Ablation
ll processes by which snow and ice are lost from a glacier, floating ice, or snow cover; or the amount which is melted. These processes include melting, evaporation, (sublimation), wind erosion, and calving. Synonym: wastage.

ACIA
Arctic Climate Impact Assessment

Advection
Transport of water or air along with its properties (e.g.,temperature, chemical tracers) by the motion of the fluid. Regarding the general distinction between advection and convection, the former describes the predominantly horizontal, large-scale motions of the atmosphere or ocean, while convection describes the predominantly vertical, locally induced motions.

Aerosole
A collection of airborne solid or liquid particles, with a typical size between 0.01 and 10 μm that reside in the atmosphere for at least several hours. Aerosols may be of either natural or anthropogenic origin. Aerosols may influence climate in several ways: directly through scattering and absorbing radiation, and indirectly by acting as cloud condensation nuclei or modifying the optical properties and lifetime of clouds.

Acclimatisation
The physiological adaptation to climatic variations.

Afforestation
Direct human-induced conversion of land that has not been forested for a period of at least 50 years to forested land through planting, seeding and/or the human-induced promotion of natural seed sources.

Albedo
The fraction of solar radiation refl ected by a surface or object, often expressed as a percentage. Snow-covered surfaces have a high albedo, the surface albedo of soils ranges from high to low, and vegetation-covered surfaces and oceans have a low albedo. The Earth’s planetary albedo varies mainly through varying cloudiness, snow, ice, leaf area and land cover changes.

Alkalinity
A measure of the capacity of a solution to neutralize acids.

Altimetry
A technique for measuring the height of the sea, lake or river, land or ice surface with respect to the centre of the Earth within a defi ned terrestrial reference frame. More conventionally, the height is with respect to a standard reference ellipsoid approximating the Earth’s oblateness, and can be measured from space by using radar or laser with centimetric precision at present. Altimetry has the advantages of being a geocentric measurement, rather than a measurement relative to the Earth’s crust as for a tide gauge, and of affording quasi-global coverage.

AMAP
Arctic Monitoring and Assessment Programme

Anabatic wind
A local wind which blows up a slope heat by sunshine, as opposed to its converse the katabatic wind.

Annex B countries
The countries included in Annex B to the Kyoto Protocol that have agreed to a target for their greenhouse-gas emissions, including all the Annex I countries (as amended in 1998) except for Turkey and Belarus.

Annex I countries
The group of countries included in Annex I (as amended in 1998) to the UNFCCC, including all the OECD countries and economies in transition. Under Articles 4.2 (a) and 4.2 (b) of the Convention, Annex I countries committed themselves specifically to the aim of returning individually or jointly to their 1990 levels of greenhousegas emissions by the year 2000. By default, the other countries are referred to as Non-Annex I countries.

Annex II countries
The group of countries included in Annex II to the UNFCCC, including all OECD countries. Under Article 4.2 (g) of the Convention, these countries are expected to provide financial resources to assist developing countries to comply with their obligations, such as preparing national reports. Annex II countries are also expected to promote the transfer of environmentally sound technologies to developing countries.

Adaptation
Initiatives and measures to reduce the vulnerability of natural and human systems against actual or expected climate change effects. Various types of adaptation exist, e.g. anticipatory and reactive, private and public, and autonomous and planned. Examples are raising river or coastal dikes, the substitution of more temperatureshock resistant plants for sensitive ones, etc.

Adaptive capacity
The whole of capabilities, resources and institutions of a country or region to implement effective adaptation measures.

Annular Modes
Preferred patterns of change in atmospheric circulation corresponding to changes in the zonally averaged midlatitude westerlies. The Northern Annular Mode has a bias to the North Atlantic and has a large correlation with the North Atlantic Oscillation. The Southern Annular Mode occurs in the Southern Hemisphere. The variability of the mid-latitude westerlies has also been known as zonal fl ow (or wind) vacillation, and defi ned through a zonal index.

Antarctic Circumpolar Current
Also called the ‘West Wind Drift’ because it is driven by powerful westerly winds north of Antarctica. This current continues eastward encircling Antarctica without changing direction. It is the largest volume current in all the oceans.

Antarctic Convergence
The Antarctic Convergence, also known as the Antarctic Polar Frontal Zone (or "Polar Front" for short), is a line encircling Antarctica where the cold, northward-flowing Antarctic waters sink beneath the relatively warmer waters of the sub-Antarctic. The line is actually a zone approximately 20 to 30 miles wide, varying somewhat in latitude in different longitudes, extending across the Atlantic, Pacific, and Indian Oceans between the 48th and 61st parallels of south latitude. The precise location at any given place and time is made evident by the sudden change in surface temperature, which averages 5 to 10 degrees Fahrenheit (2.8°C to 5.5°C).

Antarctic Divergence
In physical oceanography, a region of rapid transition located in the Antarctic Zone of Southern Ocean between the Continental Water Boundary to the south and the Polar Front to the north. It can be distinguished hydrographically by a salinity maximum below about 150 m caused by the upwelling of water of high salinity, i.e. North Atlantic Deep Water. Above this the maximum is blurred by high precipitation and the melting of ice. Its position corresponds reasonably well to the demarcation between the east and west wind drifts which, in the light of Ekman dynamics, at least partially explains its divergent nature.

Antarctic Treaty
The success of the International Geophysical Year effort led to the signing (1959) of the Antarctic Treaty by representatives of the 12 nations. The treaty prohibits military operations, nuclear explosions, and the disposal of radioactive wastes in Antarctica and provides for cooperation in scientific investigation and the exchange of scientific data. In 1991, 24 nations signed a protocol to the 1959 treaty barring for 50 years the exploration of Antarctica for oil or minerals. The accord also contained provisions covering wildlife protection, waste disposal, and marine pollution.

Anthropogenic
Resulting from or produced by human beings.

Anthropogenic emissions
Emissions of greenhouse gases, greenhouse-gas precursors, and aerosols associated with human activities. These include the burning of fossil fuels, deforestation, land-use changes, livestock, fertilization, etc. that result in a net increase in emissions.

Atlantic Multi-decadal Oscillation (AMO)
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 order 0.4°C.

AOGCM
Atmosphere Ocean General Circulation Model.

Aquaculture
The managed cultivation of aquatic plants or animals such as salmon or shellfish held in captivity for the purpose of harvesting.

AR4
Fourth Assessment Report

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% volume mixing ratio) and ozone. In addition, the atmosphere contains the greenhouse gas water vapour, whose amounts are highly variable but typically around 1% volume mixing ratio. The atmosphere also contains clouds and aerosols.

Aurora
Luminous phenomena, in the form of arcs, bands, draperies, or curtains in the high atmosphere over high latitudes. Auroras are related to magnetic storms and the influx of charged particles from the Sun. The phenomena are called aurora borealis in the Northern Hemisphere and aurora australis in the Southern Hemisphere.

Barrier
Any obstacle to reaching a goal, adaptation or mitigation potential that can be overcome or attenuated by a policy, programme, or measure. Barrier removal includes correcting market failures directly or reducing the transactions costs in the public and private sectors by e.g. improving institutional capacity, reducing risk and uncertainty, facilitating market transactions, and enforcing regulatory policies.

Baseline
The reference for measurable quantities from which an alternative outcome can be measured, e.g. a non-intervention scenario is used as a reference in the analysis of intervention scenarios.

Basin
The drainage area of a stream, river or lake.

Benchmark
A measurable variable used as a baseline or reference in evaluating the performance of an organization. Benchmarks may he drawn from internal experience, that of other organizations or from legal requirement and are often used to gauge changes in performance over time.

Benthic community
The community of organisms living on or near the bottom of a water body such as a river, a lake or an ocean.

Biocovers
Layers placed on top of landfills that are biologically active in oxidizing methane into CO₂ zu oxidieren.

Biofilters
Filters using biological material to filter or chemically process pollutants like oxidizing methane into CO₂.

Biofuel
A fuel produced from organic matter or combustible oils produced by plants. Examples of biofuel include alcohol, black liquor from the paper-manufacturing process, wood, and soybean oil.

Biodiversity
The variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.

Biofuel
A fuel produced from organic matter or combustible oils produced by plants. Examples of biofuel include alcohol, black liquor from the paper-manufacturing process, wood, and soybean oil.

