The circulation of carbon

Carbon dioxide levels have been rising, suggesting the cycle isn’t in balance due to mainly combustion of fossil fuels and deforestation.

Coal is a fossil fuel formed from trees fallen into anaerobic conditions millions of years ago so bacteria and fungi could not decompose them. The carbon becomes locked in wood rather than being released into the air and becomes a carbon sink and its accumulation involves the net removal of carbon dioxide. When fossil fuels are burned the carbon is released back into the air.

  • Carbon is absorbed by plants during photosynthesis becoming carbon compounds in their tissues
  • Carbon is passed on to animals when they eat plants and to decomposers when they decompose dead organic matter
  • Carbon is returned to the atmosphere as living organisms carry out respiration producing carbon dioxide
  • Carbon in fossil fuels is released as carbon dioxide when burnt (combustion)