B
Ablation
All processes by which snow and ice are lost from a glacier,
floating ice, or snow cover.
Acclimatization
The physiological adaptation to climatic variations.
Active Layer
The top layer of soil in permafrost that is subjected to
seasonal freezing and thawing.
Adaptability
See adaptive capacity.
Adaptation
Adjustment in natural or human systems in response to actual
or expected climatic s t i m u l i or their effects, which moderates
harm or exploits beneficial opportunities. Various types of
adaptation can be distinguished, including anticipatory and
reactive adaptation, private and public adaptation, and
autonomous and planned adaptation:
– Anticipatory Adaptation—Adaptation that takes
place before impacts of climate change are observed.
Also referred to as proactive adaptation.
– Autonomous Adaptation—Adaptation that does not
constitute a conscious response to climatic stimuli
but is triggered by ecological changes in natural
s y stems and by market or welfare changes in human
systems. Also referred to as spontaneous adaptation.
– Planned Adaptation—Adaptation that is the result of
a deliberate policy decision, based on an awareness
that conditions have changed or are about to change
and that action is required to return to, maintain, or
achieve a desired state.
– Private Adaptation—Adaptation that is initiated and
implemented by individuals, households or private
companies. Private adaptation is usually in the
actor’s rational self-interest.
– Public Adaptation—Adaptation that is initiated and
implemented by governments at all levels. Public
adaptation is usually directed at collective needs.
– Reactive Adaptation—Adaptation that takes place
after impacts of climate change have been observed.
See also adaptation assessment, adaptation benefits,
adaptation costs, adaptive capacity, and maladaptation.
Adaptation Assessment
The practice of identifying options to adapt to climate change
and evaluating them in terms of criteria such as availability,
benefits, costs, effectiveness, efficiency, and feasibility.
Adaptation Benefits
The avoided damage costs or the accrued benefits following
the adoption and implementation of adaptation measures.
Adaptation Costs
Costs of planning, preparing for, facilitating, and implementing
adaptation measures, including transition costs.
Adaptive Capacity
The ability of a system to adjust to climate change ( i n c l u d i n g
climate variability and extremes) to moderate potential
d a mages, to take advantage of opportunities, or to cope with
the consequences.
Aero-Allergens
Allergens present in the air.
Aerosols
Acollection of airborne solid or liquid particles, with a typical
size between 0.01 and 10 mm 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
l i f etime of clouds.
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).
Aggregate Impacts
Total impacts summed up across sectors and/or regions. The
aggregation of impacts requires knowledge of (or assumptions
about) the relative importance of impacts in different sectors
and regions. Measures of aggregate impacts include, for
example, the total number of people affected, change in net
primary productivity, number of systems undergoing change,
or total economic costs.
Agronomy
The branch of agriculture that deals with the theory and
practice of field-crop production and the scientific
management of soil.
Alases
Coalescing thaw depressions.
Albedo
The fraction of solar radiation reflected by a surface or
object, often expressed as a percentage. Snow-covered
s u rfaces have a high albedo; the albedo of soils ranges from
high to low; vegetation-covered surfaces and oceans have a
low albedo. The Earth’s albedo varies mainly through
v a r ying cloudiness, snow, ice, leaf area, and land-cover
changes.
Algal Blooms
A reproductive explosion of algae in a lake, river, or
ocean.
Alkalinity
A measure of the capacity of water to neutralize acids.

Allergens
Antigenic substances capable of producing immediate-type
hypersensitivity.
Alpine
The biogeographic zone made up of slopes above timberline
and characterized by the presence of rosette-forming herbaceous
plants and low shrubby slow-growing woody plants.
Alternative Risk Transfer
Capital-market alternatives to traditional insurance (e.g.,
c a tastrophe bonds).
Anadromous Species
A species of fish, such as salmon, that spawn in freshwater
then migrate into the ocean to grow to maturity.
Anaerobic
Living, active, or occurring in the absence of free oxygen.
Anoxia
A deficiency of oxygen, especially of such severity as to
result in permanent damage.
Antarctic Bottomwater
A type of water in the seas surrounding Antarctica with
t e mperatures ranging from 0 to -0.8°C, salinities from
.6 to 34.7 PSU, and a density near 27.88. This is the
densest water in the free ocean.
Antarctic Circumpolar Current
A Southern Ocean current that flows around the entire globe
driven by the circumpolar westerlies.
Antarctic Intermediate Water
Created through large-scale cooling and Ekman convergence
in the Southern Ocean.
Anthropogenic
Resulting from or produced by human beings.
AOGCM
See climate model.
Apex Consumers
Organisms at the top of food chains; top predators.
Aquaculture
Breeding and rearing fish, shellfish, etc., or growing plants
for food in special ponds.
Aquifer
Astratum of permeable rock that bears water. An unconfined
aquifer is recharged directly by local rainfall, rivers, and l a k e s ,
and the rate of recharge will be influenced by the permeability
of the overlying rocks and soils. A confined aquifer is
c h a racterized by an overlying bed that is impermeable and
the local rainfall does not influence the aquifer.
Arbovirus
Any of various viruses transmitted by arthropods and
including the causative agents of dengue fever, yellow fever,
and some types of encephalitis.
Arid Regions
Ecosystems with <250 mm precipitation per year.
Autotrophic
Organisms independent of external sources of organic
carbon (compounds) for provision of their own organic
constituents, which they can manufacture entirely from
i n o rganic material. Plants are autotrophic (photoautotrophs)
using the energy of sunlight to produce organic carbon
c o mpounds from inorganic carbon and water in the process
of photosynthesis.
Baseflow
Sustained flow in a river or stream that is primarily produced
by groundwater runoff, delayed subsurface runoff, and/or
lake outflow.
Baseline/Reference
The baseline (or reference) is any datum against which
change is measured. It might be a “current baseline,” in
which case it represents observable, present-day conditions.