Bioluminescence
production of light by living organisms as a result of a chemical reaction either within certain cells or organs or outside the cells in some form of excretion (z.B. Euphausiacea and deep see fishes).

Biome
Major and distinct regional element of the biosphere, typically consisting of several ecosystems (e.g., forests, rivers, ponds, swamps) within a region of similar climate. Biomes are characterised by typical communities of plants and animals.

Biomass
The total mass of living organisms in a given area or volume; recently dead plant material is often included as dead biomass. The quantity of biomass is expressed as a dry weight or as the energy, carbon or nitrogen content.

Biosphere
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.

Black carbon
Particle matter in the atmosphere that consists of soot, charcoal and/or possible light-absorbing refractory organic material. Black carbon is operationally defined matter based on measurement of light absorption and chemical reactivity and/or thermal stability.

Bonn Agreement
The Parties to the Kyoto Protocol achieved a victory for the earth's climate by adopting a landmark Ministerial agreement at the resumed session of COP6 in Bonn in July, 2001. This agreement demonstrated the political will of the rest of the world to move this issue forward. It puts the Kyoto Protocol on a track for ratification and implementation.

BMU
Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit

Bottom-up models
Models represent reality by aggregating characteristics of specific activities and processes, considering technological, engineering and cost details. See also top-down models.

C
Carbon.

Capacity building
In the context of climate change, capacity building is developing technical skills and institutional capabilities in developing countries and economies in transition to enable their participation in all aspects of adaptation to, mitigation of, and research on climate change, and in the implementation of the Kyoto Mechanisms, etc.

Carbon cycle
The set of processes such as photosynthesis, respiration, decomposition, and air-sea exchange, by which carbon continuously cycles through various reservoirs, such as the atmosphere, living organisms, soils, and oceans.

Carbon dioxide (CO₂)
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 and of 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 Capture and Storage (CCS)
A process consisting of separation of CO₂ from industrial and energy-related sources, transport to a storage location, and longterm isolation from the atmosphere.

Carbon intensity
The amount of emissions of CO₂ per unit of GDP.

Carbon leakage
The part of emissions reductions in Annex B countries that may be offset by an increase of the emissions in the non-constrained countries above their baseline levels. This can occur through (1) relocation of energy-intensive production in non-constrained regions; (2) increased consumption of fossil fuels in these regions through decline in the international price of oil and gas triggered by lower demand for these energies; and (3) changes in incomes (thus in energy demand) because of better terms of trade. Leakage also refers to GHG-related effects of GHG-emission reduction or CO₂-sequestration project activities that occur outside the project boundaries and that are measurable and attributable to the activity. On most occasions, leakage is understood as counteracting the initial activity. Nevertheless, there may be situations where effects attributable to the activity outside the project area lead to GHGemission reductions. These are commonly called spill-over. While (negative) leakage leads to a discount of emission reductions as verified, positive spill-over may not in all cases be accounted for.

Carbon price
What has to be paid (to some public authority as a tax rate, or on some emission permit exchange) for the emission of 1 tonne of CO₂ into the atmosphere. In the models and the IPCC report, the carbon price is the social cost of avoiding an additional unit of CO₂ equivalent emission. In some models it is represented by the shadow price of an additional unit of CO₂ emitted, in others by the rate of carbon tax, or the price of emission-permit allowances. It has also been used in the IPCC as a cut-off rate for marginal abatement costs in the assessment of economic mitigation potentials.

Catabatic wind
A phenomenon that originates with a layer of cold air forming near the ground on a night with clear skies and a low pressure gradient. If the ground is sloping, the air close to the ground is colder than air at the same level but at some horizontal distance. The result is downslope gravitational flow of the colder, denser air beneath the warmer, lighter air. This occurs on the largest scale as the outflowing winds from Greenland and Antarctica. Contrast with anabatic wind.

CCS
Carbon Capture and Storage.

CDM
Clean Development Mechanism.

CH₄
Methan.

Cholera
A water-borne intestinal infection caused by a bacterium (Vibrio cholerae) that results in frequent watery stools, cramping abdominal pain, and eventual collapse from dehydration and shock.

Clean Development Mechanism (CDM)
Defined in Article 12 of the Kyoto Protocol, the CDM is intended to meet two objectives: (1) to assist parties not included in Annex I in achieving sustainable development and in contributing to the ultimate objective of the convention; and (2) to assist parties included in Annex I in achieving compliance with their quantified emission limitation and reduction commitments. Certified Emission Reduction Units from CDM projects undertaken in Non-Annex I countries that limit or reduce GHG emissions, when certified by operational entities designated by Conference of the Parties/Meeting of the Parties, can be accrued to the investor (government or industry) from parties in Annex B. A share of the proceeds from certified project activities is used to cover administrative expenses as well as to assist developing country parties that are particularly vulnerable to the adverse effects of climate change to meet the costs of adaptation.

Chlorofluorocarbons (CFCs)
Greenhouse gases covered under the 1987 Montreal Protocol and used for refrigeration, air conditioning, packaging, insulation, solvents, or aerosol propellants. Because they are not destroyed in the lower atmosphere, CFCs drift into the upper atmosphere where, given suitable conditions, they break down ozone. These gases are being replaced by other compounds, including hydrochlorofluorocarbons and hydrofluorocarbons, which are greenhouse gases covered under the Kyoto Protocol.

Climate
Climate in a narrow sense is usually defi ned as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization. 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. In various chapters in the IPCC report different averaging periods, such as a period of 20 years, are also used.

Climate change
Climate change refers to a change in the state of the climate that can be identifi ed (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, or to persistent anthropogenic changes in the composition of the atmosphere or in land use. Note that the Framework Convention on Climate Change (UNFCCC), in its Article 1, defi nes climate change as: "a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods". The UNFCCC thus makes a distinction between climate change attributable to human activities altering the atmospheric composition, and climate variability attributable to natural causes.

Climate feedback
An interaction mechanism between processes in the climate system is called a climate feedback when the result of an initial process triggers changes in a second process that in turn influences the initial one. A positive feedback intensifies the original process, and a negative feedback reduces it.

Climate model (spectrum or hierarchy)
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 spectrum or hierarchy of models can be identifi ed, 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 General Circulation Models (AOGCMs) provide a representation of the climate system that is near the most comprehensive end of the spectrum currently available. There is an evolution towards more complex models with interactive chemistry and biology (see Chapter 8). Climate models are applied as a research tool to study and simulate the climate, and for operational purposes, including monthly, seasonal and interannual climate predictions.

Climate prediction
A climate prediction or climate forecast is the result of an attempt to produce an estimate of the actual evolution of the climate in the future, for example, at seasonal, interannual or long-term time scales. Since 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; Predictability.

Climate projection
A projection of the response of the climate system to emission or concentration scenarios of greenhouse gases and aerosols, 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 concerning, for example, future socioeconomic and technological developments that may or may not be realised and are therefore subject to substantial uncertainty.

Climate scenario
A plausible and often simplifi ed 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.

Climate sensitivity
In the IPCC reports, equilibrium climate sensitivity refers to the equilibrium change in the annual mean global surface temperature following a doubling of the atmospheric equivalent carbon dioxide concentration. Due to computational constraints, the equilibrium climate sensitivity in a climate model is usually 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 effective climate sensitivity is a related measure that circumvents the requirement of equilibrium. It is evaluated from model output for evolving 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. The climate sensitivity parameter (units: °C (Wm^-2)^-1) refers to the equilibrium change in the annual mean global surface temperature following a unit change in radiative forcing. The transient climate response is the change in the global surface temperature, averaged over a 20-year period, centred at the time of atmospheric carbon dioxide doubling, that is, at year 70 in a 1% per year compound carbon dioxide increase experiment with a global coupled climate model. It is a measure of the strength and rapidity of the surface temperature response to greenhouse gas forcing.

Climate system
The climate system is the highly complex system consisting of fi ve 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 infl uence of its own internal dynamics and because of external forcings such as volcanic eruptions, solar variations and

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).

Cloud condensation nuclei (CCN)
Airborne particles that serve as an initial site for the condensation of liquid water, which can lead to the formation of cloud droplets.

