Serge Planton (France)
Annex III: Glossary
This annex should be cited as:
IPCC, 2013: Annex III: Glossary [Planton, S. (ed.)]. In: Climate Change 2013: The Physical Science Basis. Contribution
of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F.,
D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge
University Press, Cambridge, United Kingdom and New York, NY, USA.
Annex III Glossary
This glossary defines some specific terms as the Lead Authors intend
them to be interpreted in the context of this report. Red, italicized
words indicate that the term is defined in the Glossary.
Abrupt climate change A large-scale change in the climate system
that takes place over a few decades or less, persists (or is anticipated to
persist) for at least a few decades and causes substantial disruptions in
human and natural systems.
Active layer The layer of ground that is subject to annual thawing and
freezing in areas underlain by permafrost.
Adjustment time See Lifetime. See also Response time.
Advection Transport of water or air along with its properties (e.g., tem-
perature, chemical tracers) by winds or currents. Regarding the general
distinction between advection and convection, the former describes trans-
port by large-scale motions of the atmosphere or ocean, while convection
describes the predominantly vertical, locally induced motions.
Aerosol A suspension of airborne solid or liquid particles, with a typical
size between a few nanometres and 10 μm that reside in the atmosphere
for at least several hours. For convenience 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. Aerosols may influence climate in several ways:
directly through scattering and absorbing radiation (see Aerosol–radiation
interaction) and indirectly by acting as cloud condensation nuclei or ice
nuclei, modifying the optical properties and lifetime of clouds (see Aero-
sol–cloud interaction).
Aerosol–cloud interaction A process by which a perturbation to
aerosol affects the microphysical properties and evolution of clouds
through the aerosol role as cloud condensation nuclei or ice nuclei, par-
ticularly in ways that affect radiation or precipitation; such processes can
also include the effect of clouds and precipitation on aerosol. The aerosol
perturbation can be anthropogenic or come from some natural source. The
radiative forcing from such interactions has traditionally been attributed
to numerous indirect aerosol effects, but in this report, only two levels of
radiative forcing (or effect) are distinguished:
Radiative forcing (or effect) due to aerosol–cloud interactions
(RFaci) The radiative forcing (or radiative effect, if the perturbation is
internally generated) due to the change in number or size distribution
of cloud droplets or ice crystals that is the proximate result of an aero-
sol perturbation, with other variables (in particular total cloud water
content) remaining equal. In liquid clouds, an increase in cloud droplet
concentration and surface area would increase the cloud albedo. This
effect is also known as the cloud albedo effect, first indirect effect, or
Twomey effect. It is a largely theoretical concept that cannot readily be
isolated in observations or comprehensive process models due to the
rapidity and ubiquity of rapid adjustments.
Effective radiative forcing (or effect) due to aerosol–cloud inter-
actions (ERFaci) The final radiative forcing (or effect) from the aero-
sol perturbation including the rapid adjustments to the initial change
in droplet or crystal formation rate. These adjustments include changes
in the strength of convection, precipitation efficiency, cloud fraction,
lifetime or water content of clouds, and the formation or suppression
of clouds in remote areas due to altered circulations.
The total effective radiative forcing due to both aerosol–cloud and
aerosol–radiation interactions is denoted aerosol effective radiative
forcing (ERFari+aci). See also Aerosol–radiation interaction.
Aerosol–radiation interaction An interaction of aerosol directly
with radiation produce radiative effects. In this report two levels of radia-
tive forcing (or effect) are distinguished:
Radiative forcing (or effect) due to aerosol–radiation interac-
tions (RFari) The radiative forcing (or radiative effect, if the pertur-
bation is internally generated) of an aerosol perturbation due directly
to aerosol–radiation interactions, with all environmental variables
remaining unaffected. Traditionally known in the literature as the direct
aerosol forcing (or effect).
Effective radiative forcing (or effect) due to aerosol-radiation
interactions (ERFari) The final radiative forcing (or effect) from
the aerosol perturbation including the rapid adjustments to the ini-
tial change in radiation. These adjustments include changes in cloud
caused by the impact of the radiative heating on convective or larger-
scale atmospheric circulations, traditionally known as semi-direct aero-
sol forcing (or effect).
The total effective radiative forcing due to both aerosol–cloud and
aerosol–radiation interactions is denoted aerosol effective radiative
forcing (ERFari+aci). See also Aerosolcloud interaction.
Afforestation Planting of new forests on lands that historically have
not contained forests. For a discussion of the term forest and related terms
such as afforestation, reforestation and deforestation, see the IPCC Special
Report on Land Use, Land-Use Change and Forestry (IPCC, 2000). See also
the report on Definitions and Methodological Options to Inventory Emis-
sions from Direct Human-induced Degradation of Forests and Devegeta-
tion of Other Vegetation Types (IPCC, 2003).
Airborne fraction The fraction of total CO
emissions (from fossil fuel
and land use change) remaining in the atmosphere.
Air mass A widespread body of air, the approximately homogeneous
properties of which (1) have been established while that air was situated
over a particular region of the Earth’s surface, and (2) undergo specific
modifications while in transit away from the source region (AMS, 2000).
Albedo The fraction of solar radiation reflected by a surface or object,
often expressed as a percentage. Snow-covered surfaces have a high
albedo, the albedo of soils ranges from high to low, and vegetation-cov-
ered surfaces and oceans have a low albedo. The Earth’s planetary albedo
varies mainly through varying cloudiness, snow, ice, leaf area and and
cover changes.
Alkalinity A measure of the capacity of an aqueous solution to neutral-
ize acids.
Altimetry A technique for measuring the height of the Earth’s surface
with respect to the geocentre of the Earth within a defined terrestrial refer-
ence frame (geocentric sea level).
Annular modes See Northern Annular Mode (NAM) and Southern
Annular Mode (SAM).
Anthropogenic Resulting from or produced by human activities.
Atlantic Multi-decadal Oscillation/Variability (AMO/AMV) A
multi-decadal (65- to 75-year) fluctuation in the North Atlantic, in which
sea surface temperatures showed warm phases during roughly 1860 to
1880 and 1930 to 1960 and cool phases during 1905 to 1925 and 1970 to
1990 with a range of approximately 0.4°C. See AMO Index, Box 2.5.
Atmosphere The gaseous envelope surrounding the Earth. The dry
atmosphere consists almost entirely of nitrogen (78.1% volume mixing
ratio) and oxygen (20.9% volume mixing ratio), together with a number
of trace gases, such as argon (0.93% volume mixing ratio), helium and
radiatively active greenhouse gases such as carbon dioxide (0.035%
Glossary Annex III
volume mixing ratio) and ozone. In addition, the atmosphere contains the
greenhouse gas water vapour, whose amounts are highly variable but typi-
cally around 1% volume mixing ratio. The atmosphere also contains clouds
and aerosols.
Atmosphere–Ocean General Circulation Model (AOGCM) See
Climate model.
Atmospheric boundary layer The atmospheric layer adjacent to the
Earth’s surface that is affected by friction against that boundary surface,
and possibly by transport of heat and other variables across that surface
(AMS, 2000). The lowest 100 m of the boundary layer (about 10% of the
boundary layer thickness), where mechanical generation of turbulence is
dominant, is called the surface boundary layer or surface layer.
Atmospheric lifetime See Lifetime.
Attribution See Detection and attribution.
Autotrophic respiration Respiration by photosynthetic (see photo-
synthesis) organisms (e.g., plants and algaes).
Basal lubrication Reduction of friction at the base of an ice sheet
or glacier due to lubrication by meltwater. This can allow the glacier or
ice sheet to slide over its base. Meltwater may be produced by pressure-
induced melting, friction or geothermal heat, or surface melt may drain to
the base through holes in the ice.
Baseline/reference The baseline (or reference) is the state against
which change is measured. A baseline period is the period relative to which
anomalies are computed. The baseline concentration of a trace gas is that
measured at a location not influenced by local anthropogenic emissions.
Bayesian method/approach A Bayesian method is a method by
which a statistical analysis of an unknown or uncertain quantity(ies) is car-
ried out in two steps. First, a prior probability distribution for the uncertain
quantity(ies) is formulated on the basis of existing knowledge (either by
eliciting expert opinion or by using existing data and studies). At this first
stage, an element of subjectivity may influence the choice, but in many
cases, the prior probability distribution can be chosen as neutrally as pos-
sible, in order not to influence the final outcome of the analysis. In the
second step, newly acquired data are used to update the prior distribution
into a posterior distribution. The update is carried out either through an
analytic computation or though numeric approximation, using a theorem
formulated by and named after the British mathematician Thomas Bayes
Biological pump The process of transporting carbon from the ocean’s
surface layers to the deep ocean by the primary production of marine phy-
toplankton, which converts dissolved inorganic carbon (DIC) and nutrients
into organic matter through photosynthesis. This natural cycle is limited
primarily by the availability of light and nutrients such as phosphate, nitrate
and silicic acid, and micronutrients, such as iron. See also Solubility pump.
Biomass The total mass of living organisms in a given area or volume;
dead plant material can be included as dead biomass. Biomass burning is
the burning of living and dead vegetation.
Biome A biome is a major and distinct regional element of the bio-
sphere, typically consisting of several ecosystems (e.g., forests, rivers,
ponds, swamps within a region). Biomes are characterized by typical com-
munities of plants and animals.
Biosphere (terrestrial and marine) The part of the Earth system
comprising all ecosystems and living organisms, in the atmosphere, on
land (terrestrial biosphere) or in the oceans (marine biosphere), including
derived dead organic matter, such as litter, soil organic matter and oceanic
Black carbon (BC) Operationally defined aerosol species based on
measurement of light absorption and chemical reactivity and/or thermal
stability. It is sometimes referred to as soot.
Blocking Associated with persistent, slow-moving high-pressure sys-
tems that obstruct the prevailing westerly winds in the middle and high
latitudes and the normal eastward progress of extratropical transient
storm systems. It is an important component of the intraseasonal climate
variability in the extratropics and can cause long-lived weather conditions
such as cold spells in winter and summer heat waves.
Brewer–Dobson circulation The meridional overturning circulation
of the stratosphere transporting air upward in the tropics, poleward to the
winter hemisphere, and downward at polar and subpolar latitudes. The
Brewer–Dobson circulation is driven by the interaction between upward
propagating planetary waves and the mean flow.
Burden The total mass of a gaseous substance of concern in the atmo-
C Stable isotope of carbon having an atomic weight of approximately
13. Measurements of the ratio of
C in carbon dioxide molecules are
used to infer the importance of different carbon cycle and climate pro-
cesses and the size of the terrestrial carbon reservoir.
C Unstable isotope of carbon having an atomic weight of approxi-
mately 14, and a half-life of about 5700 years. It is often used for dating
purposes going back some 40 kyr. Its variation in time is affected by the
magnetic fields of the Sun and Earth, which influence its production from
cosmic rays (see Cosmogenic radioisotopes).
Calving The breaking off of discrete pieces of ice from a glacier, ice
sheet or an ice shelf into lake or seawater, producing icebergs. This is a
form of mass loss from an ice body. See also Mass balance/budget (of
glaciers or ice sheets).
Carbonaceous aerosol Aerosol consisting predominantly of organic
substances and black carbon.
Carbon cycle The term used to describe the flow of carbon (in various
forms, e.g., as carbon dioxide) through the atmosphere, ocean, terrestrial
and marine biosphere and lithosphere. In this report, the reference unit for
the global carbon cycle is GtC or equivalently PgC (10
Carbon dioxide (CO
) A naturally occurring gas, also a by-product of
burning fossil fuels from fossil carbon deposits, such as oil, gas and coal,
of burning biomass, of land use changes and of industrial processes (e.g.,
cement production). It is the principal anthropogenic greenhouse gas that
affects the Earth’s radiative balance. It is the reference gas against which
other greenhouse gases are measured and therefore has a Global Warming
Potential of 1.
Carbon dioxide (CO
) fertilization The enhancement of the growth
of plants as a result of increased atmospheric carbon dioxide (CO
) con-
Carbon Dioxide Removal (CDR) Carbon Dioxide Removal meth-
ods refer to a set of techniques that aim to remove CO
directly from the
atmosphere by either (1) increasing natural sinks for carbon or (2) using
chemical engineering to remove the CO
, with the intent of reducing the
atmospheric CO
concentration. CDR methods involve the ocean, land and
technical systems, including such methods as iron fertilization, large-scale
afforestation and direct capture of CO
from the atmosphere using engi-
neered chemical means. Some CDR methods fall under the category of
geoengineering, though this may not be the case for others, with the dis-
tinction being based on the magnitude, scale, and impact of the particular
CDR activities. The boundary between CDR and mitigation is not clear and
Annex III Glossary
there could be some overlap between the two given current definitions
(IPCC, 2012, p. 2). See also Solar Radiation Management (SRM).
CFC See Halocarbons.
Chaotic A dynamical system such as the climate system, governed by
nonlinear deterministic equations (see Nonlinearity), may exhibit erratic or
chaotic behaviour in the sense that very small changes in the initial state
of the system in time lead to large and apparently unpredictable changes
in its temporal evolution. Such chaotic behaviour limits the predictabil-
ity of the state of a nonlinear dynamical system at specific future times,
although changes in its statistics may still be predictable given changes in
the system parameters or boundary conditions.
