Science & Environment

Climate change glossary: C-D

How does adaptation differ from mitigation? And what is REDD? The jargon of climate change can be hard to grasp. Use this glossary to decode it.


Cap and trade An emission trading scheme whereby businesses or countries can buy or sell allowances to emit greenhouse gases via an exchange. The volume of allowances issued adds up to the limit, or cap, imposed by the authorities.

Carbon capture and storage (CCS) The collection and transport of concentrated carbon dioxide gas from large emission sources, such as power plants. The gases are then injected into deep underground reservoirs. Carbon capture is sometimes referred to as geological sequestration.

Carbon dioxide (CO2) Carbon dioxide is a gas in the Earth's atmosphere. It occurs naturally and is also a by-product of human activities such as burning fossil fuels. It is the principal greenhouse gas produced by human activity.

Carbon dioxide (CO2) equivalent Six greenhouse gases are limited by the Kyoto Protocol and each has a different global warming potential. The overall warming effect of this cocktail of gases is often expressed in terms of carbon dioxide equivalent - the amount of CO2 that would cause the same amount of warming.

Carbon footprint The amount of carbon emitted by an individual or organisation in a given period of time, or the amount of carbon emitted during the manufacture of a product.

Carbon intensity A unit of measure. The amount of carbon emitted by a country per unit of Gross Domestic Product.

Carbon leakage A term used to refer to the problem whereby industry relocates to countries where emission regimes are weaker, or non-existent.

Carbon neutral A process where there is no net release of CO2. For example, growing biomass takes CO2 out of the atmosphere, while burning it releases the gas again. The process would be carbon neutral if the amount taken out and the amount released were identical. A company or country can also achieve carbon neutrality by means of carbon offsetting.

Carbon offsetting A way of compensating for emissions of CO2 by participating in, or funding, efforts to take CO2 out of the atmosphere. Offsetting often involves paying another party, somewhere else, to save emissions equivalent to those produced by your activity.

Carbon sequestration The process of storing carbon dioxide. This can happen naturally, as growing trees and plants turn CO2 into biomass (wood, leaves, and so on). It can also refer to the capture and storage of CO2 produced by industry. See Carbon capture and storage.

Carbon sink Any process, activity or mechanism that removes carbon from the atmosphere. The biggest carbon sinks are the world's oceans and forests, which absorb large amounts of carbon dioxide from the Earth's atmosphere.

Certified Emission Reduction (CER) A greenhouse gas trading credit, under the UN Clean Development Mechanism programme. A CER may be earned by participating in emission reduction programmes - installing green technology, or planting forests - in developing countries. Each CER is equivalent to one tonne of carbon dioxide.

CFCs The short name for chlorofluorocarbons - a family of gases that have contributed to stratospheric ozone depletion, but which are also potent greenhouse gases. Emissions of CFCs around the developed world are being phased out due to an international control agreement, the 1989 Montreal Protocol.

Clean coal technology Technology that enables coal to be burned without emitting CO2. Some systems currently being developed remove the CO2 before combustion, others remove it afterwards. Clean coal technology is unlikely to be widely available for at least a decade.

Clean Development Mechanism (CDM) A programme that enables developed countries or companies to earn credits by investing in greenhouse gas emission reduction or removal projects in developing countries. These credits can be used to offset emissions and bring the country or company below its mandatory target.

Climate change A pattern of change affecting global or regional climate, as measured by yardsticks such as average temperature and rainfall, or an alteration in frequency of extreme weather conditions. This variation may be caused by both natural processes and human activity. Global warming is one aspect of climate change.

CO2 See carbon dioxide.

Commitment period The time frame given to parties to the Kyoto Protocol to meet their emission reduction commitments. The first Kyoto commitment period runs from 2008-2012, during which industrialised countries are required collectively to reduce emissions to a level 5% below 1990 levels. Some countries would like the Copenhagen conference to prolong the effective life of the Kyoto Protocol by agreeing explicitly on a second commitment period.

COP15 The official title of the Copenhagen conference, which takes place from 7-18 December 2009. Alternatively, it can be called the 15th Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC).

Country in transition Broadly speaking, any ex-Soviet bloc state. At the time the Kyoto Protocol was adopted in 1997, these countries were on the path from a Communist planned economy to a market economy. Many of them would now be categorised as market economies. Countries in transition to a market economy are grouped with industrialised countries in Annex I of the Kyoto Protocol, so they have emission reduction commitments to meet in the 2008-2012 period. In some cases their industrial base collapsed to such a degree in the early 1990s that they will have no difficulty meeting these commitments.


Dangerous climate change A term referring to severe climate change that will have a negative effect on societies, economies, and the environment as a whole. The phrase was introduced by the 1992 UN Framework Convention on Climate Change, which aims to prevent "dangerous" human interference with the climate system.

Deforestation The permanent removal of standing forests that can lead to significant levels of carbon dioxide emissions.