Cloud feedback
A climate feedback involving changes in any of the properties of clouds as a response to other atmospheric changes. Understanding cloud feedbacks and determining their magnitude and sign require an understanding of how a change in climate may affect the spectrum of cloud types, the cloud fraction and height, and the radiative properties of clouds, and an estimate of the impact of these changes on the Earth’s radiation budget. At present, cloud feedbacks remain the largest source of uncertainty in climate sensitivity estimates.

CO₂
Carbon dioxide.

CO₂-equivalent concentration
The concentration of carbon dioxide that would cause the same amount of radiative forcing as a given mixture of carbon dioxide and other greenhouse gases.

CO₂-equivalent emission
The amount of CO₂ emission that would cause the same radiative forcing as an emitted amount of a well mixed greenhouse gas, or a mixture of well mixed greenhouse gases, all multiplied with their respective Global Warming Potentials to take into account the differing times they remain in the atmosphere.

Co-benefits
The benefits of policies implemented for various reasons at the same time, acknowledging that most policies designed to address greenhouse gas mitigation have other, often at least equally important, rationales (e.g., related to objectives of development, sustainability, and equity). The term co-impact is also used in a more generic sense to cover both positive and negative side of the benefits.

Compliance
Compliance is whether and to what extent countries do adhere to the provisions of an accord. Compliance depends on implementing policies ordered, and on whether measures follow up the policies. Compliance is the degree to which the actors whose behaviour is targeted by the agreement, local government units, corporations, organizations or individuals, conform to the implementing obligations.

Conference of the Parties (COP)
The supreme body of the UNFCCC, comprising countries with right to vote that have ratified or acceded to the convention. The first session of the Conference of the Parties (COP-1) was held in Berlin (1995), followed by 2.Geneva (1996), 3.Kyoto (1997), 4.Buenos Aires (1998), 5.Bonn (1999), 6.The Hague/Bonn (2000, 2001), 7.Marrakech (2001), 8.Delhi (2002), 9.Milan (2003), 10.Buenos Aires (2004), 11.Montreal (2005), 12.Nairobi (2006).

Confidence
The level of confidence in the correctness of a result is expressed in the IPCC report, using a standard terminology defined in the report.

Continental drift
In 1915, the German geologist and meteorologist Alfred Wegener first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core. The fossil record supports and gives credence to the theories of continental drift and plate tectonics.

Convection
Atmospheric motions that are predominantly vertical, resulting in vertical transport and mixing of atmospheric properties.

Coral
The term "coral" has several meanings, but is usually the common name for the Order Scleractinia, all members of which have hard limestone skeletons, and which are divided into reef-building and non-reef-building, or cold- and warm-water corals.

Coral bleaching
The paling in colour which results if a coral loses its symbiotic, energy-providing, organisms.

Coral reefs
Rock-like limestone (calcium carbonate) structures built by corals along ocean coasts (fringing reefs) or on top of shallow, submerged banks or shelves (barrier reefs, atolls), most conspicuous in tropical and sub-tropical oceans.

Cost
The consumption of resources such as labor time, capital, materials, fuels and so on as the consequence of an action. In economics all resources are valued at their opportunity cost, being the value of the most valuable alternative use of the resources. Costs are defined in a variety of ways and under a variety of assumptions that affect their value Cost types include: administrative costs of planning, management, monitoring, audits, accounting, reporting, clerical activities, etc. associated with a project or programme; damage costs to ecosystems, economies and people due to negative effects from climate change; implementation costs of changing existing rules and regulation, capacity building efforts, information, training and education, etc. to put a policy into place; private costs are carried by individuals, companies or other private entities that undertake the action, where social costs include additionally the external costs on the environment and on society as a whole Costs can be expressed as total, average (unit, specific) being the total divided by the number of units of the item for which the cost is being assessed, and marginal or incremental costs as the cost of the last additional unit. The perspectives adopted in the IPCC report are: Project level considers a standalone activity that is assumed not to have significant indirect economic impacts on markets and prices (both demand and supply) beyond the activity itself. The activity can be the implementation of specific technical facilities, infrastructure, demand-side regulations, information efforts, technical standards, etc. Technology level considers a specific greenhouse-gas mitigation technology, usually with several applications in different projects and sectors. The literature on technologies covers their technical characteristics, especially evidence on learning curves as the technology diffuses and matures. Sector level considers sector policies in a partialequilibrium context, for which other sectors and the macroeconomic variables are assumed to be as given. The policies can include economic instruments related to prices, taxes, trade, and financing, specific large-scale investment projects, and demand-side regulation efforts. Macroeconomic level considers the impacts of policies on real income and output, employment and economic welfare across all sectors and markets. The policies include all sorts of economic policies, such as taxes, subsidies, monetary policies, specific investment programmes, and technology and innovation policies. The negative of costs are benefits, and often both are considered together.

Crust of the earth
The outermost solid layer of the earth, mostly consisting of crystalline rock.

Cryosphere
The component of the climate system consisting of all snow and ice (including permafrost) on and beneath the surface of the Earth and ocean.

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).

Desertification
This refers to land degradation in arid, semi-arid, and dry subhumid areas resulting from various factors, including climatic variations and human activities. The United Nations Convention to Combat Desertification defines land degradation as a reduction or loss, in arid, semi-arid, and dry sub-humid areas, of the biological or economic productivity 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 processes, including processes arising from human activities and habitation patterns, such as soil erosion caused by wind and/or water, deterioration of the physical, chemical and biological or economic properties of soil and long-term loss of natural vegetation.

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 defi ned 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.

Development path
An evolution based on an array of technological, economic, social, institutional, cultural and biophysical characteristics that determine the interactions between human and natural systems, including production and consumption patterns in all countries, over time at a particular scale. Alternative development paths refer to different possible trajectories of development, the continuation of current trends being just one of the many paths.

Diatom
Microscopic unicellular alga with an external skeleton of silica.

Discounting
A mathematical operation making monetary (or other) amounts received or expended at different points in time (years) comparable across time. The operator uses a fixed or possibly time-varying discount rate (>0) from year to year that makes future value worth less today. In a descriptive discounting approach one accepts the discount rates people (savers and investors) actually apply in their day-to-day decisions (private discount rate). In a prescriptive (ethical or normative) discounting approach the discount rate is fixed from a social perspective, e.g. based on an ethical judgement about the interests of future generations (social discount rate).

Discount rate
The degree to which consumption now is preferred to consumption one year hence, with prices held constant, but average incomes rising in line with GDP per capita.

Drought
In general terms, drought is a "prolonged absence or marked deficiency of precipitation", a "deficiency that results in water shortage for some activity or for some group", or a "period of abnormally dry weather suffi ciently prolonged for the lack of precipitation to cause a serious hydrological imbalance". Drought has been defined in a number of ways. Agricultural drought relates to moisture deficits in the topmost 1 metre or so of soil (the root zone) that affect crops, meteorological drought is mainly a prolonged deficit of precipitation, and hydrologic drought is related to below-normal streamflow, lake and groundwater levels. A megadrought is a longdrawn out and pervasive drought, lasting much longer than normal, usually a decade or more.

Ecosystem
A system of living organisms interacting with each other and 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.

EMIC
Earth System Model of Intermediate Complexity.

Emission permit
An emission permit is a non-transferable or tradable entitlement allocated by a government to a legal entity (company or other emitter) to emit a specified amount of a substance. A tradable permit is an economic policy instrument under which rights to discharge pollution - in this case an amount of greenhouse gas emissions - can be exchanged through either a free or a controlled permit-market.

Emissions trading
A market-based approach to achieving environmental objectives. It allows those reducing GHG emissions below their emission cap to use or trade the excess reductions to offset emissions at another source inside or outside the country. In general, trading can occur at the intra-company, domestic, and international levels. The Second Assessment Report by the IPCC adopted the convention of using permits for domestic trading systems and quotas for international trading systems. Emissions trading under Article 17 of the Kyoto Protocol is a tradable quota system based on the assigned amounts calculated from the emission reduction and limitation commitments listed in Annex B of the Protocol.

Emission scenario
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 socioeconomic development technological change) and their key relationships. 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 (Nakiæenoviæ and Swart, 2000) new emission scenarios, the so-called SRES scenarios, were published, some of which were used, among others, as a basis for the climate projectionspresented in Chapters 9 to 11 of IPCC (2001) and Chapters 10 and 11 of the IPCC report. For the meaning of some terms related to these scenarios, see SRES scenarios.

