GLOSSARY OF TERMS1
[FOOTNOTE 1: Italicized words or phrases within definitions
cross-reference to other glossary terms.]
The physiological adaptation to climatic variations. Biologically,
acclimation is a physiological (phenotypic) adjustment by an organism to
an environmental change (distinguished from adaptation, which is
Adjustment in natural or
systems to a new or changing environment that exploits beneficial
opportunities or moderates negative effects.
The ability of a system to adjust to
(including climate variability and extremes) to moderate potential
damages, to take advantage of opportunities, or to cope with the
Operational decisions principally for managing entities that are
influenced by climate variability and
Adaptive management decisions
Operational decisions, principally for managing entities that are
influenced by climate variability and
decisions can apply to the management of infrastructure (e.g., a waste
water treatment plant), the integrated management of a natural resource
(e.g., a watershed), or the operation of societal response mechanisms
(e.g., health alerts, water restrictions). Adaptive management
operates within existing policy frameworks or uses existing
infrastructure, and the decisions usually occur on time scales of a year
or less. See policy decisions.
Airborne solid or liquid particles, with a typical size between 0.01
and 10 m m that reside in the atmosphere for at
least several hours. Aerosols may be of either natural or anthropogenic
origin. Aerosols may influence climate in two ways: directly
through scattering and absorbing radiation, and indirectly through acting
as condensation nuclei for cloud formation or modifying the optical
properties and lifetime of clouds.
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 soil ranges from high to low; vegetation-covered surfaces and
oceans have a low albedo. The Earth's albedo varies mainly through varying
cloudiness, snow, ice, leaf area, and land-cover changes.
Processes that involve analyzing and evaluating the state of scientific
knowledge (and the associated degree of scientific certainty) and, in
interaction with users, developing information applicable to a particular
set of issues or decisions.
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% volume mixing ratio) and ozone.
In addition, the atmosphere contains water vapor, whose amount is highly
variable but typically 1% volume mixing ratio. The atmosphere also
contains clouds and aerosols.
See detection and attribution.
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 detritus.
The term used to describe the flow of carbon [in various forms such as
carbon dioxide (CO2), organic matter, and carbonates] through
the atmosphere, ocean, terrestrial biosphere, and lithosphere.
Climate can be defined as the statistical description in terms of the
mean and variability of relevant measures of the atmosphere-ocean system
over periods of time ranging from weeks to thousands or millions of years.
A statistically significant variation in either the mean state of the
climate or in its variability, persisting for an extended period
(typically decades or longer). Climate change may be due to natural
internal processes or to external forcing, including changes in solar
radiation and volcanic eruptions, or to persistent human-induced changes
in atmospheric composition or in land use.
See also climate variability.
An interaction among processes in the climate system in which a
change in one process triggers a secondary process that influences the
first one. A positive feedback intensifies the change in the original
process, and a negative feedback reduces it.
A numerical representation of the climate system based on the
physical, chemical, and biological properties of its components, their
interactions and feedback processes, and accounting for all or some
of its known properties. The climate system can be represented by models
of varying complexity -- that is, for any one component or combination of
components a "hierarchy" of models can be identified, differing in such
aspects as the number of spatial dimensions, the extent to which physical,
chemical or biological processes are explicitly represented, or the level
at which empirical parametrizations
are involved. Coupled
atmosphere/ocean/sea-ice general circulation models provide a
comprehensive representation of the climate system. There is an evolution
towards more complex models with active chemistry and biology. Climate
models are applied, as a research tool, to study and simulate the climate,
but also for operational purposes, including monthly, seasonal, and
interannual climate predictions.
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
serving 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 about the
observed current climate. A "climate change scenario" is the difference
between a climate scenario and the current climate.
In IPCC assessments, "equilibrium climate sensitivity" refers to the
equilibrium change in global mean surface temperature following a doubling
of the atmospheric (equivalent) CO2 concentration. More
generally, equilibrium climate sensitivity refers to the equilibrium
change in surface air temperature following a unit change in
forcing (_C/Wm-2). In practice, the evaluation of the
equilibrium climate sensitivity requires very long simulations with
coupled general circulation models. The "effective climate sensitivity" is
a related measure that circumvents this requirement. It is evaluated from
model output for evolving non-equilibrium conditions. It is a measure of
the strengths of the feedbacks at a particular time and may vary
with forcing history and climate state. See climate model.
The highly complex system consisting of five major components: the
atmosphere, the hydrosphere, the
cryosphere, the land
surface, and the biosphere, and the interactions among them. The
climate system evolves in time under the influence of its own internal
dynamics and because of external forcings such as volcanic eruptions,
solar variations, and human-induced forcings such as the changing
composition of the atmosphere and land-use change.