Charcoal Material resulting from charring of biomass, usually retain-
ing some of the microscopic texture typical of plant tissues; chemically it
consists mainly of carbon with a disturbed graphitic structure, with lesser
amounts of oxygen and hydrogen.
Chronology Arrangement of events according to dates or times of
Clathrate (methane) A partly frozen slushy mix of methane gas and
ice, usually found in sediments.
Clausius–Clapeyron equation/relationship The thermodynamic
relationship between small changes in temperature and vapour pressure
in an equilibrium system with condensed phases present. For trace gases
such as water vapour, this relation gives the increase in equilibrium (or
saturation) water vapour pressure per unit change in air temperature.
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 rang-
ing from months to thousands or millions of years. The classical period for
averaging these variables is 30 years, as defined by the World Meteorologi-
cal Organization. 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–carbon cycle feedback A climate feedback involving
changes in the properties of land and ocean carbon cycle in response to cli-
mate change. In the ocean, changes in oceanic temperature and circulation
could affect the atmosphere–ocean CO
flux; on the continents, climate
change could affect plant photosynthesis and soil microbial respiration
and hence the flux of CO
between the atmosphere and the land biosphere.
Climate change Climate change refers to 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 Frame-
work Convention on Climate Change (UNFCCC), in its Article 1, defines
climate change as: ‘a change of climate which is attributed directly or indi-
rectly to human activity that alters the composition of the global atmo-
sphere 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. See also
Climate change commitment, Detection and Attribution.
Climate change commitment Due to the thermal inertia of the
ocean and slow processes in the cryosphere and land surfaces, the climate
would continue to change even if the atmospheric composition were held
fixed at today’s values. Past change in atmospheric composition leads to
a committed climate change, which continues for as long as a radiative
imbalance persists and until all components of the climate system have
adjusted to a new state. The further change in temperature after the com-
position of the atmosphere is held constant is referred to as the constant
composition temperature commitment or simply committed warming or
warming commitment. Climate change commitment includes other future
changes, for example, in the hydrological cycle, in extreme weather events,
in extreme climate events, and in sea level change. The constant emission
commitment is the committed climate change that would result from keep-
ing anthropogenic emissions constant and the zero emission commitment
is the climate change commitment when emissions are set to zero. See also
Climate change.
Climate feedback An interaction in which a perturbation in one
climate quantity causes a change in a second, and the change in the
second quantity ultimately leads to an additional change in the first. A
negative feedback is one in which the initial perturbation is weakened
by the changes it causes; a positive feedback is one in which the initial
perturbation is enhanced. In this Assessment Report, a somewhat narrower
definition is often used in which the climate quantity that is perturbed is
the global mean surface temperature, which in turn causes changes in the
global radiation budget. In either case, the initial perturbation can either
be externally forced or arise as part of internal variability. See also Climate
Feedback Parameter.
Climate Feedback Parameter A way to quantify the radiative
response of the climate system to a global mean surface temperature
change induced by a radiative forcing. It varies as the inverse of the effec-
tive climate sensitivity. Formally, the Climate Feedback Parameter (a; units:
W m
) is defined as: a = (ΔQ – ΔF)/ΔT, where Q is the global mean
radiative forcing, T is the global mean air surface temperature, F is the
heat flux into the ocean and Δ represents a change with respect to an
unperturbed climate.
Climate forecast See Climate prediction.
Climate index A time series constructed from climate variables that
provides an aggregate summary of the state of the climate system. For
example, the difference between sea level pressure in Iceland and the
Azores provides a simple yet useful historical NAO index. Because of their
optimal properties, climate indices are often defined using principal com-
ponents—linear combinations of climate variables at different locations
that have maximum variance subject to certain normalisation constraints
(e.g., the NAM and SAM indices which are principal components of North-
ern Hemisphere and Southern Hemisphere gridded pressure anomalies,
respectively). See Box 2.5 for a summary of definitions for established
observational indices. See also Climate pattern.
Climate model (spectrum or hierarchy) A numerical representa-
tion 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 com-
ponent or combination of components a spectrum or hierarchy of models
can be identified, differing in such aspects as the number of spatial dimen-
sions, the extent to which physical, chemical or biological processes are
explicitly represented or the level at which empirical parametrizations
are involved. Coupled AtmosphereOcean General Circulation Models
(AOGCMs) provide a representation of the climate system that is near or
at the most comprehensive end of the spectrum currently available. 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, sea-
sonal and interannual climate predictions. See also Earth System Model,
Earth-System Model of Intermediate Complexity, Energy Balance Model,
Process-based Model, Regional Climate Model and Semi-empirical model.
Glossary Annex III
Climate pattern A set of spatially varying coefficients obtained by
“projection” (regression) of climate variables onto a climate index time
series. When the climate index is a principal component, the climate pat-
tern is an eigenvector of the covariance matrix, referred to as an Empirical
Orthogonal Function (EOF) in climate science.
Climate prediction A climate prediction or climate forecast is the
result of an attempt to produce (starting from a particular state of the
climate system) an estimate of the actual evolution of the climate in
the future, for example, at seasonal, interannual or decadal time scales.
Because the future evolution of the climate system may be highly sensitive
to initial conditions, such predictions are usually probabilistic in nature. See
also Climate projection, Climate scenario, Model initialization and Predict-
Climate projection A climate projection is the simulated response of
the climate system to a scenario of future emission or concentration of
greenhouse gases and aerosols, 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 socioeconomic and technological developments that may or may
not be realized. See also Climate scenario.
Climate regime A state of the climate system that occurs more fre-
quently than nearby states due to either more persistence or more frequent
recurrence. In other words, a cluster in climate state space associated with
a local maximum in the probability density function.
Climate response See Climate sensitivity.
Climate scenario A plausible and often simplified representation of
the future climate, based on an internally consistent set of climatological
relationships that has been constructed for explicit use in investigating
the potential consequences of anthropogenic climate change, often serv-
ing as input to impact models. Climate projections often serve as the raw
material for constructing climate scenarios, but climate scenarios usually
require additional information such as the observed current climate. A cli-
mate change scenario is the difference between a climate scenario and the
current climate. See also Emission scenario, scenario.
Climate sensitivity In IPCC reports, equilibrium climate sensitivity
(units: °C) refers to the equilibrium (steady state) change in the annual
global mean surface temperature following a doubling of the atmospheric
equivalent carbon dioxide concentration. Owing to computational con-
straints, the equilibrium climate sensitivity in a climate model is sometimes
estimated by running an atmospheric general circulation model coupled
to a mixed-layer ocean model, because equilibrium climate sensitivity is
largely determined by atmospheric processes. Efficient models can be run
to equilibrium with a dynamic ocean. The climate sensitivity parameter
(units: °C (W m
) refers to the equilibrium change in the annual global
mean surface temperature following a unit change in radiative forcing.
The effective climate sensitivity (units: °C) is an estimate of the global
mean surface temperature response to doubled carbon dioxide concen-
tration that is evaluated from model output or observations for evolv-
ing non-equilibrium conditions. It is a measure of the strengths of the
climate feedbacks at a particular time and may vary with forcing history
and climate state, and therefore may differ from equilibrium climate
The transient climate response (units: °C) is the change in the global
mean surface temperature, averaged over a 20-year period, centred at
the time of atmospheric carbon dioxide doubling, in a climate model
simulation in which CO
increases at 1% yr
. It is a measure of the
strength and rapidity of the surface temperature response to green-
house gas forcing.
Climate sensitivity parameter See climate sensitivity.
Climate system The climate system is the highly complex 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 evolves in time under the influence of
its own internal dynamics and because of external forcings such as vol-
canic eruptions, solar variations and anthropogenic forcings such as the
changing composition of the atmosphere and land use change.
Climate variability Climate variability refers to variations in the mean
state and other statistics (such as standard deviations, the occurrence of
extremes, etc.) of the climate on all spatial and temporal scales beyond
that of individual weather events. Variability may be due to natural internal
processes within the climate system (internal variability), or to variations
in natural or anthropogenic external forcing (external variability). See also
Climate change.
Cloud condensation nuclei (CCN) The subset of aerosol particles
that serve as an initial site for the condensation of liquid water, which can
lead to the formation of cloud droplets, under typical cloud formation con-
ditions. The main factor that determines which aerosol particles are CCN at
a given supersaturation is their size.
Cloud feedback A climate feedback involving changes in any of the
properties of clouds as a response to a change in the local or global mean
surface temperature. Understanding cloud feedbacks and determining
their magnitude and sign require an understanding of how a change in cli-
mate may affect the spectrum of cloud types, the cloud fraction and height,
the radiative properties of clouds, and finally the Earth’s radiation budget.
At present, cloud feedbacks remain the largest source of uncertainty in
climate sensitivity estimates. See also Cloud radiative effect.
Cloud radiative effect The radiative effect of clouds relative to the
identical situation without clouds. In previous IPCC reports this was called
cloud radiative forcing, but that terminology is inconsistent with other uses
of the forcing term and is not maintained in this report. See also Cloud
-equivalent See Equivalent carbon dioxide.
Cold days/cold nights Days where maximum temperature, or nights
where minimum temperature, falls below the 10th percentile, where the
respective temperature distributions are generally defined with respect to
the 1961–1990 reference period. For the corresponding indices, see Box
Compatible emissions Earth System Models that simulate the land
and ocean carbon cycle can calculate CO
emissions that are compatible
with a given atmospheric CO
concentration trajectory. The compatible
emissions over a given period of time are equal to the increase of carbon
over that same period of time in the sum of the three active reservoirs: the
atmosphere, the land and the ocean.
Confidence The validity 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. Confidence is
expressed qualitatively (Mastrandrea et al., 2010). See Figure 1.11 for the
levels of confidence and Table 1.1 for the list of likelihood qualifiers. See
also Uncertainty.
Convection Vertical motion driven by buoyancy forces arising from
static instability, usually caused by near-surface cooling or increases in
salinity in the case of the ocean and near-surface warming or cloud-top
radiative cooling in the case of the atmosphere. In the atmosphere con-
vection gives rise to cumulus clouds and precipitation and is effective at
both scavenging and vertically transporting chemical species. In the ocean
convection can carry surface waters to deep within the ocean.
Annex III Glossary
Cosmogenic radioisotopes Rare radioactive isotopes that are cre-
ated by the interaction of a high-energy cosmic ray particles with atoms
nuclei. They are often used as indicator of solar activity which modulates
the cosmic rays intensity or as tracers of atmospheric transport processes,
and are also called cosmogenic radionuclides.
Cryosphere All regions on and beneath the surface of the Earth and
ocean where water is in solid form, including sea ice, lake ice, river ice,
snow cover, glaciers and ice sheets, and frozen ground (which includes
Dansgaard–Oeschger events Abrupt events characterized in Green-
land ice cores and in palaeoclimate records from the nearby North Atlantic
by a cold glacial state, followed by a rapid transition to a warmer phase,
and a slow cooling back to glacial conditions. Counterparts of Dansgaard–
Oeschger events are observed in other regions as well.
Deforestation Conversion of forest to non-forest. For a discussion of
the term forest and related terms such as afforestation, reforestation, and
deforestation see the IPCC Special Report on Land Use, Land-Use Change
and Forestry (IPCC, 2000). See also the report on Definitions and Meth-
odological Options to Inventory Emissions from Direct Human-induced
Degradation of Forests and Devegetation of Other Vegetation Types (IPCC,
Deglaciation/glacial termination Transitions from full glacial con-
ditions (ice age) to warm interglacials characterized by global warming
and sea level rise due to change in continental ice volume.
Detection and attribution Detection of change is defined as the
process of demonstrating that climate or a system affected by climate has
changed in some defined statistical sense, without providing a reason for
that change. An identified change is detected in observations if its likeli-
hood of occurrence by chance due to internal variability alone is deter-
mined to be small, for example, <10%. Attribution is defined as the pro-
cess of evaluating the relative contributions of multiple causal factors to
a change or event with an assignment of statistical confidence (Hegerl et
al., 2010).
Diatoms Silt-sized algae that live in surface waters of lakes, rivers and
oceans and form shells of opal. Their species distribution in ocean cores is
often related to past sea surface temperatures.
Direct (aerosol) effect See Aerosolradiation interaction.
Direct Air Capture Chemical process by which a pure CO
stream is
produced by capturing CO
from the ambient air.
Diurnal temperature range The difference between the maximum
and minimum temperature during a 24-hour period.
Dobson Unit (DU) A unit to measure the total amount of ozone in a
vertical column above the Earth’s surface (total column ozone). The number
of Dobson Units is the thickness in units of 10
m that the ozone column
would occupy if compressed into a layer of uniform density at a pressure
of 1013 hPa and a temperature of 0°C. One DU corresponds to a column of
ozone containing 2.69 × 10
molecules per square metre. A typical value
for the amount of ozone in a column of the Earth’s atmosphere, although
very variable, is 300 DU.
Downscaling Downscaling is a method that derives local- to regional-
scale (10 to 100 km) information from larger-scale models or data analyses.
Two main methods exist: dynamical downscaling and empirical/statistical
downscaling. The dynamical method uses the output of regional climate
models, global models with variable spatial resolution or high-resolution
global models. The empirical/statistical methods develop statistical rela-
tionships that link the large-scale atmospheric variables with local/ regional
climate variables. In all cases, the quality of the driving model remains an
important limitation on the quality of the downscaled information.
