks (precipitation) of water vapour show large spatio-temporal variations, and atmospheric
temperature exerts a strong constraint on the amount of water vapour an air parcel can hold. The
atmosphere also contains clouds and aerosols.
Avoid, Shift, Improve (ASI)
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Reducing greenhouse gas emissions by avoiding the use of an emissions-producing service entirely,
shifting to the lowest-emission mode of providing the service, and/or improving the technologies and
systems for providing the service in ways that reduce emissions.
Baseline/reference
See Reference period and Reference scenario
Baseline period
See Reference period
Biochar
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).
See also Anthropogenic removals and Carbon dioxide removal (CDR)
Biodiversity
Biodiversity or biological diversity means the variability among living organisms from all sources
including, among other things, terrestrial, marine and other aquatic ecosystems, and the ecological
complexes of which they are part; this includes diversity within species, between species, and of
ecosystems (UN 1992).
See also Bioenergy and Biomass
Bioenergy
Energy derived from any form of biomass or its metabolic by-products.
See also Biofuel
Bioenergy with carbon dioxide capture and storage (BECCS)
Carbon dioxide capture and storage (CCS) technology applied to a bioenergy facility. Note that
depending on the total emissions of the BECCS supply chain, carbon dioxide (CO2) can be removed
from the atmosphere.
See also Anthropogenic removals and Carbon dioxide removal
Biofuel
A fuel, generally in liquid form, produced from biomass. Biofuels include bioethanol from sugarcane,
sugar beet or maize, and biodiesel from canola or soybeans.
See also Bioenergy
Biogenic carbon emissions
Carbon released as carbon dioxide or methane from combustion or decomposition of biomass or
biobased products.
Biomass
Organic material excluding the material that is fossilised or embedded in geological formations.
Biomass may refer to the mass of organic matter in a specific area (ISO 2014).
See also Bioenergy and Biofuel
Traditional biomass
The combustion of wood, charcoal, agricultural residues and/or animal dung for cooking or heating in
open fires or in inefficient stoves as is common in low-income countries.
Black carbon (BC)
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A relatively pure form of carbon, also known as soot, arising from the incomplete combustion of fossil
fuels, biofuel, and biomass. It only stays in the atmosphere for days or weeks. BC is a climate forcing
agent with strong warming effect, both in the atmosphere and when deposited on snow or ice.
See also Aerosol
Blue carbon
Biologically-driven carbon fluxes and storage in marine systems that are amenable to management.
Coastal blue carbon focuses on rooted vegetation in the coastal zone, such as tidal marshes, mangroves
and seagrasses. These ecosystems have high carbon burial rates on a per unit area basis and accumulate
carbon in their soils and sediments. They provide many non-climatic benefits and can contribute to
ecosystem-based adaptation. If degraded or lost, coastal blue carbon ecosystems are likely to release
most of their carbon back to the atmosphere. There is current debate regarding the application of the
blue carbon concept to other coastal and non-coastal processes and ecosystems, including the open
ocean.
See also Sequestration.
Blue infrastructure
See Infrastructure
Business as usual (BAU)
The term business as usual scenario has been used to describe a scenario that assumes no additional
policies beyond those currently in place and that patterns of socio-economic development are consistent
with recent trends. The term is now used less frequently than in the past.
See also Reference scenario (under Scenario)
Carbon budget
Refers to two concepts in the literature:
(i) an assessment of carbon cycle sources and sinks on a global level, through the synthesis of evidence
for fossil fuel and cement emissions, emissions and removals associated with land use and land use
change, ocean and natural land sources and sinks of carbon dioxide (CO2), and the resulting change in
atmospheric CO2 concentration. This is referred to as the Global Carbon Budget;
(ii) the maximum amount of cumulative net global anthropogenic CO2 emissions that would result in
limiting global warming to a given level with a given probability, taking into account the effect of other
anthropogenic climate forcers. This is referred to as the Total Carbon Budget when expressed starting
from the pre-industrial period, and as the Remaining Carbon Budget when expressed from a recent
specified date.
[Note 1: Net anthropogenic CO2 emissions are anthropogenic CO2 emissions minus anthropogenic CO2
removals. See also Carbon Dioxide Removal (CDR).
Note 2: The maximum amount of cumulative net global anthropogenic CO2 emissions is reached at the
time that annual net anthropogenic CO2 emissions reach zero.
Note 3: The degree to which anthropogenic climate forcers other than CO2 affect the Total Carbon
Budget and Remaining Carbon Budget depends on human choices about the extent to which these
forcers are mitigated and their resulting climate effects.
Note 4: The notions of a Total Carbon Budget and Remaining Carbon Budget are also being applied in
parts of the scientific literature and by some entities at regional, national, or sub-national level. The
distribution of global budgets across individual different entities and emitters depends strongly on
considerations of equity and other value judgements.]
Carbon cycle
The flow of carbon (in various forms, e.g., as carbon dioxide (CO2), carbon in biomass, and carbon
dissolved in the ocean as carbonate and bicarbonate) through the atmosphere, hydrosphere, terrestrial
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and marine biosphere and lithosphere. In this report, the reference unit for the global carbon cycle is
GtCO2 or GtC (one Gigatonne = 1 Gt = 1015 grams; 1GtC corresponds to 3.664 GtCO2).
Carbon dioxide (CO2)
A naturally occurring gas, CO2 is also a by-product of burning fossil fuels (such as oil, gas and coal), of
burning biomass, of land use changes (LUC) and of industrial processes (e.g., cement production). It is
the principal anthropogenic greenhouse gas (GHG) that affects the Earth's radiative balance. It is the
reference gas against which other GHGs are measured and therefore has a Global Warming Potential
(GWP) of 1.
Carbon dioxide capture and storage (CCS)
A process in which a relatively pure stream of carbon dioxide (CO2) from industrial and energy-related
sources is separated (captured), conditioned, compressed and transported to a storage location for long-
term isolation from the atmosphere. Sometimes referred to as Carbon Capture and Storage.
See also Anthropogenic removals, Bioenergy with carbon dioxide capture and storage (BECCS),
Carbon dioxide capture and utilisation (CCU), Carbon dioxide removal (CDR), and Sequestration
Carbon dioxide capture and utilisation (CCU)
A process in which carbon dioxide (CO2) is captured and the carbon then used in a product. The climate
effect of CCU depends on the product lifetime, the product it displaces, and the CO2 source (fossil,
biomass or atmosphere). CCU is sometimes referred to as Carbon Dioxide Capture and Use, or Carbon
Capture and Utilisation.
See also Anthropogenic removals, Carbon dioxide capture and storage (CCS), and Carbon dioxide
removal (CDR)
Carbon dioxide removal (CDR)
Anthropogenic activities removing carbon dioxide (CO2) from the atmosphere and durably storing it in
geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential
anthropogenic enhancement of biological or geochemical CO2 sinks and direct air carbon dioxide
capture and storage (DACCS), but excludes natural CO2 uptake not directly caused by human activities.
See also Anthropogenic removals, Afforestation, Biochar, Bioenergy with carbon dioxide capture and
storage (BECCS), Carbon dioxide capture and storage (CCS), Enhanced weathering, Ocean
alkalinization/Ocean alkalinity enhancement, Reforestation, and Soil carbon sequestration (SCS)
Carbon footprint
'Measure of the exclusive total amount of emissions of carbon dioxide (CO2) that is directly and
indirectly caused by an activity or is accumulated over the lifecycle stages of a product' (Wiedmann and
Minx 2008).
Household carbon footprint
The carbon footprint of an individual household, inclusive of the direct and indirect carbon dioxide
(CO2) emissions associated with home energy use, transportation, food provision, and consumption of
other goods and services associated with household expenditures.
Carbon intensity
The amount of emissions of carbon dioxide (CO2) released per unit of another variable such as gross
domestic product (GDP), output energy use or transport.
Carbon leakage
See Leakage
Carbon neutrality
Condition in which anthropogenic carbon dioxide (CO2) emissions associated with a subject are
balanced by anthropogenic CO2 removals. The subject can be an entity such as a country, an
organisation, a district or a commodity, or an activity such as a service and an event. Carbon neutrality
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is often assessed over the life cycle including indirect ("scope 3") emissions, but can also be limited to
the emissions and removals, over a specified period, for which the subject has direct control, as
determined by the relevant scheme.
[Note 1: Carbon neutrality and net zero CO2 emissions are overlapping concepts. The concepts can be
applied at global or sub-global scales (e.g., regional, national and sub-national). At a global scale, the
terms carbon neutrality and net zero CO2 emissions are equivalent. At sub-global scales, net zero CO2
emissions is generally applied to emissions and removals under direct control or territorial responsibility
of the reporting entity, while carbon neutrality generally includes emissions and removals within and
beyond the direct control or territorial responsibility of the reporting entity. Accounting rules specified
by greenhouse gas (GHG) programmes or schemes can have a significant influence on the
quantification of relevant CO2 emissions and removals.
Note 2: In some cases achieving carbon neutrality may rely on the supplementary use of offsets to
balance emissions that remain after actions by the reporting entity are taken into account.]
See also Greenhouse gas neutrality, Land use, land-use change and forestry (LULUCF) and Net zero
CO2 emissions
Carbon price
The price for avoided or released carbon dioxide (CO2) or CO2-equivalent emissions. This may refer to
the rate of a carbon tax, or the price of emission permits. In many models that are used to assess the
economic costs of mitigation, carbon prices are used as a proxy to represent the level of effort in
mitigation policies.
Carbon sink
See Sink
Carbon stock
The quantity of carbon in a carbon pool.
Circular economy
A system with minimal input and operational losses of materials and energy through extensive reduce,
reuse, recycling, and recovery activities. Ten strategies for circularity include: Refuse, Rethink, Reduce,
Reuse, Repair, Refurbish, Remanufacture, Repurpose, Recycle, Recover.
Cities
Cities are open systems, continually exchanging resources, products and services, waste, people, ideas,
and finances with the hinterlands and broader world. Cities are complex, self-organising, adaptive, and
constantly evolving. Cities also encompass multiple actors with varying responsibilities, capabilities
and priorities, as well as processes that transcend the institutional sector-based approach to city
administration. Cities are embedded in broader ecological, economic, technical, institutional, legal, and
governance structures that enable or often constrain their systemic function, which cannot be separated
from wider power relations. Urban processes of physical, social, and economic nature are causally
interlinked, with interactions and feedbacks that result in both intended and unintended impacts on
emissions.
See also City region, Peri-urban areas and Urban
Citizen science
A voluntary participation of the public in the collection and/or processing of data as part of a scientific
study (Silvertown 2009).
City region
The areal extent of an individual city's material associations and economic or political influence. The
city region concept accepts that rural livelihoods and land uses can be incorporated within the functional
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activities of a city. This will include dormitory settlements, sources for critical inputs of water, some
food, and waste disposal.
See also Cities, Region and Urban systems
Climate
Climate in a narrow sense is usually defined as the average weather, or more rigorously, as 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 (WMO). The relevant quantities are most
often surface variables such as temperature, precipitation and wind. Climate in a wider sense is the state,
including a statistical description, of the climate system.
Climate change
A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in
the mean and/or the variability of its properties and that persists for an extended period, typically
decades or longer. Climate change may be due to natural internal processes or external forcings such as
modulations of the solar cycles, volcanic eruptions and persistent anthropogenic changes in the
composition of the atmosphere or in land use. Note that the United Nations Framework Convention on
Climate Change (UNFCCC), in its Article 1, defines climate change as: 'a change of climate which is
attributed directly or indirectly to human activity that alters the composition of the global atmosphere
and which is in addition to natural climate variability observed over comparable time periods'. The
UNFCCC thus makes a distinction between climate change attributable to human activities altering the
atmospheric composition and climate variability attributable to natural causes.
Climate change commitment
The unavoidable future climate change resulting from inertia in the geophysical and socio-economic
systems. Different types of climate change commitment are discussed in the literature. Climate change
commitment is usually quantified in terms of the further change in temperature, but it includes other
future changes, for example in the hydrological cycle, in extreme weather events, in extreme climate
events, and in sea level.
Zero emissions commitment
The zero emissions commitment is an estimate of the subsequent global warming that would result after
anthropogenic emissions are set to zero. It is determined by both inertia in physical climate system
components (ocean, cryosphere, land surface) and carbon cycle inertia. In its widest sense it refers to
emissions of each climate forcer including greenhouses gases, aerosols and their pre-cursors. The
climate response to this can be complex due to the different timescale of response of each climate forcer.
