Climate Change
Global Warming
Air Pollution
Weather & Climate

Absorption of radiation
The uptake of radiation by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted.

The response, either of whole ecosystems, or individual species to changing climate. This may involve gradual evolution if the change is slow enough, or shifting habitats if it occurs quickly. Where species are unable to adapt, for example if climate change is too fast, extinction may occur.

Particles of matter, solid or liquid, larger than a molecule but small enough to remain suspended in the atmosphere (up to 100 microns diameter). Natural origins include salt particles from sea spray and clay particles as a result of weathering of rocks. Aerosols can also originate as a result of man's activities and in this case are often considered pollutants. Aerosols are important due to their role as participants in chemical reactions in the atmosphere and as absorbers and scatterers of solar radiation where they are considered as negative radiative forcing agents.

The conversion of non-forested areas to forest by tree planting.

Agenda 21
Developed at the United Nations Conference on Environment and Development (UNED) in Brazil in June 1992. A "blueprint" for sustainable development. Focuses up to the year 2000 and projects into the 21st century.

The degree of reflection of incident light or radiation reflected by a surface, often expressed as a percentage or a fraction of 1. Snow covered areas have a high albedo (0.9 or 90%) due to their white colour, whilst vegetation has a low albedo (0.1 or 10%) due to the light absorbed for photosynthesis. Cloud is the chief cause for variations in the Earth's albedo.

Anaerobic digestion
The breakdown of organic material to produce methane, carbon dioxide, and heat. In the context of waste management, it can be utilised as an energy supply.

Man-made or human induced.

A general term used to describe areas suffering from lack of rain or drought. More specifically, a condition in which evaporation exceeds precipitation.

A mixture of gases surrounding the Earth. Earth's atmosphere consists of 79.1% nitrogen (by volume), 20.9% oxygen, 0.036% carbon dioxide and trace amounts of other gases. It can be divided into a number of layers according to thermal properties (temperature). The layer nearest the earth is the troposphere (up to about 10-15km above the surface), next is the stratosphere (up to about 50km). There is little mixing of gases between layers.

In the context of climate change, this is the linking of observed global warming during the 20th century to the enhanced greenhouse effect. This is achieved by comparing observed changes in temperature with those predicted to occur by computer modelling. See also detection.

Biological diversity of flora and fauna species and their habitats. Ecosystems with large numbers of species / habitats are said to be biologically diverse.

Biomass burning
The burning of organic matter for energy production, forest clearing and agricultural purposes. Carbon dioxide is a by-product of biomass burning.

The region on land, in the oceans and in the atmosphere inhabited by living organisms.

"Business as Usual" scenario
A greenhouse gas emissions scenario which involves no precautionary action of greenhouse gas emission reduction

Carbon cycle
The process of removal and uptake of carbon on a global scale. This involves components in food chains, in the atmosphere as carbon dioxide, in the hydrosphere and in the geosphere. The major movement of carbon results from photosynthesis and from respiration. See also sink and source.

Carbon dioxide (CO2)
A molecule formed from one atom of carbon and two of oxygen. Carbon dioxide (CO2) is a greenhouse gas of major concern in the study of global warming. It is estimated that the amount in the air is increasing by 0.27% annually. Anthropogenic carbon dioxide is emitted mainly through the burning of fossil fuels and deforestation.

Catalytic converter
A device fitted to car exhausts which remove harmful emissions of air pollutants such as hydrocarbons.

Chlorofluorocarbons (CFCs)
Synthetically produced compounds containing varying amounts of chlorine, fluorine and carbon. Used in industrial processes and as a propellant for gases and sprays. In the atmosphere they are responsible for the depletion of ozone and can destroy as many as 10,000 molecules of ozone in their long lifetime. Their use is now currently restricted under the Montreal Protocol.

The prevalent long-term weather conditions in a particular area. Climatic elements include precipitation, temperature, humidity, sunshine and wind velocity and phenomena such as fog, frost, and hail storms. Climate cannot be considered a satisfactory indicator of actual conditions since it is based upon a synthesis of a vast number of elements taken as an average.

Climate change
This strictly refers to all forms of climatic inconsistency but since climate is never a static figure and based on an aggregate the term is often used in a more restricted sense to imply a significant change. Within the media, climate change has been used synonymously with global warming. Scientists, however, use the term in a wider sense to include past climate changes also.