Emission trajectories
These are projections of future emission pathways, or observed emission patterns.

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.

Energy
The amount of work or heat delivered. Energy is classified in a variety of types and becomes useful to human ends when it flows from one place to another or is converted from one type into another. Primary energy (also referred to as energy sources) is the energy embodied in natural resources (e.g., coal, crude oil, natural gas, uranium) that has not undergone any anthropogenic conversion. It is transformed into secondary energy by cleaning (natural gas), refining (oil in oil products) or by conversion into electricity or heat. When the secondary energy is delivered at the end-use facilities it is called final energy (e.g., electricity at the wall outlet), where it becomes usable energy (e.g., light). Daily, the sun supplies large quantities of energy as rainfall, winds, radiation, etc. Some share is stored in biomass or rivers that can be harvested by men. Some share is directly usable such as daylight, ventilation or ambient heat. Renewable energy is obtained from the continuing or repetitive currents of energy occurring in the natural environment and includes non-carbon technologies such as solar energy, hydropower, wind, tide and waves and geothermal heat, as well as carbon-neutral technologies such as biomass. Embodied energy is the energy used to produce a material substance (such as processed metals or building materials), taking into account energy used at the manufacturing facility (zero order), energy used in producing the materials that are used in the manufacturing facility (first order), and so on.

Energy balance
The difference between the total incoming and total outgoing energy. If this balance is positive, warming occurs; if it is negative, cooling occurs. Averaged over the globe and over long time periods, this balance must be zero. Because the climate system derives virtually all its energy from the Sun, zero balance implies that, globally, the amount of incoming solar radiation on average must be equal to the sum of the outgoing refl ected solar radiation and the outgoing thermal infrared radiation emitted by the climate system. A perturbation of this global radiation balance, be it anthropogenic or natural, is called radiative forcing.

Energy efficiency
The ratio of useful energy output of a system, conversion process or activity to its energy input.

Energy intensity
The ratio of energy use to economic output. At the national level, energy intensity is the ratio of total domestic primary energy use or final energy use to Gross Domestic Product.

Energy security
The various security measures that a given nation, or the global community as a whole, must carry out to maintain an adequate energy supply.

Energy Service Company (ESCO)
A company that offers energy services to end-users, guarantees the energy savings to be achieved tying them directly to its remuneration, as well as finances or assists in acquiring financing for the operation of the energy system, and retains an on-going role in monitoring the savings over the financing term.

Ensemble
A group of parallel model simulations used for climate projections. Variation of the results across the ensemble members gives an estimate of uncertainty. Ensembles made with the same model but different initial conditions only characterise the uncertainty associated with internal climate variability, whereas multi-model ensembles including simulations by several models also include the impact of model differences. Perturbedparameter ensembles, in which model parameters are varied in a systematic manner, aim to produce a more objective estimate of modelling uncertainty than is possible with traditional multi-model ensembles.

Environmental effectiveness
The extent to which a measure, policy or instrument produces a decided, decisive or desired environmental effect.

Epiphytic
Plant that derives moisture and nutrients from the air and rain; usually grows on another plant but not parasitic on it e.g. algae, fresses or moss.

Renewable energy
Is energy generated from natural resources such as sunlight, wind, rain, tides and geothermal heat which are renewable (naturally replenished). Renewable energy technologies range from solar power, wind power, hydroelectricity/micro hydro, biomass and biofuels for transportation.

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.

EU-burden sharing
Under the Kyoto Protocol, the EU committed itself to reducing its greenhouse gases emissions by 8% during the first commitment period from 2008 to 2012. This target is shared between the Member States under a legally so-called binding Burden Sharing Agreement, which sets individual emissions targets for each Member State. The emission reduction target to the base year of 1990; Luxembourg: -28%; Germany, Denemark: -21%; Austria: -13%; United Kingdom: -12,5%; Belgium: -7,5%; Italy: -6,5%; Netherlands: -6%; Finnland, France: +/-0%; Sweden: +4%; Ireland: +13%; Spain: +15%; Greece: +25%; Portugal: +27%.

Euphausiacea
Small commonly luminescent crustaceans; important element of marine plankton.

Euphausiacea superba
The Antarctic krill, a species of marine crustacean plankton in the family Euphausiidae of the order Euphausiacea - most abundant krill species, food for whales, penguins, fish, seals and birds - keystone organism of the Antarctic ecosystem.

Evaporation
The transition process from liquid to gaseous state.

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.

Externality/External cost/External benefit
Externalities arise from a human activity, when agents responsible for the activity do not take full account of the activity’s impact on others’ production and consumption possibilities, while there exists no compensation for such impact. When the impact is negative, so are external costs. When positive they are referred to as external benefits.

Extinction
The global disappearance of an entire species (biol). Loss of light in the atmosphere. Extinction is the sum of actual absorption, and scattering (optic).

Extreme weather event
An extreme weather event is an event that is rare at a particular place and time of year. Defi nitions of rare vary, but an extreme weather event would normally be as rare as or rarer than the 10th or 90th percentile of the observed probability density function. By defi nition, the characteristics of what is called extreme weather may vary from place to place in an absolute sense. Single extreme events cannot be simply and directly attributed to anthropogenic climate change, as there is always a fi nite chance the event in question might have occurred naturally. When a pattern 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).

FAQ
Frequently Asked Questions.

Feed-in tariff
The price per unit of electricity that a utility or power supplier has to pay for distributed or renewable electricity fed into the grid by non-utility generators. A public authority regulates the tariff.

Feedback
An interaction mechanism between processes is called a feedback. When the result of an initial process triggers changes in a second process and that in turn influences the initial one.Apositive feedback intensifies the original process, and a negative feedback reduces it.

Fingerprint
The climate response pattern in space and/or time to a specifi c forcing is commonly referred to as a fi ngerprint. Fingerprints are used to detect the presence of this response in observations and are typically estimated using forced climate model simulations.

Flaring
Open air burning of waste gases and volatile liquids, through a chimney, at oil wells or rigs, in refineries or chemical plants and at landfills.

Flexible mechanisms
This refers to Clean Development Mechanism (CDM), technology transfer in developing countries leading to a reduction in the emissions of greenhouse gases, Joint Implementation (JI), emission-diminishing investments of industrial nations in other industrial nations or those undergoing transformation, and emission trading (ET), trading emission permits within and among industrial countries.

Flux adjustment
To avoid the problem of coupled Atmosphere-Ocean General Circulation Models (AOGCMs) drifting into some unrealistic climate state, adjustment terms can be applied to the atmosphere-ocean fl uxes of heat and moisture (and sometimes the surface stresses resulting from the effect of the wind on the ocean surface) before these fl uxes are imposed on the model ocean and atmosphere. Because these adjustments are pre-computed and therefore independent of the coupled model integration, they are uncorrelated with the anomalies that develop during the integration. Chapter 8 of IPCC concludes that most models used (Fourth Assessment Report AOGCMs) do not use flux adjustments, and that in general, fewer models use them.

Forest
Defined under the Kyoto Protocol as a minimum area of land of 0.05-1.0 ha with tree-crown cover (or equivalent stocking level) of more than 10-30 % with trees with the potential to reach a minimum height of 2-5 m at maturity in situ. A forest may consist either of closed forest formations where trees of various storey and undergrowth cover a high proportion of the ground or of open forest. Young natural stands and all plantations that have yet to reach a crown density of 10-30 % or tree height of 2-5 m are included under forest, as are areas normally forming part of the forest area that are temporarily un-stocked as a result of human intervention such as harvesting or natural causes but which are expected to revert to forest.

Fossil fuels
Carbon-based fuels from fossil hydrocarbon deposits, including coal, peat, oil and natural gas.

Fossil fuel emissions
Emissions of greenhouse gases (in particular carbon dioxide) resulting from the combustion of fuels from fossil carbon deposits such as oil, gas and coal.

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

Fuel switching
In general, this is substituting fuel A for fuel B. In the climate change discussion it is implicit that fuel A has lower carbon content than fuel B, e.g., natural gas for coal.

°C
Grad Celsius

10°C-Isotherm
Dbe defined as being the area where the average temperature for the warmest month (July) is below 10°C / 50°F.