A specific sub-category of zero emissions commitment is the Zero CO2 Emissions Commitment which
refers to the climate system response to CO2 emissions after setting these to net zero. The CO2-only
definition is of specific use in estimating remaining carbon budgets.
Climate extreme (extreme weather or climate event)
The occurrence of a value of a weather or climate variable above (or below) a threshold value near the
upper (or lower) ends of the range of observed values of the variable. By definition, the characteristics
of what is called extreme weather may vary from place to place in an absolute sense. When a pattern of
extreme weather persists for some time, such as a season, it may be classified as an extreme climate
event, especially if it yields an average or total that is itself extreme (e.g., high temperature, drought, or
heavy rainfall over a season). For simplicity, both extreme weather events and extreme climate events
are referred to collectively as 'climate extremes'.
Climate finance
There is no agreed definition of climate finance. The term 'climate finance' is applied to the financial
resources devoted to addressing climate change by all public and private actors from global to local
scales, including international financial flows to developing countries to assist them in addressing
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climate change. Climate finance aims to reduce net greenhouse gas emissions and/or to enhance
adaptation and increase resilience to the impacts of current and projected climate change. Finance can
come from private and public sources, channelled by various intermediaries, and is delivered by a range
of instruments, including grants, concessional and non-concessional debt, and internal budget
reallocations.
Climate governance
See Governance
Climate justice
See Justice
Climate model
A qualitative or quantitative 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. The climate system can be represented by models of varying complexity;
that is, for any one component or combination of components a spectrum or hierarchy of models can be
identified, differing in such aspects as the number of spatial dimensions, the extent to which physical,
chemical or biological processes are explicitly represented, or the level at which empirical
parametrisations are involved. There is an evolution towards more complex models with interactive
chemistry and biology. 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.
See also Simple climate model (SCM) and Emulators
Climate projection
Simulated response of the climate system to a scenario of future emissions or concentrations of
greenhouse gases (GHGs) and aerosols and changes in land use, generally derived using climate
models. Climate projections are distinguished from climate predictions by their dependence on the
emission/concentration/radiative forcing scenario used, which is in turn based on assumptions
concerning, for example, future socio-economic and technological developments that may or may not
be realised.
Climate sensitivity
The change in the surface temperature in response to a change in the atmospheric carbon dioxide (CO2)
concentration or other radiative forcing.
Transient climate response (TCR)
The surface temperature response for the hypothetical scenario in which atmospheric carbon dioxide
(CO2) increases at 1% yr-1 from pre-industrial to the time of a doubling of atmospheric CO2
concentration (year 70).
Transient climate response to cumulative CO2 emissions (TCRE)
The transient surface temperature change per unit cumulative carbon dioxide (CO2) emissions, usually
1000 GtC. TCRE combines both information on the airborne fraction of cumulative CO2 emissions (the
fraction of the total CO2 emitted that remains in the atmosphere, which is determined by carbon cycle
processes) and on the transient climate response (TCR).
Climate services
Climate services involve the provision of climate information in such a way as to assist decision-
making. The service includes appropriate engagement from users and providers, is based on
scientifically credible information and expertise, has an effective access mechanism, and responds to
user needs (Hewitt et al. 2012).
Climate system
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The global system consisting of five major components: the atmosphere, the hydrosphere, the
cryosphere, the lithosphere and the biosphere and the interactions between them. The climate system
changes in time under the influence of its own internal dynamics and because of external forcings such
as volcanic eruptions, solar variations, orbital forcing, and anthropogenic forcings such as the changing
composition of the atmosphere and land-use change.
Climate variability
Deviations of climate variables from a given mean state (including the occurrence of extremes, etc.) at
all spatial and temporal scales beyond that of individual weather events. Variability may be intrinsic,
due to fluctuations of processes internal to the climate system (internal variability), or extrinsic, due to
variations in natural or anthropogenic external forcing (forced variability).
See also Climate change
Co-benefits
A positive effect that a policy or measure aimed at one objective has on another objective, thereby
increasing the total benefit to society or the environment. Co-benefits are also referred to as ancillary
benefits.
See also Adverse side-effect and Trade-off
CO2 equivalent (CO2-eq) emission
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.
[Note: Under the Paris Rulebook [Decision 18/CMA.1, annex, paragraph 37], parties have agreed to
use GWP100 values from the IPCC AR5 or GWP100 values from a subsequent IPCC Assessment
Report to report aggregate emissions and removals of GHGs. In addition, parties may use other metrics
to report supplemental information on aggregate emissions and removals of GHGs.]
Concentrations scenario
See Scenario
Conference of the Parties (COP)
The supreme body of UN conventions, such as the United Nations Framework Convention on Climate
Change (UNFCCC), comprising parties with a right to vote that have ratified or acceded to the
convention.
Confidence
The robustness of a finding based on the type, amount, quality and consistency of evidence (e.g.,
mechanistic understanding, theory, data, models, expert judgment) and on the degree of agreement
across multiple lines of evidence. In this report, confidence is expressed qualitatively (Mastrandrea et
al. 2010).
Conservation agriculture
A farming system that promotes minimum soil disturbance (e.g., by using no till practices), maintenance
of a permanent soil cover, and diversification of plant species. It aims to prevent land degradation and
regenerate degraded lands by enhancing biodiversity and natural biological processes above and below
the ground surface, that contribute to increased water and nutrient use efficiency and improved and
sustained crop production. (FAO 2016)
Consumption-based emissions
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Emissions released to the atmosphere in order to generate the goods and services consumed by a certain
entity (e.g., a person, firm, country, or region)
See also Production-based emissions
Coping capacity
The ability of people, institutions, organizations, and systems, using available skills, values, beliefs,
resources, and opportunities, to address, manage, and overcome adverse conditions in the short to
medium term. (UNISDR 2009; IPCC 2012)
See also Resilience
Cost-benefit analysis
A type of economic evaluation that compares all monetised negative and positive impacts associated
with a given action. Cost-benefit analysis enables comparison of different interventions, investments or
strategies and reveal how a given investment or policy effort pays off for a particular person, company
or country, or at a global scale. Cost-benefit analyses representing society's point of view are important
for climate change decision-making, but there are difficulties in aggregating costs and benefits across
different actors and across timescales.
See also Discounting
Cost-effectiveness analysis (CEA)
A type of economic evaluation that compares the costs of different courses of action reaching the same
outcome. In this report, CEA focuses on comparing the costs of mitigation strategies designed to meet
a prespecified climate change mitigation goal (e.g., an emission-reduction target or a temperature
stabilisation target).
Cumulative emissions
The total amount of emissions released over a specified period of time.
See also Carbon budget and Transient climate response to cumulative CO2 emissions (TCRE)
Decarbonisation
Human actions to reduce carbon dioxide emissions from human activities.
Decent Living Standard
A set of essential material preconditions for human wellbeing which includes nutrition, shelter, basic
amenities, healthcare, transportation, information, education, and public space (Rao and Baer 2012; Rao
and Min 2018; O’Neill et al. 2018).
Decoupling
Decoupling (in relation to climate change) is where economic growth is no longer strongly associated
with another relevant indicator such as greenhouse gas emissions. Relative decoupling is where both
grow but the other indicators grow more slowly than the economy. Absolute decoupling is where there
is economic growth but there is a decline in the other indicator.
Deforestation
Conversion of forest to non-forest. [Note: For a discussion of the term forest and related terms such as
afforestation, reforestation and deforestation, see the 2006 IPCC Guidelines for National Greenhouse
Gas Inventories and their 2019 Refinement, and information provided by the United Nations
Framework Convention on Climate Change (IPCC 2006, 2019; UNFCCC 2021a,b)]
See also Reducing Emissions from Deforestation and Forest Degradation (REDD+)
Deliberative governance
See Governance
Demand
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Disciplinary approaches use the term in different ways. In economics, demand by a consumer is
willingness and ability to purchase in a market place. However, the motivation for purchase may vary
and can include economic utility, welfare, Decent standard of living (DSL), or for the good/services.
Demand- and supply-side measures
Demand-side measures
Policies and programmes for influencing the demand for goods and/or services. In the energy sector,
demand-side mitigation measures aim at reducing the amount of greenhouse gas emissions emitted per
unit of energy service used.
Supply-side measures
Policies and programmes for influencing how a certain demand for goods and/or services is met. In the
energy sector, supply-side mitigation measures aim at reducing the amount of greenhouse gas emissions
emitted per unit of energy service produced.
Demand-side management
See Demand-side measures
Desertification
Land degradation in arid, semi-arid, and dry sub-humid areas resulting from many factors, including
climatic variations and human activities (UNCCD 1994).
Developed / developing countries (Industrialised / developed / developing countries)
There is a diversity of approaches for categorising countries on the basis of their level of development,
and for defining terms such as industrialised, developed, or developing. Several categorisations are used
in this Report. (1) In the United Nations (UN) system, there is no established convention for the
designation of developed and developing countries or areas. (2) The UN Statistics Division specifies
developed and developing regions based on common practice. In addition, specific countries are
designated as least developed countries, landlocked developing countries, small island developing
states (SIDS), and transition economies. Many countries appear in more than one of these categories.
(3) The World Bank uses income as the main criterion for classifying countries as low, lower middle,
upper middle, and high income. (4) The UN Development Programme (UNDP) aggregates indicators
for life expectancy, educational attainment, and income into a single composite Human Development
Index (HDI) to classify countries as low, medium, high, or very high human development.
Development pathway
See Pathways
Diet
‘The kinds of food that follow a particular pattern that a person or community eats’ (FAO, 2014).
Direct air capture (DAC)
Chemical process by which a pure carbon dioxide (CO2) stream is produced by capturing CO2 from the
ambient air.
See also Anthropogenic removals, Carbon dioxide removal (CDR) and Direct air carbon dioxide
capture and storage (DACCS)
Direct air carbon dioxide capture and storage (DACCS)
Chemical process by which carbon dioxide (CO2) is captured directly from the ambient air, with
subsequent storage. Also known as direct air capture and storage (DACS).
See also Anthropogenic removals, Carbon dioxide removal (CDR) and Direct air capture (DAC)
Direct and indirect services
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Direct Services: Services (e.g., passenger mobility) required by end-users (consumers).
Indirect services: Services required (e.g., goods transport, manufacturing) for provisioning systems of
direct services.
Direct emissions
Emissions that physically arise from activities within well-defined boundaries of, for instance, a region,
an economic sector, a company, or a process.
See also Indirect emissions
Disaster
A ‘serious disruption of the functioning of a community or a society at any scale due to hazardous
events interacting with conditions of exposure, vulnerability and capacity, leading to one or more of the
following: human, material, economic and environmental losses and impacts’ (UNGA 2016).
See also Exposure, Hazard, Risk and Vulnerability
Disaster risk management (DRM)
Processes for designing, implementing, and evaluating strategies, policies, and measures to improve the
understanding of current and future disaster risk, foster disaster risk reduction and transfer, and promote
continuous improvement in disaster preparedness, prevention and protection, response, and recovery
practices, with the explicit purpose of increasing human security, wellbeing, quality of life, and
sustainable development (SD).
Discount rate
See Discounting
Discounting
A mathematical operation that aims to make monetary (or other) amounts received or expended at
different times (years) comparable across time. If the discount rate is positive, future values are given
less weight than those today. The choice of discount rate(s) is debated as it is a judgement based on
hidden and/or explicit values.
Disruptive innovation
Demand-led technological change that leads to significant system change and is characterised by strong
exponential growth.
Distributive equity
See Equity
Drought
An exceptional period of water shortage for existing ecosystems and the human population (due to low
rainfall, high temperature, and/or wind).
Ecosystem
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.
See also Ecosystem services
Ecosystem services
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
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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.
See also Ecosystem and Nature’s Contribution to People
Ecosystem-based adaptation (EBA)
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).
Embodied (embedded) [emissions, water, land]
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).
Emission and Socioeconomic Scenario Ensemble
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).
Emission factor/Emissions intensity
A coefficient that quantifies the emissions or removals of a gas per unit activity. Emission factors are
often based on a sample of measurement data, averaged to develop a representative rate of emission for
a given activity level under a given set of operating conditions.
Emission trajectories
A projected development in time of the emission of a greenhouse gas (GHG) or group of GHGs,
aerosols, and GHG precursors.