Climate feedback
A secondary process resulting from primary climate change which may increase (positive feedback) or diminish (negative feedback) the magnitude of climate change. See also ice-albedo feedback.

Climate Forcing Mechanism
See forcing mechanism.

Climate modelling
The simulation of the climate by computers.

Climate sensitivity
The natural variation in climate in response to a change in radiative forcing, for example, the enhancement of the greenhouse effect.

Climate system
The Earth's climate is determined by the interactive behaviour of the atmosphere, the oceans, the biosphere, the cryosphere and the geosphere, which all make up the climate system.

Climatic extreme
A significant departure from the normal state of the climate, which may or may not affect natural ecosystems and human societies. These include hurricanes, tornadoes, floods and droughts.

Cloud condensation nuclei (CCN)
Microscopic particles in the atmosphere, including aerosols, which act as nuclei, or "seeds" for the formation of clouds.

Burning, e.g. of fossil fuels or biomass.

A measure of the atmospheric content of a gas, defined in terms of the proportion of the total volume that it accounts for. Greenhouse gases are trace gases in the atmosphere and are usually measured in parts per million by volume (ppmv), parts per billion by volume (ppbv) or parts per trillion (million million) by volume (pptv).

Conference of Parties
A meeting of nations which signed and ratified the Framework Convention on Climate Change. There have been three Conference of Parties since the 1992 Earth Summit, in Berlin (1995), Geneva (1996) and Kyoto (1997).

That part of the earth's surface consisting of ice masses and snow deposits. This includes continental ice sheets, mountain glaciers, sea ice, surface snow cover, and lake and river ice. Areas such as this tend to have a high albedo, and include Antarctica, Greenland, Northern Canada, Siberia and the Arctic Ocean.

Those practices or processes that result in the long-term change in land-use to non-forest uses. This is often cited as one of the major causes of the enhanced greenhouse effect for two reasons: a) the burning or decomposition of the wood releases carbon dioxide; and b) trees that once removed carbon dioxide from the atmosphere in the process of photosynthesis are lost. See also sink.

The study of relationships between annual tree growth and climate. Tree rings are an example of a non-instrumental record.

The progressive destruction or degradation of existing vegetative cover to form desert. This can occur due to overgrazing, deforestation, drought and the burning of extensive areas. Once formed, desert can only support a sparse range of vegetation. Climatic effects associated with this phenomenon include increased albedo, reduced atmospheric humidity and greater atmospheric dust loading, which can cause wind erosion and atmospheric pollution.

Aridification, due to prolonged drought, lasting many years or decades, sometimes resulting in desertification.

In the context of climate change, this is the identification of a significant change in climate which is the result of the enhanced greenhouse effect.

A period of abnormally dry weather over a prolonged time period sufficient to cause a serious hydrological (water cycle) imbalance in the affected area. This can cause such problems as crop damage and water supply shortage. The severity of the drought depends upon the degree of moisture deficiency, the duration of the drought and the size of the affected area.

Earth Summit
The United Nation Conference on Environment and Development at Rio de Janeiro, Brazil, in June 1992. Agenda 21, the Framework Convention on Climate Change, the Biodiversity Convention and a statement of principles for the management and conservation of the world's forests were all negotiated.

A system of interconnected habitats and their species of flora (plants) and fauna (animals), usually defined by a specific geographical area and/or climatic regime, e.g. mountain, polar, forest ecosystems.

El Niño
A climatic phenomenon occurring every 3 to 7 years, usually beginning around Christmas (El Niño means Christ Child) in the surface oceans of the eastern equatorial Pacific. The phenomenon involves seasonal changes in the direction of Pacific winds and abnormally warm surface ocean temperatures. The changes normally only effect the Pacific region, but major events can disrupt weather patterns over much of the globe. The relationship between these events and global weather patterns are poorly understood and are currently the subject of much research.

El Niño Southern Oscillation (ENSO)
The quasi-periodic variation in atmospheric pressure, trade wind and surface ocean temperature in the equatorial Pacific region between South America and Australia. See also El Niño and La Niña.

The release of a substance (usually a gas when referring to the subject of climate change) into the atmosphere.

Energy balance model (EBM)
A computer model used to simulate human-induced climate change. EBMs are much simpler than general circulation models and model the global radiation budget between incoming solar radiation and outgoing terrestrial radiation, as well as the latitudinal energy transfer from the equator to the poles.