Drought A period of abnormally dry weather long enough to cause a
serious hydrological imbalance. Drought is a relative term; therefore any
discussion in terms of precipitation deficit must refer to the particular
precipitation-related activity that is under discussion. For example, short-
age of precipitation during the growing season impinges on crop produc-
tion or ecosystem function in general (due to soil moisture drought, also
termed agricultural drought), and during the runoff and percolation season
primarily affects water supplies (hydrological drought). Storage changes
in soil moisture and groundwater are also affected by increases in actual
evapotranspiration in addition to reductions in precipitation. A period with
an abnormal precipitation deficit is defined as a meteorological drought. A
megadrought is a very lengthy and pervasive drought, lasting much longer
than normal, usually a decade or more. For the corresponding indices, see
Box 2.4.
Dynamical system A process or set of processes whose evolution in
time is governed by a set of deterministic physical laws. The climate system
is a dynamical system. See also Abrupt climate change, Chaotic, Nonlinear-
ity and Predictability.
Earth System Model (ESM) A coupled atmosphereocean general
circulation model in which a representation of the carbon cycle is includ-
ed, allowing for interactive calculation of atmospheric CO
or compatible
emissions. Additional components (e.g., atmospheric chemistry, ice sheets,
dynamic vegetation, nitrogen cycle, but also urban or crop models) may be
included. See also Climate model.
Earth System Model of Intermediate Complexity (EMIC) A cli-
mate model attempting to include all the most important earth system
processes as in ESMs but at a lower resolution or in a simpler, more ideal-
ized fashion.
Earth System sensitivity The equilibrium temperature response of
the coupled atmosphere–ocean–cryosphere–vegetation–carbon cycle
system to a doubling of the atmospheric CO
concentration is referred to
as Earth System sensitivity. Because it allows slow components (e.g., ice
sheets, vegetation) of the climate system to adjust to the external pertur-
bation, it may differ substantially from the climate sensitivity derived from
coupled atmosphere–ocean models.
Ecosystem An ecosystem is 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 spa-
tial 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
Effective climate sensitivity See Climate sensitivity.
Effective radiative forcing See Radiative forcing.
Efficacy A measure of how effective a radiative forcing from a given
anthropogenic or natural mechanism is at changing the equilibrium global
mean surface temperature compared to an equivalent radiative forc-
ing from carbon dioxide. A carbon dioxide increase by definition has an
efficacy of 1.0. Variations in climate efficacy may result from rapid adjust-
ments to the applied forcing, which differ with different forcings.
Ekman pumping Frictional stress at the surface between two fluids
(atmosphere and ocean) or between a fluid and the adjacent solid sur-
face (the Earth’s surface) forces a circulation. When the resulting mass
Glossary Annex III
transport is converging, mass conservation requires a vertical flow away
from the surface. This is called Ekman pumping. The opposite effect, in case
of divergence, is called Ekman suction. The effect is important in both the
atmosphere and the ocean.
Ekman transport The total transport resulting from a balance between
the Coriolis force and the frictional stress due to the action of the wind on
the ocean surface. See also Ekman pumping.
Electromagnetic spectrum Wavelength or energy range of all elec-
tromagnetic radiation. In terms of solar radiation, the spectral irradiance is
the power arriving at the Earth per unit area, per unit wavelength.
El Niño-Southern Oscillation (ENSO) The term El Niño was initially
used to describe a warm-water current that periodically flows along the
coast of Ecuador and Peru, disrupting the local fishery. It has since become
identified with a basin-wide warming of the tropical Pacific Ocean east of
the dateline. This oceanic event is associated with a fluctuation of a global-
scale tropical and subtropical surface pressure pattern called the Southern
Oscillation. This coupled atmosphere–ocean phenomenon, with preferred
time scales of two to about seven years, is known as the El Niño-Southern
Oscillation (ENSO). It is often measured by the surface pressure anomaly
difference between Tahiti and Darwin or the sea surface temperatures in
the central and eastern equatorial Pacific. During an ENSO event, the pre-
vailing trade winds weaken, reducing upwelling and altering ocean cur-
rents such that the sea surface temperatures warm, further weakening the
trade winds. This event has a great impact on the wind, sea surface tem-
perature and precipitation patterns in the tropical Pacific. It has climatic
effects throughout the Pacific region and in many other parts of the world,
through global teleconnections. The cold phase of ENSO is called La Niña.
For the corresponding indices, see Box 2.5.
Emission scenario A plausible representation of the future develop-
ment of emissions of substances that are potentially radiatively active
(e.g., greenhouse gases, aerosols) based on a coherent and internally con-
sistent set of assumptions about driving forces (such as demographic and
socioeconomic development, technological change) and their key relation-
ships. Concentration scenarios, derived from emission scenarios, are used
as input to a climate model to compute climate projections. In IPCC (1992)
a set of emission scenarios was presented which were used as a basis
for the climate projections in IPCC (1996). These emission scenarios are
referred to as the IS92 scenarios. In the IPCC Special Report on Emission
Scenarios (Nakićenović and Swart, 2000) emission scenarios, the so-called
SRES scenarios, were published, some of which were used, among others,
as a basis for the climate projections presented in Chapters 9 to 11 of IPCC
(2001) and Chapters 10 and 11 of IPCC (2007). New emission scenarios
for climate change, the four Representative Concentration Pathways, were
developed for, but independently of, the present IPCC assessment. See also
Climate scenario and Scenario.
Energy balance The difference between the total incoming and total
outgoing energy. If this balance is positive, warming occurs; if it is nega-
tive, cooling occurs. Averaged over the globe and over long time periods,
this balance must be zero. Because the climate system derives virtually all
its energy from the Sun, zero balance implies that, globally, the absorbed
solar radiation, that is, incoming solar radiation minus reflected solar radi-
ation at the top of the atmosphere and outgoing longwave radiation emit-
ted by the climate system are equal. See also Energy budget.
Energy Balance Model (EBM) An energy balance model is a sim-
plified model that analyses the energy budget of the Earth to compute
changes in the climate. In its simplest form, there is no explicit spatial
dimension and the model then provides an estimate of the changes in
globally averaged temperature computed from the changes in radiation.
This zero-dimensional energy balance model can be extended to a one-
dimensional or two-dimensional model if changes to the energy budget
with respect to latitude, or both latitude and longitude, are explicitly con-
sidered. See also Climate model.
Energy budget (of the Earth) The Earth is a physical system with
an energy budget that includes all gains of incoming energy and all losses
of outgoing energy. The Earth’s energy budget is determined by measur-
ing how much energy comes into the Earth system from the Sun, how
much energy is lost to space, and accounting for the remainder on Earth
and its atmosphere. Solar radiation is the dominant source of energy into
the Earth system. Incoming solar energy may be scattered and reflected
by clouds and aerosols or absorbed in the atmosphere. The transmitted
radiation is then either absorbed or reflected at the Earth’s surface. The
average albedo of the Earth is about 0.3, which means that 30% of the
incident solar energy is reflected into space, while 70% is absorbed by
the Earth. Radiant solar or shortwave energy is transformed into sensible
heat, latent energy (involving different water states), potential energy, and
kinetic energy before being emitted as infrared radiation. With the average
surface temperature of the Earth of about 15°C (288 K), the main outgoing
energy flux is in the infrared part of the spectrum. See also Energy balance,
Latent heat flux, Sensible heat flux.
Ensemble A collection of model simulations characterizing a climate
prediction or projection. Differences in initial conditions and model formu-
lation result in different evolutions of the modelled system and may give
information on uncertainty associated with model error and error in initial
conditions in the case of climate forecasts and on uncertainty associated
with model error and with internally generated climate variability in the
case of climate projections.
Equilibrium and transient climate experiment An equilibrium
climate experiment is a climate model experiment in which the model is
allowed to fully adjust to a change in radiative forcing. Such experiments
provide information on the difference between the initial and final states
of the model, but not on the time-dependent response. If the forcing is
allowed to evolve gradually according to a prescribed emission scenario,
the time-dependent response of a climate model may be analysed. Such
an experiment is called a transient climate experiment. See also Climate
Equilibrium climate sensitivity See Climate sensitivity.
Equilibrium line The spatially averaged boundary at a given moment,
usually chosen as the seasonal mass budget minimum at the end of
summer, between the region on a glacier where there is a net annual loss
of ice mass (ablation area) and that where there is a net annual gain (accu-
mulation area). The altitude of this boundary is referred to as equilibrium
line altitude (ELA).
Equivalent carbon dioxide (CO
) concentration The concentra-
tion of carbon dioxide that would cause the same radiative forcing as
a given mixture of carbon dioxide and other forcing components. Those
values may consider only greenhouse gases, or a combination of green-
house gases and aerosols. Equivalent carbon dioxide concentration is a
metric for comparing radiative forcing of a mix of different greenhouse
gases at a particular time but does not imply equivalence of the corre-
sponding climate change responses nor future forcing. There is generally
no connection between equivalent carbon dioxide emissions and resulting
equivalent carbon dioxide concentrations.
Equivalent carbon dioxide (CO
) emission The amount of carbon
dioxide emission that would cause the same integrated radiative forcing,
over a given time horizon, as an emitted amount of a greenhouse gas or
a mixture of greenhouse gases. The equivalent carbon dioxide emission is
obtained by multiplying the emission of a greenhouse gas by its Global
Warming Potential for the given time horizon. For a mix of greenhouse
Annex III Glossary
gases it is obtained by summing the equivalent carbon dioxide emissions
of each gas. Equivalent carbon dioxide emission is a common scale for
comparing emissions of different greenhouse gases but does not imply
equivalence of the corresponding climate change responses. See also
Equivalent carbon dioxide concentration.
Evapotranspiration The combined process of evaporation from the
Earth’s surface and transpiration from vegetation.
Extended Concentration Pathways See Representative Concentra-
tion Pathways.
External forcing External forcing refers to a forcing agent outside the
climate system causing a change in the climate system. Volcanic eruptions,
solar variations and anthropogenic changes in the composition of the
atmosphere and land use change are external forcings. Orbital forcing is
also an external forcing as the insolation changes with orbital parameters
eccentricity, tilt and precession of the equinox.
Extratropical cyclone A large-scale (of order 1000 km) storm in
the middle or high latitudes having low central pressure and fronts with
strong horizontal gradients in temperature and humidity. A major cause
of extreme wind speeds and heavy precipitation especially in wintertime.
Extreme climate event See Extreme weather event.
Extreme sea level See Storm surge.
Extreme weather event An extreme weather event is 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. When a pat-
tern of extreme weather persists for some time, such as a season, it may
be classed as an extreme climate event, especially if it yields an average or
total that is itself extreme (e.g., drought or heavy rainfall over a season).
Faculae Bright patches on the Sun. The area covered by faculae is great-
er during periods of high solar activity.
Feedback See Climate feedback.
Fingerprint The climate response pattern in space and/or time to a spe-
cific forcing is commonly referred to as a fingerprint. The spatial patterns of
sea level response to melting of glaciers or ice sheets (or other changes in
surface loading) are also referred to as fingerprints. Fingerprints are used
to detect the presence of this response in observations and are typically
estimated using forced climate model simulations.
Flux adjustment To avoid the problem of coupled AtmosphereOcean
General Circulation Models (AOGCMs) drifting into some unrealistic cli-
mate state, adjustment terms can be applied to the atmosphere-ocean
fluxes of heat and moisture (and sometimes the surface stresses resulting
from the effect of the wind on the ocean surface) before these fluxes are
imposed on the model ocean and atmosphere. Because these adjustments
are pre-computed and therefore independent of the coupled model inte-
gration, they are uncorrelated with the anomalies that develop during the
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. For a discussion
of the term forest and related terms such as afforestation, reforestation and
deforestation see the IPCC Report on Land Use, Land-Use Change and For-
estry (IPCC, 2000). See also the Report on Definitions and Methodological
Options to Inventory Emissions from Direct Human-induced Degradation of
Forests and Devegetation of Other Vegetation Types (IPCC, 2003).
Fossil fuel emissions Emissions of greenhouse gases (in particular
carbon dioxide), other trace gases and aerosols resulting from the combus-
tion of fuels from fossil carbon deposits such as oil, gas and coal.
Framework Convention on Climate Change See United Nations
Framework Convention on Climate Change (UNFCCC).
Free atmosphere The atmospheric layer that is negligibly affected by
friction against the Earth’s surface, and which is above the atmospheric
boundary layer.
Frozen ground Soil or rock in which part or all of the pore water is
frozen. Frozen ground includes permafrost. Ground that freezes and thaws
annually is called seasonally frozen ground.
General circulation The large-scale motions of the atmosphere and
the ocean as a consequence of differential heating on a rotating Earth.
General circulation contributes to the energy balance of the system
through transport of heat and momentum.
General Circulation Model (GCM) See Climate model.
Geoengineering Geoengineering refers to a broad set of methods and
technologies that aim to deliberately alter the climate system in order to
alleviate the impacts of climate change. Most, but not all, methods seek
to either (1) reduce the amount of absorbed solar energy in the climate
system (Solar Radiation Management) or (2) increase net carbon sinks
from the atmosphere at a scale sufficiently large to alter climate (Carbon
Dioxide Removal). Scale and intent are of central importance. Two key
characteristics of geoengineering methods of particular concern are that
they use or affect the climate system (e.g., atmosphere, land or ocean)
globally or regionally and/or could have substantive unintended effects
that cross national boundaries. Geoengineering is different from weather
modification and ecological engineering, but the boundary can be fuzzy
(IPCC, 2012, p. 2).