See also Pathways
Emissions
See Anthropogenic emissions, Direct emissions, Cumulative emissions, Indirect emissions,
Consumption-based emissions, Production-based emissions and Embodied (embedded) [emissions,
water, land]
Emission pathways
See Pathways
Emissions scenario
See Scenario
Emulation
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.
Emulators
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A broad class of heavily parametrised 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.
See also Emulation and Simple climate models (SCMs)
Enabling conditions (for adaptation and mitigation options)
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.
Energy access
Access to clean, reliable and affordable energy services for cooking and heating, lighting,
communications, and productive uses (with special reference to Sustainable Development Goal 7)
(AGECC 2010).
See also Traditional biomass
Energy efficiency
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.
Energy poverty
'The absence of sufficient choice in accessing adequate, affordable, reliable, high quality, safe and
environmentally benign energy services to support economic and human development' (Reddy 2000).
See also Fuel poverty
Energy security
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.
Energy services
A benefit or amenity (for example, mobility, communication, thermal comfort) received as a result of
energy or other resources use.
Enhanced weathering
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.
See also Anthropogenic removals and Carbon dioxide removal (CDR)
Ensemble
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.
See also Emission and Socioeconomic Scenario Ensemble and Integrated Assessment Scenario
Ensemble
Enteric fermentation
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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).
Equality
A principle that ascribes equal worth to all human beings, including equal opportunities, rights, and
obligations, irrespective of origins.
Inequality
Uneven opportunities and social positions, and processes of discrimination within a group or society,
based on gender, class, ethnicity, age, and (dis)ability, often produced by uneven development. Income
inequality refers to gaps between highest and lowest income earners within a country and between
countries.
See also Equity and Fairness
Equity
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.
Distributive equity
Equity in the consequences, outcomes, costs and benefits of actions or policies. In the case of climate
change or climate policies for different people, places and countries, including equity aspects of sharing
burdens and benefits for mitigation and adaptation.
Gender equity
Equity between women and men with regard to their rights, resources and opportunities. In the case of
climate change, gender equity recognises that women are often more vulnerable to the impacts of
climate change and may be disadvantaged in the process and outcomes of climate policy.
Inter-generational equity
Equity between generations. In the context of climate change, inter-generational equity acknowledges
that the effects of past and present emissions, vulnerabilities and policies impose costs and benefits for
people in the future and of different age groups.
Evidence
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.
See also Agreement, Confidence, Likelihood, and Uncertainty
Exergy
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 including also alternative service delivery systems. (Grubler et al. 2012)
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Exposure
The presence of people; livelihoods; species or ecosystems; environmental functions, services, and
resources; infrastructure; or economic, social, or cultural assets in places and settings that could be
adversely affected.
Extreme weather event
An event that is rare at a particular place and time of year. Definitions of ‘rare’ vary, but an extreme
weather event would normally be as rare as or rarer than the 10th or 90th percentile of a probability
density function estimated from observations. By definition, the characteristics of what is called
extreme weather may vary from place to place in an absolute sense.
See also Climate extreme (extreme weather or climate event)
Fairness
Impartial and just treatment without favouritism or discrimination in which each person is considered
of equal worth with equal opportunity.
See also Equality and Equity
Feasibility
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.
See also Enabling conditions (for adaptation and mitigation options)
Final energy
The energy delivered to final users (firms, individuals, institutions), where it becomes usable energy in
supplying energy services (e.g., light, heat, mobility).
See also Primary energy
Flexibility (demand and supply)
Adjustment of energy load characteristics by technical and/or non-technical change to balance energy
demand and supply.
Flexible governance
See Governance
Flood
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).
Food loss and waste
‘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).
Food security
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
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healthy life. The four pillars of food security are availability, access, utilisation and stability. The
nutritional dimension is integral to the concept of food security. (FAO 2009, 2018)
Availability
Physical availability of food. Food availability addresses the supply side of food security and is
determined by the levels of food production, stocks and net trade.
Access
Economic and/ or physical access to food. Economic access is determined by disposable income, food
prices and the provision of and access to social support. Physical access is determined by the availability
and quality of land and other infrastructure, property rights or the functioning of markets.
Utilisation
The way in which the body uses the various nutrients in food. Individuals achieve sufficient energy and
nutrient intake through good care and feeding practices, food preparation, diet diversity and
intrahousehold distribution of food. Combined with biological utilisation of the food consumed, energy
and nutrient intake determine the nutrition status of individuals.
Stability
The stability of the other three dimensions over time. Even if individuals’ food intake is adequate today,
they are still considered food-insecure if periodically they have inadequate access to food, risking
deterioration of their nutrition status. Adverse weather conditions, political instability or economic
factors (unemployment, rising food prices) may have an impact on individuals’ food security status.
Food system
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.]
Forest
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).]
Fossil fuels
Carbon-based fuels from fossil hydrocarbon deposits, including coal, oil, and natural gas.
Fuel poverty
A condition in which a household is unable to guarantee a certain level of consumption of domestic
energy services (especially heating) or suffers disproportionate expenditure burdens to meet these
needs.
See also Energy poverty
Fugitive emissions (oil and natural gas systems)
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.
Geothermal energy
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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.
See also Renewable energy
Gender equity
See Equity
Gini coefficient
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).
Global carbon budget
See Carbon budget
Global mean surface air temperature (GSAT)
Global average of near-surface air temperatures over land, oceans and sea ice. Changes in GSAT are
often used as a measure of global temperature change in climate models.
See also Global mean surface temperature (GMST)
Global mean surface temperature (GMST)
Estimated global average of near-surface air temperatures over land and sea ice, and sea surface
temperature (SST) over ice-free ocean regions, with changes normally expressed as departures from a
value over a specified reference period.
See also Global mean surface air temperature (GSAT)
Global warming
Global warming refers to the increase in global surface temperature relative to a baseline reference
period, averaging over a period sufficient to remove interannual variations (e.g., 20 or 30 years). A
common choice for the baseline is 1850–1900 (the earliest period of reliable observations with sufficient
geographic coverage), with more modern baselines used depending upon the application.
See also Climate change and Climate variability
Global warming potential (GWP)
An index measuring the radiative forcing following an emission of a unit mass of a given substance,
accumulated over a chosen time horizon, relative to that of the reference substance, carbon dioxide
(CO2). The GWP thus represents the combined effect of the differing times these substances remain in
the atmosphere and their effectiveness in causing radiative forcing.
See also Greenhouse gas emission metric
Governance
The structures, processes, and actions through which private and public actors interact to address
societal goals. This includes formal and informal institutions and the associated norms, rules, laws and
procedures for deciding, managing, implementing and monitoring policies and measures at any
geographic or political scale, from global to local.
Adaptive governance
Adjusting to changing conditions, such as climate change, through governance interactions that seek to
maintain a desired state in a social-ecological system.
Climate governance
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The structures, processes, and actions through which private and public actors seek to mitigate and
adapt to climate change.
Deliberative governance
Deliberative governance involves decision making through inclusive public conversation which allows
opportunity for developing policy options through public discussion rather than collating individual
preferences through voting or referenda (although the latter governance mechanisms can also be
proceeded and legitimated by public deliberation processes).
Flexible governance
Strategies of governance at various levels, which prioritise the use of social learning and rapid feedback
mechanisms in planning and policy making, often through incremental, experimental and iterative
management processes.
Multilevel governance
The dispersion of governance across multiple levels of jurisdiction and decision-making, including,
global, regional, national and local, as well as trans-regional and trans-national levels.
Participatory governance
A governance system that enables direct public engagement in decision-making using a variety of
techniques for example, referenda, community deliberation, citizen juries or participatory budgeting.
The approach can be applied in formal and informal institutional contexts from national to local, but is
usually associated with devolved decision making (Fung and Wright 2003; Sarmiento and Tilly 2018).
Governance capacity
The ability of governance institutions, leaders, and non-state and civil society to plan, co-ordinate, fund,
implement, evaluate and adjust policies and measures over the short, medium and long term, adjusting
for uncertainty, rapid change and wide-ranging impacts and multiple actors and demands.
See also Governance
Grazing land
The sum of rangelands and pastures not considered as cropland, and subject to livestock grazing or hay
production. It includes a wide range of ecosystems, e.g., systems with vegetation that fall below the
threshold used in the forest land category, silvo-pastoral systems, as well as natural, managed grasslands
and semideserts.
Green Climate Fund (GCF)
The Green Climate Fund was established by the 16th Session of the Conference of the Parties (COP)
in 2010 as an operating entity of the financial mechanism of the United Nations Framework Convention
on Climate Change (UNFCCC), in accordance with Article 11 of the Convention, to support projects,
programmes and policies and other activities in developing country Parties. The Fund is governed by a
Board and will receive guidance of the COP.
See also Climate finance
Green infrastructure
See Infrastructure
Grey infrastructure
See Infrastructure
Greenhouse gas emission metric
A simplified relationship used to quantify the effect of emitting a unit mass of a given greenhouse gas
(GHG) on a specified key measure of climate change. A relative GHG emission metric expresses the
effect from one gas relative to the effect of emitting a unit mass of a reference GHG on the same measure
of climate change. There are multiple emission metrics, and the most appropriate metric depends on the
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application. GHG emission metrics may differ with respect to (i) the key measure of climate change
they consider, (ii) whether they consider climate outcomes for a specified point in time or integrated
over a specified time horizon, (iii) the time horizon over which the metric is applied, (iv) whether they
apply to a single emission pulse, emissions sustained over a period of time, or a combination of both,
and (v) whether they consider the climate effect from an emission compared to the absence of that
emission or compared to a reference emissions level or climate state.
[Notes: Most relative GHG emission metrics (such as the global warming potential (GWP), global
temperature change potential (GTP), global damage potential, and GWP*), use carbon dioxide (CO2)
as the reference gas. Emissions of non-CO2 gases, when expressed using such metrics, are often referred
to as ‘carbon dioxide equivalent’ emissions. A metric that establishes equivalence regarding one key
measure of the climate system response to emissions does not imply equivalence regarding other key
measures. The choice of a metric, including its time horizon, should reflect the policy objectives for
which the metric is applied.]
Greenhouse gas neutrality
Condition in which metric-weighted anthropogenic greenhouse gas (GHG) emissions associated with
a subject are balanced by metric-weighted anthropogenic GHG removals. The subject can be an entity
such as a country, an organisation, a district or a commodity, or an activity such as a service and an
event. GHG neutrality is often assessed over the life cycle, including indirect (‘scope 3’) emissions, but
can also be limited to the emissions and removals, over a specified period, for which the subject has
direct control, as determined by the relevant scheme. The quantification of GHG emissions and
removals depends on the GHG emission metric chosen to compare emissions and removals of different
gases, as well as the time horizon chosen for that metric.
[Note 1: Greenhouse gas neutrality and net zero greenhouse gas emissions are overlapping concepts.
The concepts can be applied at global or sub-global scales (e.g., regional, national and sub-national).
At a global scale, the terms greenhouse gas neutrality and net zero greenhouse gas emissions are
equivalent. At sub-global scales, net zero GHG emissions is generally applied to emissions and
removals under direct control or territorial responsibility of the reporting entity, while GHG neutrality
generally includes emissions and removals within and beyond the direct control or territorial
responsibility of the reporting entity. Accounting rules specified by GHG programmes or schemes can
have a significant influence on the quantification of relevant emissions and removals.
Note 2. Under the Paris Rulebook (Decision 18/CMA.1, annex, paragraph 37), parties have agreed to
use GWP100 values from the IPCC AR5 or GWP100 values from a subsequent IPCC Assessment
Report to report aggregate emissions and removals of GHGs. In addition, parties may use other metrics
to report supplemental information on aggregate emissions and removals of GHGs.
Note 3: In some cases, achieving greenhouse gas neutrality may rely on the supplementary use of offsets
to balance emissions that remain after actions by the reporting entity are taken into account.]
See also Carbon neutrality, Greenhouse gas emission metric, Land use, Land-use change and forestry
(LULUCF) and Net zero greenhouse gas emissions
Greenhouse gases (GHGs)
Gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation
at specific wavelengths within the spectrum of radiation emitted by the Earth’s surface, by the
atmosphere itself, and by clouds. This property causes the greenhouse effect. Water vapour (H2O),
carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and ozone (O3) are the primary GHGs in the
Earth’s atmosphere. Human-made GHGs include sulphur hexafluoride (SF6), hydrofluorocarbons
(HFCs), chlorofluorocarbons (CFCs) and perfluorocarbons (PFCs); several of these are also O3-
depleting (and are regulated under the Montreal Protocol).