Energy efficiency
Quantitatively, the more energy that can be produced per unit mass of fuel, the more efficient is the energy production. The efficiency with which energy is utilised can be increased by both improving energy supply technology and managing energy demand more effectively.

Enhanced greenhouse effect
The natural greenhouse effect has been enhanced by man's emissions of greenhouse gases. Increased concentrations of carbon dioxide, methane and nitrous oxide trap more infrared radiation, so heating up the atmosphere. See also greenhouse effect.

The sum of all external conditions affecting the life, development and survival of an organism or system.

Water evaporated from the Earth's surface and transpired by vegetation.

Feedback mechanisms
Factors which increase or amplify (positive feedback) or decrease (negative feedback) the rate of a process. An example of positive climatic feedback is the ice-albedo feedback.

See climate feedback.

A term used to denote increased plant growth due to higher carbon dioxide concentrations, warmer temperatures or increased dispersion of nitrogen-based fertiliser.

In the context of climate change, this is a climatic or climate-dependent variable, such as surface temperature, stratospheric temperature, precipitation or sea level, whose signal has a structure unique to the predicted enhanced greenhouse effect. Climatic fingerprints are used to detect man-made climate change, i.e. to attribute observed climate changes to the increase in atmospheric greenhouse gas concentrations.

Forcing mechanism
A process which alters the energy balance of the climate system e.g. a change in the relative balance between incoming solar short-wave radiation and outgoing long-wave radiation from Earth. Such mechanisms include changes in solar output and the enhanced greenhouse effect. See also radiative forcing.

Fossil fuel
Any hydrocarbon deposit that can be burned for heat or power such as coal, oil or natural gas. Fossil fuels are formed from the decomposition of ancient animal and plant remains. A major concern is that they emit carbon dioxide into the atmosphere when burnt, a major contributor to the enhanced greenhouse effect.

Framework Convention on Climate Change
The climate treaty signed at the Earth Summit in Brazil, 1992, by over 150 countries, to protect the Earth's climate system from dangerous anthropogenic interference by mankind.

Another word for "flow", used to describe energy flows or movement of greenhouse gases through the climate system.

General circulation model (GCM)
A computer model used to simulate human-induced climate change. GCMs are highly complex and model such factors as reflective and absorptive properties of clouds, annual and daily solar heating, ocean temperatures and ice boundaries. The most recent ones are coupled to models of ocean circulation.

The soils, sediments and rock layers of the Earth's crust, both continental and beneath the ocean floors.

A period of global frigidity (cold) during which glaciers and ice sheets advance towards the lower latitudes. They usually last about 100,000 years and are associated with the Milankovitch Cycles. The last major glacial ended about 10,000 to 14,000 years ago. See also interglacial.

Global warming
A theory that increased concentrations of greenhouse gases are causing an elevation in the Earth's surface temperature. See also enhanced greenhouse effect.

Global warming potential (GWP)
An index used to approximate the effect of an instantaneous release of a unit mass (1kg) of a greenhouse gas in atmosphere, relative to that of carbon dioxide. The index takes into account the lifetime of the gas and describes the relative effectiveness of the gas in contributing to global warming.

Greenhouse effect
A term used to describe the effect where greenhouse gases trap re-emitted infrared radiation, so heating up the atmosphere. This is a natural phenomenon and increases the Earth's average surface temperature from -18C to +15C. This should not be confused with the enhanced greenhouse effect, the increase of the greenhouse effect as a result of human activities. Also see radiative forcing.

Greenhouse feedbacks
Climate feedback mechanisms which develop as a result of the enhanced greenhouse effect. These include the ice-albedo feedback, water vapour feedback and cloud feedback.

Greenhouse gases
These include water vapour, carbon dioxide, tropospheric ozone, nitrous oxide, methane and other lesser gases. They allow short-wave ultraviolet (UV) radiation to pass through unimpeded but trap long-wave infrared radiation re-emitted from the Earth. Water vapour is the most important greenhouse gas but it is thought that concentrations in the atmosphere are being little affected by human activity. This is not the case with carbon dioxide, methane and nitrous oxide where human activity is leading to increased levels of these gases in the atmosphere and enhancing the natural greenhouse effect.

Gulf Stream
A warm surface ocean current which originates in the Gulf of Mexico and flows northeast across the Atlantic. It influences the climate of the UK and northwest Europe by bring within humid mild air.

Man-made substances including the chlorofluorocarbons and halons.