It might also be a “future baseline,” which is a projected
future set of conditions excluding the driving factor of
i n t e rest. Alternative interpretations of the reference conditions
can give rise to multiple baselines.
Basin
The drainage area of a stream, river, or lake.
Benthic Organisms
The biota living on, or very near, the bottom of the sea,
river, or lake.
Biodiversity
The numbers and relative abundances of different
genes (genetic diversity), species, and ecosystems
(communities) in a particular area. See also functional
diversity.
Biodiversity Hot Spots
Areas with high concentrations of endemic species facing
extraordinary habitat destruction.
Biofuels
A fuel produced from dry organic matter or combustible oils
produced by plants. Examples of biofuel include alcohol (from
fermented sugar), black liquor from the paper manufacturing
process, wood, and soybean oil.
Biomass
The total mass of living organisms in a given area or
volume; recently dead plant material is often included as
dead biomass.

Biome
A grouping of similar plant and animal communities into
broad landscape units that occur under similar environmental
conditions.
Biosphere
The part of the Earth system comprising all ecosystems and
living organisms in the atmosphere, on land (terrestrial
b i o sphere), or in the oceans (marine biosphere), including
derived dead organic matter, such as litter, soil org a n i c
m a tter, and oceanic detritus.
Biota
All living organisms of an area; the flora and fauna considered
as a unit.
Bog
A poorly drained area rich in accumulated plant material,
frequently surrounding a body of open water and
having a characteristic flora (such as sedges, heaths, and
sphagnum).
Boreal Forest
Forests of pine, spruce, fir, and larch stretching from the
east coast of Canada westward to Alaska and continuing
from Siberia westward across the entire extent of Russia to
the European Plain.
Breakwater
An offshore structure (such as a wall or jetty) that, by
b r e a king the force of the wave, protects a harbor, anchorage,
beach, or shore area.
C3 Plants
Plants that produce a three-carbon compound during
photosynthesis, including most trees and agricultural
crops such as rice, wheat, soybeans, potatoes, and
vegetables.
C4 Plants
Plants that produce a four-carbon compound during
photosynthesis (mainly of tropical origin), including grasses
and the agriculturally important crops maize, sugar cane,
millet, and sorghum.
Carbon Cycle
The term used to describe the flow of carbon (in various
forms, e.g., as in carbon dioxide) through the atmosphere,
ocean, terrestrial biosphere, and lithosphere.
Carbon Dioxide (CO2)
A naturally occurring gas, also a by-product of burning
fossil fuels and biomass, as well as from land-use changes
and other industrial processes. 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 Fertilization
The enhancement of the growth of plants as a result of
increased atmospheric carbon dioxide concentration.
Depending on their mechanism of photosynthesis, certain
types of plants are more sensitive to changes in atmospheric
CO2 concentration. In particular, C3 plants generally show a
larger response to CO2 than C4 plants.
Carbon Flux
Transfer of carbon from one carbon pool to another in units
of measurement of mass per unit area and time (e.g., t C).
Carrying Capacity
The number of individuals in a population that the resources
of a habitat can support.
Catchment
An area that collects and drains rainwater.
Chagas’Disease
A parasitic disease caused by the Trypanosoma cruzi and
transmitted by triatomine bugs in the Americas, with two
clinical periods: acute (fever, swelling of the spleen, edemas) and
chronic (digestive syndrome, potentially fatal heart condition).
Cholera
An intestinal infection that results in frequent watery stools,
cramping abdominal pain, and eventual collapse from
dehydration.
Climate
Climate in a narrow sense is usually defined as the “average
weather,” or more rigorously, as the statistical description in
terms of the mean and variability of relevant quantities over
a period of time ranging from months to thousands of years.
The classical period is 3 decades, as defined by the World
Meteorological Organization (WMO). These quantities are
most often surface variables such as temperature,
precipitation, and wind. Climate in a wider sense is the s t a t e ,
including a statistical description, of the climate system.
Climate Change
Climate change refers to any change in climate over time,
whether due to natural variability or as a result of human
activity. This usage differs from that in the United Nations
Framework Convention on Climate Change (UNFCCC),
which defines “climate change” as: “a change of climate
which is attributed directly or indirectly to human activity
that alters the composition of the global atmosphere and
which is in addition to natural climate variability observed
over comparable time periods.” See also climate variability.
Climate Model (Hierarchy)
A numerical representation of the climate system based on
the physical, chemical, and biological properties of its
c o mponents, their interactions and feedback processes, and
accounting for all or some of its known properties. T h e
c l imate system can be represented by models of varying

complexity (i.e., for any one component or combination of
components a hierarchy of models can be identified, diff e ring
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
parameterizations are involved. Coupled atmosphere/ocean/
sea-ice General Circulation Models (AOGCMs) 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
i n t e rannual climate predictions.
Climate Prediction
A climate prediction or climate forecast is the result of an
attempt to produce a most likely description or estimate of
the actual evolution of the climate in the future (e.g., at
s e asonal, interannual, or long-term time scales. See also
c l imate projection and climate scenario.
Climate Projection
Aprojection of the response of the climate system to emission
or concentration scenarios of g reenhouse gases and a e ro s o l s,
or radiative forcing scenarios, often based upon simulations
by climate models. Climate projections are distinguished
from climate predictions in order to emphasize that climate
projections depend upon the emission/concentration/radiative
forcing scenario used, which are based on assumptions,
c o ncerning, for example, future socioeconomic and
technological developments that may or may not be realized
and are therefore subject to substantial uncertainty.
Climate Scenario
A plausible and often simplified representation of the future
c l i m a t e, 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
c o nstructing climate scenarios, but climate scenarios usually
require additional information such as about the observed
current climate. A “climate change scenario” is the diff e rence
between a climate scenario and the current climate.
Climate System
The climate system is the highly complex system consisting
of five major components: the atmosphere, the hydrosphere,
the cryosphere, the land surface, 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 volcanic eruptions, solar
variations and human-induced forcings such as the changing
composition of the atmosphere and land use.