Gross domestic product (GDP)
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The sum of gross value added, at purchasers' prices, by all resident and non-resident producers in the
economy, plus any taxes and minus any subsidies not included in the value of the products in a country
or a geographic region for a given period, normally one year. GDP is calculated without deducting for
depreciation of fabricated assets or depletion and degradation of natural resources.
Halocarbons
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.
Human behaviour
The responses of persons or groups to a particular situation, here likely to relate to climate change.
Human behaviour covers the range of actions by individuals, communities, organisations, governments
and at the international level.
Human rights
Rights that are inherent to all human beings, universal, inalienable, and indivisible, typically expressed
and guaranteed by law. They include the right to life, economic, social, and cultural rights, and the right
to development and self-determination (OHCHR 2018).
Human security
A condition that is met when the vital core of human lives is protected, and when people have the
freedom and capacity to live with dignity. In the context of climate change, the vital core of human
lives includes the universal and culturally specific, material and non-material elements necessary for
people to act on behalf of their interests and to live with dignity.
Human system
Any system in which human organisations and institutions play a major role. Often, but not always, the
term is synonymous with society or social system. Systems such as agricultural systems, urban systems,
political systems, technological systems and economic systems are all human systems in the sense
applied in this Report.
Hydropower
Power harnessed from the flow of water.
See also Renewable energy
Impacts
The consequences of realised risks on natural and human systems, where risks result from the
interactions of climate-related hazards (including extreme weather/climate events), exposure, and
vulnerability. Impacts generally refer to effects on lives, livelihoods, health and well-being, ecosystems
and species, economic, social and cultural assets, services (including ecosystem services), and
infrastructure. Impacts may be referred to as consequences or outcomes, and can be adverse or
beneficial.
See also Adaptation, Loss and Damage, and losses and damages
Indigenous knowledge
The understandings, skills and philosophies developed by societies with long histories of interaction
with their natural surroundings. For many indigenous peoples, indigenous knowledge informs decision-
making about fundamental aspects of life, from day-to-day activities to longer term actions. This
knowledge is integral to cultural complexes, which also encompass language, systems of classification,
resource use practices, social interactions, values, ritual and spirituality. These distinctive ways of
knowing are important facets of the world’s cultural diversity (UNESCO 2018).
See also Local knowledge
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Indirect emissions
Emissions that are a consequence of the activities within well-defined boundaries of, for instance, a
region, an economic sector, a company or process, but which occur outside the specified boundaries.
For example, emissions are described as indirect if they relate to the use of heat but physically arise
outside the boundaries of the heat user, or to electricity production but physically arise outside of the
boundaries of the power supply sector.
See also Direct emissions
Indirect land-use change (iLUC)
See Land-use change (LUC)
Industrial revolution
A period of rapid industrial growth with far-reaching social and economic consequences, beginning in
Britain during the second half of the 18th century and spreading to Europe and later to other countries
including the United States. The invention of the steam engine was an important trigger of this
development. The industrial revolution marks the beginning of a strong increase in the use of fossil
fuels, initially coal, and hence emission of carbon dioxide (CO2).
Inequality
See Equality
Infrastructure
The designed and built set of physical systems and corresponding institutional arrangements that
mediate between people, their communities, and the broader environment to provide services that
support economic growth, health, quality of life, and safety. (Chester 2019; Dawson et al. 2018)
Blue infrastructure
Blue infrastructure includes bodies of water, watercourses, ponds, lakes and storm drainage, that
provide ecological and hydrological functions including evaporation, transpiration, drainage,
infiltration, and temporarily storage of runoff and discharge.
Green infrastructure
The strategically planned interconnected set of natural and constructed ecological systems, green spaces
and other landscape features that can provide functions and services including air and water purification,
temperature management, floodwater management and coastal defence often with co-benefits for
people and biodiversity. Green infrastructure includes planted and remnant native vegetation, soils,
wetlands, parks and green open spaces, as well as building and street level design interventions that
incorporate vegetation. (Culwick and Bobbins 2016)
Grey infrastructure
Engineered physical components and networks of pipes, wires, roads, tracks that underpin energy,
transport, communications (including digital), built form, water and sanitation and solid waste
management systems.
Social infrastructure
The social, cultural, and financial activities and institutions as well as associated property, buildings
and artefacts and policy domains such as social protection, health and education that support wellbeing
and public life (Latham and Layton 2019; Frolova et al. 2016).
Institutional capacity
Building and strengthening individual organisations and providing technical and management training
to support integrated planning and decision-making processes between organisations and people, as
well as empowerment, social capital, and an enabling environment, including the culture, values and
power relations (Willems and Baumert 2003).
See also Governance and Institutions
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Institutions
Rules, norms and conventions that guide, constrain or enable human behaviours and practices.
Institutions can be formally established, for instance through laws and regulations, or informally
established, for instance by traditions or customs. Institutions may spur, hinder, strengthen, weaken or
distort the emergence, adoption and implementation of climate action and climate governance.
[Note: Institutions can also refer to a large organisation.]
See also Institutional capacity
Integrated assessment
A method of analysis that combines results and models from the physical, biological, economic and
social sciences and the interactions among these components in a consistent framework to evaluate the
status and the consequences of environmental change and the policy responses to it.
See also Integrated assessment model (IAM)
Integrated assessment model (IAM)
Models that integrate knowledge from two or more domains into a single framework. They are one of
the main tools for undertaking integrated assessments. One class of IAM used with respect to climate
change mitigation may include representations of: multiple sectors of the economy, such as energy,
land use and land-use change; interactions between sectors; the economy as a whole; associated
greenhouse gas (GHG) emissions and sinks; and reduced representations of the climate system. This
class of model is used to assess linkages between economic, social and technological development and
the evolution of the climate system. Another class of IAM additionally includes representations of the
costs associated with climate change impacts, but includes less detailed representations of economic
systems. These can be used to assess impacts and mitigation in a cost–benefit framework and have been
used to estimate the social cost of carbon.
See also Integrated Assessment Scenario Ensemble
Integrated Assessment Scenario Ensemble
A set of modelled scenarios from an intercomparison of integrated assessment models (IAMs) based on
a systematic variation of harmonised scenario designs.
Inter-generational equity
See Equity
Internet of Things (IoT)
The network of computing devices embedded in everyday objects such as cars, phones and computers,
connected via the internet, enabling them to send and receive data.
Irreversibility
A perturbed state of a dynamical system is defined as irreversible on a given time scale if the recovery
from this state due to natural processes takes substantially longer than the time scale of interest.
See also Tipping point
Just transitions
A set of principles, processes and practices that aim to ensure that no people, workers, places, sectors,
countries or regions are left behind in the transition from a high-carbon to a low-carbon economy. It
stresses the need for targeted and proactive measures from governments, agencies, and authorities to
ensure that any negative social, environmental or economic impacts of economy-wide transitions are
minimised, whilst benefits are maximised for those disproportionally affected. Key principles of just
transitions include: respect and dignity for vulnerable groups; fairness in energy access and use, social
dialogue and democratic consultation with relevant stakeholders; the creation of decent jobs; social
protection; and rights at work. Just transitions could include fairness in energy, land use and climate
planning and decision-making processes; economic diversification based on low-carbon investments;
realistic training/retraining programs that lead to decent work; gender specific policies that promote
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equitable outcomes; the fostering of international cooperation and coordinated multilateral actions; and
the eradication of poverty. Lastly, just transitions may embody the redressing of past harms and
perceived injustices. (ILO 2015; UNFCCC 2016)
Justice
Justice is concerned with ensuring that people get what is due to them, setting out the moral or legal
principles of fairness and equity in the way people are treated, often based on the ethics and values of
society.
Climate justice
Justice that links development and human rights to achieve a human-centred approach to addressing
climate change, safeguarding the rights of the most vulnerable people and sharing the burdens and
benefits of climate change and its impacts equitably and fairly (MRFCJ 2018).
Kaya identity
In this identity global emissions are equal to the population size, multiplied by per capita output (gross
world product), multiplied by the energy intensity of production, multiplied by the carbon intensity of
energy.
Land
The terrestrial portion of the biosphere that comprises the natural resources (soil, near-surface air,
vegetation and other biota, and water), the ecological processes, topography, and human settlements
and infrastructure that operate within that system (FAO 2007; UNCCD 1994).
Land cover
The biophysical coverage of land (e.g., bare soil, rocks, forests, buildings and roads or lakes). Land
cover is often categorised in broad land-cover classes (e.g., deciduous forest, coniferous forest, mixed
forest, grassland, bare ground). [Note: In some literature, land cover and land use are used
interchangeably, but the two represent distinct classification systems. For example, the land cover class
woodland can be under various land uses such as livestock grazing, recreation, conservation, or wood
harvest.]
Land cover change
Change from one land cover class to another, due to change in land use or change in natural conditions
(Pongratz et al. 2018).
Land degradation
A negative trend in land condition, caused by direct or indirect human-induced processes including
anthropogenic climate change, expressed as long-term reduction or loss of at least one of the following:
biological productivity, ecological integrity or value to humans. [Note: This definition applies to forest
and non-forest land. Changes in land condition resulting solely from natural processes (such as volcanic
eruptions) are not considered to be land degradation. Reduction of biological productivity or ecological
integrity or value to humans can constitute degradation, but any one of these changes need not
necessarily be considered degradation.]
See also Desertification
Land degradation neutrality
A state whereby the amount and quality of land resources necessary to support ecosystem functions and
services and enhance food security remain stable or increase within specified temporal and spatial scales
and ecosystems (UNCCD 2020).
Land management
Sum of land-use practices (e.g., sowing, fertilizing, weeding, harvesting, thinning, clear-cutting) that
take place within broader land-use categories. (Pongratz et al. 2018)
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Land management change
A change in land management that occurs within a land-use category.
Land potential
The inherent, long-term potential of the land to sustainably generate ecosystem services, which reflects
the capacity and resilience of the land-based natural capital, in the face of ongoing environmental
change (UNEP 2016).
Land rehabilitation
Direct or indirect actions undertaken with the aim of reinstating a level of ecosystem functionality,
where the goal is provision of goods and services rather than ecological restoration (McDonald et al.
2016).
Land restoration
The process of assisting the recovery of land from a degraded state (IPBES 2018; McDonald et al.
2016).
Land use
The total of arrangements, activities and inputs applied to a parcel of land. The term land use is also
used in the sense of the social and economic purposes for which land is managed (e.g., grazing, timber
extraction, conservation and city dwelling). In national greenhouse gas (GHG) inventories, land use is
classified according to the IPCC land-use categories of forest land, cropland, grassland, wetlands,
settlements, other lands (see the 2006 IPCC Guidelines for National GHG Inventories and their 2019
Refinement for details (IPCC 2006, 2019)).
Land use, land-use change and forestry (LULUCF)
In the context of national greenhouse gas (GHG) inventories under the United Nations Framework
Convention on Climate Change (UNFCCC 2019), LULUCF is a GHG inventory sector that covers
anthropogenic emissions and removals of GHG in managed lands, excluding non-CO2 agricultural
emissions. Following the 2006 IPCC Guidelines for National GHG Inventories and their 2019
Refinement, ‘anthropogenic’ land-related GHG fluxes are defined as all those occurring on ‘managed
land’, i.e., ‘where human interventions and practices have been applied to perform production,
ecological or social functions’. Since managed land may include carbon dioxide (CO2) removals not
considered as ‘anthropogenic’ in some of the scientific literature assessed in this report (e.g., removals
associated with CO2 fertilisation and N deposition), the land-related net GHG emission estimates from
global models included in this report are not necessarily directly comparable with LULUCF estimates
in National GHG Inventories. (IPCC 2006, 2019)
Land-use change (LUC)
The change from one land use category to another. Note that in some scientific literature, land-use
change encompasses changes in land-use categories as well as changes in land management.
See also Afforestation, Agriculture, Forestry and Other Land Use (AFOLU), Deforestation, Land use,
land-use change and forestry (LULUCF), and Reforestation
Indirect land-use change (iLUC)
Land-use change outside the area of focus that occurs as a consequence of change in use or management
of land within the area of focus, such as through market or policy drivers. For example, if agricultural
land is diverted to biofuel production, forest clearance may occur elsewhere to replace the former
agricultural production.