Geoid The equipotential surface having the same geopotential at each
latitude and longitude around the world (geodesists denoting this poten-
tial W0) that best approximates the mean sea level. It is the surface of
reference for measurement of altitude. In practice, several variations of
definitions of the geoid exist depending on the way the permanent tide
(the zero-frequency gravitational tide due to the Sun and Moon) is consid-
ered in geodetic studies.
Geostrophic winds or currents A wind or current that is in balance
with the horizontal pressure gradient and the Coriolis force, and thus is out-
side of the influence of friction. Thus, the wind or current is directly parallel
to isobars and its speed is proportional to the horizontal pressure gradient.
Glacial–interglacial cycles Phase of the Earth’s history marked by
large changes in continental ice volume and global sea level. See also Ice
age and Interglacials.
Glacial isostatic adjustment (GIA) The deformation of the Earth
and its gravity field due to the response of the earth–ocean system to
changes in ice and associated water loads. It is sometimes referred to as
glacio-hydro isostasy. It includes vertical and horizontal deformations of
the Earth’s surface and changes in geoid due to the redistribution of mass
during the ice–ocean mass exchange.
Glacier A perennial mass of land ice that originates from compressed
snow, shows evidence of past or present flow (through internal deforma-
tion and/or sliding at the base) and is constrained by internal stress and
friction at the base and sides. A glacier is maintained by accumulation of
snow at high altitudes, balanced by melting at low altitudes and/or dis-
charge into the sea. An ice mass of the same origin as glaciers, but of
continental size, is called an ice sheet. For the purpose of simplicity in this
Assessment Report, all ice masses other than ice sheets are referred to as
Glossary Annex III
glaciers. See also Equilibrium line and Mass balance/budget (of glaciers or
ice sheets).
Global dimming Global dimming refers to a widespread reduction of
solar radiation received at the surface of the Earth from about the year
1961 to around 1990.
Global mean surface temperature An estimate of the global mean
surface air temperature. However, for changes over time, only anomalies,
as departures from a climatology, are used, most commonly based on the
area-weighted global average of the sea surface temperature anomaly and
land surface air temperature anomaly.
Global Warming Potential (GWP) An index, based on radiative
properties of greenhouse gases, measuring the radiative forcing following
a pulse emission of a unit mass of a given greenhouse gas in the present-
day atmosphere integrated over a chosen time horizon, relative to that of
carbon dioxide. The GWP represents the combined effect of the differing
times these gases remain in the atmosphere and their relative effective-
ness in causing radiative forcing. The Kyoto Protocol is based on GWPs
from pulse emissions over a 100-year time frame.
Greenhouse effect The infrared radiative effect of all infrared-absorb-
ing constituents in the atmosphere. Greenhouse gases, clouds, and (to a
small extent) aerosols absorb terrestrial radiation emitted by the Earth’s
surface and elsewhere in the atmosphere. These substances emit infra-
red radiation in all directions, but, everything else being equal, the net
amount emitted to space is normally less than would have been emitted
in the absence of these absorbers because of the decline of temperature
with altitude in the troposphere and the consequent weakening of emis-
sion. An increase in the concentration of greenhouse gases increases the
magnitude of this effect; the difference is sometimes called the enhanced
greenhouse effect. The change in a greenhouse gas concentration because
of anthropogenic emissions contributes to an instantaneous radiative forc-
ing. Surface temperature and troposphere warm in response to this forcing,
gradually restoring the radiative balance at the top of the atmosphere.
Greenhouse gas (GHG) Greenhouse gases are those gaseous con-
stituents of the atmosphere, both natural and anthropogenic, that absorb
and emit radiation at specific wavelengths within the spectrum of terres-
trial radiation emitted by the Earth’s surface, the atmosphere itself, and by
clouds. This property causes the greenhouse effect. Water vapour (H
carbon dioxide (CO
), nitrous oxide (N
O), methane (CH
) and ozone (O
are the primary greenhouse gases in the Earth’s atmosphere. Moreover,
there are a number of entirely human-made greenhouse gases in the
atmosphere, such as the halocarbons and other chlorine- and bromine-
containing substances, dealt with under the Montreal Protocol. Beside CO
O and CH
, the Kyoto Protocol deals with the greenhouse gases sul-
phur hexafluoride (SF
), hydrofluorocarbons (HFCs) and perfluorocarbons
(PFCs). For a list of well-mixed greenhouse gases, see Table 2.A.1.
Gross Primary Production (GPP) The amount of carbon fixed by the
autotrophs (e.g. plants and algaes).
Grounding line The junction between a glacier or ice sheet and ice
shelf; the place where ice starts to float. This junction normally occurs over
a finite zone, rather than at a line.
Gyre Basin-scale ocean horizontal circulation pattern with slow flow
circulating around the ocean basin, closed by a strong and narrow (100 to
200 km wide) boundary current on the western side. The subtropical gyres
in each ocean are associated with high pressure in the centre of the gyres;
the subpolar gyres are associated with low pressure.
Hadley Circulation A direct, thermally driven overturning cell in the
atmosphere consisting of poleward flow in the upper troposphere, subsid-
ing air into the subtropical anticyclones, return flow as part of the trade
winds near the surface, and with rising air near the equator in the so-called
Inter-Tropical Convergence Zone.
Halocarbons A collective term for the group of partially halogenated
organic species, which includes the chlorofluorocarbons (CFCs), hydro-
chlorofluorocarbons (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.
Halocline A layer in the oceanic water column in which salinity changes
rapidly with depth. Generally saltier water is denser and lies below less
salty water. In some high latitude oceans the surface waters may be colder
than the deep waters and the halocline is responsible for maintaining
water column stability and isolating the surface waters from the deep
waters. See also Thermocline.
Halosteric See Sea level change.
HCFC See Halocarbons.
Heat wave A period of abnormally and uncomfortably hot weather. See
also Warm spell.
Heterotrophic respiration The conversion of organic matter to
carbon dioxide by organisms other than autotrophs.
HFC See Halocarbons.
Hindcast or retrospective forecast A forecast made for a period in
the past using only information available before the beginning of the fore-
cast. A sequence of hindcasts can be used to calibrate the forecast system
and/or provide a measure of the average skill that the forecast system has
exhibited in the past as a guide to the skill that might be expected in the
Holocene The Holocene Epoch is the latter of two epochs in the Qua-
ternary System, extending from 11.65 ka (thousand years before 1950) to
the present. It is also known as Marine Isotopic Stage (MIS) 1 or current
Hydroclimate Part of the climate pertaining to the hydrology of a
Hydrological cycle The cycle in which water evaporates from the
oceans and the land surface, is carried over the Earth in atmospheric
circulation as water vapour, condenses to form clouds, precipitates over
ocean and land as rain or snow, which on land can be intercepted by trees
and vegetation, provides runoff on the land surface, infiltrates into soils,
recharges groundwater, discharges into streams and ultimately flows out
into the oceans, from which it will eventually evaporate again. The vari-
ous systems involved in the hydrological cycle are usually referred to as
hydrological systems.
Hydrosphere The component of the climate system comprising liquid
surface and subterranean water, such as oceans, seas, rivers, fresh water
lakes, underground water, etc.
Hypsometry The distribution of land or ice surface as a function of
Ice age An ice age or glacial period is characterized by a long-term
reduction in the temperature of the Earth’s climate, resulting in growth of
ice sheets and glaciers.
Ice–albedo feedback A climate feedback involving changes in the
Earth’s surface albedo. Snow and ice have an albedo much higher (up to
~0.8) than the average planetary albedo (~0.3). With increasing tempera-
tures, it is anticipated that snow and ice extent will decrease, the Earth’s
overall albedo will decrease and more solar radiation will be absorbed,
warming the Earth further.
Annex III Glossary
Ice core A cylinder of ice drilled out of a glacier or ice sheet.
Ice sheet A mass of land ice of continental size that is sufficiently thick
to cover most of the underlying bed, so that its shape is mainly determined
by its dynamics (the flow of the ice as it deforms internally and/or slides at
its base). An ice sheet flows outward from a high central ice plateau with
a small average surface slope. The margins usually slope more steeply, and
most ice is discharged through fast flowing ice streams or outlet glaciers,
in some cases into the sea or into ice shelves floating on the sea. There are
only two ice sheets in the modern world, one on Greenland and one on
Antarctica. During glacial periods there were others.
Ice shelf A floating slab of ice of considerable thickness extending from
the coast (usually of great horizontal extent with a very gently sloping
surface), often filling embayments in the coastline of an ice sheet. Nearly
all ice shelves are in Antarctica, where most of the ice discharged into the
ocean flows via ice shelves.
Ice stream A stream of ice with strongly enhanced flow that is part of
an ice sheet. It is often separated from surrounding ice by strongly sheared,
crevassed margins. See also Outlet glacier.
Incoming solar radiation See Insolation.
Indian Ocean Dipole (IOD) Large–scale mode of interannual variabil-
ity of sea surface temperature in the Indian Ocean. This pattern manifests
through a zonal gradient of tropical sea surface temperature, which in one
extreme phase in boreal autumn shows cooling off Sumatra and warming
off Somalia in the west, combined with anomalous easterlies along the
Indirect aerosol effect See Aerosol-cloud interaction.
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 revolu-
tion marks the beginning of a strong increase in the use of fossil fuels and
emission of, in particular, fossil carbon dioxide. In this report the terms pre-
industrial and industrial refer, somewhat arbitrarily, to the periods before
and after 1750, respectively.
Infrared radiation See Terrestrial radiation.
Insolation The amount of solar radiation reaching the Earth by lati-
tude and by season measured in W m
. Usually insolation refers to the
radiation arriving at the top of the atmosphere. Sometimes it is specified
as referring to the radiation arriving at the Earth’s surface. See also Total
Solar Irradiance.
Interglacials or interglaciations The warm periods between ice age
glaciations. Often defined as the periods at which sea levels were close
to present sea level. For the Last Interglacial (LIG) this occurred between
about 129 and 116 ka (thousand years) before present (defined as 1950)
although the warm period started in some areas a few thousand years
earlier. In terms of the oxygen isotope record interglaciations are defined
as the interval between the midpoint of the preceding termination and
the onset of the next glaciation. The present interglaciation, the Holocene,
started at 11.65 ka before present although globally sea levels did not
approach their present position until about 7 ka before present.
Internal variability See Climate variability.
Inter-Tropical Convergence Zone (ITCZ) The Inter-Tropical Conver-
gence Zone is an equatorial zonal belt of low pressure, strong convection
and heavy precipitation near the equator where the northeast trade winds
meet the southeast trade winds. This band moves seasonally.
Iron fertilization Deliberate introduction of iron to the upper ocean
intended to enhance biological productivity which can sequester addition-
al atmospheric carbon dioxide into the oceans.
Irreversibility A perturbed state of a dynamical system is defined as
irreversible on a given timescale, if the recovery timescale from this state
due to natural processes is significantly longer than the time it takes for the
system to reach this perturbed state. In the context of WGI, the time scale
of interest is centennial to millennial. See also Tipping point.
Isostatic or Isostasy Isostasy refers to the response of the earth to
changes in surface load. It includes the deformational and gravitational
response. This response is elastic on short time scales, as in the earth–
ocean response to recent changes in mountain glaciation, or viscoelastic
on longer time scales, as in the response to the last deglaciation following
the Last Glacial Maximum. See also Glacial Isostatic Adjustment (GIA).
Isotopes Atoms of the same chemical element that have the same the
number of protons but differ in the number of neutrons. Some proton–
neutron configurations are stable (stable isotopes), others are unstable
undergoing spontaneous radioactive decay (radioisotopes). Most elements
have more than one stable isotope. Isotopes can be used to trace transport
processes or to study processes that change the isotopic ratio. Radioiso-
topes provide in addition time information that can be used for radiometric
Kyoto Protocol The Kyoto Protocol to the United Nations Framework
Convention on Climate Change (UNFCCC) was adopted in 1997 in Kyoto,
Japan, at the Third Session of the Conference of the Parties (COP) to the
UNFCCC. It contains legally binding commitments, in addition to those
included in the UNFCCC. Countries included in Annex B of the Protocol
(most Organisation for Economic Cooperation and Development countries
and countries with economies in transition) agreed to reduce their anthro-
pogenic greenhouse gas emissions (carbon dioxide, methane, nitrous
oxide, hydrofluorocarbons, perfluorocarbons, and sulphur hexafluoride) by
at least 5% below 1990 levels in the commitment period 2008–2012. The
Kyoto Protocol entered into force on 16 February 2005.
Land surface air temperature The surface air temperature as mea-
sured in well-ventilated screens over land at 1.5 m above the ground.
Land use and Land use change Land use refers to the total of
arrangements, activities and inputs undertaken in a certain land cover type
(a set of human actions). 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 and conservation). Land use change refers to a change
in the use or management of land by humans, which may lead to a change
in land cover. Land cover and land use change may have an impact on
the surface albedo, evapotranspiration, sources and sinks of greenhouse
gases, or other properties of the climate system and may thus give rise to
radiative forcing and/or other impacts on climate, locally or globally. See
also the IPCC Report on Land Use, Land-Use Change, and Forestry (IPCC,
Land water storage Water stored on land other than in glaciers and
ice sheets (that is water stored in rivers, lakes, wetlands, the vadose zone,
aquifers, reservoirs, snow and permafrost). Changes in land water storage
driven by climate and human activities contribute to sea level change.