Variations in the mean state and other statistics of climatic features
on temporal and spatial scales beyond those of individual weather
events. These often are due to internal processes within the
system. Examples of cyclical forms of climate variability include
El Nino Southern Oscillation, the
North Atlantic Oscillation (NAO),
and Pacific Decadal Variability (PDV).
See also climate change.
Topics within the Strategic Plan for which progress in one research
element is only possible if related research is first completed in other
The component of the climate system consisting of all snow, ice,
and permafrost on and beneath the surface of the Earth and ocean.
The provision of timely and useful information that addresses specific
questions. See also decision support resources.
Decision support resources
The set of observations, analyses, interdisciplinary research
products, communication mechanisms, and operational services that provide
timely and useful information to address questions confronting
policymakers, resource managers, and other users. See also
Detection and attribution
Climate varies continually on all time scales. Detection of
climate change is the process of demonstrating that climate has
changed in some defined statistical sense, without providing a reason for
that change. Attribution of causes of climate change is the process of
establishing the most likely causes for the detected change with some
defined level of confidence.
A community (i.e., an assemblage of populations of plants, animals,
fungi, and microorganisms that live in an environment and interact with
one another, forming together a distinctive living system with its own
composition, structure, environmental relations, development, and
function) and its environment treated together as a functional system of
complementary relationships and transfer and circulation of energy and
Ecosystem goods and services
Through numerous biological, chemical, and physical processes,
ecosystems provide both goods and services to humanity. Goods include
food, feed, fiber, fuel, pharmaceutical products, and wildlife. Services
include maintenance of hydrologic cycles, cleansing of water and air,
regulation of climate and weather, storage and cycling of nutrients, and
provision of beauty and inspiration. Many goods pass through markets, but
services rarely do.
El Nino Southern Oscillation (ENSO)
El Nino, in its original sense, is a warmwater current that
periodically flows along the coast of Ecuador and Peru, disrupting the
local fishery. This oceanic event is associated with a fluctuation of the
intertropical surface pressure pattern and circulation in the Indian and
Pacific Oceans, called the Southern Oscillation. This coupled
atmosphere-ocean phenomenon is collectively known as El Nino Southern
Oscillation, or ENSO. During an El Nino event, the prevailing trade winds
weaken and the equatorial countercurrent strengthens, causing warm surface
waters in the Indonesian area to flow eastward to overlie the cold waters
of the Peru current. This event has great impact on the wind, sea surface
temperature, and precipitation patterns in the tropical Pacific. It has
climatic effects throughout the Pacific region and in many other parts of
the world. The opposite of an El Nino event is called La NiŅa.
In the climate change context, emissions refer to the release of
greenhouse gases and/or their precursors and aerosols
into the atmosphere over a specified area and period of time.
A plausible representation of the future development of emissions
of substances that are potentially radiatively active (e.g., greenhouse
gases, aerosols), based on a coherent and internally consistent
set of assumptions about driving forces (such as demographic and
socio-economic development, technological change) and their key
relationships. Concentration scenarios, derived from emissions scenarios,
are used as input into a climate model to compute
projections. See SRES scenarios.
The combined process of evaporation from the Earth's surface and
transpiration from vegetation.
See climate system.
Extreme weather event
An extreme weather event is an event that is rare within its
statistical reference distribution at a particular place. Definitions of
"rare" vary, but an extreme weather event would normally be as rare as or
rarer than the 10th or 90th percentile. By definition, the characteristics
of what is called extreme weather may vary from place to place. An extreme
climate event is an average of a number of weather events over a
certain period of time, an average which is itself extreme (e.g., rainfall
over a season).
See climate feedback.
Full carbon accounting
Complete accounting of all carbon stocks and changes in them for all
carbon pools related to a given spatial area in a given time period.
Changes in the global environment (including alterations in
land productivity, oceans or other water resources, atmospheric chemistry,
and ecological systems) that may alter the capacity of the Earth to
sustain life (from the
Global Change Research Act
of 1990, PL 101-606).
Global change research
Study, monitoring, assessment, prediction, and information
management activities to describe and understand the interactive physical,
chemical, and biological processes that regulate the total Earth system;
the unique environment that the Earth provides for life; changes that are
occurring in the Earth system; and the manner in which such system,
environment, and changes are influenced by human actions.
Greenhouse gases are those gaseous constituents of the atmosphere, both
natural and anthropogenic, that absorb and emit radiation at specific
wavelengths within the spectrum of infrared radiation emitted by the
Earth's surface, the atmosphere, and clouds. This property causes the
greenhouse effect. Water vapor (H2O), carbon dioxide (CO2),
nitrous oxide (N2O), methane (CH4), and ozone (O3)
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.