G77 - Group of G77 anc China
Die Gruppe der 77 (G77) ist ein loser Zusammenschluss von Staaten der Dritten Welt. Die Vereinigung Originally 77, now more than 130, developing countries that act as a major negotiating bloc in the UNFCCC process. G77/China is also referred to as Non-Annex I countries in the context of the UNFCCC. Developing Countries" (GSTP).

GDP (Gross domestic product)
An estimate of the total money value of all the final goods and services produced in a given one-year period using the factors of production located within a particular country's borders

GEF
Global Environment Facility.

GHG
Greenhouse gas.

Geo-engineering
Technological efforts to stabilize the climate system by direct intervention in the energy balance of the Earth for reducing global warming.

Geology
The study of the planet Earth - the materials of which it is made, the processes that act on these materials, the products formed, and the history of the planet and its life forms since its origin

Glaciology
Glaciology is the study of ice in all of its manifestations and the study of all natural phenomena where ice is involved, including processes at or near the base of glaciers and ice sheets on Earth.

Glacier
A mass of land ice that flows downhill under gravity (through internal deformation 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 or discharge into the sea.

Global Conveyor Belt
Differential heating at the poles and equator (the poles and the equator get very different amounts of heat from the sun) drives this system of thermohaline circulation (thermo = temperature, haline = salinity.) Water that travels to the poles gets cold and sinks. Water that is warmed on the surface at the equator evaporates and leaves salt behind, making surface water heavier than the water below it and causing it to sink. These two basic mechanisms along with major ocean currents drive the Global Conveyor Belt, which moves ocean water all over the globe over thousands of years.

Global surface temperature
The global surface temperature is 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 upon radiative properties of well-mixed greenhouse gases, measuring the radiative forcing of a unit mass of a given well-mixed 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 effectiveness in absorbing outgoing thermal infrared radiation. The Kyoto Protocol is based on GWPs from pulse emissions over a 100-year time frame.

Global Environmental Facility (GEF)
The Global Environment Facility (GEF), established in 1991, helps developing countries fund projects and programmes that protect the global environment. GEF grants support projects related to biodiversity, climate change, international waters, land degradation, the ozone layer, and persistent organic pollutants.

Gondwana
A supercontinent that existed from Cambrian to Jurassic time, mainly composed of South America, Africa, Madagascar, India, Antarctica, and Australia.

Greenhouse effect
Greenhouse gases effectively absorb thermal infrared radiation, emitted 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 surface. Thus, greenhouse gases trap heat within the surface-troposphere system. This is called the greenhouse effect. Thermal infrared radiation in the troposphere is strongly coupled to the temperature of the atmosphere at the altitude 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 greenhouse 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 that leads to an enhancement of the greenhouse effect, the so-called enhanced greenhouse effect.

Greenhouse gases (GHGs)
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 vapour (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, dealt with under the Montreal Protocol. Besides carbon dioxide, nitrous oxide and methane, the Kyoto Protocol deals with the greenhouse gases sulphur hexafluoride, hydrofluorocarbons, and perfluorocarbons.

Gt
Gigatonne.

Gulf Stream
The strong western boundary current of the North Atlantic Ocean subtropical gyre that flows poleward off the east coast of the United States.

GWP
Global Warming Potential.

Habitat
The place or environment where a plant or animal naturally lives and grows

Halocarbons
A collective term for the group of partially halogenated organic species, including the chlorofluorocarbons (CFCs), hydrochlorofl uorocarbons (HCFCs), hydrofl uorocarbons (HFCs), halons, methyl chloride, methyl bromide, etc. Many of the halocarbons have large Global Warming Potentials. The chlorineand bromine-containing halocarbons are also involved in the depletion of the ozone layer.

Halocline
A layer in the ocean in which salinity changes rapidly with depth.

Hot air
Under the terms of the 1997 Kyoto Protocol, national emission targets in Annex B are expressed relative to emissions in the year 1990. For countries in the former Soviet Union and Eastern Europe this target has proven to be higher than their current and projected emissions for reasons unrelated to climate-change mitigation activities. Russia and Ukraine, in particular, are expected to have a substantial volume of excess emission allowances over the period 2008-2012 relative to their forecast emissions. These allowances are sometimes referred to as hot air because, while they can be traded under the Kyoto Protocol’s flexibility mechanisms, they did not result from mitigation activities.

Hybrid vehicle
Any vehicle that employs two sources of propulsion, especially a vehicle that combines an internal combustion engine with an electric motor.

Hydrofluorocarbons (HFCs)
One of the six gases or groups of gases to be curbed under the Kyoto Protocol. They are produced commercially as a substitute for chlorofluorocarbons. HFCs are largely used in refrigeration and semiconductor manufacturing. Their Global Warming Potentials range from 1,300 to 11,700.

Hydrosphere
The component of the climate system comprising liquid surface and subterranean water, such as oceans, seas, rivers, fresh water lakes, underground water, etc.

Implementation
Implementation describes the actions taken to meet commitments under a treaty and encompasses legal and effective phases. Legal implementation refers to legislation, regulations, judicial decrees, including other actions such as efforts to administer progress, which governments take to translate international accords into domestic law and policy. Effective implementation needs policies and programmes that induce changes in the behaviour and decisions of target groups. Target groups then take effective measures of mitigation and adaptation.

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 USA. The industrial revolutionmarks the beginning of a strong increase in combustion of fossil fuels and related emissions of carbon dioxide. In the AR4, the term ‘pre-industrial’ refers, somewhat arbitrarily, to the period before 1750.

Ice age
An ice age or glacial period is characterised by a long-term reduction in the temperature of the Earth’s climate, resulting in growth of continental ice sheets and mountain glaciers (glaciation).

Ice algae
Is a general term used to describe all the various types of algal communities encountered in annual and multi-year sea-ice. The ice algal communities play an important role in primary production and are therefore considered an important part of both Polar ecosystems. Sea-ice algal communities can be found between ice crystals or attached to them, in the interstitial water or brine channels between ice crystals, or simply associated with the undersurface of the ice. Although phytoplankton production is greater than that of ice algae on an annual basis in most offshore regions of the Southern Ocean, blooms of sea-ice algae differ considerably from the phytoplankton in terms of timing and distribution. Thus sea-ice algae provide food resources for higher trophic level organisms in seasons and regions where water column biological production is low or negligible.

Ice cap
A dome shaped ice mass, usually covering a highland area, which is considerably smaller in extent than an ice sheet.

Ice core
A cylinder of ice drilled out of a glacier or ice sheet.

Ice sheet
A mass of land ice that is suffi ciently deep to cover most of the underlying bedrock topography, so that its shape is mainly determined by its dynamics (the fl ow 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 fl oating on the sea. There are only three large ice sheets in the modern world, one on Greenland and two on Antarctica, the East and West Antarctic Ice Sheets, divided by the Transantarctic Mountains. During glacial periods there were others.

Inland ice sheet
An ice sheet of considerable thickness and an area of more than about 50,000 square kilometers (12.4 million acres), resting on rock; inland ice sheets near sea level may merge into ice shelves.

Integrated Design Process (IDP) of buildings
Optimizing the orientation and shape of buildings and providing high-performance envelopes for minimizing heating and cooling loads. Passive techniques for heat transfer control, ventilation and daylight access reduce energy loads further. Properly sized and controlled, efficient mechanical systems address the left-over loads. IDP requires an iterative design process involving all the major stakeholders from building users to equipment suppliers, and can achieve 30-75% savings in energy use in new buildings at little or no additional investment cost.

Intelligent controls
In the IPCC report, the notion of ‘intelligent control’ refers to the application of information technology in buildings to control heating, ventilation, air-conditioning, and electricity use effectively. It requires effective monitoring of parameters such as temperature, convection, moisture, etc., with appropriate control measurements (smart metering).

IPCC
Zwischenstaatlicher Ausschuss für Klimaänderung (Intergovernmental Panel on Climate Change)

Joint Implementation (JI)
A market-based implementation mechanism defined in Article 6 of the Kyoto Protocol, allowing Annex I countries or companies from these countries to implement projects jointly that limit or reduce emissions or enhance sinks, and to share the Emissions Reduction Units. JI activity is also permitted in Article 4.2(a) of the UNFCCC.

Joint attribution
Involves both attribution of observed changes to regional climate change and attribution of a measurable portion of either regional climate change or the associated observed changes in the system to anthropogenic causes, beyond natural variability. This process involves statistically linking climate-change simulations from climate models with the observed responses in the natural or managed system. Confidence in joint attribution statements must be lower than the confidence in either of the individual attribution steps alone due to the combination of two separate statistical assessments.