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 temporal and spatial
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.
CO2 Fertilization
See carbon dioxide fertilization.
Communicable Disease
An infectious disease caused by transmission of an infective
biological agent (virus, bacterium, protozoan, or multicellular
macroparasite).
Coping Range
The variation in climatic stimuli that a system can absorb
without producing significant impacts.
Coral Bleaching
The paling in color of corals resulting from a loss of symbiotic
algae. Bleaching occurs in response to physiological shock in
response to abrupt changes in temperature, salinity, and turbidity.
Cordillera
An individual mountain chain with closely connected,
distinct summits. In South America, “cordillera” refers to an
individual mountain range.
Cryosphere
The component of the climate system consisting of all snow,
ice, and permafrost on and beneath the surface of the earth
and ocean.
Cryptosporidiosis
An opportunistic infection caused by an intestinal parasite
common in animals. Transmission occurs through ingestion
of food or water contaminated with animal feces. The parasite
causes severe chronic diarrhea, especially in people with HIV.
Deepwater Formation
Occurs when seawater freezes to form sea ice. The local
release of salt and consequent increase in water density
leads to the formation of saline coldwater that sinks to the
ocean floor. See Antarctic bottomwater.
Deforestation
Conversion of forest to non-forest. For a discussion of the
term forest and related terms such as afforestation,
re f o re s t a t i o n, and d e f o re s t a t i o n, see the IPCC Special Report
on Land Use, Land-Use Change, and Fore s t ry (IPCC, 2000).
Dengue Fever
An infectious viral disease spread by mosquitoes, often
called breakbone fever because it is characterized by severe
pain in joints and back. Subsequent infections of the virus
may lead to dengue haemorrhagic fever (DHF) and dengue
shock syndrome (DSS), which may be fatal.

Desert
An ecosystem with <100 mm precipitation per year.
Desertification
Land degradation in arid, semi-arid, and dry sub-humid areas
resulting from various factors, including climatic variations
and human activities. Further, the United Nations
Convention to Combat Desertification (UNCCD) defines
land degradation as a reduction or loss in arid, semi-arid,
and dry sub-humid areas of the biological or economic
p r oductivity and complexity of rain-fed cropland, irrigated
cropland, or range, pasture, forest, and woodlands resulting
from land uses or from a process or combination of
p r o c e s ses, including those arising from human activities and
habitation patterns, such as: (i) soil erosion caused by wind
and/or water; (ii) deterioration of the physical, chemical,
and biological or economic properties of soil; and (iii) longterm
loss of natural vegetation.
Diatom
A class of unicellular algae (Bacillariophyceae) that are
widespread on soil surfaces and in freshwater and marine
systems, especially cold waters of relatively low salinity.
These have cell sizes ranging from 5 to 2000 μm.
Disturbance Regime
Frequency, intensity, and types of disturbances, such as
fires, inspect or pest outbreaks, floods, and droughts.
Diurnal Temperature Range
The difference between the maximum and minimum
temperature during a day.
Downscaling
Reducing the scale of a model from a global to regional level.
Drought
The phenomenon that exists when precipitation has been
significantly below normal recorded levels, causing serious
hydrological imbalances that adversely affect land resource
production systems.
Ecosystem
A distinct system of interacting living organisms, together
with their physical environment. The boundaries of what
could be called an ecosystem are somewhat arbitrary,
depending on the focus of interest or study. Thus the extent
of an ecosystem may range from very small spatial scales
to, ultimately, the entire Earth.
Ecosystem Services
Ecological processes or functions which have value to
individuals or society
Ecotone
Transition area between adjacent ecological communities
(e.g., between forests and grasslands), usually involving
competition between organisms common to both.
Edaphic
Of or relating to the soil; factors inherent in the soil.
Effective Rainfall
The portion of the total rainfall that becomes available for
plant growth.
El Niño-Southern Oscillation (ENSO)
El Niño, in its original sense, is a warmwater current that
periodically flows along the coast of Ecuador and Peru,
d i srupting 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
p h enomenon is collectively known as El Niño-Southern
Oscillation. During an El Niño 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 Niño event is
called La Niña.
Emission Scenario
A plausible representation of the future development of
emissions of substances that are potentially radiatively
active (e.g., g reenhouse gases, a e ro s o l s), based on a
c o h e rent and internally consistent set of assumptions about
driving forces (such as demographic and socioeconomic
development, technological change) and their key
r e l a t i o nships. In 1992, the IPCC presented a set of emission
scenarios that were used as a basis for the climate projections
in the Second Assessment Report (IPCC, 1996). These
emission scenarios are referred to as the IS92 scenarios. In
the IPCC Special Report on Emission Scenarios
(Nakicenovic et al., 2000), new emission scenarios—the
s o -called SRES scenarios—were published.
Endemic
Restricted or peculiar to a locality or region. With regard to
human health, endemic can refer to a disease or agent present
or usually prevalent in a population or geographical area at
all times.
Endorheic Lake
A lake with no outflow; also known as a closed lake.
Enzootic
A disease affecting the animals in an area. It corresponds to
an endemic disease among humans.
Epidemic
Occurring suddenly in numbers clearly in excess of normal
expectancy, said especially of infectious diseases but applied
also to any disease, injury, or other health-related event
occurring in such outbreaks.

Erosion
The process of removal and transport of soil and rock by
weathering, mass wasting, and the action of streams, glaciers,
waves, winds, and underground water.
Eustatic Sea-Level Rise
See sea-level rise.
Eutrophication
The process by which a body of water (often shallow)
becomes (either naturally or by pollution) rich in
dissolved nutrients with a seasonal deficiency in dissolved
oxygen.
Evaporation
The process by which a liquid becomes a gas.
Evapotranspiration
The combined process of e v a p o r a t i o n from the Earth’s surface
and transpiration from vegetation.
Exoheic Lake
A lake drained by outflowing rivers.
Exotic Species
See introduced species.
Exposure
The nature and degree to which a system is exposed to
s i gnificant climatic variations.
