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Savannas, greenhouse gasses and carbon storage | Why the carbon cycle is important |

Why the carbon cycle is important

MANY elements cycle from the atmosphere to living things, the oceans or the soil and then back to the atmosphere, but the cycling of carbon atoms is particularly important. One reason is that carbon dioxide (CO2) plays a key role in trapping heat in the atmosphere—one of the basic mechanisms be­hind the greenhouse effect, which raises temperatures near the earth’s surface.

Another factor that makes the cycling of carbon important is that carbon plays a central role in combustion—burning—and in the last 200 years we have dramatically changed the carbon cycle through burning fossil fuels, which has released large volumes of CO2 into the atmosphere. Also, substantial areas of forest have been cut down, removing a pathway for CO2 absorption (see diagram below). Consequently, recent times have seen the amount of CO2 in the air increase and the amount of oxygen decrease.

Because there is so much oxygen in the air, the oxygen drop is hardly noticeable, but as there is very little CO2 (0.038% of the atmosphere) the extra CO2 from burning and deforestation has caused a dramatic rise as shown in the graph at right. This has contributed to an enhanced greenhouse effect in recent decades. Given the potentially serious consequences for the earth’s climate of this enhanced greenhouse effect, great importance is now placed on ways of reducing CO2 emissions and on reducing the CO2 already in the air.

  carbon_cycle
The global carbon cycle where black numbers indicate the annual flows of carbon in pre-industrial times and red numbers indicate recent human-caused annual flows.  The flows and stores are in billions of tonnes or Gigatonnes of carbon GtC. Source: IPCC AR4 2007

C02_curve
Atmospheric CO2 concentrations over the last 20,000 years from various sources including ice cores. The grey bars show the reconstructed ranges of natural variability for the past 650,000 years. Note the dramatic increase in recent times.  Modified from IPCC AR4 2007.

 

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