Krill
Small abundant shrimp-like crustaceans mostly present in Antarctic waters that form an important part of the food chain and that are a major source of food for baleen whales, for example.

Kyoto Protocol
The Kyoto Protocol to the UNFCCC was adopted at the Third Session of the Conference of the Parties (COP) in 1997 in Kyoto. It contains legally binding commitments, in addition to those included in the FCCC. Annex B countries agreed to reduce their anthropogenic GHG 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 came into force on 16 February 2005.

Landfill
A landfill is a solid waste disposal site where waste is deposited below, at or above ground level. Limited to engineered sites with cover materials, controlled placement of waste and management of liquids and gases. It excludes uncontrolled waste disposal.

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 have a 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, 2000).

Land surface air temperature
The surface air temperature as measured in well-ventilated screens over land at 1.5 m above the ground.

Lapse rate
The rate of change of an atmospheric variable, usually temperature, with height. The lapse rate is considered positive when the variable decreases with height.

Last Glacial Maximum (LGM)
The Last Glacial Maximum refers to the time of maximum extent of the ice sheets during the last glaciation, approximately 21 ka. This period has been widely studied because the radiative forcings and boundary conditions are relatively well known and because the global cooling during that period is comparable with the projected warming over the 21st century.

Level of Scientific Understanding (LOSU)
This is an index on a 5-step scale (high, medium, medium-low, low and very low) designed to characterise the degree of scientific understanding of the radiative forcing agents that affect climate change. For each agent, the index represents a subjective judgement about the evidence for the physical/chemical mechanisms determining the forcing and the consensus surrounding the quantitative estimate and its uncertainty.

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 lithosphere, is not considered as part of the climate system, but acts as an external forcing factor.

Lifetime
Lifetime is a general term used for various time scales characterising 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_a) is the time scale characterising the decay of an instantaneous pulse input into the reservoir. The term adjustment time is also used to characterise 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_a. 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_a no longer holds. Carbon dioxide (CO₂) is an extreme example. Its turnover time is only about four years because of the rapid exchange between the 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 methane (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 rate S is not proportional to its total mass M.

Likelihood
The likelihood of an occurrence, an outcome or a result, where this can be estimated probabilistically, is expressed in the IPCC report using a standard terminology defined in the report.

Lock in-Effect
Technologies that cover large market shares continue to be used due to factors such as sunk investment costs, related infrastructure development, use of complementary technologies and associated social and institutional habits and structures.

LULUCF
Land Use, Land Use Change, and Forestry

Market barriers
In the context of climate change mitigation, market barriers are conditions that prevent or impede the diffusion of cost-effective technologies or practices that would mitigate GHG emissions.

Market-based regulation
Regulatory approaches using price mechanisms (e.g., taxes and auctioned tradable permits), among other instruments, to reduce GHG emissions.

Market distortions and imperfections
In practice, markets will always exhibit distortions and imperfections such as lack of information, distorted price signals, lack of competition, and/or institutional failures related to regulation, inadequate delineation of property rights, distortion-inducing fiscal systems, and limited financial markets.

Market Exchange Rate (MER)
This is the rate at which foreign currencies are exchanged. Most economies post such rates daily and they vary little across all the exchanges. For some developing economies official rates and blackmarket rates may differ significantly and the MER is difficult to pin down.

Mass balance (of glaciers, ice caps or ice sheets)
The balance between the mass input to the ice body (accumulation) and the mass loss (ablation, iceberg calving). Mass balance terms include the following:

Measures
Measures are technologies, processes, and practices that reduce GHG emissions or effects below anticipated future levels. Examples of measures are renewable energy technologies, waste minimization processes and public transport commuting practices, etc. See also policies.

Meridional Overturning Circulation (MOC)
Meridional (northsouth) 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 observable quantity) is often identified with the Thermohaline Circulation (THC), which is a conceptual interpretation. However, it must be borne in mind that the MOC can also include shallower, wind-driven overturning cells such as occur in the upper ocean in the tropics and subtropics, in which warm (light) waters moving poleward are transformed to slightly denser waters and subducted equatorward at deeper levels.

Methan (CH₄)
Methane is one of the six greenhouse gases to be mitigated under the Kyoto Protocol. It is the major component of natural gas and associated with all hydrocarbon fuels, animal husbandry and agriculture. Coal-bed methane is the gas found in coal seams.

Methane recovery
Methane emissions, e.g., from oil or gas wells, coal beds, peat bogs, gas transmission pipelines, landfills, or anaerobic digesters, are captured and used as a fuel or for some other economic purpose (e.g., chemical feedstock).

Mid-ocean ridge
A submarine mountain chain located along the divergent plate boundaries in the ocean. New oceanic crust forms as magma cools and solidifies at the ridge.

MOC
Meridional Overturning Circulation.

Meeting of the Parties (to the Kyoto Protocol) (MOP)
The Conference of the Parties (COP) of the UNFCCC serves as the Meeting of the Parties (MOP), the supreme body of the Kyoto Protocol, since the latter entered into force on 16 February 2005. Only parties to the Kyoto Protocol may participate in deliberations and make decisions.

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 ozone, such as chlorofluorocarbons, methylchloroform, carbon tetrachloride, and many others.

Multi-Gas
Next to CO₂ also the other greenhouse gases (methane, nitrous, oxide and fluorinated gases) are taken into account in e.g. achieving reduction of emissions (multi-gas reduction) or stabilization of concentrations (multi-gas stabilization).

Nitrous oxide (N₂O)
One of the six types of greenhouse gases to be curbed under the Kyoto Protocol.

Nonlinearity
A process is called nonlinear when there is no simple proportional relation between cause and effect. The climate system contains many such nonlinear processes, resulting in a system with a potentially very complex behaviour. Such complexity may lead to abrupt climate change.

North Atlantic Oscillation (NAO)
The North Atlantic Oscillation consists of opposing variations of barometric 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 cyclones with their associated frontal systems.

Northern Annular Mode (NAM)
A winter fl uctuation in the amplitude of a pattern characterised 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 has a large correlation with the North Atlantic Oscillation.

Non-Annex I Countries/Parties
The countries that have ratified or acceded to the UNFCCC but are not included in Annex I.

Non-Annex B Countries/Parties
The countries not included in Annex B of the Kyoto Protocol.

No-regret policy (options/potential)
Such policy would generate net social benefits whether or not there is climate change associated with anthropogenic emissions of greenhouse gases. No-regret options for GHG emissions reduction refer to options whose benefits (such as reduced energy costs and reduced emissions of local/regional pollutants) equal or exceed their costs to society, excluding the benefits of avoided climate change.

N₂O
One of the six types of greenhouse gases to be curbed under the Kyoto Protocol.

Ocean heat uptake efficiency
This is a measure (W m^-2 °C^-1) of the rate at which heat storage by the global ocean increases as global 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 sensitivity 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 a 1% yr^-1 atmospheric carbon dioxide increase experiment as the ratio of the global average top-of-atmosphere net downward radiative flux to the transient climate response.

Oceanography
The science of the sea; including physical oceanography, marine chemistry, marine geology, and marine biology. The need to know more about the impact of marine pollution and possible effects of the exploitation of marine resources, together with the role of the ocean in possible global warming and climate change, means that oceanography is an important scientific discipline.

ODS
Ozone Depleting Substances.

Oil sands and oil shale
Unconsolidated porous sands, sandstone rock and shales containing bituminous material that can be mined and converted to a liquid fuel.

Opportunities
Circumstances to decrease the gap between the market potential of any technology or practice and the economic potential or technical potential.

Ozone (O₃)
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 (smog). Tropospheric ozone acts as a greenhouse gas. In the stratosphere, it is created by the interaction between solar ultraviolet radiation and molecular oxygen (O₂). 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 concentration 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 is being 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 region, caused by anthropogenic chlorine and bromine compounds in combination with the specifi c meteorological conditions of that region. This phenomenon is called the ozone hole.

Pacific decadal variability
Coupled decadal-to-inter-decadal variability 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 Pacifi c sea surface temperatures, and are linked to decadal variations in atmospheric circulation, sea surface temperatures and ocean circulation throughout the whole Pacifi c Basin. Such fl uctuations 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.