Latent heat flux
The turbulent flux of heat from the Earth’s surface to the atmosphere that is associated with evaporation
or condensation of water vapour at the surface; a component of the surface energy budget.
Leakage
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The effects of policies that result in a displacement of the environmental impact, thereby counteracting
the intended effects of the initial policies.
Leapfrogging
The ability of developing countries to bypass intermediate technologies and jump straight to advanced
clean technologies.
Lifecycle assessment (LCA)
Compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product
or service throughout its life cycle (ISO 2018).
Likelihood
The chance of a specific outcome occurring, where this might be estimated probabilistically. Likelihood
is expressed in this report using a standard terminology (Mastrandrea et al. 2010).
See also Agreement, Confidence, Evidence, and Uncertainty
Livelihood
The resources used and the activities undertaken in order for people to live. Livelihoods are usually
determined by the entitlements and assets to which people have access. Such assets can be categorised
as human, social, natural, physical or financial.
Local knowledge (LK)
The understandings and skills developed by individuals and populations, specific to the places where
they live. Local knowledge informs decision-making about fundamental aspects of life, from day-to-
day activities to longer term actions. This knowledge is a key element of the social and cultural systems
which influence observations of and responses to climate change; it also informs governance decisions
(UNESCO 2018).
See also Indigenous knowledge
Lock-in
A situation in which the future development of a system, including infrastructure, technologies,
investments, institutions, and behavioural norms, is determined or constrained (‘locked in’) by historic
developments.
See also Path dependence
Long-lived greenhouse gases (LLGHGs)
A set of well-mixed greenhouse gases with long atmospheric lifetimes. This set of compounds includes
carbon dioxide (CO2) and nitrous oxide (N2O), together with some fluorinated gases. They have a
warming effect on climate. These compounds accumulate in the atmosphere at decadal to centennial
timescales, and their effect on climate hence persists for decades to centuries after their emission. On
timescales of decades to a century already emitted emissions of long-lived climate forcers can only be
abated by greenhouse gas removal (GGR).
Loss and Damage, and losses and damages
Research has taken Loss and Damage (capitalised letters) to refer to political debate under the United
Nations Framework Convention on Climate Change (UNFCCC) following the establishment of the
Warsaw Mechanism on Loss and Damage in 2013, which is to ‘address loss and damage associated
with impacts of climate change, including extreme events and slow onset events, in developing
countries that are particularly vulnerable to the adverse effects of climate change.’ Lowercase letters
(losses and damages) have been taken to refer broadly to harm from (observed) impacts and (projected)
risks and can be economic or non-economic (Mechler et al. 2018).
Maladaptive actions (Maladaptation)
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Actions that may lead to increased risk of adverse climate-related outcomes, including via increased
greenhouse gas (GHG) emissions, increased vulnerability to climate change, or diminished welfare,
now or in the future. Maladaptation is usually an unintended consequence.
Malnutrition
Deficiencies, excesses, or imbalances in a person’s intake of energy and/or nutrients. The term
malnutrition addresses three broad groups of conditions: undernutrition, which includes wasting (low
weight-for-height), stunting (low height-for-age) and underweight (low weight-for-age); micronutrient-
related malnutrition, which includes micronutrient deficiencies (a lack of important vitamins and
minerals) or micronutrient excess; and overweight, obesity and diet-related noncommunicable diseases
(such as heart disease, stroke, diabetes and some cancers) (WHO 2018). Micronutrient deficiencies are
sometimes termed ‘hidden hunger’ to emphasise that people can be malnourished in the sense of
deficient without being deficient in calories. Hidden hunger can apply even where people are obese.
Managed forest
Forests subject to human interventions (notably silvicultural management such as planting, pruning,
thinning), timber and fuelwood harvest, protection (fire suppression, insect suppression) and
management for amenity values or conservation, with defined geographical boundaries (Ogle et al.
2018). [Note: For a discussion of the term ‘forest’ in the context of National GHG inventories, see the
2006 IPCC Guidelines for National GHG Inventories (IPCC 2006).]
See also Managed land
Managed grassland
Grasslands on which human interventions are carried out, such as grazing domestic livestock or hay
removal.
Managed land
In the context of national greenhouse gas (GHG) inventories under the United Nations Framework
Convention on Climate Change (UNFCCC), the 2006 IPCC Guidelines for National GHG Inventories
(IPCC, 2006) defines managed land ‘where human interventions and practices have been applied to
perform production, ecological or social functions’. The IPCC (2006) defines anthropogenic GHG
emissions and removals in the LULUCF sector as all those occurring on ‘managed land’. The key
rationale for this approach is that the preponderance of anthropogenic effects occurs on managed lands.
[Note: More details can be found in IPCC 2006 Guidelines for National GHG Inventories, Volume 4,
Chapter 1.]
Market failure
When private decisions are based on market prices that do not reflect the real scarcity of goods and
services but rather reflect market distortions, they do not generate an efficient allocation of resources
but cause welfare losses. A market distortion is any event in which a market reaches a market clearing
price that is substantially different from the price that a market would achieve while operating under
conditions of perfect competition and state enforcement of legal contracts and the ownership of private
property. Examples of factors causing market prices to deviate from real economic scarcity are
environmental externalities, public goods, monopoly power, information asymmetry, transaction costs,
and non-rational behaviour.
Material substitution
Replacement of one material (including an energy carrier used as a feedstock) by another, due to
scarcity, price, technological change, or because of lower environmental impacts or greenhouse gas
emissions.
Measurement, Reporting and Verification (MRV)
Measurement
‘Processes of data collection over time, providing basic datasets, including associated accuracy and
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precision, for the range of relevant variables. Possible data sources are field measurements, field
observations, detection through remote sensing and interviews’ (UN-REDD 2009).
Reporting
‘The process of formal reporting of assessment results to the UNFCCC, according to predetermined
formats and according to established standards, especially the Intergovernmental Panel on Climate
Change (IPCC) Guidelines and GPG (Good Practice Guidance)’ (UN-REDD 2009).
Verification
‘The process of formal verification of reports, for example, the established approach to verify national
communications and national inventory reports to the UNFCCC’ (UN-REDD 2009).
Megacity
Urban agglomerations with 10 million inhabitants or more.
See also City
Methane (CH4)
The greenhouse gas (GHG) methane is the major component of natural gas and associated with all
hydrocarbon fuels. Significant anthropogenic emissions also occur as a result of animal husbandry and
paddy rice production. Methane is also produced naturally where organic matter decays under anaerobic
conditions, such as in wetlands. Under future global warming, there is potential for increased methane
emissions from thawing permafrost, wetlands and sub-sea gas hydrates.
See also Short-lived climate forcers (SLCFs)
Migrant
‘Any person who is moving or has moved across an international border or within a State away from
his/her habitual place of residence, regardless of (1) the person’s legal status; (2) whether the movement
is voluntary or involuntary; (3) what the causes for the movement are; or (4) what the length of the stay
is’ (IOM 2018).
Migration (of humans)
‘Movement of a person or a group of persons, either across an international border, or within a State. It
is a population movement, encompassing any kind of movement of people, whatever its length,
composition and causes; it includes migration of refugees, displaced persons, economic migrants, and
persons moving for other purposes, including family reunification’ (IOM 2018).
Mitigation (of climate change)
A human intervention to reduce emissions or enhance the sinks of greenhouse gases.
Mitigation measures
In climate policy, mitigation measures are technologies, processes or practices that contribute to
mitigation, for example renewable energy technologies, waste minimisation processes, and public
transport commuting practices.
Mitigation option
A technology or practice that reduces greenhouse gas emissions or enhances sinks.
Mitigation pathways
See Pathways
Mitigation potential
The quantity of net greenhouse gas emission reductions that can be achieved by a given mitigation
option relative to specified emission baselines.
[Note: Net greenhouse gas emission reductions is the sum of reduced emissions and/or enhanced sinks.]
See also Sequestration potential
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Biogeophysical potential
The mitigation potential constrained by biological, geophysical and geochemical limits and
thermodynamics, without taking into account technical, social, economic and/or environmental
considerations.
Economic potential
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.
Technical potential
The mitigation potential constrained by biogeophysical limits as well as availability of technologies and
practices. Quantification of technical potentials takes into account primarily technical considerations,
but social, economic and/or environmental considerations are occasionally also included, if these
represent strong barriers for the deployment of an option.
Mitigation scenario
See Scenario
Multilevel governance
See Governance
Narrative
See Storyline
Nature's contributions to people (NCP)
‘All the contributions, both positive and negative, of living nature (i.e., diversity of organisms,
ecosystems, and their associated ecological and evolutionary processes) to the quality of life for people.
Beneficial contributions from nature include such things as food provision, water purification, flood
control, and artistic inspiration, whereas detrimental contributions include disease transmission and
predation that damages people or their assets. Many NCP may be perceived as benefits or detriments
depending on the cultural, temporal or spatial context’ (Díaz et al. 2018)
See also Ecosystem services
Nature-based solutions
'Actions to protect, sustainably manage and restore natural or modified ecosystems that address societal
challenges effectively and adaptively, simultaneously providing human well-being and biodiversity
benefits.' (IUCN 2016)
See also Biodiversity and Ecosystem
Net negative greenhouse gas emissions
A situation of net negative greenhouse gas emissions is achieved when metric-weighted anthropogenic
greenhouse gas (GHG) removals exceed metric-weighted anthropogenic GHG emissions. Where
multiple GHG are involved, the quantification of net emissions depends on the metric chosen to
compare emissions of different gases (such as global warming potential, global temperature change
potential, and others, as well as the chosen time horizon).
See also Carbon dioxide removal (CDR), Greenhouse gas emission metric, Net zero CO2 emissions;
Net zero greenhouse gas emissions, and Negative greenhouse gas emissions
Net zero CO2 emissions
Condition in which anthropogenic carbon dioxide (CO2) emissions are balanced by anthropogenic CO2
removals over a specified period.
[Note: Carbon neutrality and net zero CO2 emissions are overlapping concepts. The concepts can be
applied at global or sub-global scales (e.g., regional, national and sub-national). At a global scale, the
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terms carbon neutrality and net zero CO2 emissions are equivalent. At sub-global scales, net zero CO2
emissions is generally applied to emissions and removals under direct control or territorial responsibility
of the reporting entity, while carbon neutrality generally includes emissions and removals within and
beyond the direct control or territorial responsibility of the reporting entity. Accounting rules specified
by GHG programmes or schemes can have a significant influence on the quantification of relevant CO2
emissions and removals.]
See also Carbon neutrality, Land use, land-use change and forestry (LULUCF) and Net zero
greenhouse gas emissions
Net zero greenhouse gas emissions
Condition in which metric-weighted anthropogenic greenhouse gas (GHG) emissions are balanced by
metric-weighted anthropogenic GHG removals over a specified period. The quantification of net zero
GHG emissions depends on the GHG emission metric chosen to compare emissions and removals of
different gases, as well as the time horizon chosen for that metric.
[Note 1: Greenhouse gas neutrality and net zero GHG emissions are overlapping concepts. The concept
of net zero GHG emissions can be applied at global or sub-global scales (e.g., regional, national and
sub-national). At a global scale, the terms GHG neutrality and net zero GHG emissions are equivalent.
At sub-global scales, net zero GHG emissions is generally applied to emissions and removals under
direct control or territorial responsibility of the reporting entity, while GHG neutrality generally
includes anthropogenic emissions and anthropogenic removals within and beyond the direct control or
territorial responsibility of the reporting entity. Accounting rules specified by GHG programmes or
schemes can have a significant influence on the quantification of relevant emissions and removals.
Note 2. Under the Paris Rulebook (Decision 18/CMA.1, annex, paragraph 37), parties have agreed to
use GWP100 values from the IPCC AR5 or GWP100 values from a subsequent IPCC Assessment
Report to report aggregate emissions and removals of GHGs. In addition, parties may use other metrics
to report supplemental information on aggregate emissions and removals of GHGs.]
See also Greenhouse gas neutrality, Net zero CO2 emissions, and Land use, land-use change and
forestry (LULUCF)
Nitrous oxide (N2O)
The main anthropogenic source of N2O, a greenhouse gas (GHG), is agriculture (soil and animal
manure management), but important contributions also come from sewage treatment, fossil fuel
combustion, and chemical industrial processes. N2O is also produced naturally from a wide variety of
biological sources in soil and water, particularly microbial action in wet tropical forests.
