FACT SHEET/ The carbon Cycle

Image source: The carbon cycle, NASA Earth observatory

The most important GHG is carbon dioxide (CO2), which persists in the atmosphere for thousands of years. Other important GHGs are methane (CH4), nitrous oxide (N2O) and fluorinated gases. CO2 has the largest impact on climate change. In 2014, the average atmospheric concentration of CO2 was almost 400 parts per million (ppm), up from 280 ppm in pre-industrial times.

   The carbon cycle is the flow of carbon through the earth's systems. Carbon is released by plants, soils and oceans, and taken up by plants and oceans, and over very long time periods (thousands of years) also by rocks. A CO2 molecule, made up of one carbon atom and two oxygen atoms, is created when carbon reacts with oxygen, for example in the burning of wood or when humans and animals breathe. CO2 is destroyed when the carbon is separated from the oxygen, for example by plants through photosynthesis.

   Human activities lead to additional releases of carbon, from the burning of fossil fuels, deforestation and land use change, as well as cement production. About half of this additional carbon is taken up by plants and oceans, while the rest remains in the atmosphere as CO2. However, the take-up of CO2 in plants and oceans appears to be slowing down, as these carbon stores become saturated. Carbon dioxide removal would involve modifications of elements of the carbon cycle to enhance the uptake and storage of CO2 in biomass, soils, oceans and geological formations