These man-made substances are similar to chlorofluorocarbons but contain bromine. They also destroy the ozone layer.

Substances containing only hydrogen and carbon. They are found especially in fossil fuels. Some hydrocarbon compounds are major air pollutants.

Hydrochlorofluorocarbons (HCFCs)
Synthetically produced compounds containing varying amounts of hydrogen, chlorine, fluorine and carbon. Used as replacements for chlorofluorocarbons. They have large global warming potentials and current emissions are helping to enhance the natural greenhouse effect.

Hydrofluorocarbons (HFCs)
Synthetically produced compounds containing varying amounts of hydrogen, fluorine and carbon. Used as replacements for chlorofluorocarbons. They have large global warming potentials and current emissions are helping to enhance the natural greenhouse effect.

Hydrological (water) cycle
The exchange of water between the atmosphere, the land and the oceans.

Hydroxyl radical (OH)
A highly reactive molecule containing one oxygen and one hydrogen atom. Reacts in the atmosphere with methane to produce carbon dioxide.

Ice age
Periods in the history of the Earth characterised by a growth of the ice caps towards the equator and a general lowering of global surface temperatures, especially in temperate mid-latitudes. The most recent ice age ended about 10,000 years ago. Ice advances in this period are known to have altered the whole pattern of global atmospheric and ocean circulation.

Ice-albedo feedback
This is an example of a positive climatic feedback. If the enhanced greenhouse effect warms the Earth's surface, some of the ice caps will melt. The exposed ground is darker and therefore has a lower albedo, thus absorbing more radiation, which heats up the atmosphere further. In turn, more ice will melt, surface albedo will fall still further, more warming will occur, with subsequent ice melt, and so on.

Ice core
Obtained by drilling into ice sheet, for example in Greenland or Antarctica, an ice core provides information which can be used to reconstruct past climates and climate change. Ice cores are an example of a non-instrumental record.

See waste incineration.

Industrial Revolution
Traditionally taken to begin around 1765, this period marks the transition to a more energy and resource consuming society, marked by rapid increases in the use of fossil fuels for electricity, heating and transport.

Infra-red radiation
Electromagnetic radiation of lower frequencies and longer wavelengths than visible light (>0.7 microns). Solar ultraviolet radiation is absorbed by the Earth's surface and re-emitted as infrared radiation.

Instrumental record
A direct record of climate, such as temperature, precipitation, wind and atmospheric pressure, recorded by man-made instruments. See also non-instrumental record.

A period of global warmth during which glaciers and ice sheets retreat towards the poles. They usually last about 10,000 years, and with the glacial, are associated with the Milankovitch Cycles. We are currently within an interglacial.

Intergovernmental Panel on Global Climate Change (IPCC)
A scientific body established in 1988 by the UNEP (United Nations Environmental Programme) and WMO (World Meteorological Organisation) with three main objectives. The first to assess the available scientific information on climate change, the second to assess the environmental and socio-economic impacts of climate change and the third to formulate response strategies. The group played a large part in the formulation of a UN framework convention on climate change, signed in 1992, and have produced two major assessment reports; the first in 1990 and the second in 1996.

Jet Stream
A fast high altitude flow of air. Jet streams are found in equatorial regions and also in the mid-latitudes.

Joint Implementation
Agreements made between two or more nations to help reduce greenhouse gas emissions, as part of the Framework Convention on Climate Change.

Kyoto Protocol
The third Conference of Parties took place at Kyoto, Japan, in December 1997, at which further greenhouse gas emission reduction targets were negotiated (a global reduction of greenhouse gases by 5.2% by 2008 to 2012). As a Protocol, the agreement will become legally binding once enough countries have ratified it.

See waste landfill.

La Niña
An accumulation of abnormally cold water in the eastern and central Pacific as a result of strengthened easterly trade winds. La Niña events sometimes but not always follow El Niño episodes.

Lifetime (Atmospheric)
Also known as residence time. The approximate amount of time a pollutant will spend in the atmosphere before either being converted into another chemical compound or being taken out of the atmosphere via a sink. This time depends on the pollutant's sources and sinks as well as its reactivity. Lifetime affects the mixing of pollutants in the atmosphere; a long lifetime will allow the pollutant to mix well in the atmosphere. Average lifetimes can vary from one day (nitrogen dioxide) to five thousand years (oxygen) and beyond.

The science of weather-related phenomena.

Methane (CH4)
Another greenhouse gas, consisting of four molecules of hydrogen and one of carbon.