Exposure Unit
An activity, group, region, or resource that is subjected to
climatic stimuli.
Externalities
By-products of activities that affect the well-being of people
or the environment, where those impacts are not reflected in
market prices. The costs (or benefits) associated with
externalities do not enter cost-accounting schemes.
Extinction
The complete disappearance of an entire species.
Extirpation
The disappearance of a species from part of its range; local
extinction.
Extreme Weather Event
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).
Extrinsic Incubation Period
In blood-feeding anthropod vectors, the time between
a c q u isition of the infectious blood meal and the time when
the anthropod becomes capable of transmitting the agent. In
the case of malaria, the life stages of the plasmodium parasite
spent within the female mosquito vector (i.e., outside the
human host).
Feedback
A process that triggers changes in a second process that in
turn influences the original one; a positive feedback
i n t e n s ifies the original process, and a negative feedback
reduces it.
Fen
Low land covered wholly or partly with water unless
artificially drained.
Fiber
Wood, fuelwood (either woody or non-woody).
Food Insecurity
A situation that exists when people lack secure access to
sufficient amounts of safe and nutritious food for normal
growth and development and an active and healthy life. It
may be caused by the unavailability of food, insufficient
purchasing power, inappropriate distribution, or inadequate
use of food at the household level. Food insecurity may be
chronic, seasonal, or transitory.
Forecast
See climate prediction and climate projection.
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 f o re s t and related
terms such as afforestation, reforestation, and deforestation,
see the IPCC Special Report on Land Use, Land-Use
Change, and Forestry (IPCC, 2000).
Freshwater Lens
Alenticular fresh groundwater body that underlies an oceanic
island. It is underlain by saline water.
Functional Diversity
The number of functionally different organisms in an
ecosystem (also referred to as “functional types” and
“ f u n ctional groups”).
General Circulation Model (GCM)
See climate model.
General Equilibrium Analysis
An approach that considers simultaneously all the markets
in an economy, allowing for feedback effects between
i n d ividual markets.

Geomorphic
Pertaining to the form of the Earth or its surface features.
Glacier
Amass of land ice flowing downhill (by internal deformation
and sliding at the base) and constrained by the surrounding
topography (e.g., the sides of a valley or surrounding
peaks); the bedrock topography is the major influence on
the dynamics and surface slope of a glacier. A glacier is
maintained by accumulation of snow at high altitudes,
b a lanced by melting at low altitudes or discharge into the
sea.
Greenhouse Effect
Greenhouse gases effectively absorb infrared radiation
e m i tted by the Earth’s surface, by the atmosphere itself due
to the same gases, and by clouds. Atmospheric radiation is
emitted to all sides, including downward to the Earth’s
s u rface. Thus greenhouse gases trap heat within the surfacetroposphere
system. This is called the “natural greenhouse
effect.” Atmospheric radiation is strongly coupled to the
temperature of the level at which it is emitted. In the
troposphere, the temperature generally decreases with height.
Effectively, infrared radiation emitted to space originates
from an altitude with a temperature of on average -19°C,
in balance with the net incoming solar radiation, whereas
the Earth’s surface is kept at a much higher temperature of
on average 14°C. An increase in the concentration of
g r e e nhouse gases leads to an increased infrared opacity of
the atmosphere, and therefore to an effective radiation into
space from a higher altitude at a lower temperature. This
causes a radiative forcing, an imbalance that can only be
compensated for by an increase of the temperature of the
surface-troposphere system. This is called the “enhanced
greenhouse effect.”
Greenhouse Gas
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 g re e nhouse
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 chlorineand
bromine-containing substances which are dealt with
under the Montreal Protocol. Beside CO2, N2O, and CH4,
the Kyoto Protocol deals with the greenhouse gases sulfur
hexaflouride (SF6), hydrofluorocarbons (HFCs) and
perfluorocarbons (PFCs).
Groin
A l o w, narrow jetty, usually extending roughly perpendicular
to the shoreline, designed to protect the shore from erosion
by currents, tides, or waves, or to trap sand for the purpose
of building up or making a beach.
Gross Primary Production
The amount of carbon fixed from the atmosphere through
photosynthesis.
Groundwater Recharge
The process by which external water is added to the zone of
saturation of an aquifer, either directly into a formation or
indirectly by way of another formation.
Habitat
The particular environment or place where an organism or
species tends to live; a more locally circumscribed portion
of the total environment.
Halocline
Alayer in the ocean in which the rate of salinity variation with
depth is much larger than layers immediately above or below it.
Hantavirus
A virus in the family Bunyaviridae that causes a type of
haemorrhagic fever. It is thought that humans catch the
d i sease mainly from infected rodents, either through direct
contact with the animals or by inhaling or ingesting dust
that contains their dried urine.
Heath
Any of the various low-growing shrubby plants of open
wastelands, usually growing on acidic, poorly drained soils.
Heat Island
An area within an urban area characterized by ambient
t e mperatures higher than those of the surrounding area because
of the absorption of solar energy by materials like asphalt.
Herbaceous
Flowering, non-woody plants.
Heterotrophic Respiration
The release of CO2 from decomposition of organic matter.
Highland Malaria
Malaria that occurs around the altitudinal limits of its
distribution.
Human Settlement
A place or area occupied by settlers.
Human System
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, economic system); all are
human systems in the sense applied in the TAR.
Hypolimnion
The part of a lake below the thermocline made up of water
that is stagnant and of essentially uniform temperature
except during the period of overturn.

Ice Cap
A dome-shaped ice mass covering a highland area that is
considerably smaller in extent than ice sheets.
Ice Jam
An accumulation of broken river or sea ice caught in a narrow
channel.
Ice Sheet
A mass of land ice which is sufficiently deep to cover most
of the underlying bedrock topography, so that its shape is
mainly determined by its internal dynamics (the flow of the
ice as it deforms internally and slides at its base). An ice
sheet flows outwards from a high central plateau with a
small average surface slope. The margins slope steeply, and
the 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 large ice sheets in
the modern world—on Greenland and Antarctica, the
Antarctic ice sheet being divided into east and west by the
Transantarctic Mountains; during glacial periods there were
others.
