What are carbon sources and carbon sinks?
All living organisms contain carbon. Soil, natural gas, peat and coal are mainly made of carbon. If any of these absorb more carbon dioxide from the atmosphere than they emit, they are known as carbon sinks. If they emit more carbon dioxide than they absorb, they are carbon sources.
Carbon moves around the Earth's systems in vast quantities - from the atmosphere, to the soils and oceans. Since the industrial revolution a large amount of carbon dioxide has been released into the atmosphere in a relatively short time.
Rainforests and oceans absorb more carbon dioxide than they emit. They absorb about half the carbon dioxide humans release into the atmosphere. They are known as carbon sinks. When plants or marine organisms die, the carbon they store is removed from the atmosphere, often for millions of years.
Temperature changes in the atmosphere and oceans will affect how carbon (and hence carbon dioxide) is stored, released and transported around the globe.
We need to know more about carbon movement, for example, warmer conditions might encourage faster plant growth, locking away carbon. But warmer soils could also mean the carbon plants fix in photosynthesis rots down faster, releasing carbon back to the atmosphere.
Scientists are concerned that the icy tundra of Siberia and Alaska may thaw for the first time since before the last ice age, which ended 11,000 years ago. The permafrost has ensured that carbon, locked in the frozen soil, was kept from the atmosphere for many thousands of years. If natural systems start releasing more carbon dioxide into the atmosphere because of industrial emissions, this may kick-start accelerated warming around the globe.
External links
- QUEST - Quantifying & Understanding the Earth System
- QUEST at NERC
- CTCD Centre for Terrestrial Carbon Dynamics
- New Scientist article - The lungs of the planet are belching methane