La Niña See El Niño-Southern Oscillation.
Lapse rate The rate of change of an atmospheric variable, usually tem-
perature, with height. The lapse rate is considered positive when the vari-
able decreases with height.
Last Glacial Maximum (LGM) The period during the last ice age when
the glaciers and ice sheets reached their maximum extent, approximately
Glossary Annex III
21 ka ago. This period has been widely studied because the radiative forc-
ings and boundary conditions are relatively well known.
Last Interglacial (LIG) See Interglacials.
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.
Lifetime Lifetime is a general term used for various time scales char-
acterizing the rate of processes affecting the concentration of trace gases.
The following lifetimes may be distinguished:
Turnover time (T) (also called global atmospheric lifetime) is the
ratio of the mass M of a reservoir (e.g., a gaseous compound in the
atmosphere) and the total rate of removal S from the reservoir: T = M/S.
For each removal process, separate turnover times can be defined. In
soil carbon biology, this is referred to as Mean Residence Time.
Adjustment time or response time (T
) is the time scale character-
izing the decay of an instantaneous pulse input into the reservoir. The
term adjustment time is also used to characterize the adjustment of
the mass of a reservoir following a step change in the source strength.
Half-life or decay constant is used to quantify a first-order exponential
decay process. See Response time for a different definition pertinent to
climate variations.
The term lifetime is sometimes used, for simplicity, as a surrogate for
adjustment time.
In simple cases, where the global removal of the compound is directly
proportional to the total mass of the reservoir, the adjustment time
equals the turnover time: T = T
. An example is CFC-11, which is
removed from the atmosphere only by photochemical processes in the
stratosphere. In more complicated cases, where several reservoirs are
involved or where the removal is not proportional to the total mass,
the equality T = T
no longer holds. Carbon dioxide (CO
) is an extreme
example. Its turnover time is only about 4 years because of the rapid
exchange between the atmosphere and the ocean and terrestrial biota.
However, a large part of that CO
is returned to the atmosphere within
a few years. Thus, the adjustment time of CO
in the atmosphere is
actually determined by the rate of removal of carbon from the surface
layer of the oceans into its deeper layers. Although an approximate
value of 100 years may be given for the adjustment time of CO
in the
atmosphere, the actual adjustment is faster initially and slower later
on. In the case of methane (CH
), the adjustment time is different from
the turnover time because the removal is mainly through a chemical
reaction with the hydroxyl radical (OH), the concentration of which
itself depends on the CH
concentration. Therefore, the CH
rate S is not proportional to its total mass M.
Likelihood The chance of a specific outcome occurring, where this
might be estimated probabilistically. This is expressed in this report using a
standard terminology, defined in Table 1.1. See also Confidence and Uncer-
Lithosphere The upper layer of the solid Earth, both continental and
oceanic, which comprises all crustal rocks and the cold, mainly elastic
part of the uppermost mantle. Volcanic activity, although part of the litho-
sphere, is not considered as part of the climate system, but acts as an
external forcing factor. See also Isostatic.
Little Ice Age (LIA) An interval during the last millennium charac-
terized by a number of extensive expansions of mountain glaciers and
moderate retreats in between them, both in the Northern and Southern
Hemispheres. The timing of glacial advances differs between regions and
the LIA is, therefore, not clearly defined in time. Most definitions lie in the
period 1400 CE and 1900 CE. Currently available reconstructions of aver-
age Northern Hemisphere temperature indicate that the coolest periods at
the hemispheric scale may have occurred from 1450 to 1850 CE.
Longwave radiation See Terrestrial radiation.
Madden–Julian Oscillation (MJO) The largest single component of
tropical atmospheric intraseasonal variability (periods from 30 to 90 days).
The MJO propagates eastwards at around 5m s
in the form of a large-
scale coupling between atmospheric circulation and deep convection.As it
progresses, it is associated with large regions of both enhanced and sup-
pressed rainfall, mainly over theIndianand western Pacific Oceans. Each
MJO event lasts approximately 30 to 60 days, hence the MJO is also known
as the30- to 60-day wave, or the intraseasonal oscillation.
Marine-based ice sheet An ice sheet containing a substantial region
that rests on a bed lying below sea level and whose perimeter is in contact
with the ocean. The best known example is the West Antarctic ice sheet.
Mass balance/budget (of glaciers or ice sheets) The balance
between the mass input to the ice body (accumulation) and the mass loss
(ablation and iceberg calving) over a stated period of time, which is often
a year or a season. Point mass balance refers to the mass balance at a
particular location on the glacier or ice sheet. Surface mass balance is the
difference between surface accumulation and surface ablation. The input
and output terms for mass balance are:
Accumulation All processes that add to the mass of a glacier. The
main contribution to accumulation is snowfall. Accumulation also
includes deposition of hoar, freezing rain, other types of solid precipita-
tion, gain of wind-blown snow, and avalanching.
Ablation Surface processes that reduce the mass of a glacier. The
main contributor to ablation is melting with runoff but on some gla-
ciers sublimation, loss of wind-blown snow and avalanching are also
significant processes of ablation.
Discharge/outflow Mass loss by iceberg calving or ice discharge
across the grounding line of a floating ice shelf. Although often treated
as an ablation term, in this report iceberg calving and discharge is con-
sidered separately from surface ablation.
Mean sea level The surface level of the ocean at a particular point
averaged over an extended period of time such as a month or year. Mean
sea level is often used as a national datum to which heights on land are
Medieval Climate Anomaly (MCA) See Medieval Warm Period.
Medieval Warm Period (MWP) An interval of relatively warm con-
ditions and other notable climate anomalies such as more extensive
drought in some continental regions. The timing of this interval is not
clearly defined, with different records showing onset and termination of
the warmth at different times, and some showing intermittent warmth.
Most definitions lie within the period 900 to 1400 CE. Currently available
reconstructions of average Northern Hemisphere temperature indicate that
the warmest period at the hemispheric scale may have occurred from 950
to 1250 CE. Currently available records and temperature reconstructions
indicate that average temperatures during parts of the MWP were indeed
warmer in the context of the last 2 kyr, though the warmth may not have
been as ubiquitous across seasons and geographical regions as the 20th
century warming. It is also called Medieval Climate Anomaly.
Meridional Overturning Circulation (MOC) Meridional (north–
south) overturning circulation in the ocean quantified by zonal (east–west)
sums of mass transports in depth or density layers. In the North Atlantic,
away from the subpolar regions, the MOC (which is in principle an observ-
able quantity) is often identified with the thermohaline circulation (THC),
Annex III Glossary
which is a conceptual and incomplete interpretation. It must be borne in
mind that the MOC is also driven by wind, and can also include shallower
overturning cells such as occur in the upper ocean in the tropics and sub-
tropics, in which warm (light) waters moving poleward are transformed to
slightly denser waters and subducted equatorward at deeper levels.
Metadata Information about meteorological and climatological data
concerning how and when they were measured, their quality, known prob-
lems and other characteristics.
Methane (CH
) Methane is one of the six greenhouse gases to be miti-
gated under the Kyoto Protocol and is the major component of natural gas
and associated with all hydrocarbon fuels, animal husbandry and agricul-
Metric A consistent measurement of a characteristic of an object or
activity that is otherwise difficult to quantify. Within the context of the
evaluation of climate models, this is a quantitative measure of agreement
between a simulated and observed quantity which can be used to assess
the performance of individual models.
Microwave Sounding Unit (MSU) A microwave sounder on National
Oceanic and Atmospheric Administration (NOAA) polar orbiter satellites,
that estimates the temperature of thick layers of the atmosphere by mea-
suring the thermal emission of oxygen molecules from a complex of emis-
sion lines near 60 GHz. A series of nine MSUs began making this kind
of measurement in late 1978. Beginning in mid 1998, a follow-on series
of instruments, the Advanced Microwave Sounding Units (AMSUs), began
Mineralization/Remineralization The conversion of an element
from its organic form to an inorganic form as a result of microbial decom-
position. In nitrogen mineralization, organic nitrogen from decaying plant
and animal residues (proteins, nucleic acids, amino sugars and urea) is
converted to ammonia (NH
) and ammonium (NH
) by biological activity.
Mitigation A human intervention to reduce the sources or enhance the
sinks of greenhouse gases.
Mixing ratio See Mole fraction.
Model drift Since model climate differs to some extent from observed
climate, climate forecasts will typically ‘drift’ from the initial observation-
based state towards the model’s climate. This drift occurs at different time
scales for different variables, can obscure the initial-condition forecast
information and is usually removed a posteriori by an empirical, usually
linear, adjustment.
Model hierarchy See Climate model (spectrum or hierarchy).
Model initialization A climate forecast typically proceeds by integrat-
ing a climate model forward in time from an initial state that is intended
to reflect the actual state of the climate system. Available observations of
the climate system are ‘assimilated’ into the model. Initialization is a com-
plex process that is limited by available observations, observational errors
and, depending on the procedure used, may be affected by uncertainty in
the history of climate forcing. The initial conditions will contain errors that
grow as the forecast progresses, thereby limiting the time for which the
forecast will be useful. See also Climate prediction.
Model spread The range or spread in results from climate models,
such as those assembled for Coupled Model Intercomparison Project
Phase 5 (CMIP5). Does not necessarily provide an exhaustive and formal
estimate of the uncertainty in feedbacks, forcing or projections even when
expressed numerically, for example, by computing a standard deviation of
the models’ responses. In order to quantify uncertainty, information from
observations, physical constraints and expert judgement must be com-
bined, using a statistical framework.
Mode of climate variability Underlying space–time structure with
preferred spatial pattern and temporal variation that helps account for the
gross features in variance and for teleconnections. A mode of variability
is often considered to be the product of a spatial climate pattern and an
associated climate index time series.
Mole fraction Mole fraction, or mixing ratio, is the ratio of the number
of moles of a constituent in a given volume to the total number of moles
of all constituents in that volume. It is usually reported for dry air. Typical
values for well-mixed greenhouse gases are in the order of μmol mol
(parts per million: ppm), nmol mol
(parts per billion: ppb), and fmol mol
(parts per trillion: ppt). Mole fraction differs from volume mixing ratio,
often expressed in ppmv etc., by the corrections for non-ideality of gases.
This correction is significant relative to measurement precision for many
greenhouse gases (Schwartz and Warneck, 1995).
Monsoon A monsoon is a tropical and subtropical seasonal reversal in
both the surface winds and associated precipitation, caused by differential
heating between a continental-scale land mass and the adjacent ocean.
Monsoon rains occur mainly over land in summer.
Montreal Protocol The Montreal Protocol on Substances that Deplete
the Ozone Layer was adopted in Montreal in 1987, and subsequently
adjusted and amended in London (1990), Copenhagen (1992), Vienna
(1995), Montreal (1997) and Beijing (1999). It controls the consump-
tion and production of chlorine- and bromine-containing chemicals that
destroy stratospheric ozone, such as chlorofluorocarbons, methyl chloro-
form, carbon tetrachloride and many others.
Near-surface permafrost A term frequentlyused in climate model
applications to refer to permafrost at depths close to the ground surface
(typically down to 3.5 m). In modelling studies, near-surface permafrost
is usually diagnosed from 20 or 30 year climate averages, whichis dif-
ferent from the conventional definition of permafrost. Disappearance of
near-surface permafrost in a location does not preclude the longer-term
persistence of permafrost at greater depth. See also Active layer, Frozen
ground and Thermokarst.
Near-term climate forcers (NTCF) Near-term climate forcers (NTCF)
refer to those compounds whose impact on climate occurs primarily within
the first decade after their emission. This set of compounds is primarily
composed of those with short lifetimes in the atmosphere compared to
well-mixed greenhouse gases, and has been sometimes referred to as
short lived climate forcers or short-lived climate pollutants. However, the
common property that is of greatest interest to a climate assessment is
the timescale over which their impact on climate is felt. This set of com-
pounds includes methane, which is also a well-mixed greenhouse gas, as
well as ozone and aerosols, or their precursors, and some halogenated
species that are not well-mixed greenhouse gases. These compounds do
not accumulate in the atmosphere at decadal to centennial timescales,
and so their effect on climate is predominantly in the near term following
their emission.
Nitrogen deposition Nitrogen deposition is defined as the nitrogen
transferred from the atmosphere to the Earth’s surface by the processes of
wet deposition and dry deposition.
Nitrous oxide (N
O) One of the six greenhouse gases to be mitigat-
ed under the Kyoto Protocol. The main anthropogenic source of nitrous
oxide is agriculture (soil and animal manure management), but important
contributions also come from sewage treatment, combustion of fossil fuel,
and chemical industrial processes. Nitrous oxide is also produced naturally
from a wide variety of biological sources in soil and water, particularly
microbial action in wet tropical forests.
Glossary Annex III
Nonlinearity A process is called nonlinear when there is no simple pro-
portional relation between cause and effect. The climate system contains
many such nonlinear processes, resulting in a system with potentially very
complex behaviour. Such complexity may lead to abrupt climate change.
See also Chaotic and Predictability.
North Atlantic Oscillation (NAO) The North Atlantic Oscillation con-
sists of opposing variations of surface pressure near Iceland and near the
Azores. It therefore corresponds to fluctuations in the strength of the main
westerly winds across the Atlantic into Europe, and thus to fluctuations in
the embedded extratropical cyclones with their associated frontal systems.
See NAO Index, Box 2.5.