Ice Shelf
A floating ice sheet of considerable thickness attached to a
coast (usually of great horizontal extent with a level or
g e ntly undulating surface); often a seaward extension of ice
sheets.
Immunosuppression
Reduced functioning of an individual’s immune system.
(Climate) Impact Assessment
The practice of identifying and evaluating the detrimental
and beneficial consequences of climate change on natural
and human systems.
(Climate) Impacts
Consequences of climate change on natural and human
s y stems. 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 after adaptation.
See also a g g regate impacts, market impacts, and n o n - m a rket
impacts.
Indigenous Peoples
People whose ancestors inhabited a place or a country when
persons from another culture or ethnic background arrived
on the scene and dominated them through conquest,
settlement, or other means and who today live more in
conformity with their own social, economic, and cultural
customs and traditions than those of the country of which they
now form a part (also referred to as “native,” “aboriginal,” or
“tribal” peoples)
Industrial Revolution
A period of rapid industrial growth with far-reaching social
and economic consequences, beginning in England during
the second half of the 18th century and spreading to Europe
and later to other countries including the United States. The
industrial revolution marks the beginning of a strong increase
in the use of fossil fuels and emission of in particular fossil
carbon dioxide. In the TAR, the terms “pre-industrial” and
“industrial” refer, somewhat arbitrarily, to the periods before
and after 1750, respectively.
Infectious Diseases
Any disease that can be transmitted from one person to
a n o t h e r. This may occur by direct physical contact, by
c o mmon handling of an object that has picked up infective
o rganisms, through a disease carrier, or by spread of infected
droplets coughed or exhaled into the air.
Infrastructure
The basic equipment, utilities, productive enterprises,
i n s t a llations, and services essential for the development,
operation, and growth of an organization, city, or nation.
Insolvency
Inability to meet financial obligations; bankruptcy.
Integrated Assessment
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.
Introduced Species
A species occurring in an area outside its historically known
natural range as a result of accidental dispersal by humans
(also referred to as “exotic species” or “alien species”).
Invasive Species
An introduced species that invades natural habitats.
Keystone Species
A species that has a central servicing role affecting many
other organisms and whose demise is likely to result in the
loss of a number of species and lead to major changes in
ecosystem function.
Kyoto Protocol
The Kyoto Protocol was adopted at the Third Session of the
Conference of the Parties (COP) to the UN Framework
Convention on Climate Change (UNFCCC) in 1997 in
Kyoto, Japan. It contains legally binding commitments, in
addition to those included in the UNFCCC. Countries included
in Annex B of the Protocol (most OECD countries and
EITs) agreed to reduce their anthropogenic GHG emissions
( C O2, CH4, N2O, HFCs, PFCs, and SF6) by at least 5% below
levels in the commitment period 2008 to 2012. The
Kyoto Protocol has not yet entered into force (as of June 2001).

La Niña
See El Niño-Southern Oscillation (ENSO).
Land Use
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, conservation).
Landslide
A mass of material that has slipped downhill by gravity,
often assisted by water when the material is saturated; rapid
movement of a mass of soil, rock, or debris down a slope.
Large-Scale Singularities
Abrupt and dramatic changes in systems in response to
smooth changes in driving forces. For example, a gradual
increase in atmospheric greenhouse gas concentrations may
lead to such large-scale singularities as slowdown or collapse
of the thermohaline circulation or collapse of the West
Antarctic Ice Sheet. The occurrence, magnitude, and timing
of large-scale singularities are difficult to predict.
Leaching
The removal of soil elements or applied chemicals through
percolation.
Legume
Plants that are able to fix nitrogen from the air through a
symbiotic relationship with soil bacteria (e.g., peas, beans,
alfalfa, clovers).
Limnology
Study of lakes and their biota.
Littoral Zone
A coastal region; the shore zone between high and low
watermarks.
Local Agenda 21
Local Agenda 21s are the local plans for environment and
development that each local authority is meant to develop
through a consultative process with their populations, with
particular attention paid to involving women and youth.
Many local authorities have developed Local Agenda 21s
through consultative processes as a means of reorienting
their policies, plans, and operations towards the achievement
of sustainable development goals. The term comes from
Chapter 28 of Agenda 21—the document formally endorsed
by all government representatives attending the UN
Conference on Environment and Development (also known
as the Earth Summit) in Rio de Janeiro in 1992.
Maladaptation
Any changes in natural or human systems that inadvertently
increase vulnerability to climatic stimuli; an adaptation that
does not succeed in reducing vulnerability but increases it
instead.
Malaria
Endemic or epidemic parasitic disease caused by species of
the genus Plasmodium (protozoa) and transmitted by
mosquitoes of the genus Anopheles; produces high fever
attacks and systemic disorders, and kills approximately
million people every year.
Market Impacts
Impacts that are linked to market transactions and directly
affect gross domestic product (GDP, a country’s national
accounts)—for example, changes in the supply and price of
agricultural goods. See also non-market impacts.
Mass Movement
Applies to all unit movements of land material propelled
and controlled by gravity.
Meningitis
Inflammation of the meninges (part of the covering of the
brain).
Metazoan
An animal whose body consists of many cells. See also
protozoan
Microbial Loop
Complex food web involving bacteria, single-celled animals
and plants, viruses, and dissolved and particulate organic
material. Dissolved and particulate material, released from
o rganisms, is utilized by bacteria, which are grazed by
p r otozoa which in turn are grazed by metazoa. Around 50%
(often more) of primary production passes through the
microbial loop rather than along the classical food chain of
phytoplankton to herbivore.
Microclimate
Local climate at or near the Earth’s surface. See also
climate.
Mitigation
An anthropogenic intervention to reduce the sources or
enhance the sinks of greenhouse gases.