Any system in which human organizations play a major role. Often, but
not always, the term is synonymous with "society" or "social system"
(e.g., agricultural system, political system, technological system,
The component of the climate system
composed of liquid surface
and subterranean water, such as oceans, seas, rivers, freshwater lakes,
underground water, etc.
(Climate) Impact assessment
The practice of identifying and evaluating the detrimental and
beneficial consequences of climate change on natural and human
Consequences of climate change on natural and human systems.
Depending on the consideration of adaptation, one can distinguish
between potential impacts and residual impacts.
Potential impacts: All impacts that may occur given a projected
change in climate, without considering adaptation.
Residual impacts: The impacts of climate change that would occur
Knowledge derived from study, experience, or instruction.
A method of analysis that combines results and models from the
physical, biological, economic, and social sciences, and the interactions
between these components, in a consistent framework, to evaluate the
status and the consequences of environmental change and the policy
responses to it.
The vegetation and artificial built-up materials covering the land
surface. This includes areas of vegetation (forests, shrublands, crops,
deserts, lawns), bare soil, developed surfaces (paved land, buildings),
and wet areas and bodies of water (watercourses, wetlands).
The total of arrangements, activities, and inputs undertaken in a
certain land cover type (a set of human actions). The social and economic
purposes for which land is managed (e.g., grazing, timber extraction, and
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 albedo, evapotranspiration, sources, and sinks
greenhouse gases, or other properties of the
and may thus have an impact on climate, locally or globally.
Lifetime is a general term used for various time scales
characterizing the rate of processes affecting the concentration of trace
gases. In general, lifetime denotes the average length of time that an
atom or molecule spends in a given reservoir, such as the atmosphere or
oceans. The following lifetimes may be distinguished:
"Turnover time" (T) or "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.
"Adjustment time," "response time," or "perturbation lifetime" (Ta)
is the time scale characterizing 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 = Ta. 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 = Ta no longer holds. CO2 is an extreme
example. Its turnover time is only about 4 years because of the rapid
exchange between atmosphere and the ocean and terrestrial biota. However,
a large part of that CO2 is returned to the atmosphere within a
few years. Thus, the adjustment time of CO2 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 CO2 in the
atmosphere, the actual adjustment is faster initially and slower later on.
In the case of CH4, 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 CH4 concentration. Therefore the CH4 removal S
is not proportional to its total mass M.
Mitigation (climate change)
An intervention to reduce the causes of change in climate. This could
include approaches devised to reduce emissions of greenhouse gases to the
atmosphere; to enhance their removal from the atmosphere through storage
in geological formations, soils, biomass, or the ocean; or to alter
incoming solar radiation through several "geo-engineering" options.
The social, political, and economic structures and conditions that are
required for effective mitigation.
A scientifically designed system of continuing standardized
measurements and observations and the evaluation thereof.
North Atlantic Oscillation (NAO)
The North Atlantic Oscillation consists of opposing variations of
barometric pressure near Iceland and near the Azores. On average, a
westerly current, between the Icelandic low pressure area and the Azores
high pressure area, carries cyclones with their associated frontal systems
towards Europe. However, the pressure difference between Iceland and the
Azores fluctuates on time scales of days to decades, and can be
reversed at times. It is the dominant mode of winter climate variability
in the North Atlantic region, ranging from central North America to
Standardized measurements (either continuing or episodic) of variables
in climate and related systems.
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
relationships between the area- or time-averaged effect of such
sub-grid-scale processes and the larger scale flow.
Related to the locus (regional, sectoral, cultural) of a particular
object or action (e.g., place-based decisions).
A process inherently important for both policy decisions and
adaptive management. It usually occurs in the framework of established
or projected policy options.
Decisions that result in laws, regulations, or other public actions.
These decisions are typically made in government settings (federal, state,
local) by elected or appointed officials. These decisions, which usually
involve balancing competing value issues, can be assisted by -- but not
specified by -- scientific analyses. See
adaptive management decisions.
A probabilistic description or forecast of a future
outcome based on observations of past and current climatological
conditions and quantitative models of climate processes (e.g., a
prediction of an El Nino event).
A description of the response of the climate system to an
assumed level of future radiative forcing. Changes in radiative forcing
may be due to either natural sources (e.g., volcanic emissions) or
human-induced causes (e.g., emissions of greenhouse gases and
aerosols, or changes in
land use and land cover).
Climate "projections" are distinguished from climate "predictions" in
order to emphasize that climate projections depend on scenarios of
future socioeconomic, technological, and policy developments that may or
may not be realized.