Pacific-North American (PNA) pattern
An atmospheric large-scale wave pattern featuring a sequence of tropospheric high- and lowpressure anomalies stretching from the subtropical west Pacific to the east coast of North America.

Pack ice
ice that is not attached to the shoreline and drifts in response to winds, currents, and other forces; some prefer the generic term drift ice, and reserve pack ice to mean drift ice that is closely packed.

Palaeoclimate
Climate during periods prior to the development of measuring instruments, including historic and geologic time, for which only proxy climate records are available.

Passive solar design
Structural design and construction techniques that enable a building to utilize solar energy for heating, cooling, and lighting by nonmechanical means.

Permafrost
Ground (soil or rock and included ice and organic material) that remains at or below 0°C for at least two consecutive years.

pH
pH is a dimensionless measure of the acidity of water (or any solution) given by its concentration of hydrogen ions (H⁺). pH is measured on a logarithmic scale where pH = -log10(H⁺). 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.

Phytoplankton
The plant forms of plankton. Phytoplankton are the dominant plants in the sea, and are the basis of the entire marine food web. These single-celled organisms are the principal agents of photosynthetic carbon fixation in the ocean.

Plankton
Microorganisms living in the upper layers of aquatic systems. A distinction is made between phytoplankton, which depend on photosynthesis for their energy supply, and zooplankton, which feed on phytoplankton.

Policies
In UNFCCC parlance, policies are taken and/or mandated by a government - often in conjunction with business and industry within its own country, or with other countries - to accelerate mitigation and adaptation measures. Examples of policies are carbon or other energy taxes, fuel efficiency standards for automobiles, etc. Common and co-ordinated or harmonised policies refer to those adopted jointly by parties.

Polynja
Areas of permanently unfrozen sea water resulting from warmer local water currents in otherwise sea-ice covered oceans. They are biological hotspots, since they serve as breathing holes or refuges for marine mammals such as whales and seals, and fishhunting birds.

Post-consumer waste
Waste from consumption activities, e.g. packaging materials, paper, glass, rests from fruits and vegetables, etc.

Potential
In the context of climate change, potential is the amount of mitigation or adaptation that could be - but is not yet realized over time. As potential levels are identified: market, economic, technical and physical.

Precursors
Atmospheric compounds which themselves are not greenhouse gases or aerosols, but which have an effect on greenhouse gas or aerosol concentrations by taking part in physical or chemical processes regulating their production or destruction rates.

Pre-industrial
The era before the industrial revolution of the late 18th and 19th centuries, after which the use of fossil fuel for mechanization started to increase.

ppm
Parts per million.

ppm
Parts per million.

Predictability
The extent to which future states of a system may be predicted based on knowledge of current and past states of the system.

Projection
The potential evolution of a quality or set of quantities, often computed with the aid of a model. Projections are distinguished from predictions in order to emphasise that projections involve assumptions concerning, for example, future socio-economic and technological developments, that may or may not be realised and are therefore subject to substantial uncertainty.

Proxy
A proxy climate indicator is a local 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, characteristics of corals and various data derived from ice cores.

Public sector leadership programmes in energy efficiency
Government purchasing and procurement of energy-efficient products and services. Government agencies are responsible for a wide range of energy-consuming facilities and services such as government office buildings, schools, and health care facilities. The government is often a country’s largest consumer of energy and largest buyer of energy-using equipment. Indirect beneficial impacts occur when governments act effectively as market leaders. First, government buying power can create or expand demand for energy-efficient products and services. Second, visible government energy-saving actions can serve as an example for others.

Purchasing Power Parity (PPP)
The purchasing power of a currency is expressed using a basket of goods and services that can be bought with a given amount in the home country. International comparison of, e.g., Gross Domestic Products of countries can be based on the purchasing power of currencies rather than on current exchange rates. PPP estimates tend to lower per capita GDPs in industrialized countries and raise per capita GDPs in developing countries. (PPP is also an acronym for polluter-pays-principle).

Radiative forcing
Radiative forcing is the change in the net, downward minus upward, irradiance (expressed in W m^-2) at the tropopause due to a change in an external driver of climate change, such as, for example, a change in the concentration of carbon dioxide or the output of the Sun. Radiative forcing is computed with all tropospheric properties held fixed at their unperturbed values, and after allowing for stratospheric temperatures, if perturbed, to readjust to radiative-dynamical equilibrium. Radiative forcing is called instantaneous if no change in stratospheric temperature is accounted for. For the purposes of the IPCC 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, a similar terminology for describing an unrelated measure of the impact of clouds on the irradiance at the top of the atmosphere.

Reanalysis
Reanalyses are atmospheric and oceanic analyses of temperature, wind, current, and other meteorological and oceanographic quantities, created by processing past meteorological and oceanographic data using fixed state-of-the-art weather forecasting models and data assimilation techniques. Using fixed data assimilation avoids effects from the changing analysis system that occurs in operational analyses. Although continuity is improved, global reanalyses still suffer from changing coverage and biases in the observing systems.

Reconstruction
The use of climate indicators to help determine (generally past) climates.

Regime
A regime is preferred states of the climate system, often representing one phase of dominant patterns or modes of climate variability.

Region
A region is a territory characterised by specific geographical and climatological features. The climate of a region is affected by regional and local scale forcings like topography, land use characteristics, lakes, etc., as well as remote influences from other regions.

Relative sea-level rise
See sea-level rise.

Reservoir
A component of the climate system, other than the atmosphere, 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 defi nition of pool often includes the atmosphere). The absolute quantity of the substance of concern held within a reservoir at a specifi ed time iscalled the stock.

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 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 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 concentration of trace gases.

SAR
Second Assessment Report

SCAR
Scientific Commitee for Antarctic Research.

Scenario
A plausible description of how the future may develop based on a coherent and internally consistent set of assumptions about key driving forces (e.g., rate of technological change, prices) and relationships. Note that scenarios are neither predictions nor forecasts, but are useful to provide a view of the implications of developments and actions.

Sea ice
Any form of ice found at sea that has originated from the freezing 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 less than one year old is called first-year ice. Multi-year ice is sea ice that has survived at least one summer melt season.

Sea ice biom
The biome formed by all marine organisms living within or on the floating sea ice (frozen sea water) of the polar oceans.)

Sea level change
Sea level can change, both globally and locally, due to (i) changes in the shape of the ocean basins, (ii) changes in the total mass of water and (iii) changes in water density. Sea level changes induced by changes in water density are called steric. Density changes induced by temperature changes only are called thermosteric, while density changes induced by salinity changes are called halosteric.

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 increase in the volume of the world ocean. Relative sea-level rise occurs where there is a local increase in the level of the ocean relative to the land, which might be due to ocean rise and/or land level subsidence. In areas subject to rapid land-level uplift, relative sea level can fall.

Sea surface temperature (SST)
The sea surface temperature is the temperature of 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.

SF₆
Sulphurhexafluorid.

Shelf ice
An ice shelf is the floating extension of the ice sheets that have formed on land from thousands or millions of years of snowfall. It is therefore made up entirely of fresh water, in contrast to sea ice, which still has some salt in it from the ocean. Most of the world’s ice is located in Antarctica and Greenland. The ice sheet slowly flows downhill due to gravity, usually as glaciers which can also become ice streams. When the ice sheet reaches the coast, it starts to float when the depth of the floating ice is less than the water depth.

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.

Snow pack
A seasonal accumulation of slow-melting snow.

Solar activity
The Sun exhibits periods of high activity observed in numbers of sunspots, as well as radiative output, magnetic activity and emission of high-energy particles. These variations take place on a range of time scales from millions of years to minutes.

Solar (11 year) cycle
A quasi-regular modulation of solar activity with varying amplitude and a period of between 9 and 13 years.

Solar radiation
Electromagnetic radiation emitted by the Sun. It is also referred to as shortwave radiation. Solar radiation has a distinctive range of wavelengths (spectrum) determined by the temperature of the Sun, peaking in visible wavelengths.

Soot
Particles formed during the quenching of gases at the outer edge of fl ames of organic vapours, consisting predominantly of carbon, with lesser amounts of oxygen and hydrogen present as carboxyl and phenolic groups and exhibiting an imperfect graphitic structure.

