Greenhouse gas (GHG)

Basics

Greenhouse gases are the gaseous components of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of terrestrial radiation emitted by the earth’s surface, the atmosphere itself and clouds. This property causes the greenhouse effect: Carbon dioxide (CO2), water vapour (H2O), nitrous oxide (N2O), methane (CH4) and ozone (O3) are the main greenhouse gases in the Earth’s atmosphere. In addition, there are a number of entirely man-made GHGs in the atmosphere, such as halocarbons and other substances containing chlorine and bromine, which are dealt with under the Montreal Protocol. Besides CO2, N2O and CH4, the Kyoto Protocol deals with the do called F-Gases containing different kind of fluorides:Sulphur hexafluoride (SF6), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs).

They are covered by accounting standards such as the Greenhouse Gas Protocol.

CO2 equivalents

Carbon dioxide or carbon dioxide (or CO2 for short) is the most important and best known greenhouse gas. However, it is not the only one, but all of them have a different climate damage or climate impact. In order to compare this effect, all greenhouse gases are converted into CO2 equivalents (CO2eq or also CO2e or CO2-e):

This also makes it easier to summarize greenhouse gases so that it is not necessary to list them all individually. For example, a flight not only releases CO2, but also climate-changing water vapor and ozone. All of this adds up to a certain amount of CO2eq. So when we talk about CO2 or CO2 emissions, we often mean CO2 equivalents.

CO2 is the chemical sum formula for the molecule carbon dioxide, also known as carbon dioxide, consisting of carbon and oxygen. The gas carbon dioxide is colourless, easily soluble in water, non-flammable, odourless and non-toxic.

CO2 accounts for only about 0.038 per cent of the air. In its function as a greenhouse gas, however, it plays a decisive role for our climate: CO2 absorbs part of the heat emitted from the earth into space and radiates it back to earth. This natural greenhouse effect creates the moderate climate we know on earth, which allows flora and fauna to thrive.
Carbon dioxide occurs naturally and in large quantities in the Earth’s atmosphere. It is a natural by-product of the cellular respiration of many living creatures and is also produced during the combustion of wood, coal, oil or gas. Carbon dioxide is also released when dead organisms decay or through natural CO2 sources such as volcanic gases.

Once released into the atmosphere, CO2 does not decompose itself, unlike other substances. In the course of the so-called carbon cycle, released CO2 is either physically stored by water bodies or decomposed by green plants in the course of photosynthesis. With the help of sunlight, carbon dioxide is converted into glucose (which, as a carbohydrate-containing biomass, is a basic substance for all organisms) and oxygen. The oxygen is released into the environment. These natural carbon dioxide stores are also called “carbon sinks”.

Reference:

IPCC, 2018: Annex I: Glossary [Matthews, J.B.R. (ed.)]. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. In Press