Non-overshoot pathways
See Pathways
Ocean alkalinisation/Ocean alkalinity enhancement
A proposed carbon dioxide removal (CDR) method that involves deposition of alkaline minerals or
their dissociation products at the ocean surface. This increases surface total alkalinity, and may thus
increase ocean carbon dioxide (CO2) uptake and ameliorate surface ocean acidification.
See also Anthropogenic removals
Ocean fertilisation
A proposed carbon dioxide removal (CDR) method that relies on the deliberate increase of nutrient
supply to the near-surface ocean with the aim of sequestering additional CO2 from the atmosphere
through biological production. Methods include direct addition of micro-nutrients or macro-nutrients.
To be successful, the additional carbon needs to reach the deep ocean where it has the potential to be
sequestered on climatically relevant time scales.
See also Anthropogenic removals
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Offset (in climate policy)
The reduction, avoidance or removal of a unit of greenhouse gas (GHG) emissions by one entity,
purchased by another entity to counterbalance a unit of GHG emissions by that other entity. Offsets are
commonly subject to rules and environmental integrity criteria intended to ensure that offsets achieve
their stated mitigation outcome. Relevant criteria include, but are not limited to, the avoidance of double
counting and leakage, use of appropriate baselines, additionality, and permanence or measures to
address impermanence.
See also Greenhouse gas emission metric and Carbon neutrality
Organic farming
An agricultural production system that aims to utilise natural processes and cycles to limit off-farm and
notably synthetic inputs, while also aiming to enhance agroecosystems and society. Organic farming is
often legally defined and governed by standards, typically guided by principles outlined by the
International Federation of Organic Agriculture Movements (IFOAM - Organics International).
(IFOAM-Organics International 2014)
Overshoot pathways
See Pathways
Ozone (O3)
The triatomic form of oxygen, and a gaseous atmospheric constituent. In the troposphere, O3 is created
both naturally and by photochemical reactions involving gases resulting from human activities (e.g.,
smog). Tropospheric O3 acts as a greenhouse gas (GHG). In the stratosphere, O3 is created by the
interaction between solar ultraviolet radiation and molecular oxygen (O2). Stratospheric O3 plays a
dominant role in the stratospheric radiative balance. Its concentration is highest in the ozone layer.
Pareto optimum
A state in which no one's welfare can be increased without reducing someone else's welfare.
Participatory governance
See Governance
Particulate matter (PM)
Very small solid particles emitted during the combustion of biomass and fossil fuels. PM may consist
of a wide variety of substances. Of greatest concern for health are particulates of diameter less than or
equal to 10 nanometers, usually designated as PM10.
Path dependence
The generic situation where decisions, events, or outcomes at one point in time constrain adaptation,
mitigation, or other actions or options at a later point in time.
See also Lock-in
Pathways
The temporal evolution of natural and/or human systems towards a future state. Pathway concepts range
from sets of quantitative and qualitative scenarios or narratives of potential futures to solution-oriented
decision-making processes to achieve desirable societal goals. Pathway approaches typically focus on
biophysical, techno-economic, and/or socio-behavioural trajectories and involve various dynamics,
goals, and actors across different scales.
See also Scenario and Storyline
1.5°C pathway
A pathway of emissions of greenhouse gases and other climate forcers that provides an approximately
one-in-two to two-in-three chance, given current knowledge of the climate response, of global warming
either remaining below 1.5°C or returning to 1.5°C by around 2100 following an overshoot.
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Adaptation pathways
A series of adaptation choices involving trade-offs between short-term and long-term goals and values.
These are processes of deliberation to identify solutions that are meaningful to people in the context of
their daily lives and to avoid potential maladaptation.
Climate-resilient pathways
Iterative processes for managing change within complex systems in order to reduce disruptions and
enhance opportunities associated with climate change.
Development pathways
Development pathways evolve as the result of the countless decisions being made and actions being
taken at all levels of societal structure, as well due to the emergent dynamics within and between
institutions, cultural norms, technological systems and other drivers of behavioural change.
See also Shifting development pathways (SDP) and Shifting development pathways to sustainability
(SDPS)
Emission pathways
Modelled trajectories of global anthropogenic emissions over the 21st century.
Mitigation pathways
A temporal evolution of a set of mitigation scenario features, such as greenhouse gas emissions and
socio-economic development.
Non-overshoot pathways
Pathways that stay below a specified concentration, forcing, or global warming level during a specified
period of time (e.g., until 2100).
Overshoot pathways
Pathways that first exceed a specified concentration, forcing, or global warming level, and then return
to or below that level again before the end of a specified period of time (e.g., before 2100). Sometimes
the magnitude and likelihood of the overshoot is also characterised. The overshoot duration can vary
from one pathway to the next, but in most overshoot pathways in the literature and referred to as
overshoot pathways in the AR6, the overshoot occurs over a period of at least one decade and up to
several decades.
Representative Concentration Pathways (RCPs)
Scenarios that include time series of emissions and concentrations of the full suite of greenhouse gases
(GHGs) and aerosols and chemically active gases, as well as land use/land cover (Moss et al. 2010).
The word representative signifies that each RCP provides only one of many possible scenarios that
would lead to the specific radiative forcing characteristics. The term pathway emphasises that not only
the long-term concentration levels are of interest, but also the trajectory taken over time to reach that
outcome (Moss et al. 2010).
RCPs usually refer to the portion of the concentration pathway extending up to 2100, for which
integrated assessment models produced corresponding emission scenarios. Extended concentration
pathways describe extensions of the RCPs from 2100 to 2300 that were calculated using simple rules
generated by stakeholder consultations, and do not represent fully consistent scenarios. Four RCPs
produced from integrated assessment models were selected from the published literature and used in
the Fifth IPCC Assessment, and are also used in this Assessment for comparison, spanning the range
from approximately below 2°C warming to high (>4°C) warming best-estimates by the end of the 21st
century: RCP2.6, RCP4.5 and RCP6.0 and RCP8.5.
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• RCP2.6: One pathway where radiative forcing peaks at approximately 3 W m –2 and then
declines to be limited at 2.6 W m–2 in 2100 (the corresponding Extended Concentration
Pathway, or ECP, has constant emissions after 2100).
• RCP4.5 and RCP6.0: Two intermediate stabilisation pathways in which radiative forcing is
limited at approximately 4.5 W m–2 and 6.0 W m–2 in 2100 (the corresponding ECPs have
constant concentrations after 2150).
• RCP8.5: One high pathway which leads to >8.5 W m–2 in 2100 (the corresponding ECP has
constant emissions after 2100 until 2150 and constant concentrations after 2250).
See also Shared socio-economic pathways (SSPs) (under Pathways)
Shared Socio-economic Pathways (SSPs)
Shared Socio-economic Pathways (SSPs) have been developed to complement the Representative
Concentration Pathways (RCPs). By design, the RCP emission and concentration pathways were
stripped of their association with a certain socio-economic development. Different levels of emissions
and climate change along the dimension of the RCPs can hence be explored against the backdrop of
different socio-economic development pathways (SSPs) on the other dimension in a matrix. This
integrative SSP-RCP framework is now widely used in the climate impact and policy analysis literature,
where climate projections obtained under the RCP scenarios are analysed against the backdrop of
various SSPs. As several emission updates were due, a new set of emission scenarios was developed in
conjunction with the SSPs. Hence, the abbreviation SSP is now used for two things: On the one hand
SSP1, SSP2, …, SSP5 are used to denote the five socio-economic scenario families. On the other hand,
the abbreviations SSP1-1.9, SSP1-2.6, …, SSP5-8.5 are used to denote the newly developed emission
scenarios that are the result of an SSP implementation within an integrated assessment model. Those
SSP scenarios are bare of climate policy assumption, but in combination with so-called shared policy
assumptions (SPAs), various approximate radiative forcing levels of 1.9, 2.6, …, or 8.5 W m–2 are
reached by the end of the century, respectively.
Transformation pathways
Trajectories describing consistent sets of possible futures of greenhouse gas (GHG) emissions,
atmospheric concentrations, or global mean surface temperatures implied from mitigation and
adaptation actions associated with a set of broad and irreversible economic, technological, societal, and
behavioural changes. This can encompass changes in the way energy and infrastructure are used and
produced, natural resources are managed and institutions are set up and in the pace and direction of
technological change.
Peri-urban areas
Dynamic transition zones that have intense interaction between rural and urban economies, activities,
households, and lifestyles. Neither fully rural or urban. (Seto et al. 2010)
Policies (for climate change mitigation and adaptation)
Strategies that enable actions to be undertaken to accelerate adaptation and mitigation. Policies include
those developed by national and subnational public agencies, and with the private sector. Policies for
adaptation and mitigation often take the form of economic incentives, regulatory instruments, and
decision-making and engagement processes.
Political economy
The set of interlinked relationships between people, the state, society and markets as defined by law,
politics, economics, customs and power that determine the outcome of trade and transactions and the
distribution of wealth in a country or economy.
Pool, carbon and nitrogen
A reservoir in the Earth System where elements, such as carbon and nitrogen, reside in various chemical
forms for a period of time. See also Sequestration, Sink, Source and Uptake
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Poverty
A complex concept with several definitions stemming from different schools of thought. It can refer to
material circumstances (such as need, pattern of deprivation or limited resources), economic conditions
(such as standard of living, inequality or economic position) and/or social relationships (such as social
class, dependency, exclusion, lack of basic security or lack of entitlement).
Poverty eradication
A set of measures to end poverty in all its forms everywhere.
See also Sustainable Development Goals (SDGs)
Precursors
Atmospheric compounds that are not greenhouse gases (GHGs) or aerosols, but that have an effect on
GHG or aerosol concentrations by taking part in physical or chemical processes regulating their
production or destruction rates.
Pre-industrial (period)
The multi-century period prior to the onset of large-scale industrial activity around 1750. The reference
period 1850–1900 is used to approximate pre-industrial global mean surface temperature (GMST).
See also Industrial revolution
Primary energy
The energy that is embodied in resources as they exist in nature (e.g., coal, biomass uranium, solar
radiation, wind, ocean currents) (Grubler et al. 2012).
[Note: Primary energy is defined in several alternative ways. The method used in this report is the direct
equivalent method, which counts one unit of secondary energy provided from non-combustible sources
as one unit of primary energy. For more details on the methodology, see Section 7 in Working Group
III Annex II.]
See also Final energy
Primary production
The synthesis of organic compounds by plants and microbes, on land or in the ocean, primarily by
photosynthesis using light and carbon dioxide (CO2) as sources of energy and carbon respectively. It
can also occur through chemosynthesis, using chemical energy, for example, in deep sea vents.
Private costs
Costs carried by individuals, companies or other private entities that undertake an action, whereas social
costs include additionally the external costs on the environment and on society as a whole. Quantitative
estimates of both private and social costs may be incomplete, because of difficulties in measuring all
relevant effect.
Production-based emissions
Emissions released to the atmosphere for the production of goods and services by a certain entity (e.g.,
a person, firm, country, or region).
See also Consumption-based emissions
Projection
A potential future evolution of a quantity or set of quantities, often computed with the aid of a model.
Unlike predictions, projections are conditional on assumptions concerning, for example, future socio-
economic and technological developments that may or may not be realised.
See also Climate projection, Pathways and Scenario
Prosumers
A consumer that also produces energy and inputs energy to the system, for which it is an active agent
in the energy system and market.
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Radiative forcing
The change in the net, downward minus upward, radiative flux (expressed in W m –2) due to a change
in an external driver of climate change, such as a change in the concentration of carbon dioxide (CO2),
the concentration of volcanic aerosols or in the output of the Sun. The stratospherically adjusted
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 both stratospheric and tropospheric adjustments are accounted
for is termed the effective radiative forcing.
Rebound effect
Phenomena whereby the reduction in energy consumption or emissions (relative to a baseline)
associated with the implementation of mitigation measures in a jurisdiction is offset to some degree
through induced changes in consumption, production, and prices within the same jurisdiction. The
rebound effect is most typically ascribed to technological energy efficiency improvements.
Reducing Emissions from Deforestation and Forest Degradation (REDD+)
REDD+ refers to reducing emissions from deforestation; reducing emissions from forest degradation;
conservation of forest carbon stocks; sustainable management of forests; and enhancement of forest
carbon stocks (see UNFCCC decision 1/CP.16, para. 70).
Reference period
A time period of interest, or a period over which some relevant statistics are calculated. A reference
period can be used as a baseline period or as a comparison to a baseline period.