Northern Annular Mode (NAM) A winter fluctuation in the ampli-
tude of a pattern characterized by low surface pressure in the Arctic and
strong mid-latitude westerlies. The NAM has links with the northern polar
vortex into the stratosphere. Its pattern has a bias to the North Atlantic and
its index has a large correlation with the North Atlantic Oscillation index.
See NAM Index, Box 2.5.
Ocean acidification Ocean acidification refers to a reduction in the pH
of the ocean over an extended period, typically decades or longer, which
is caused primarily by uptake of carbon dioxide from the atmosphere, but
can also be caused by other chemical additions or subtractions from the
ocean. Anthropogenic ocean acidification refers to the component of pH
reduction that is caused by human activity (IPCC, 2011, p. 37).
Ocean heat uptake efficiency This is a measure (W m
) of
the rate at which heat storage by the global ocean increases as global
mean surface temperature rises. It is a useful parameter for climate change
experiments in which the radiative forcing is changing monotonically,
when it can be compared with the Climate Feedback Parameter to gauge
the relative importance of climate response and ocean heat uptake in
determining the rate of climate change. It can be estimated from such an
experiment as the ratio of the rate of increase of ocean heat content to the
global mean surface air temperature change.
Organic aerosol Component of the aerosol that consists of organic
compounds, mainly carbon, hydrogen, oxygen and lesser amounts of other
elements. See also Carbonaceous aerosol.
Outgoing longwave radiation Net outgoing radiation in the infra-
red part of the spectrum at the top of the atmosphere. See also Terrestrial
Outlet glacier A glacier, usually between rock walls, that is part of, and
drains an ice sheet. See also Ice stream.
Ozone Ozone, the triatomic form of oxygen (O
), is a gaseous atmospher-
ic constituent. In the troposphere, it is created both naturally and by photo-
chemical reactions involving gases resulting from human activities (smog).
Tropospheric ozone acts as a greenhouse gas. In the stratosphere, it is cre-
ated by the interaction between solar ultraviolet radiation and molecular
oxygen (O
). Stratospheric ozone plays a dominant role in the stratospheric
radiative balance. Its concentration is highest in the ozone layer.
Ozone hole See Ozone layer.
Ozone layer The stratosphere contains a layer in which the concentra-
tion of ozone is greatest, the so-called ozone layer. The layer extends from
about 12 to 40 km above the Earth’s surface. The ozone concentration
reaches a maximum between about 20 and 25 km. This layer has been
depleted by human emissions of chlorine and bromine compounds. Every
year, during the Southern Hemisphere spring, a very strong depletion of
the ozone layer takes place over the Antarctic, caused by anthropogenic
chlorine and bromine compounds in combination with the specific meteo-
rological conditions of that region. This phenomenon is called the Ozone
hole. See also Montreal Protocol.
Pacific Decadal Oscillation (PDO) The pattern and time series of
the first empirical orthogonal function of sea surface temperature over the
North Pacific north of 20°N. The PDO broadened to cover the whole Pacific
Basin is known as the Inter-decadal Pacific Oscillation. The PDO and IPO
exhibit similar temporal evolution. See also Pacific Decadal Variability.
Pacific decadal variability Coupled decadal-to-inter-decadal vari-
ability of the atmospheric circulation and underlying ocean in the Pacific
Basin. It is most prominent in the North Pacific, where fluctuations in the
strength of the winter Aleutian Low pressure system co-vary with North
Pacific sea surface temperatures, and are linked to decadal variations in
atmospheric circulation, sea surface temperatures and ocean circulation
throughout the whole Pacific Basin. Such fluctuations have the effect of
modulating the El Niño-Southern Oscillation cycle. Key measures of Pacific
decadal variability are the North Pacific Index (NPI), the Pacific Decadal
Oscillation (PDO) index and the Inter-decadal Pacific Oscillation (IPO)
index, all defined in Box 2.5.
Pacific–North American (PNA) pattern An atmospheric large-scale
wave pattern featuring a sequence of tropospheric high and low pressure
anomalies stretching from the subtropical west Pacific to the east coast of
North America. See PNA pattern index, Box 2.5.
Paleoclimate Climate during periods prior to the development of mea-
suring instruments, including historic and geologic time, for which only
proxy climate records are available.
Parameterization In climate models, this term refers to the technique
of representing processes that cannot be explicitly resolved at the spatial
or temporal resolution of the model (sub-grid scale processes) by relation-
ships between model-resolved larger-scale variables and the area- or time-
averaged effect of such subgrid scale processes.
Percentiles The set of partition values which divides the total popula-
tion of a distribution into 100 equal parts, the 50th percentile correspond-
ing to the median of the population.
Permafrost Ground (soil or rock and included ice and organic material)
that remains at or below 0°C for at least two consecutive years. See also
Near-surface permafrost.
pH pH is a dimensionless measure of the acidity of water (or any solu-
tion) given by its concentration of hydrogen ions (H
). pH is measured on
a logarithmic scale where pH = –log
). Thus, a pH decrease of 1 unit
corresponds to a 10-fold increase in the concentration of H
, or acidity.
Photosynthesis The process by which plants take carbon dioxide from
the air (or bicarbonate in water) to build carbohydrates, releasing oxygen
in the process. There are several pathways of photosynthesis with different
responses to atmospheric carbon dioxide concentrations. See also Carbon
dioxide fertilization.
Plankton Microorganisms living in the upper layers of aquatic systems.
A distinction is made between phytoplankton, which depend on photo-
synthesis for their energy supply, and zooplankton, which feed on phyto-
Pleistocene The Pleistocene Epoch is the earlier of two epochs in the
Quaternary System, extending from 2.59 Ma to the beginning of the Holo-
cene at 11.65 ka.
Pliocene The Plionece Epoch is the last epoch of the Neogene System
and extends from 5.33 Ma to the beginning of the Pleistocene at 2.59 Ma.
Pollen analysis A technique of both relative dating and environmental
reconstruction, consisting of the identification and counting of pollen types
preserved in peat, lake sediments and other deposits. See also Proxy.
Annex III Glossary
Precipitable water The total amount of atmospheric water vapour in
a vertical column of unit cross-sectional area. It is commonly expressed in
terms of the height of the water if completely condensed and collected in
a vessel of the same unit cross section.
Precursors Atmospheric compounds that are not greenhouse gases or
aerosols, but that have an effect on greenhouse gas or aerosol concen-
trations by taking part in physical or chemical processes regulating their
production or destruction rates.
Predictability The extent to which future states of a system may be
predicted based on knowledge of current and past states of the system.
Because knowledge of the climate systems past and current states is gen-
erally imperfect, as are the models that utilize this knowledge to produce a
climate prediction, and because the climate system is inherently nonlinear
and chaotic, predictability of the climate system is inherently limited. Even
with arbitrarily accurate models and observations, there may still be limits
to the predictability of such a nonlinear system (AMS, 2000).
Prediction quality/skill Measures of the success of a prediction
against observationally based information. No single measure can sum-
marize all aspects of forecast quality and a suite of metrics is considered.
Metrics will differ for forecasts given in deterministic and probabilistic
form. See also Climate prediction.
Pre-industrial See Industrial Revolution.
Probability Density Function (PDF) A probability density function
is a function that indicates the relative chances of occurrence of different
outcomes of a variable. The function integrates to unity over the domain
for which it is defined and has the property that the integral over a sub-
domain equals the probability that the outcome of the variable lies within
that sub-domain. For example, the probability that a temperature anomaly
defined in a particular way is greater than zero is obtained from its PDF
by integrating the PDF over all possible temperature anomalies greater
than zero. Probability density functions that describe two or more variables
simultaneously are similarly defined.
Process-based Model Theoretical concepts and computational meth-
ods that represent and simulate the behaviour of real-world systems
derived from a set of functional components and their interactions with
each other and the system environment, through physical and mechanistic
processes occurring over time. See also Climate model.
Projection A projection is a potential future evolution of a quantity or
set of quantities, often computed with the aid of a model. Unlike predic-
tions, projections are conditional on assumptions concerning, for example,
future socioeconomic and technological developments that may or may
not be realized. See also Climate prediction and Climate projection.
Proxy A proxy climate indicator is a record that is interpreted, using
physical and biophysical principles, to represent some combination of
climate-related variations back in time. Climate-related data derived in
this way are referred to as proxy data. Examples of proxies include pollen
analysis, tree ring records, speleothems, characteristics of corals and vari-
ous data derived from marine sediments and ice cores. Proxy-data can be
calibrated to provide quantitative climate information.
Quasi-Biennal Oscillation (QBO) A near-periodic oscillation of the
equatorial zonal wind between easterlies and westerlies in the tropical
stratosphere with a mean period of around 28 months. The alternating
wind maxima descend from the base of the mesosphere down to the tro-
popause, and are driven by wave energy that propagates up from the tro-
Quaternary The Quaternary System is the latter of three systems that
make up the Cenozoic Era (65 Ma to present), extending from 2.59 Ma to
the present, and includes the Pleistocene and Holocene epochs.
Radiative effect The impact on a radiation flux or heating rate (most
commonly, on the downward flux at the top of atmosphere) caused by
the interaction of a particular constituent with either the infrared or solar
radiation fields through absorption, scattering and emission, relative to
an otherwise identical atmosphere free of that constituent. This quanti-
fies the impact of the constituent on the climate system. Examples include
the aerosolradiation interactions, cloud radiative effect, and greenhouse
effect. In this report, the portion of any top-of-atmosphere radiative effect
that is due to anthropogenic or other external influences (e.g., volcanic
eruptions or changes in the sun) is termed the instantaneous radiative forc-
Radiative forcing Radiative forcing is the change in the net, down-
ward minus upward, radiative flux (expressed in W m
) at the tropopause
or top of atmosphere due to a change in an external driver of climate
change, such as, for example, a change in the concentration of carbon diox-
ide or the output of the Sun. Sometimes internal drivers are still treated as
forcings even though they result from the alteration in climate, for example
aerosol or greenhouse gas changes in paleoclimates. The traditional radia-
tive 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 forc-
ing is called instantaneous if no change in stratospheric temperature is
accounted for. The radiative forcing once rapid adjustments are accounted
for is termed the effective radiative forcing. For the purposes of this report,
radiative forcing is further defined as the change relative to the year 1750
and, unless otherwise noted, refers to a global and annual average value.
Radiative forcing is not to be confused with cloud radiative forcing, which
describes an unrelated measure of the impact of clouds on the radiative
flux at the top of the atmosphere.
Rapid adjustment The response to an agent perturbing the climate
system that is driven directly by the agent, independently of any change
in the global mean surface temperature. For example, carbon dioxide and
aerosols, by altering internal heating and cooling rates within the atmo-
sphere, can each cause changes to cloud cover and other variables thereby
producing a radiative effect even in the absence of any surface warming or
cooling. Adjustments are rapid in the sense that they begin to occur right
away, before climate feedbacks which are driven by warming (although
some adjustments may still take significant time to proceed to completion,
for example those involving vegetation or ice sheets). It is also called the
rapid response or fast adjustment. For further explanation on the concept,
see Sections 7.1 and 8.1.
Rapid climate change See Abrupt climate change.
Rapid dynamical change (of glaciers or ice sheets) Changes in
glacier or ice sheet mass controlled by changes in flow speed and dis-
charge rather than by accumulation or ablation. This can result in a rate
of mass change larger than that due to any imbalance between accumula-
tion and ablation. Rapid dynamical change may be initiated by a climatic
trigger, such as incursion of warm ocean water beneath an ice shelf, or
thinning of a grounded tidewater terminus, which may lead to reactions
within the glacier system, that may result in rapid ice loss. See also Mass
balance/budget (of glaciers or ice sheets).
Reanalysis Reanalyses are estimates of historical atmospheric tem-
perature and wind or oceanographic temperature and current, and other
quantities, created by processing past meteorological or oceanographic
data using fixed state-of-the-art weather forecasting or ocean circulation
models with data assimilation techniques. Using fixed data assimilation
avoids effects from the changing analysis system that occur in operational
analyses. Although continuity is improved, global reanalyses still suffer
from changing coverage and biases in the observing systems.
Glossary Annex III
Rebound effect When CO
is removed from the atmosphere, the CO
concentration gradient between atmospheric and land/ocean carbon reser-
voirs is reduced. This leads to a reduction or reversal in subsequent inher-
ent rate of removal of CO
from the atmosphere by natural carbon cycle
processes on land and ocean.
Reconstruction (of climate variable) Approach to reconstructing
the past temporal and spatial characteristics of a climate variable from
predictors. The predictors can be instrumental data if the reconstruction is
used to infill missing data or proxy data if it is used to develop paleoclimate
reconstructions. Various techniques have been developed for this purpose:
linear multivariate regression based methods and nonlinear Bayesian and
analog methods.
Reforestation Planting of forests on lands that have previously
contained forests but that have been converted to some other use. For
a discussion of the term forest and related terms such as afforestation,
reforestation and deforestation, see the IPCC Report on Land Use, Land-
Use Change and Forestry (IPCC, 2000). See also the Report on Definitions
and Methodological Options to Inventory Emissions from Direct Human-
induced Degradation of Forests and Devegetation of Other Vegetation
Types (IPCC, 2003).
Region A region is a territory characterized by specific geographical
and climatological features. The climate of a region is affected by regional
and local scale features like topography, land use characteristics and lakes,
as well as remote influences from other regions. See also Teleconnection.