Mixed Layer
The upper region of the ocean well-mixed by interaction
with the overlying atmosphere.
Monsoon
Wind in the general atmospheric circulation typified
by a seasonal persistent wind direction and by a
pronounced change in direction from one season to the
next.
Montane
The biogeographic zone made up of relatively moist, cool
upland slopes below timberline and characterized by the
presence of large evergreen trees as a dominant life
form.

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 consumption and production of chlorine- and
bromine-containing chemicals that destroy stratospheric o z o n e,
such as CFCs, methyl chloroform, carbon tetrachloride, and
many others.
Morbidity
Rate of occurrence of disease or other health disorder within
a population, taking account of the age-specific morbidity
rates. Health outcomes include chronic disease incidence/
prevalence, rates of hospitalization, primary care consultations,
disability-days (i.e., days when absent from work), and
prevalence of symptoms.
Morphology
The form and structure of an organism or any of its parts.
Mortality
Rate of occurrence of death within a population within a
specified time period; calculation of mortality takes
account of age-specific death rates, and can thus yield
measures of life expectancy and the extent of premature
death.
Nanoplankton
Phytoplankton whose lengths range from 10-50 μm.
Net Biome Production (NBP)
Net gain or loss of carbon from a region. NBP is equal to
Net Ecosystem Production minus the carbon lost due to a
disturbance (e.g., a forest fire or a forest harvest).
Net Ecosystem Production (NEP)
Net gain or loss of carbon from an ecosystem. NEP is equal
to Net Primary Production minus the carbon lost through
heterotrophic respiration.
Net Primary Production (NPP)
The increase in plant biomass or carbon of a unit of a
l a n dscape. NPP is equal to Gross Primary Production minus
carbon lost through autotrophic respiration.
Nitrogen Oxides (NOx)
Any of several oxides of nitrogen.
Non-Linearity
A process is called “non-linear” when there is no simple
proportional relation between cause and effect.
Non-Market Impacts
Impacts that affect ecosystems or human welfare, but that
are not directly linked to market transactions—for example,
an increased risk of premature death. See also market
impacts.
Non-Point-Source Pollution
Pollution from sources that cannot be defined as discrete
points, such as areas of crop production, timber, surface
mining, disposal of refuse, and construction. See also pointsource
pollution.
No Regrets Policy
One that would generate net social benefits whether or not
there is anthropogenic climate change.
North Atlantic Oscillation (NAO)
The North Atlantic Oscillation consists of opposing variations
of barometric pressure near Iceland and near the Azores. It
is the dominant mode of winter climate variability in the
North Atlantic region ranging from central North America to
Europe.
Obligate Species
Species restricted to one particularly characteristic mode of
life.
Ocean Conveyor Belt
The theoretical route by which water circulates around the
entire global ocean, driven by wind and the thermohaline
circulation.
Ocean Ventilation
Downwelling of water from near the surface to the deep
ocean. See also deepwater formation.
Oligotrophic
Relatively unproductive areas of the sea, lakes, and rivers
with low nutrient content. See also eutrophic.
Opportunity Costs
The cost of an economic activity forgone by the choice of
another activity.
Orography
The study of the physical geography of mountains and
mountain systems.
Ozone
Ozone, the triatomic form of oxygen (O3), is a gaseous
atmospheric constituent. In the troposphere, it is created
both naturally and by photochemical reactions involving
gases resulting from human activities (photochemical
smog). In high concentrations, tropospheric ozone can be
harmful to a wide-range of living organisms. Tropospheric
ozone acts as a g reenhouse gas. In the stratosphere, ozone
is created by the interaction between solar ultraviolet
r a d i ation and molecular oxygen (O2). Stratospheric
ozone plays a decisive role in the stratospheric
radiative balance. Depletion of stratospheric
ozone, due to chemical reactions that may be enhanced
by climate change, results in an increased ground-level
flux of ultraviolet (UV-) B radiation. See also Montreal
Protocol.

Particulates
Very small solid exhaust particles emitted during the
combustion of fossil and biomass fuels. Particulates may
consist of a wide variety of substances. Of greatest concern
for health are particulates of less than or equal to 10 nm in
diameter, usually designated as PM10.
Peat
Unconsolidated soil material consisting largely of partially
decomposed organic matter accumulated under conditions
of excess moisture or other conditions that decrease
decomposition rates.
Pelagic
Of, relating to, or living or occurring in the open sea.
Permafrost
Perennially frozen ground that occurs wherever the
temperature remains below 0°C for several years.
Phenology
The study of natural phenomena that recur periodically
(e.g., blooming, migrating) and their relation to climate and
seasonal changes.
Photic Zone
The upper waters of lakes, rivers, and sea sufficiently
illuminated for photosynthesis to occur.
Photochemical Smog
A mix of photochemical oxidant air pollutants produced by
the reaction of sunlight with primary air pollutants, especially
hydrocarbons.
Photosynthate
The product of photosynthesis.
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
CO2 concentrations. See also CO2 fertilization, C3 plants,
and C4 plants.
Physiographic
Of, relating to, or employing a description of nature or
n a tural phenomena.
Phytophagous Insects
Insects that feed on plants.
Phytoplankton
The plant forms of plankton (e.g., diatoms). Phytoplankton
are the dominant plants in the sea, and are the bast of the
entire marine food web. These single-celled organisms are
the principal agents for photosynthetic carbon fixation in the
ocean. See also zooplankton.
Plankton
Aquatic organisms that drift or swim weakly. See also
phytoplankton and zooplankton.
Point-Source Pollution
Pollution resulting from any confined, discrete source, such
as a pipe, ditch, tunnel, well, container, concentrated animalfeeding
operation, or floating craft. See also n o n - p o i n t - s o u rc e
pollution.
Polynyas
Areas of open water in pack ice or sea ice.
Pool
See reservoir.
Potential Production
Estimated production of a crop under conditions when
n u t r ients and water are available at optimum levels for plant
growth and development; other conditions such as day
length, temperature, soil characteristics, etc., determined by
site characteristics.
