2.2 Terrestrial and marine carbon cycles

There are many routes by which an atom of carbon in the atmosphere can enter the terrestrial or marine carbon cycle. For example, it might get taken up in an organism that lives for a few hours, or a tree that lives for hundreds of years. So it's difficult to say exactly how long carbon stays in the atmosphere (i.e. its residence time) – the accepted range is 0–200 years, with 100 years taken as the typical residence time.

  • Play the carbon cycle game from the University Corporation for Atmospheric Research (UCAR) to see some of the possibilities.

  • A useful animation from the US Environmental Protection Agency illustrates key components of the carbon cycle and how human activity affects it.

2. Why is there so much concern about current climate change?

2.3 What is the greenhouse gas effect?