Baseline period
A time period against which differences are calculated (e.g., expressed as anomalies relative to a
baseline)
Reference scenario
See Scenario
Reforestation
Conversion to forest of land that has previously contained forests but that has been converted to some
other use. [Note: For a discussion of the term forest and related terms such as afforestation, reforestation
and deforestation, see the 2006 IPCC Guidelines for National Greenhouse Gas Inventories and their
2019 Refinement, and information provided by the United Nations Framework Convention on Climate
Change (IPCC 2006, 2019; UNFCCC 2021a,b).]
See also Anthropogenic removals, Carbon dioxide removal (CDR) and Reducing Emissions from
Deforestation and Forest Degradation (REDD+)
Regenerative agriculture
A universally agreed definition of this relatively new farming approach has yet to be established, but
regenerative agriculture broadly refers to the implementation of varying combinations of agricultural
management practices, to ensure the continued restoration and enhancement of soil health, biodiversity
and ecosystem functioning, in conjunction with profitable agricultural production.
Region
Land and/or ocean area characterised by specific geographical and/or climatological features. The
climate of a region emerges from a multi-scale combination of its own features, remote influences from
other regions, and global climate conditions.
Remaining carbon budget
See Carbon budget
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Renewable energy (RE)
Any form of energy that is replenished by natural processes at a rate that equals or exceeds its rate of
use.
Variable renewable energy (VRE)
Renewable energy sources such as wind and solar energy whose output is determined by weather, in
contrast to ‘dispatchable’ generators that adjust their output as a reaction to economic incentives.
Variable renewables have also been termed intermittent, fluctuating, or non-dispatchable. (Hirth 2013)
Representative Concentration Pathways (RCPs)
See Pathways
Resilience
The capacity of interconnected social, economic and ecological systems to cope with a hazardous event,
trend or disturbance, responding or reorganising in ways that maintain their essential function, identity
and structure. Resilience is a positive attribute when it maintains capacity for adaptation, learning
and/or transformation (Arctic Council 2016).
See also Hazard, Risk and Vulnerability
Resource cascade
Tracking resource use (materials, energy, water, etc.), efficiency and losses through all conversion steps
from primary resource extraction to various conversion steps, all the way to final service delivery.
Risk
The potential for adverse consequences for human or ecological systems, recognising the diversity of
values and objectives associated with such systems. In the context of climate change, risks can arise
from potential impacts of climate change as well as human responses to climate change. Relevant
adverse consequences include those on lives, livelihoods, health and well-being, economic, social and
cultural assets and investments, infrastructure, services (including ecosystem services), ecosystems and
species.
In the context of climate change impacts, risks result from dynamic interactions between climate-related
hazards with the exposure and vulnerability of the affected human or ecological system to the hazards.
Hazards, exposure and vulnerability may each be subject to uncertainty in terms of magnitude and
likelihood of occurrence, and each may change over time and space due to socio-economic changes and
human decision-making (see also risk management, adaptation and mitigation).
In the context of climate change responses, risks result from the potential for such responses not
achieving the intended objective(s), or from potential trade-offs with, or negative side-effects on, other
societal objectives, such as the Sustainable Development Goals (SDGs) (see also risk trade-off). Risks
can arise, for example, from uncertainty in implementation, effectiveness or outcomes of climate policy,
climate-related investments, technology development or adoption, and system transitions.
See also Hazard and Impacts
Risk assessment
The qualitative and/or quantitative scientific estimation of risks.
See also Risk management and Risk perception
Risk management
Plans, actions, strategies or policies to reduce the likelihood and/or magnitude of adverse potential
consequences, based on assessed or perceived risks.
See also Risk assessment, Risk perception and Risk transfer
Risk perception
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The subjective judgement that people make about the characteristics and severity of a risk.
See also Risk assessment, Risk management, and Risk transfer
Risk trade-off
The change in the portfolio of risks that occurs when a countervailing risk is generated (knowingly or
inadvertently) by an intervention to reduce the target risk (Wiener and Graham 2009).
Sea surface temperature (SST)
The subsurface bulk temperature in the top few metres of the ocean, measured by ships, buoys and
drifters. From ships, measurements of water samples in buckets were mostly switched in the 1940s to
samples from engine intake water. Satellite measurements of skin temperature (uppermost layer; a
fraction of a millimetre thick) in the infrared or the top centimetre or so in the microwave are also used,
but must be adjusted to be compatible with the bulk temperature.
Scenario
A plausible 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 technological change, prices) and relationships.
Note that scenarios are neither predictions nor forecasts, but are used to provide a view of the
implications of developments and actions.
Baseline scenario
See Reference Scenario (under Scenario)
Concentrations scenario
A plausible representation of the future development of atmospheric concentrations of substances that
are radiatively active (e.g., greenhouse gases, aerosols, tropospheric ozone), plus human-induced land
cover changes that can be radiatively active via albedo changes, and often used as input to a climate
model to compute climate projections.
Emissions scenario
A plausible representation of the future development of emissions of substances that are radiatively
active (e.g., greenhouse gases or aerosols), plus human-induced land-cover changes that can be
radiatively active via albedo changes, based on a coherent and internally consistent set of assumptions
about driving forces (such as demographic and socio-economic development, technological change,
energy and land use) and their key relationships. Concentration scenarios, derived from emission
scenarios, are often used as input to a climate model to compute climate projections.
Mitigation scenario
A plausible description of the future that describes how the (studied) system responds to the
implementation of mitigation policies and measures.
Reference scenario
Scenario used as starting or reference point for a comparison between two or more scenarios.
[Note 1: In many types of climate change research, reference scenarios reflect specific assumptions
about patterns of socio-economic development and may represent futures that assume no climate
policies or specified climate policies, for example those in place or planned at the time a study is carried
out. Reference scenarios may also represent futures with limited or no climate impacts or adaptation, to
serve as a point of comparison for futures with impacts and adaptation. These are also referred to as
baseline scenarios in the literature.
Note 2: Reference scenarios can also be climate policy or impact scenarios, which in that case are taken
as a point of comparison to explore the implications of other features, for example, of delay,
technological options, policy design and strategy or to explore the effects of additional impacts and
adaptation beyond those represented in the reference scenario.
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Note 3: The term business as usual scenario has been used to describe a scenario that assumes no
additional policies beyond those currently in place and that patterns of socio-economic development
are consistent with recent trends. The term is now used less frequently than in the past.
Note 4: In climate change attribution or impact attribution research reference scenarios may refer to
counterfactual historical scenarios assuming no anthropogenic greenhouse gas (GHG) emissions
(climate change attribution) or no climate change (impact attribution).]
Socio-economic scenario
A scenario that describes a plausible future in terms of population, gross domestic product (GDP), and
other socio-economic factors relevant to understanding the implications of climate change.
Scenario storyline
See Storyline
Sequestration
The process of storing carbon in a carbon pool.
See also Pool, carbon and nitrogen, Sequestration potential, Sink, Soil carbon sequestration (SCS),
Source, and Uptake
Sequestration potential
The quantity of greenhouse gases that can be removed from the atmosphere by anthropogenic
enhancement of sinks and stored in a pool. See Mitigation potential for different subcategories of
sequestration potential.
See also Pool, carbon and nitrogen, Sequestration, Sink, Source, and Uptake
Service provisioning
Various services (such as illumination and mobility) can be provided by ‘systems’ through the use of
energy, materials, and other resources comprising 1) Resource flows (e.g., energy), 2) Technologies for
resource use and energy conversion (e.g., vehicles and their engines), and 3) Social/organisational forms
of service delivery (e.g., publicly owned companies, or privately owned companies, e-commerce).
Services
Activities that help satisfy human wants or needs. While they usually involve relationships between
producers and consumers, services are less tangible and less storable than goods since they represent
flows not stocks, and when their regeneration conditions are protected they may be reused over time.
Settlements
Places of concentrated human habitation. Settlements can range from isolated rural villages to urban
regions with significant global influence. They can include formally planned and informal or illegal
habitation and related infrastructure.
See also Cities and Urban
Shared policy assumptions (SPAs)
See Shared Socio-economic Pathways (SSPs)
Sharing economy
A system which allows people to share goods and services by enabling collaborative use, access or
ownership.
Shared Socio-economic Pathways (SSPs)
See Pathways
Shifting development pathways (SDP)
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In this report, shifting development pathways describes transitions aimed at re-directing existing
developmental trends. Societies may put in place enabling conditions to influence their future
development pathways, when they endeavour to achieve certain outcomes. Some outcomes may be
common, while others may be context-specific, given different starting points.
See also Development pathways (under Pathways), and Shifting development pathways to sustainability
Shifting development pathways to sustainability
Shifting development pathways to sustainability involves transitions aligned with a shared aspiration in
the Sustainable Development Goals (SDGs) agreed globally, though sustainability may be interpreted
differently in various contexts as societies pursue a variety of sustainable development objectives.
See also Development pathways (under Pathways), and Shifting development pathways (SDP)
Short-lived climate forcers (SLCFs)
A set of chemically reactive compounds with short (relative to carbon dioxide) atmospheric lifetimes
(from hours to about two decades) but characterised by different physiochemical properties and
environmental effects. Their emission or formation has a significant effect on radiative forcing over a
period determined by their respective atmospheric lifetimes. Changes in their emissions can also induce
long-term climate effects via, in particular, their interactions with some biogeochemical cycles. SLCFs
are classified as direct or indirect, with direct SLCFs exerting climate effects through their radiative
forcing and indirect SLCFs being the precursors of other direct climate forcers. Direct SLCFs include
methane (CH4), ozone (O3), primary aerosols and some halogenated species. Indirect SLCFs are
precursors of ozone or secondary aerosols. SLCFs can be cooling or warming through interactions with
radiation and clouds. They are also referred to as near-term climate forcers. Many SLCFs are also air
pollutants. A subset of exclusively warming SLCFs is also referred to as short-lived climate pollutants
(SLCPs), including methane, ozone, and black carbon (BC).
Short-lived climate pollutants (SLCP)
See Short-lived climate forcers
Simple climate model (SCM)
A broad class of lower-dimensional models of the energy balance, radiative transfer, carbon cycle, or a
combination of such physical components. SCMs are also suitable for performing emulations of
climate-mean variables of Earth system models (ESMs), given that their structural flexibility can
capture both the parametric and structural uncertainties across process-oriented ESM responses. They
can also be used to test consistency across multiple lines of evidence with regard to climate sensitivity
ranges, transient climate responses (TCRs), transient climate response to cumulative CO2 emissions
(TCREs) and carbon cycle feedbacks.
See also Emulators
Sink
Any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a
greenhouse gas from the atmosphere (UNFCCC Article 1.8 (UNFCCC 1992)).
See also Pool, carbon and nitrogen, Sequestration, Source and Uptake
Small Island Developing States (SIDS)
Small Island Developing States (SIDS), as recognised by the United Nations OHRLLS (UN Office of
the High Representative for the Least Developed Countries, Landlocked Developing Countries and
Small Island Developing States), are a distinct group of developing countries facing specific social,
economic and environmental vulnerabilities (UN-OHRLLS 2011). They were recognised as a special
case both for their environment and development at the Rio Earth Summit in Brazil in 1992. Fifty-eight
countries and territories are presently classified as SIDS by the UN OHRLLS, with 38 being UN
member states and 20 being Non-UN Members or Associate Members of the Regional Commissions
(UN-OHRLLS 2018).
Smart grids
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A smart grid uses information and communications technology to gather data on the behaviours of
suppliers and consumers in the production, distribution, and use of electricity. Through automated
responses or the provision of price signals, this information can then be used to improve the efficiency,
reliability, economics, and sustainability of the electricity network.
Social cost of carbon (SCC)
The net present value of aggregate climate damages (with overall harmful damages expressed as a
number with positive sign) from one more tonne of carbon in the form of carbon dioxide (CO2),
conditional on a global emissions trajectory over time.
Social costs
The full costs of an action in terms of social welfare losses, including external costs associated with the
impacts of this action on the environment, the economy (GDP, employment) and on the society as a
whole.
Social group
A collective of people who share similar characteristics and collectively may have a sense of unity
(Forsyth 2010).
Social identity
The portion of an individual's self-concept derived from perceived membership in a relevant social
group (Tajfel and Turner 1986).
Social inclusion
A process of improving the terms of participation in society, particularly for people who are
disadvantaged, through enhancing opportunities, access to resources, and respect for rights (UNDESA
2018).
