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The element carbon (C) is essential to life. All living things are based on, or put together, with molecules containing carbon. Carbon molecules needed for life are not created from scratch or destroyed when something dies. These molecules cycle or move from one place to another and are constantly recycled and reused through the carbon cycle.

A place where carbon is stored is called a reservoir. The main reservoirs for carbon molecules are:

  • Rocks - 65,000,000 billion tons (bt)
  • Oceans - 39,000 bt
  • Soils - 1,580 bt
  • Atmosphere - 750 bt
  • Land plants - 610 bt

When a carbon atom moves from one reservoir to another, it is called a flux. The main fluxes and how many billions of tons of carbon is moved on average each year is shown in the diagram below:


Compare the amount of carbon entering the atmosphere and the amount leaving. Is it equal, or is the amount of carbon in the atmosphere increasing or decreasing? Let's do a little math to see:

  • Total atmospheric inputs:
    • (plant respiration + soil respiration + biomass burning + fossil fuel burning + oceanic carbon release) = billion tons
  • Total atmospheric outputs:
    • (photosynthesis + oceanic carbon intake) = billion tons

Now, to figure out if the input and output is equal or not, use the following equation:

  • Net carbon flux: total inputs - total output =

What did you get? From measurements of the levels of atmospheric carbon, the average increase is 3.2 billion tons per year. Does that match our calculations? We are "missing" 1-2 billion tons of carbon! Where did it go? Is the math wrong?

We do not fully understand all of the different fluxes and reservoirs of the global carbon cycle. This extra carbon could be deposited in vegetation, soils or in the ocean. Recent models show that the most likely location for this carbon is somewhere in the terrestrial ecosystems.

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Updated October 24, 2008 by: Glen Westbroek

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