Southern Annular Mode (SAM)
The fluctuation of a pattern like the Northern Annular Mode, but in the Southern Hemisphere.

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
See El Niño-Southern Oscillation (ENSO).

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).

SPM
Summary for Policymakers.

SRCCS
Special Report on Carbon Capture and Storage.

SRES
Special Report on Emission Scenarios.

SRES scenarios
SRES scenarios are emission scenarios developed by Nakiæenoviæ and Swart (2000) and used, among others, as a basis for some of the climate projections shown in Chapter 10 of the IPCC report. The following terms are relevant for a better understanding of the structure and use of the set of SRES scenarios:

SROC
Special Report on Safeguarding the Ozone Layer and the Global Climate System.

Stabilization
Keeping constant the atmospheric concentrations of one or more GHG (e.g., CO₂) or of a CO₂)-equivalent basket of GHG. Stabilization analyses or scenarios address the stabilization of the concentration of GHG in the atmosphere.

Standards
Set of rules or codes mandating or defining product performance (e.g., grades, dimensions, characteristics, test methods, and rules for use). Product, technology or performance standards establish minimum requirements for affected products or technologies. Standards impose reductions in GHG emissions associated with the manufacture or use of the products and/or application of the technology.

Stratosphere
The highly stratifi ed region of the atmosphere above the troposphere extending from about 10 km (ranging from 9 km at high latitudes to 16 km in the tropics on average) to about 50 km altitude.

Sustainable Development (SD)
The concept of sustainable development was introduced in the World Conservation Strategy (IUCN 1980) and had its roots in the concept of a sustainable society and in the management of renewable resources. Adopted by the WCED in 1987 and by the Rio Conference in 1992 as a process of change in which the exploitation of resources, the direction of investments, the orientation of technological development and institutional change are all in harmony and enhance both current and future potential to meet human needs and aspirations. SD integrates the political, social, economic and environmental dimensions.

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.

Subsidy
Direct payment from the government or a tax reduction to a private party for implementing a practice the government wishes to encourage. The reduction of GHG emissions is stimulated by lowering existing subsidies that have the effect of raising emissions (such as subsidies to fossil fuel use) or by providing subsidies for practices that reduce emissions or enhance sinks (e.g. for insulation of buildings or for planting trees).

Sulphur hexafluoride (SF6)
One of the six greenhouse gases to be curbed under the Kyoto Protocol. It is largely used in heavy industry to insulate high-voltage equipment and to assist in the manufacturing of cable-cooling systems and semi-conductors. Its Global Warming Potential is 23,900.

Taiga
The northernmost belt of boreal forest adjacent to theArctic tundra.

TAR
Third Assessment Report.

Tax
A carbon tax is a levy on the carbon content of fossil fuels. Because virtually all of the carbon in fossil fuels is ultimately emitted as CO₂, a carbon tax is equivalent to an emission tax on each unit of CO₂-equivalent emissions. An energy tax - a levy on the energy content of fuels - reduces demand for energy and so reduces CO₂emissions from fossil fuel use. An eco-tax is designed to influence human behaviour (specifically economic behaviour) to follow an ecologically benign path. An international carbon/emission/energy tax is a tax imposed on specified sources in participating countries by an international authority. The revenue is distributed or used as specified by this authority or by participating countries. A harmonized tax commits participating countries to impose a tax at a common rate on the same sources, because imposing different rates across countries would not be cost-effective. A tax credit is a reduction of tax in order to stimulate purchasing of or investment in a certain product, like GHG emission reducing technologies. A carbon charge is the same as a carbon tax.

Technology
The practical application of knowledge to achieve particular tasks that employs both technical artefacts (hardware, equipment) and (social) information (‘software’, know-how for production and use of artefacts).

Technological change
Mostly considered as technological improvement, i.e., more or better goods and services can be provided from a given amount of resources (production factors). Economic models distinguish autonomous (exogenous), endogenous and induced technological change. Autonomous (exogenous) technological change is imposed from outside the model, usually in the form of a time trend affecting energy demand or world output growth. Endogenous technological change is the outcome of economic activity within the model, i.e., the choice of technologies is included within the model and affects energy demand and/or economic growth. Induced technological change implies endogenous technological change but adds further changes induced by policies and measures, such as carbon taxes triggering R&D efforts.

Technology transfer
The exchange of knowledge, hardware and associated software, money and goods among stakeholders, which leads to the spreading of technology for adaptation or mitigation The term encompasses both diffusion of technologies and technological cooperation across and within countries.

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.

Thermal infrared radiation
Radiation emitted by the Earth’s surface, the atmosphere and the clouds. It is also known as terrestrial or longwave radiation, and is to be distinguished from the near-infrared radiation 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 colour in the visible part of the spectrum. The spectrum of thermal infrared radiation is practically distinct from that of shortwave or solar radiation because of the difference in temperature between the Sun and the Earth-atmosphere system.

Thermocline
A layer in the ocean in which temperature changes rapidly with depth. This often occurs in the area directly below the ocean surface layer that is most warmed by the sun and well-mixed by wind-derived energy.

Thermohaline Circulation
The vertical movement of ocean water driven by density differences resulting from the combined effects of variations in temperature and salinity.

Tide gauge
A device at a coastal location (and some deep-sea locations) that continuously 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.

Top-down models
MModels applying macroeconomic theory, econometric and optimization techniques to aggregate economic variables. Using historical data on consumption, prices, incomes, and factor costs, top-down models assess final demand for goods and services, and supply from main sectors, such as the energy sector, transportation, agriculture, and industry. Some top-down models incorporate technology data, narrowing the gap to bottom-up models.

TPES
Total Primary Energy Supply.

Tree rings
Concentric rings of secondary wood evident in a crosssection 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 temperature and precipitation.

Trend
In the IPCC 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 stratosphere.

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 latitudes to 16 km in the tropics on average), where clouds and weather phenomena occur. In the troposphere, temperatures generally decrease with height.

TS
Technical Summary.

Tundra
Atreeless, level, or gently undulating plain characteristic of the Arctic and sub-Arctic regions characterised by low temperatures and short growing seasons.

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 defi ned concepts or terminology, or uncertain projections of human behaviour. Uncertainty can therefore be represented by quantitative measures, for example, a range of values calculated by various models, or by qualitative statements, for example, reflecting the judgement of a team of experts.

Upwelling
Upwelling brings cold, nutrient-rich water from the depths up to the surface. Earth's rotation and strong seasonal winds push surface water away from some western coasts, so water rises on the western edges of continents to replace it. Marine life thrives in these nutrient-rich waters. Coastal upwelling is usually induced by Ekman transport. Large-scale equatorial upwelling results at the equator due to the divergence of the Ekman transports at the Equator. The trade winds predominantly blow from east-to-west in the tropics. In the N. Hemisphere, this leads to an Ekman transport poleward to the north and in the S. Hemisphere, poleward to the south. Deeper, colder and more nutrient rich waters replace the poleward moving surface waters.

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 Economic 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 aimed to return greenhouse gas emission not controlled by the Montreal Protocol to 1990 levels by the year 2000. The convention came into force in March 1994.

Urban heat island (UHI)
The relative warmth of a city compared with surrounding rural areas, associated with changes in runoff, the concrete jungle effects on heat retention, changes in surface albedo, changes in pollution and aerosols, and so on.

Urbanisation
The conversion of land from a natural state or managed natural state (such as agriculture) to cities; a process driven by net ruralto- 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 centres.

Voluntary action
Informal programmes, self-commitments and declarations, where the parties (individual companies or groups of companies) entering into the action set their own targets and often do their own monitoring and reporting.

Voluntary agreement
An agreement between a government authority and one or more private parties to achieve environmental objectives or to improve environmental performance beyond compliance to regulated obligations. Not all voluntary agreements are truly voluntary; some include rewards and/or penalties associated with joining or achieving commitments.

Wm^-2
Direct thermally driven zonal overturning circulation in the atmosphere over the tropical Pacific Ocean, with rising air in the western and sinking air in the eastern Pacific.

Walker Circulation
Watt per square meter.

Wetland
soils, often between an aquatic and a terrestrial ecosystem, fed from rain, surface water or groundwater. Wetlands are characterised by a prevalence of vegetation adapted for life in saturated soil conditions.

Zooplankton
The animal forms of plankton. They consume phytoplankton or other zooplankton.

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