Social infrastructure
See Infrastructure
Social learning
A process of social interaction through which people learn new behaviours, capacities, values, and
attitudes.
Social-ecological system
An integrated system that includes human societies and ecosystems, in which humans are part of nature.
The functions of such a system arise from the interactions and interdependence of the social and
ecological subsystems. The system’s structure is characterised by reciprocal feedbacks, emphasising
that humans must be seen as a part of, not apart from, nature (Berkes and Folke 1998; Arctic Council
2016).
Socio-economic scenario
See Scenario
Socio-technical transitions
Where technological change is associated with social systems and the two are inextricably linked.
Soil carbon sequestration (SCS)
Land management changes which increase the soil organic carbon content, resulting in a net removal
of carbon dioxide (CO2) from the atmosphere.
See also Anthropogenic removals and Carbon dioxide removal (CDR)
Soil organic carbon
Carbon contained in soil organic matter.
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Soil organic matter
The organic component of soil, comprising plant and animal residue at various stages of decomposition,
and soil organisms.
Solar energy
Energy from the sun. Often the phrase is used to mean energy that is captured from solar radiation either
as heat, as light that is converted into chemical energy by natural or artificial photosynthesis, or by
photovoltaic panels and converted directly into electricity.
See also Renewable energy
Solar radiation modification (SRM)
Refers to a range of radiation modification measures not related to greenhouse gas (GHG) mitigation
that seek to limit global warming. Most methods involve reducing the amount of incoming solar
radiation reaching the surface, but others also act on the longwave radiation budget by reducing optical
thickness and cloud lifetime.
Source
Any process or activity which releases a greenhouse gas (GHG), an aerosol or a precursor of a GHG
into the atmosphere (UNFCCC Article 1.9 (UNFCCC 1992)).
See also Sink, Pool, carbon and nitrogen, Sequestration, Sequestration Potential and Uptake
Spill-over effect
The effects of domestic or sector mitigation measures on other countries or sectors. Spill-over effects
can be positive or negative and include effects on trade, (carbon) leakage, transfer of innovations, and
diffusion of environmentally sound technology and other issues.
Storyline
A way of making sense of a situation or a series of events through the construction of a set of explanatory
elements. Usually, it is built on logical or causal reasoning. In climate research, the term storyline is
used both in connection to scenarios as related to a future trajectory of the climate and human systems
or to a weather or climate event. In this context, storylines can be used to describe plural, conditional
possible futures or explanations of a current situation, in contrast to single, definitive futures or
explanations.
Scenario storyline
A narrative description of a scenario (or family of scenarios), highlighting the main scenario
characteristics, relationships between key driving forces and the dynamics of their evolution.
Stranded assets
Assets exposed to devaluations or conversion to ‘liabilities’ because of unanticipated changes in their
initially expected revenues due to innovations and/or evolutions of the business context, including
changes in public regulations at the domestic and international levels.
Subnational actors
State/provincial, regional, metropolitan and local/municipal governments as well as non-party
stakeholders, such as civil society, the private sector, cities and other subnational authorities, local
communities and indigenous peoples.
Sufficiency
In this report, sufficiency refers to avoiding the demand for materials and energy while delivering a
decent living standard for all within planetary boundaries.
Sustainability
A dynamic process that guarantees the persistence of natural and human systems in an equitable manner.
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Sustainable development (SD)
Development that meets the needs of the present without compromising the ability of future generations
to meet their own needs (WCED 1987) and balances social, economic and environmental concerns.
See also Development pathways and Sustainable Development Goals (SDGs)
Sustainable Development Goals (SDGs)
The 17 global goals for development for all countries established by the United Nations through a
participatory process and elaborated in the 2030 Agenda for Sustainable Development, including ending
poverty and hunger; ensuring health and wellbeing, education, gender equality, clean water and energy,
and decent work; building and ensuring resilient and sustainable infrastructure, cities and consumption;
reducing inequalities; protecting land and water ecosystems; promoting peace, justice and partnerships;
and taking urgent action on climate change.
See also Sustainable development
Sustainable forest management
The stewardship and use of forests and forest lands in a way, and at a rate, that maintains their
biodiversity, productivity, regeneration capacity, vitality and their potential to fulfil, now and in the
future, relevant ecological, economic and social functions, at local, national, and global levels, and that
does not cause damage to other ecosystems (Forest Europe 1993).
Sustainable intensification (of agriculture)
Increasing yields from the same area of land while decreasing negative environmental impacts of
agricultural production and increasing the provision of environmental services (CGIAR 2019).
[Note: this definition is based on the concept of meeting demand from a finite land area, but it is scale-
dependent. Sustainable intensification at a given scale (e.g., global or national) may require a decrease
in production intensity at smaller scales and in particular places (often associated with previous,
unsustainable, intensification) to achieve sustainability (Garnett et al. 2013).]
Sustainable land management
The stewardship and use of land resources, including soils, water, animals and plants, to meet changing
human needs, while simultaneously ensuring the long-term productive potential of these resources and
the maintenance of their environmental functions. (WOCAT)
Systems of Innovation (SI)
The set of public and private sector organisations (i.e., formally organised entities such as firms and
universities; ‘actors’) and institutions, whose activities and interactions generate, modify and deploy
new technologies. The SI approach has been used to understand and analyse innovation at the national,
regional, and technological levels, and in transnational contexts. (Lundvall 1992, 1988)
Technology deployment
The act of bringing technology into effective application, involving a set of actors and activities to
initiate, facilitate and/or support its implementation.
See also Technology diffusion
Technology diffusion
The spread of a technology across different groups users/markets over time.
See also Technology deployment and Technology transfer
Technology transfer
The exchange of knowledge, hardware and associated software, money and goods among stakeholders,
which leads to the spread of technology for adaptation or mitigation. The term encompasses both
diffusion of technologies and technological cooperation across and within countries.
See also Technology diffusion
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Teleconnection
Association between climate variables at widely separated, geographically fixed locations related to
each other through physical processes and oceanic and/or atmospheric dynamical pathways.
Teleconnections can be caused by several climate phenomena, such as Rossby wave-trains, mid-latitude
jet and storm track displacements, fluctuations of the Atlantic Meridional Overturning Circulation
(AMOC), fluctuations of the Walker circulation, etc. They can be initiated by modes of climate
variability, thus providing the development of remote climate anomalies at various temporal lags.
Temperature overshoot
Exceedance of a specified global warming level, followed by a decline to or below that level during a
specified period of time (e.g., before 2100). Sometimes the magnitude and likelihood of the overshoot
is also characterised. The overshoot duration can vary from one pathway to the next, but in most
overshoot pathways in the literature and as referred to as overshoot pathways in the AR6, the overshoot
occurs over a period of at least one decade and up to several decades.
Tipping point
A critical threshold beyond which a system reorganises, often abruptly and/or irreversibly.
See also Irreversibility
Total carbon budget
See Carbon budget
Trade-off
A competition between different objectives within a decision situation, where pursuing one objective
will diminish achievement of other objective(s). A trade-off exists when a policy or measure aimed at
one objective (e.g., reducing greenhouse gas emissions) reduces outcomes for other objective(s) (e.g.,
biodiversity conservation, energy security) due to adverse side effects, thereby potentially reducing the
net benefit to society or the environment.
See also Co-benefit
Transformation pathways
See Pathways
Transient climate response (TCR)
See Climate sensitivity
Transient climate response to cumulative CO2 emissions (TCRE)
See Climate sensitivity
Transformation
A change in the fundamental attributes of natural and human systems.
Transition
The process of changing from one state or condition to another in a given period of time. Transition can
occur in individuals, firms, cities, regions and nations, and can be based on incremental or
transformative change.
Uncertainty
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, incomplete understanding of critical processes, or
uncertain projections of human behaviour. Uncertainty can therefore be represented by quantitative
measures (e.g., a probability density function) or by qualitative statements (e.g., reflecting the
judgement of a team of experts) (Moss and Schneider 2000; Mastrandrea et al. 2010).
See also Confidence and Likelihood
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United Nations Convention to Combat Desertification (UNCCD)
A legally binding international agreement linking environment and development to sustainable land
management, established in 1994. The Convention’s objective is ‘to combat desertification and mitigate
the effects of drought in countries experiencing drought and/or desertification’. The Convention
specifically addresses the arid, semi-arid and dry sub-humid areas, known as the drylands, and has a
particular focus on Africa. As of September 2020, the UNCCD had 197 Parties.
See also Desertification, Drought and Land degradation
United Nations Framework Convention on Climate Change (UNFCCC)
The UNFCCC was adopted in May 1992 and opened for signature at the 1992 Earth Summit in Rio de
Janeiro. It entered into force in March 1994 and as of September 2020 had 197 Parties (196 States and
the European Union). The Convention’s ultimate objective is the ‘stabilisation of greenhouse gas
concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference
with the climate system’ (UNFCCC, 1992). The provisions of the Convention are pursued and
implemented by two further treaties: the Kyoto Protocol and the Paris Agreement.
Uptake
The transfer of substances (such as carbon) or energy (e.g., heat) from one compartment of a system to
another; for example, in the Earth system from the atmosphere to the ocean or to the land.
See also Pool, carbon and nitrogen, Sequestration, Sequestration potential, Sink and Source
Urban
The categorisation of areas as ‘urban’ by government statistical departments is generally based either
on population size, population density, economic base, provision of services, or some combination of
the above. Urban systems are networks and nodes of intensive interaction and exchange including
capital, culture, and material objects. Urban areas exist on a continuum with rural areas and tend to
exhibit higher levels of complexity, higher populations and population density, intensity of capital
investment, and a preponderance of secondary (processing) and tertiary (service) sector industries. The
extent and intensity of these features varies significantly within and between urban areas. Urban places
and systems are open with much movement and exchange between more rural areas as well as other
urban regions. Urban areas can be globally interconnected facilitating rapid flows between them – of
capital investment, of ideas and culture, human migration, and disease.
See also Cities, Peri-urban areas, and Urbanisation
Urban heat island
The relative warmth of a city compared with surrounding rural areas, associated with heat trapping due
to land use, the configuration and design of the built environment, including street layout and building
size, the heat-absorbing properties of urban building materials, reduced ventilation, reduced greenery
and water features, and domestic and industrial heat emissions generated directly from human activities.
See also City region, Urban, and Urban System
Urban Systems
Urban systems refer to two interconnected systems: first, the comprehensive collections of city elements
with multiple dimensions and characteristics: a) encompass physical, built, socio-economic-technical,
political, and ecological subsystems; b) integrate social agent/constituency/processes with physical
structure and processes; and c) exist within broader spatial and temporal scales and governance and
institutional contexts; and second, the global system of cities and towns.
See also City region, Urban and Urban areas
Urbanisation
Urbanisation is a multi-dimensional process that involves at least three simultaneous changes: 1) land
use change: transformation of formerly rural settlements or natural land into urban settlements; 2)
demographic change: a shift in the spatial distribution of a population from rural to urban areas; and 3)
infrastructure change: an increase in provision of infrastructure services including electricity, sanitation,
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etc. Urbanisation often includes changes in lifestyle, culture, and behaviour, and thus alters the
demographic, economic, and social structure of both urban and rural areas. (Stokes and Seto 2019; Seto
et al. 2014; UNDESA 2018)
See also Urban, Urban areas, and Urban Systems
Variable renewable energy (VRE)
See Renewable energy
Vulnerability
The propensity or predisposition to be adversely affected. Vulnerability encompasses a variety of
concepts and elements including sensitivity or susceptibility to harm and lack of capacity to cope and
adapt.
See also Exposure, Hazard and Risk
Well-being
A state of existence that fulfils various human needs, including material living conditions, meaningful
social and community relationships and quality of life, as well as the ability to pursue one’s goals, to
thrive, and feel satisfied with one’s life. Ecosystem well-being refers to the ability of ecosystems to
maintain their diversity and quality.
Eudaimonic
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).
Hedonic
Subjective well-being concept based on the idea that attaining pleasure and avoiding pain leads to
happiness (Ryan and Deci 2001).
Wind energy
Kinetic energy from airflow arising from the uneven heating of the Earth's surface. The wind's kinetic
energy is converted to mechanical shaft energy and electricity by a wind turbine, a rotating machine. A
wind farm, wind project, wind park, or wind power plant is a group of wind turbines interconnected to
a common utility system through a system of transformers, distribution lines, and (usually) one
substation.
See also Renewable energy
Zero emissions commitment
See Climate change commitment
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