Pre-Industrial
See Industrial Revolution.
Primary Energy
Energy embodied in natural resources (e.g., coal, crude oil,
sunlight, uranium) that has not undergone any a n t h ropogenic
conversion or transformation.
Producer Surplus
Returns beyond the cost of production that provide
compensation for owners of skills or assets that are scarce
(e.g., agriculturally productive land).
Projection (Generic)
A projection is a potential future evolution of a quality or
set of quantities, often computed with the aid of a model.
Projections are distinguished from predictions in order to
emphasize that projections involve assumptions—concerning,
for example, future socioeconomic and technological
developments that may or may not be realized—and are
therefore subject to substantial uncertainty. See also climate
projection and climate prediction.
Protozoan
A single-celled animal.
Radiative Forcing
Radiative forcing is the change in the net vertical irradiance
[expressed in Watts per square meter (Wm-2)] at the
tropopause due to an internal change or a change in the
external forcing of the climate system, such as a change in
the concentration of CO2 or the output of the Sun. Usually
radiative forcing is computed after allowing for stratospheric
temperatures to readjust to radiative equilibrium, but with all
tropospheric properties held fixed at their unperturbed values.

Rangeland
Unimproved grasslands, shrublands, savannas, and tundra.
Reference Scenario
See baseline/reference.
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
Special Report on Land Use, Land-Use Change, and
Forestry (IPCC, 2000).
Regeneration
The renewal of a stand of trees through either natural means
(seeded onsite or adjacent stands or deposited by wind,
birds, or animals) or artificial means (by planting seedlings
or direct seeding).
Reinsurance
The transfer of a portion of primary insurance risks to a
s e condary tier of insurers (reinsurers); essentially “insurance
for insurers.”
Reservoir
Acomponent of the climate system, other than the atmosphere,
that has the capacity to store, accumulate, or release a substance
of concern (e.g., carbon, a greenhouse gas, or precursor).
Oceans, soils, and f o re s t s 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
substances of concern held within a reservoir at a specified
time is called the “stock.” The term also means an artificial
or natural storage place for water, such as a lake, pond, or
aquifer, from which the water may be withdrawn for such
purposes as irrigation, water supply, or irrigation.
Reservoir Host
Any animal, plant, soil, or inanimate matter in which a
pathogen normally lives and multiplies, and on which it
depends primarily for survival (e.g., foxes are a reservoir for
rabies). Reservoir hosts may be asymptomatic.
Resilience
Amount of change a system can undergo without changing state.
Respiration
The process whereby living organisms convert organic matter
to carbon dioxide, releasing energy and consuming oxygen.
Riparian
Relating to or living or located on the bank of a natural
watercourse (as a river) or sometimes of a lake or a tidewater.
Runoff
That part of precipitation that does not evaporate. In some
countries, runoff implies surface runoff only.
Salinization
The accumulation of salts in soils.
Saltwater Intrusion/Encroachment
Displacement of fresh surface water or groundwater by the
advance of saltwater due to its greater density, usually in
coastal and estuarine areas.
Scenario (Generic)
A plausible and often simplified description of how the
future may develop, based on a coherent and internally
c o nsistent set of assumptions about driving forces and key
relationships. Scenarios may be derived from projections,
but are often based on additional information from other
sources, sometimes combined with a “narrative storyline.”
See also climate scenario and emissions scenario.
Sea-Level Rise
An increase in the mean level of the ocean. Eustatic sea-level
rise is a change in global average sea level brought about by
an alteration to the volume of the world ocean. Relative sealevel
rise occurs where there is a net increase in the level of
the ocean relative to local land movements. Climate modelers
largely concentrate on estimating eustatic sea-level change.
Impact researchers focus on relative sea-level change.
Seawall
Ahuman-made wall or embankment along a shore to prevent
wave erosion.
Semi-Arid Regions
Ecosystems that have >250 mm precipitation per year, but
are not highly productive; usually classified as rangelands.
Sensitivity
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).
Sequestration
The process of increasing the carbon content of a carbon
pool other than the atmosphere.
Silt
Unconsolidated or loose sedimentary material whose
constituent rock particles are finer than grains of sand and
larger than clay particles.
Silviculture
Development and care of forests.
Sink
Any process, activity, or mechanism that removes a
greenhouse gas, an aerosol, or a precursor of a greenhouse
gas or aerosol from the atmosphere.

Snowpacks
A seasonal accumulation of slow-melting snow.
Soil Carbon Pool
Refers to the relevant carbon in the soil. It includes various
forms of soil organic carbon (humus) and inorganic soil
c a rbon and charcoat. It excludes soil biomass (e.g., roots,
bulbs, etc.) as well as the soil fauna (animals).
Source
Any process, activity, or mechanism that releases a
greenhouse gas, an aerosol, or a precursor of a greenhouse
gas or aerosol into the atmosphere.
Southern Oscillation
A l a rge-scale atmospheric and hydrospheric fluctuation
c e ntered in the equatorial Pacific Ocean, exhibiting a pressure
anomaly, alternatively high over the Indian Ocean and high
over the South Pacific. Its period is slightly variable, averaging
.33 years. The variation in pressure is accompanied by
variations in wind strengths, ocean currents, sea-surface
temperatures, and precipitation in the surrounding areas.
Stakeholders
Person or entity holding grants, concessions, or any other type
of value that would be affected by a particular action or policy.
Stimuli (Climate-Related)
All the elements of climate change, including mean climate
characteristics, climate variability, and the frequency and
magnitude of extremes.
Stochastic Events
Events involving a random variable, chance, or probability.
Stock
See reservoir.
Stratosphere
Highly stratified region of atmosphere above the t ro p o s p h e re
extending from about 10 km (ranging from 9 km in high
l a titudes to 16 km in the tropics on average) to about 50 km.
Streamflow
Water within a river channel, usually expressed in m3 sec-1.