Regional Climate Model (RCM) A climate model at higher resolu-
tion over a limited area. Such models are used in downscaling global cli-
mate results over specific regional domains.
Relative humidity The relative humidity specifies the ratio of actual
water vapour pressure to that at saturation with respect to liquid water or
ice at the same temperature. See also Specific humidity.
Relative sea level Sea level measured by a tide gauge with respect to
the land upon which it is situated. See also Mean sea level and Sea level
Representative Concentration Pathways (RCPs) Scenarios that
include time series of emissions and concentrations of the full suite of
greenhouse gases and aerosols and chemically active gases, as well as land
use/land cover (Moss et al., 2008). 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 emphasizes
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 extend-
ing up to 2100, for which Integrated Assessment Models produced
corresponding emission scenarios. Extended Concentration Pathways
(ECPs) describe extensions of the RCPs from 2100 to 2500 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 are used in the present IPCC Assess-
ment as a basis for the climate predictions and projections presented
in Chapters 11 to 14:
RCP2.6 One pathway where radiative forcing peaks at approxi-
mately 3 W m
before 2100 and then declines (the corresponding ECP
assuming constant emissions after 2100)
RCP4.5 and RCP6.0 Two intermediate stabilization pathways in
which radiative forcing is stabilized at approximately 4.5 W m
6.0 W m
after 2100 (the corresponding ECPs assuming constant con-
centrations after 2150)
RCP8.5 One high pathway for which radiative forcing reaches great-
er than 8.5 W m
by 2100 and continues to rise for some amount of
time (the corresponding ECP assuming constant emissions after 2100
and constant concentrations after 2250)
For further description of future scenarios, see Box 1.1.
Reservoir A component of the climate system, other than the atmo-
sphere, which has the capacity to store, accumulate or release a substance
of concern, for example, carbon, a greenhouse gas or a precursor. Oceans,
soils and forests are examples of reservoirs of carbon. Pool is an equivalent
term (note that the definition of pool often includes the atmosphere). The
absolute quantity of the substance of concern held within a reservoir at a
specified time is called the stock.
Resolution In climate models, this term refers to the physical distance
(metres or degrees) between each point on the grid used to compute the
equations. Temporal resolution refers to the time step or time elapsed
between each model computation of the equations.
Respiration The process whereby living organisms convert organic
matter to carbon dioxide, releasing energy and consuming molecular
Response time The response time or adjustment time is the time
needed for the climate system or its components to re-equilibrate to a
new state, following a forcing resulting from external processes. It is very
different for various components of the climate system. The response time
of the troposphere is relatively short, from days to weeks, whereas the
stratosphere reaches equilibrium on a time scale of typically a few months.
Due to their large heat capacity, the oceans have a much longer response
time: typically decades, but up to centuries or millennia. The response
time of the strongly coupled surface–troposphere system is, therefore,
slow compared to that of the stratosphere, and mainly determined by the
oceans. The biosphere may respond quickly (e.g., to droughts), but also
very slowly to imposed changes. See lifetime for a different definition of
response time pertinent to the rate of processes affecting the concentra-
tion of trace gases.
Return period An estimate of the average time interval between
occurrences of an event (e.g., flood or extreme rainfall) of (or below/above)
a defined size or intensity. See also Return value.
Return value The highest (or, alternatively, lowest) value of a given
variable, on average occurring once in a given period of time (e.g., in 10
years). See also Return period.
River discharge See Streamflow.
Runoff That part of precipitation that does not evaporate and is not
transpired, but flows through the ground or over the ground surface and
returns to bodies of water. See also Hydrological cycle.
Scenario A plausible description of how the future may develop based
on a coherent and internally consistent set of assumptions about key driv-
ing forces (e.g., rate of technological change, prices) and relationships.
Note that scenarios are neither predictions nor forecasts, but are useful to
provide a view of the implications of developments and actions. See also
Climate scenario, Emission scenario, Representative Concentration Path-
ways and SRES scenarios.
Sea ice Ice found at the sea surface that has originated from the freez-
ing of seawater. Sea ice may be discontinuous pieces (ice floes) moved on
the ocean surface by wind and currents (pack ice), or a motionless sheet
attached to the coast (land-fast ice). Sea ice concentration is the fraction
of the ocean covered by ice. Sea ice less than one year old is called first-
year ice. Perennial ice is sea ice that survives at least one summer. It may
be subdivided into second-year ice and multi-year ice, where multiyear ice
has survived at least two summers.
Annex III Glossary
Sea level change Sea level can change, both globally and locally due
to (1) changes in the shape of the ocean basins, (2) a change in ocean
volume as a result of a change in the mass of water in the ocean, and (3)
changes in ocean volume as a result of changes in ocean water density.
Global mean sea level change resulting from change in the mass of the
ocean is called barystatic. The amount of barystatic sea level change due to
the addition or removal of a mass of water is called its sea level equivalent
(SLE). Sea level changes, both globally and locally, resulting from changes
in water density are called steric. Density changes induced by tempera-
ture changes only are called thermosteric, while density changes induced
by salinity changes are called halosteric. Barystatic and steric sea level
changes do not include the effect of changes in the shape of ocean basins
induced by the change in the ocean mass and its distribution. See also
Relative Sea Level and Thermal expansion.
Sea level equivalent (SLE) The sea level equivalent of a mass of
water (ice, liquid or vapour) is that mass, converted to a volume using a
density of 1000 kg m
, and divided by the present-day ocean surface area
of 3.625 × 10
. Thus, 362.5 Gt of water mass added to the ocean will
cause 1 mm of global mean sea level rise. See also Sea level change.
Seasonally frozen ground See Frozen ground.
Sea surface temperature (SST) The sea surface temperature is 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.
Semi-direct (aerosol) effect See Aerosol–radiation interaction.
Semi-empirical model Model in which calculations are based on a
combination of observed associations between variables and theoretical
considerations relating variables through fundamental principles (e.g.,
conservation of energy). For example, in sea level studies, semi-empirical
models refer specifically to transfer functions formulated to project future
global mean sea level change, or contributions to it, from future global
mean surface temperature change or radiative forcing.
Sensible heat flux The turbulent or conductive flux of heat from the
Earth’s surface to the atmosphere that is not associated with phase chang-
es of water; a component of the surface energy budget.
Sequestration See Uptake.
Shortwave radiation See Solar radiation.
Significant wave height The average trough-to-crest height of the
highest one third of the wave heights (sea and swell) occurring in a par-
ticular time period.
Sink Any process, activity or mechanism that removes a greenhouse
gas, an aerosol or a precursor of a greenhouse gas or aerosol from the
Slab-ocean model A simplified representation in a climate model of
the ocean as a motionless layer of water with a depth of 50 to 100 m.
Climate models with a slab ocean can be used only for estimating the equi-
librium response of climate to a given forcing, not the transient evolution
of climate. See also Equilibrium and transient climate experiment.
Snow cover extent The areal extent of snow covered ground.
Snow water equivalent (SWE) The depth of liquid water that would
result if a mass of snow melted completely.
Soil moisture Water stored in the soil in liquid or frozen form.
Soil temperature The temperature of the soil. This can be measured or
modelled at multiple levels within the depth of the soil.
Solar activity General term describing a variety of magnetic phenome-
na on the Sun such as sunspots, faculae (bright areas), and flares (emission
of high-energy particles). It varies on time scales from minutes to millions
of years. See also Solar cycle.
Solar (‘11-year’) cycle A quasi-regular modulation of solar activity
with varying amplitude and a period of between 8 and 14 years.
Solar radiation Electromagnetic radiation emitted by the Sun with a
spectrum close to the one of a black body with a temperature of 5770 K.
The radiation peaks in visible wavelengths. When compared to the ter-
restrial radiation it is often referred to as shortwave radiation. See also
Insolation and Total solar irradiance (TSI).
Solar Radiation Management (SRM) Solar Radiation Management
refers to the intentional modification of the Earth’s shortwave radiative
budget with the aim to reduce climate change according to a given metric
(e.g., surface temperature, precipitation, regional impacts, etc). Artificial
injection of stratospheric aerosols and cloud brightening are two examples
of SRM techniques. Methods to modify some fast-responding elements of
the longwave radiative budget (such as cirrus clouds), although not strictly
speaking SRM, can be related to SRM. SRM techniques do not fall within
the usual definitions of mitigation and adaptation (IPCC, 2012, p. 2). See
also Solar radiation, Carbon Dioxide Removal (CDR) and Geoengineering.
Solubility pump Solubility pump is an important physicochemical pro-
cess that transports dissolved inorganic carbon from the ocean’s surface
to its interior. This process controls the inventory of carbon in the ocean.
The solubility of gaseous carbon dioxide can alter carbon dioxide concen-
trations in the oceans and the overlying atmosphere. See also Biological
Source Any process, activity or mechanism that releases a greenhouse
gas, an aerosol or a precursor of a greenhouse gas or aerosol into the
Southern Annular Mode (SAM) The leading mode of variability of
Southern Hemisphere geopotential height, which is associated with shifts
in the latitude of the midlatitude jet. See SAM Index, Box 2.5.
Southern Oscillation See El Niño-Southern Oscillation (ENSO).
South Pacific Convergence Zone (SPCZ) A band of low-level con-
vergence, cloudiness and precipitation ranging from the west Pacific warm
pool south-eastwards towards French Polynesia, which is one of the most
significant features of subtropical Southern Hemisphere climate. It shares
some characteristics with the ITCZ, but is more extratropical in nature,
especially east of the Dateline.
Spatial and temporal scales Climate may vary on a large range of
spatial and temporal scales. Spatial scales may range from local (less than
100 000 km
), through regional (100 000 to 10 million km
) to continental
(10 to 100 million km
). Temporal scales may range from seasonal to geo-
logical (up to hundreds of millions of years).
Specific humidity The specific humidity specifies the ratio of the mass
of water vapour to the total mass of moist air. See also Relative humidity.
SRES scenarios SRES scenarios are emission scenarios developed by
Nakićenović and Swart (2000) and used, among others, as a basis for some
of the climate projections shown in Chapters 9 to 11 of IPCC (2001) and
Chapters 10 and 11 of IPCC (2007). The following terms are relevant for a
better understanding of the structure and use of the set of SRES scenarios:
Scenario family Scenarios that have a similar demographic, soci-
etal, economic and technical change storyline. Four scenario families
comprise the SRES scenario set: A1, A2, B1 and B2.
Glossary Annex III
Illustrative Scenario A scenario that is illustrative for each of
the six scenario groups reflected in the Summary for Policymakers of
Nakićenović and Swart (2000). They include four revised marker scenar-
ios for the scenario groups A1B, A2, B1, B2 and two additional scenar-
ios for the A1FI and A1T groups. All scenario groups are equally sound.
Marker Scenario A scenario that was originally posted in draft form
on the SRES website to represent a given scenario family. The choice of
markers was based on which of the initial quantifications best reflected
the storyline, and the features of specific models. Markers are no more
likely than other scenarios, but are considered by the SRES writing team
as illustrative of a particular storyline. They are included in revised form
in Nakićenović and Swart (2000). These scenarios received the closest
scrutiny of the entire writing team and via the SRES open process. Sce-
narios were also selected to illustrate the other two scenario groups.
Storyline A narrative description of a scenario (or family of sce-
narios), highlighting the main scenario characteristics, relationships
between key driving forces and the dynamics of their evolution.
Steric See Sea level change.
Stock See Reservoir.
Storm surge The temporary increase, at a particular locality, in the
height of the sea due to extreme meteorological conditions (low atmo-
spheric pressure and/or strong winds). The storm surge is defined as being
the excess above the level expected from the tidal variation alone at that
time and place.
Storm tracks Originally, a term referring to the tracks of individual
cyclonic weather systems, but now often generalized to refer to the main
regions where the tracks of extratropical disturbances occur as sequences
of low (cyclonic) and high (anticyclonic) pressure systems.
Stratosphere The highly stratified region of the atmosphere above the
troposphere extending from about 10 km (ranging from 9 km at high lati-
tudes to 16 km in the tropics on average) to about 50 km altitude.
Streamflow Water flow within a river channel, for example expressed
in m
. A synonym for river discharge.
Subduction Ocean process in which surface waters enter the ocean
interior from the surface mixed layer through Ekman pumping and lateral
advection. The latter occurs when surface waters are advected to a region
where the local surface layer is less dense and therefore must slide below
the surface layer, usually with no change in density.
Sunspots Dark areas on the Sun where strong magnetic fields reduce
the convection causing a temperature reduction of about 1500 K com-
pared to the surrounding regions. The number of sunspots is higher during
periods of higher solar activity, and varies in particular with the solar cycle.
Surface layer See Atmospheric boundary layer.
Surface temperature See Global mean surface temperature, Land
surface air temperature and Sea surface temperature.
Talik A layer of year-round unfrozen ground that lies in permafrost
Teleconnection A statistical association between climate variables at
widely separated, geographically-fixed spatial locations. Teleconnections
are caused by large spatial structures such as basin-wide coupled modes
of ocean–atmosphere variability, Rossby wave-trains, mid-latitude jets and
storm tracks, etc. See also Teleconnection pattern.
Teleconnection pattern A correlation map obtained by calculating
the correlation between variables at different spatial locations and a cli-
mate index. It is the special case of a climate pattern obtained for stan-
dardized variables and a standardized climate index, that is, the variables
and index are each centred and scaled to have zero mean and unit vari-
ance. One-point teleconnection maps are made by choosing a variable at
one of the locations to be the climate index. See also Teleconnection.