10-6 metre (or one millionth of a metre).

Mie scattering
The scattering of solar radiation by aerosols in the atmosphere, whose size is comparable to the wavelength of the solar radiation. See also Rayleigh scattering.

Milankovitch Cycles
Variations in the Earth's orbit around the Sun, for example the tilt of the Earth's axis and the strength of the ellipse of the orbit (the Earth passage around the Sun is not perfectly circular). These variations can initiate climate change over periods of time lasting tens of thousands of years. The Cycles are named after the Yugoslavian Mathematician who first proposed their climatic influences.

Montreal Protocol
The discovery of an ozone hole over Antarctica prompted action to control the use of gases which have a destructive effect on the ozone layer. From this concern emerged the Montreal Protocol on substances that deplete the ozone layer, signed by 24 countries in 1987. It came into force in 1989 and has since been ratified by 120 countries. The original agreement was to control and phase out the production and supply of ozone depleting chemicals, specifically CFCs (chlorofluorocarbons) and derivatives. A meeting in 1992 was held in Copenhagen to revise the Protocol. This meeting agreed to bring forward the phase out of halons to 1994, and CFCs and other halocarbons to 1996. These targets have since been met.

10-9 metre (or one billionth of a metre).

Nitrous Oxide (N2O)
Another greenhouse gas, consisting of two molecules of nitrogen and one of oxygen.

Non-instrumental record
An indirect or proxy record of climate, reconstructed by information taken from tree rings (dendroclimatology) and ice cores.

North Atlantic Deep Water (NADW)
A thermohaline current in the North Atlantic which transfers cold saline surface water to the ocean deep. It forms part of the global ocean circulation.

Ozone hole
Stratospheric ozone depletion over the Antarctic. The hole appears every southern hemisphere spring (August to October) before disappearing during the summer months (December / January).

Ozone Layer
The ozone in the stratosphere is very diffuse, occupying a region many kilometres in thickness, but is conventionally described as a layer to aid understanding.

Ozone (O3)
Ozone consists of three atoms of oxygen bonded together in contrast to normal atmospheric oxygen which consists of two atoms of oxygen. Ozone is formed in the atmosphere and is extremely reactive and thus has a short lifetime. In the stratosphere ozone is both an effective greenhouse gas (absorber of infrared radiation) and a filter for solar ultraviolet radiation. Ozone in the troposphere can be dangerous since it is toxic to human beings and living matter. Elevated levels of ozone in the troposphere exist in some areas, especially large cities as a result of photolytic reactions of hydrocarbons and oxides of nitrogen, released from vehicle emissions and power stations.

The study of climate and climate change during the geological past.

Parts per million by volume (ppmv)

See concentration.

Parts per billion (thousand million) by volume (ppbv)
See concentration.

Parts per trillion (million million) by volume (pptv)
See concentration.

A chemical reaction involving sunlight in which molecules are split into their constituent atoms. Also known as photodissociation.

The process by which green plants use light to synthesise organic compounds from carbon dioxide and water. In the process oxygen and water are released. Increased levels of carbon dioxide can increase net photosynthesis in some plants. Plants create a very important sink for carbon dioxide. See also carbon cycle.

Aquatic and usually microscopic organisms that feed in the world's oceans. Phytoplankton feed by photosynthesis whilst zooplankton refers to animal life forms.

Strictly too much of any substance in the wrong place or at the wrong time is a pollutant. More specifically, atmospheric pollution may be defined as 'the presence of substances in the atmosphere, resulting from man-made activities or from natural processes, causing adverse effects to man and the environment'.

Precautionary approach
The approach promoted by the Framework Convention on Climate Change to help "achieve stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous man-made interference with the climate system".

Rainfall, snowfall and hail.

Energy emitted in the form of electromagnetic waves. Radiation has differing characteristics depending upon the wavelength. Radiation from the Sun has a short wavelength (ultraviolet and light) whilst energy re-radiated from the Earth's surface and the atmosphere has a long wavelength (infrared).

Radiative-convective model
A computer model used to simulate human-induced climate change. RCMs are more complex than energy balance models but less complex than general circulation models. They model the radiative transfers throughout the atmosphere, such as absorption and scattering.

Radiative or climate forcing
A variation in the balance of energy absorbed by the Earth and that emitted by it. This can be due to natural causes such as variation in the solar output or by anthropogenic causes, such as the enhanced greenhouse effect. Positive radiative forcing has the effect of warming the surface of the Earth, whilst negative forcing has a cooling effect.