Sub-Antarctic Mode Water (SAMW)
A type of water in the Sub-Antarctic Zone of the Southern
Ocean. The SAMW is the deep surface layer of water with
uniform temperature and salinity created by convective
processes in the winter. It can be identified by a temperature
of around -1.8°C and a salinity of around 34.4 PSU, and is
separated from the overlying surface water by a halocline at
around 50 m in the summer. Although it is not considered to
be a water mass, it contributes to the Central Water of the
Southern Hemisphere, and is additionally responsible for the
formation of Antarctic Intermediate Water in the eastern part
of the South Pacific Ocean. It is also known as Winter Wa t e r.
Submergence
A rise in the water level in relation to the land, so that areas
of formerly dry land become inundated; it results either
from a sinking of the land or from a rise of the water level.
Subsidence
The sudden sinking or gradual downward settling of the
Earth’s surface with little or no horizontal motion.
Succession
Transition in the composition of plant communities following
disturbance.
Surface Runoff
The water that travels over the soil surface to the nearest
surface stream; runoff of a drainage basin that has not
passed beneath the surface since precipitation.
Sustainable Development
Development that meets the needs of the present without
compromising the ability of future generations to meet their
own needs.
Synoptic
Relating to or displaying atmospheric and weather conditions
as they exist simultaneously over a broad area.
Taiga
Coniferous forests of northern North America and Eurasia.
Thermal Erosion
The erosion of ice-rich permafrost by the combined thermal
and mechanical action of moving water.
Thermal Expansion
In connection with sea-level rise, 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.
Thermocline
The region in the world’s ocean, typically at a depth of
km, where temperature decreases rapidly with depth and
which marks the boundary between the surface and the
ocean.
Thermohaline Circulation
Large-scale density-driven circulation in the ocean, caused
by differences in temperature and salinity. In the North
Atlantic, the thermohaline circulation consists of warm
s u rface water flowing northward and cold deepwater flowing
southward, resulting in a net poleward transport of heat. The
surface water sinks in highly restricted sinking regions
located in high latitudes.
Thermokarst
Irregular, hummocky topography in frozen ground caused
by melting of ice.

Timberline
The upper limit of tree growth in mountains or high latitudes.
Transpiration
The emission of water vapor from the surfaces of leaves or
other plant parts.
Troposphere
The lowest part of the atmosphere from the surface to about
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.
Tsunami
A large tidal wave produced by a submarine earthquake,
landslide, or volcanic eruption.
Tundra
A treeless, level, or gently undulating plain characteristic of
arctic and subarctic regions.
Ultraviolet (UV)-B Radiation
Solar radiation within a wavelength range of 280–320 nm,
the greater part of which is absorbed by stratospheric ozone.
Enhanced UV-B radiation suppresses the immune system
and can have other adverse effects on living organisms.
Uncertainty
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).
Undernutrition
The result of food intake that is insufficient to meet dietary
energy requirements continuously, poor absorption, and/or
poor biological use of nutrients consumed.
Unique and Threatened Systems
Entities that are confined to a relatively narrow geographical
range but can affect other, often larger entities beyond their
range; narrow geographical range points to sensitivity to
environmental variables, including climate, and therefore
attests to potential vulnerability to climate change.
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 “stabilization 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 aim to return
g r e e nhouse gas emissions not controlled by the Montreal
Protocol to 1990 levels by the year 2000. The Convention
entered in force in March 1994. See also Kyoto Protocol.
Ungulate
Ahoofed, typically herbivorous, quadruped mammal (such as
a ruminant, swine, camel, hippopotamus, horse, rhinoceros,
or elephant).
Upwelling
Transport of deeper water to the surface, usually caused by
horizontal movements of surface water.
Urbanization
The conversion of land from a natural state or managed
n a tural state (such as agriculture) to cities; a process driven
by net rural-to-urban migration through which an increasing
percentage of the population in any nation or region come to
live in settlements that are defined as “urban centers.”
Vector
An organism, such as an insect, that transmits a pathogen
from one host to another. See also vector-borne diseases and
vectorial capacity.
Vector-Borne Diseases
Disease that is transmitted between hosts by a v e c t o r o rg a nism
(such as a mosquito or tick— for example, malaria, dengue
fever, and leishmaniasis.
Vectorial Capacity
Quantitative term used in the study of the transmission
dynamics of malaria to express the average number of
potentially infective bites of all vectors feeding upon one
host in one day, or the number of new inoculations with a
vector-borne disease transmitted by one vector species from
one infective host in one day.
Vernalization
The act or process of hastening the flowering and fruiting of
plants by treating seeds, bulbs, or seedlings so as to induce a
shortening of the vegetative period.
Vulnerability
The degree to which a system is susceptible to, or unable to
cope with, adverse effects of climate change, including climate
variability and extremes. Vulnerability is a function of the
character, magnitude, and rate of climate variation to which
a system is exposed, its sensitivity, and its adaptive capacity.
Water Consumption
Amount of extracted water irretrievably lost at a given territory
during it’s use (evaporation and goods production). Water
consumption is equal to water withdrawal minus return flow.


Water Stress
Acountry is water stressed if the available freshwater supply
relative to water withdrawals acts as an important constraint
on development. Withdrawals exceeding 20% of renewable
water supply has been used as an indicator of water stress.
Water Withdrawal
Amount of water extracted from water bodies.
Water Use Efficiency
Carbon gain in photosynthesis per unit water lost in
evapotranspiration. It can be expressed on a short-term basis
as the ratio of photosynthetic carbon gain per unit
transpirational water loss, or on a seasonal basis as the ratio
of net primary production or agricultural yield to the
amount of available water.
Xeric
Requiring only a small amount of moisture.
Zoonosis
The transmission of a disease from an animal or nonhuman
species to humans. The natural reservoir is a nonhuman
a n imal.
Zooplankton
The animal forms of plankton. They consume phytoplankton
or other zooplankton. See also phytoplankton.