Terrestrial radiation Radiation emitted by the Earth’s surface, the
atmosphere and the clouds. It is also known as thermal infrared or long-
wave radiation, and is to be distinguished from the near-infrared radia-
tion that is part of the solar spectrum. Infrared radiation, in general, has a
distinctive range of wavelengths (spectrum) longer than the wavelength of
the red light in the visible part of the spectrum. The spectrum of terrestrial
radiation is almost entirely distinct from that of shortwave or solar radia-
tion because of the difference in temperature between the Sun and the
Earth–atmosphere system. See also Outgoing longwave radiation.
Thermal expansion In connection with sea level, this refers to the
increase in volume (and decrease in density) that results from warming
water. A warming of the ocean leads to an expansion of the ocean volume
and hence an increase in sea level. See also Sea level change.
Thermocline The layer of maximum vertical temperature gradient in
the ocean, lying between the surface ocean and the abyssal ocean. In sub-
tropical regions, its source waters are typically surface waters at higher
latitudes that have subducted (see Subduction) and moved equatorward.
At high latitudes, it is sometimes absent, replaced by a halocline, which is
a layer of maximum vertical salinity gradient.
Thermohaline circulation (THC) Large-scale circulation in the ocean
that transforms low-density upper ocean waters to higher-density interme-
diate and deep waters and returns those waters back to the upper ocean.
The circulation is asymmetric, with conversion to dense waters in restrict-
ed regions at high latitudes and the return to the surface involving slow
upwelling and diffusive processes over much larger geographic regions.
The THC is driven by high densities at or near the surface, caused by cold
temperatures and/or high salinities, but despite its suggestive though
common name, is also driven by mechanical forces such as wind and tides.
Frequently, the name THC has been used synonymously with Meridional
Overturning Circulation.
Thermokarst The process by which characteristic landforms result from
the thawing of ice-rich permafrost or the melting of massive ground ice.
Thermosteric See Sea level change.
Tide gauge A device at a coastal or deep-sea location that continu-
ously measures the level of the sea with respect to the adjacent land. Time
averaging of the sea level so recorded gives the observed secular changes
of the relative sea level.
Tipping point In climate, a hypothesized critical threshold when global
or regional climate changes from one stable state to another stable state.
The tipping point event may be irreversible. See also Irreversibility.
Total solar irradiance (TSI) The total amount of solar radiation in
watts per square metre received outside the Earth’s atmosphere on a
surface normal to the incident radiation, and at the Earth’s mean distance
from the Sun.
Reliable measurements of solar radiation can only be made from space
and the precise record extends back only to 1978. The generally accept-
ed value is 1368 W m
with an accuracy of about 0.2%. It has recently
been estimated to 1360.8 ± 0.5 W m
for the solar minimum of 2008.
Variations of a few tenths of a percent are common, usually associ-
ated with the passage of sunspots across the solar disk. The solar cycle
variation of TSI is of the order of 0.1% (AMS, 2000). Changes in the
ultraviolet part of the spectrum during a solar cycle are comparatively
larger (percent) than in TSI. See also Insolation.
Annex III Glossary
Transient climate response See Climate sensitivity.
Transient climate response to cumulative CO
emissions (TCRE)
The transient global average surface temperature change per unit cumu-
lated CO
emissions, usually 1000 PgC. TCRE combines both information
on the airborne fraction of cumulated CO
emissions (the fraction of the
total CO
emitted that remains in the atmosphere), and on the transient
climate response (TCR).
Tree rings Concentric rings of secondary wood evident in a cross sec-
tion of the stem of a woody plant. The difference between the dense, small-
celled late wood of one season and the wide-celled early wood of the
following spring enables the age of a tree to be estimated, and the ring
widths or density can be related to climate parameters such as tempera-
ture and precipitation. See also Proxy.
Trend In this report, the word trend designates a change, generally
monotonic in time, in the value of a variable.
Tropopause The boundary between the troposphere and the strato-
Troposphere The lowest part of the atmosphere, from the surface to
about 10 km in altitude at mid-latitudes (ranging from 9 km at high lati-
tudes to 16 km in the tropics on average), where clouds and weather phe-
nomena occur. In the troposphere, temperatures generally decrease with
height. See also Stratosphere.
Turnover time See Lifetime.
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, or uncertain projections
of human behaviour. Uncertainty can therefore be represented by quantita-
tive measures (e.g., a probability density function) or by qualitative state-
ments (e.g., reflecting the judgment of a team of experts) (see Moss and
Schneider, 2000; Manning et al., 2004; Mastrandrea et al., 2010). See also
Confidence and Likelihood.
United Nations Framework Convention on Climate Change
(UNFCCC) The Convention was adopted on 9 May 1992 in New York
and signed at the 1992 Earth Summit in Rio de Janeiro by more than 150
countries and the European Community. Its ultimate objective is the ‘sta-
bilisation of greenhouse gas concentrations in the atmosphere at a level
that would prevent dangerous anthropogenic interference with the climate
system’. It contains commitments for all Parties. Under the Convention,
Parties included in Annex I (all OECD countries and countries with econo-
mies in transition) aim to return greenhouse gas emissions not controlled
by the Montreal Protocol to 1990 levels by the year 2000. The convention
entered in force in March 1994. In 1997, the UNFCCC adopted the Kyoto
Uptake The addition of a substance of concern to a reservoir. The
uptake of carbon containing substances, in particular carbon dioxide, is
often called (carbon) sequestration.
Urban heat island (UHI) The relative warmth of a city compared with
surrounding rural areas, associated with changes in runoff, effects on heat
retention, and changes in surface albedo.
Ventilation The exchange of ocean properties with the atmospheric
surface layer such that property concentrations are brought closer to equi-
librium values with the atmosphere (AMS, 2000), and the processes that
propagate these properties into the ocean interior.
Volatile Organic Compounds (VOC) Important class of organic
chemical air pollutants that are volatile at ambient air conditions. Other
terms used to represent VOCs are hydrocarbons (HCs), reactive organic
gases (ROGs) and non-methane volatile organic compounds (NMVOCs).
NMVOCs are major contributors (together with NO
and CO) to the forma-
tion of photochemical oxidants such as ozone.
Walker Circulation Direct thermally driven zonal overturning circula-
tion in the atmosphere over the tropical Pacific Ocean, with rising air in the
western and sinking air in the eastern Pacific.
Warm days/warm nights Days where maximum temperature, or
nights where minimum temperature, exceeds the 90th percentile, where
the respective temperature distributions are generally defined with respect
to the 1961–1990 reference period. For the corresponding indices, see Box
Warm spell A period of abnormally hot weather. For the corresponding
indices, see Box 2.4. See also Heat wave.
Water cycle See Hydrological cycle.
Water mass A body of ocean water with identifiable properties (tem-
perature, salinity, density, chemical tracers) resulting from its unique for-
mation process. Water masses are often identified through a vertical or
horizontal extremum of a property such as salinity. North Pacific Intermedi-
ate Water (NPIW) and Antarctic Intermediate Water (AAIW) are examples
of water masses.
Weathering The gradual removal of atmospheric CO
through disso-
lution of silicate and carbonate rocks. Weathering may involve physical
processes (mechanical weathering) or chemical activity (chemical weath-
Well-mixed greenhouse gas See Greenhouse gas.
Younger Dryas A period 12.85 to 11.65 ka (thousand years before
1950), during the deglaciation, characterized by a temporary return to
colder conditions in many locations, especially around the North Atlantic.
Glossary Annex III
AMS, 2000: AMS Glossary of Meteorology, 2nd ed. American Meteorological Society,
Boston, MA, http://amsglossary.allenpress.com/glossary/browse.
Hegerl, G. C., O. Hoegh-Guldberg, G. Casassa, M. P. Hoerling, R. S. Kovats, C. Parmesan,
D. W. Pierce, and P. A. Stott, 2010: Good practice guidance paper on detection
and attribution related to anthropogenic climate change. In: Meeting Report of
the Intergovernmental Panel on Climate Change Expert Meeting on Detection
and Attribution of Anthropogenic Climate Change [T. F. Stocker, C. B. Field, D.
Qin, V. Barros, G.-K. Plattner, M. Tignor, P. M. Midgley and K. L. Ebi (eds.)]. IPCC
Working Group I Technical Support Unit, University of Bern, Bern, Switzerland.
IPCC, 1992: Climate Change 1992: The Supplementary Report to the IPCC Scientific
Assessment [J. T. Houghton, B. A. Callander and S. K. Varney (eds.)]. Cambridge
University Press, Cambridge, United Kingdom and New York, NY, USA, 116 pp.
IPCC, 1996: Climate Change 1995: The Science of Climate Change. Contribution of
Working Group I to the Second Assessment Report of the Intergovernmental
Panel on Climate Change [J. T. Houghton., L. G. Meira . A. Callander, N. Harris,
A. Kattenberg and K. Maskell (eds.)]. Cambridge University Press, Cambridge,
United Kingdom and New York, NY, USA, 572 pp.
IPCC, 2000: Land Use, Land-Use Change, and Forestry. Special Report of the
Intergovernmental Panel on Climate Change [R. T. Watson, I. R. Noble, B. Bolin,
N. H. Ravindranath, D. J. Verardo, and D. J. Dokken (eds.)]. Cambridge University
Press, Cambridge, United Kingdom and New York, NY, USA, 377 pp.
IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working
Group I to the Third Assessment Report of the Intergovernmental Panel on
Climate Change [T. Houghton, Y. Ding, D. J. Griggs, M. Noquer, P. J. van der
Linden, X. Dai, K. Maskell and C. A. Johnson (eds.)]. Cambridge University Press,
Cambridge, United Kingdom and New York, NY, USA, 881 pp.
IPCC, 2003: Definitions and Methodological Options to Inventory Emissions from
Direct Human-Induced Degradation of Forests and Devegetation of Other
Vegetation Types [Penman, J., M. Gytarsky, T. Hiraishi, T. Krug, D. Kruger, R. Pipatti,
L. Buendia, K. Miwa, T. Ngara, K. Tanabe and F. Wagner (eds.)]. The Institute for
Global Environmental Strategies (IGES), Japan, 32 pp.
IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the Intergovernmental
Panel on Climate Change. [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis,
K. B. Averyt, M. Tignor and H. L. Miller (eds.)]. Cambridge University Press,
Cambridge, United Kingdom and New York, NY, USA, 996 pp.
IPCC, 2011: Workshop Report of the Intergovernmental Panel on Climate Change
Workshop on Impacts of Ocean Acidification on Marine Biology and Ecosystems
[C. B. Field, V. Barros, T. F. Stocker, D. Qin, K.J. Mach, G.-K. Plattner, M. D.
Mastrandrea, M. Tignor and K. L. Ebi (eds.)]. IPCC Working Group II Technical
Support Unit, Carnegie Institution, Stanford, CA, USA, 164 pp.
IPCC, 2012: Meeting Report of the Intergovernmental Panel on Climate Change
Expert Meeting on Geoengineering [O. Edenhofer, R. Pichs-Madruga, Y. Sokona,
C. Field, V. Barros, T. F. Stocker, Q. Dahe, J. Minx, K. Mach, G.-K. Plattner, S. Schlömer,
G. Hansen and M. Mastrandrea (eds.)]. IPCC Working Group III Technical Support
Unit, Potsdam Institute for Climate Impact Research, Potsdam, Germany, 99 pp.
Manning, M., et al., 2004: IPCC Workshop on Describing Scientific Uncertainties in
Climate Change to Support Analysis of Risk of Options. Workshop Report. IPCC
Working Group I Technical Support Unit, Boulder, CO, USA, 138 pp.
Mastrandrea, M. D., C. B. Field, T. F. Stocker, O. Edenhofer, K. L. Ebi, D. J. Frame, H.
Held, E. Kriegler, K. J. Mach, P. R. Matschoss, G.-K. Plattner, G. W. Yohe, and F.
W. Zwiers, 2010: Guidance Note for Lead Authors of the IPCC Fifth Assessment
Report on Consistent Treatment of Uncertainties. Intergovernmental Panel on
Climate Change (IPCC). http://www.ipcc.ch.
Moss, R., and S. Schneider, 2000: Uncertainties in the IPCC TAR: Recommendations
to Lead Authors for More Consistent Assessment and Reporting. In: IPCC
Supporting Material: Guidance Papers on Cross Cutting Issues in the Third
Assessment Report of the IPCC. [Pachauri, R., T. Taniguchi, and K. Tanaka (eds.)].
Intergovernmental Panel on Climate Change, Geneva, pp. 33–51.
Moss, R., et al., 2008: Towards new scenarios for analysis of emissions, climate
change, impacts and response strategies. Intergovernmental Panel on Climate
Change, Geneva, 132 pp.
Moss, R. et al., 2010: The next generation of scenarios for climate change research
and assessment. Nature, 463, 747–756.
Nakićenović, N., and R. Swart (eds.), 2000: Special Report on Emissions Scenarios. A
Special Report of Working Group III of the Intergovernmental Panel on Climate
Change. Cambridge University Press, Cambridge, United Kingdom and New
York, NY, USA, 599 pp.
Schwartz, S.E., and P. Warneck, 1995: Units for use in atmospheric chemistry. Pure
Appl. Chem., 67, 1377–1406.