Biodegradable: a product made from natural materials that can be broken down by microorganisms, heat and moisture.

Biomass and biofuel: a natural material, from trees to poultry litter, that can be used as fuel, or a liquid or gas fuel derived from such materials.

Carbon capture: stripping CO2 from waste gases before they reach the atmosphere. Still an experimental technology.

Carbon offset: negating the unavoidable release of CO2 by contributing to emissions-reducing projects, such as wind farms or forestry. Nice idea but hard to measure.

Carbon tax: taxing fossil fuels according to how much CO2 they release to try to curb usage as well as raising revenue.

Carbon trading: a financial device for reducing emissions. Companies are issued “carbon credits” according to their emissions levels. If a firm exceeds its emissions limit, it must buy more credits; if it emits less than the limit, it can sell the surplus credits. The scheme relies on credits being in short supply so the price rises, giving firms a financial incentive to cut emissions.

Greenhouse gas: some gases can absorb infrared radiation and retain it in the atmosphere. CO2 is the best known but others include water vapour, methane, nitrous oxide and a variety of fluorocarbons – artificial gases made by man.

Greenhouse effect: the trapping of the sun’s heat in the atmosphere by greenhouse gases. Humanity’s addition to the greenhouse gases in the atmosphere is altering the delicate balance that has kept the earth’s weather conditions relatively stable, so leading to climate change.

Microgeneration: small-scale generation of energy by, for example, solar panels or domestic wind turbines.

Renewable energy: energy obtained from sources that will not run out, unlike oil and coal. Examples include wood, wind, solar, geothermal, tidal and waste.

Sustainable development: economic development that meets the needs of the present without compromising the ability of future generations to meet their own needs.