Rayleigh scattering
The scattering of solar radiation by gas molecules in the atmosphere, whose size is smaller than the wavelength of the solar radiation. See also Mie scattering.

Recovery period
In the context of climate, it is the period of time taken for a society to recover from a climatic extreme events. See also return period.

Return period
In the context of climate, it is the period of time between two climatic extreme events. See also recovery period.

Renewable energy
Energy sources which are not used up or depleted by over-consumption, and which are naturally replenished so that they can effectively be used indefinitely. Renewable energy sources include solar energy, wind energy, geothermal energy, hydroelectric power, and biomass energy.

Residence Time
See lifetime.

The process by which animals use up stored foods (by combustion with oxygen) to produce energy.

The region of Africa, south of the Sahara Desert and north of the equatorial zone, spanning most of the width of the continent, characterised by semi-desert scrubland and seasonally intermittent rainfall. In the last 30 years the Sahel has experienced significant drought and desiccation.


A reservoir that uptakes a pollutant from another part of its cycle. See also carbon cycle.

Solar constant
The amount of solar energy intercepted by a surface perpendicular to the direction of radiation at the top of the Earth's troposphere, measured in Watt per square metre (Wm-2). Satellite measurements reveal the current solar constant to be 1368Wm-2.

Solar radiation
Radiation emitted from the Sun, which has wavelengths in the visible (light) and ultraviolet parts of the electromagnetic spectrum.

The point or place from which a pollutant is released.

The range of wavelengths of electromagnetic radiation.

Statistical-dynamical model
A computer model used to simulate human-induced climate change. They combine the simulation of an energy balance model with a radiative-convective model.

A layer in the atmosphere above the troposphere extending upwards to about 50km. The stratosphere contains much of the total atmospheric ozone. The temperature in this region increases with height and can exceed 0C in the summer. The air density here is much less than in the troposphere. It is not thought that the stratosphere has much influence on the weather on the Earth's surface.

Stratospheric ozone depletion
Loss of ozone in the stratosphere due to its photolytic destruction by the chlorofluorocarbons and halons. Most commonly associated with the annual appearance of an ozone hole over the Antarctic every southern hemisphere springtime.

Sustainable development
Development which meets the needs of the present without compromising the ability of future generations to meet their own needs. Sustainable development tries to reconcile the needs of social and economic development with ecological conservation and environmental protection.

Terrestrial radiation
Radiation emitted from the Earth surface, with wavelengths in the infrared part of the electromagnetic spectrum.

Thermal expansion
The increase in volume (or decrease in density) of ocean water as a result of increased temperature of the water. Results in sea level rise.

Thermohaline circulation
The vertical movement of water in the oceans driven by differences in temperature and salinity. Cold, salty water is heavier than warmer, less saline water and will sink into the deep ocean, e.g. the North Atlantic Deep Water.

The boundary between the troposphere and the stratosphere.

The lowest layer of the atmosphere. The altitude of the troposphere varies with latitude, from about 16km at the equator to only 8km at the poles. Normally there is a decrease in temperature with height. This layer contains 75% of the total gaseous mass of the atmosphere and virtually all the water vapour and aerosols. This zone is responsible for most of the weather phenomena experienced and where atmospheric turbulence is most marked.

UK Programme
The UK programme of greenhouse gas emission monitoring and control as demanded by the Framework Convention on Climate Change.

Ultraviolet radiation (UV)
Electromagnetic radiation of higher frequencies and shorter wavelength than visible light.

Volatile organic compounds
These are an important class of air pollutant found in the atmosphere at ground level in urban and industrial centres. They are usually defined as carbon-containing organic compounds present in the atmosphere as gases, excluding elemental carbon, carbon monoxide, methane and carbon dioxide. Sometimes, they are referred to as hydrocarbons.

Waste incineration
The burning or combustion of waste. Can be used as a source of energy. See renewable energy.

Waste landfill
The (commercial) burial of solid municipal and domestic waste. Emissions from landfilled waste include methane and carbon dioxide. See also anaerobic digestion.

A unit of power output or energy output per unit time (Joules per second). Watts per square metre (Wm-2) is a measure of the energy output per unit area (e.g. the amount of solar energy received at the Earth's surface).

A measure of the length of electromagnetic radiation waves.