A process that directly changes the average energy balance of the
Earth-atmosphere system by affecting the balance between incoming
solar radiation and outgoing or "back" radiation. A positive forcing tends
to warm the surface of the Earth and a negative forcing tends to cool the
Rapid climate change
The non-linearity of the climate system may lead to rapid
climate change, sometimes called abrupt events or even surprises. Some
such abrupt events may be imaginable, such as a dramatic reorganization of
the thermohaline circulation, rapid deglaciation, or massive melting of
permafrost leading to fast changes in the carbon cycle. Others may
be truly unexpected, as a consequence of a strong, rapidly changing,
forcing of a non-linear system.
The process of "freezing" or holding constant a recent version of a
regional climate or weather model with the latest process representations
and assimilation capabilities, and rerunning that model with historical
satellite and in situ data sets to generate products for the period
covered by the historic records. This process allows climatological
analyses to be carried out using the best consistent data products
The ability of an organism or other entity to recover from or to adjust
easily to change or other stress.
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 and internal processes or
feedbacks. 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
comes into 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 fast (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 concentration of trace gases.
A coherent description of a potential future situation that serves as
input to more detailed analyses or modeling. Scenarios are tools to
explore, "if ..., then..." statements, and are not predictions of or
prescriptions for the future. See also SRES scenarios,
scenario, and emissions scenario.
Sensitivity is the degree to which a system is affected, either
adversely or beneficially, by climate-related stimuli. The effect may be
direct (e.g., a change in crop yield in response to a change in the mean,
range, or variability of temperature) or indirect (e.g., damages caused by
an increase in the frequency of coastal flooding due to sea-level rise).
See also climate sensitivity.
Stepwise decisionmaking aiming to identify short-term strategies in the
face of long-term uncertainties, by incorporating additional information
over time and making mid-course corrections.
The process of increasing the carbon content of a carbon reservoir
other than the atmosphere. Biological approaches to sequestration include
direct removal of CO2 from the atmosphere through
change, afforestation, reforestation, and practices that enhance
soil carbon in agriculture. Physical approaches include separation and
disposal of CO2 from flue gases or from processing fossil
fuels to produce hydrogen- and CO2-rich fractions and
long-term storage in underground depleted oil and gas reservoirs, coal
seams, and saline aquifers.
Any process, activity, or mechanism that removes a
an aerosol, or a precursor of a greenhouse gas or aerosol from the
The socio-economic potential represents the level of greenhouse gas
mitigation that would be approached by overcoming social and cultural
obstacles to the use of technologies that are cost-effective.
Any process, activity, or mechanism that releases a
an aerosol, or a precursor of a greenhouse gas or aerosol into the
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 km2),
through regional (100,000 to 10 million km2) to continental (10
to 100 million km2). Temporal scales may range from seasonal to
geological (up to hundreds of millions of years).
The achievement of stabilization of atmospheric concentrations of one
or more greenhouse gases.
Individuals or groups whose interests (financial, cultural,
value-based, or other) are affected by climate variability,
climate change, or options for adapting to or mitigating these
phenomena. Stakeholders are important partners with the research community
for development of decision support resources.
The highly stratified region of the atmosphere above the
troposphere extending from about 10 km (ranging from 9 km in high latitudes to 16 km
in the tropics on average) to about 50 km.
Integration of interrelated, interacting, or interdependent components
into a complex whole.
A piece of equipment or a technique for performing a particular
The broad set of processes that cover the exchange of knowledge, money,
and goods among different stakeholders that lead to the spreading
of technology for adapting to or mitigating
As a generic concept, the term is used to encompass both diffusion of
technologies and technological cooperation across and within countries.
Characteristic time for a process to be expressed. Since many processes
exhibit most of their effects early, and then have a long period during
which they gradually approach full expression, for the purpose of this
report the time scale is numerically defined as the time required for a
perturbation in a process to show at least half of its final effect.
The lowest part of the atmosphere from the surface to about 10 km in
altitude in mid-latitudes (ranging from 9 km in high latitudes to 16 km in
the tropics on average) where clouds and "weather" phenomena occur. In the
troposphere, temperatures generally decrease with height.
An expression of the degree to which a value (e.g., the future state of
the climate system) is unknown. Uncertainty can result from lack of
information or from disagreement about what is known or even knowable. It
may have many types of sources, from quantifiable errors in the data to
ambiguously defined concepts or terminology, or uncertain projections
of human behavior. Uncertainty can therefore be represented by
quantitative measures (e.g., a range of values calculated by various
models) or by qualitative statements (e.g., reflecting the judgment of a
team of experts).
The degree to which a system is susceptible to, or unable to cope with,
adverse effects of climate change, including
and extremes. Vulnerability is a function of the character, magnitude, and
rate of climate variation to which a system is exposed, its
and its adaptive capacity.
The specific condition of the atmosphere at a particular place and
time. It is measured in terms of parameters such as wind, temperature,
humidity, atmospheric pressure, cloudiness, and precipitation.