Carbon Reservoirs and Fluxes

To understand the human impact of increasing atmospheric carbon dioxide, we first must consider the natural reservoirs and fluxes of carbon in the earth/atmosphere/ocean system. We must include inventories of the carbon stored in terrestrial plants and animals, carbon in the ocean, carbon in the atmosphere, and reserves of fossil carbon that represent terrestrial carbon taken out of the biosphere at times in the distant past. Each of these reservoirs takes up and releases carbon at different rates that must be estimated to put anthropogenic emissions into perspective.

The accompanying sketch (Figure 11) shows these reservoirs, with amounts given in petagrams of carbon and fluxes in units of petagrams of carbon per year. So, for instance, the atmosphere contains about 740 units of carbon. Terrestrial biology, including all of the plants from phytoplankton to giant sequoia trees and animals from mice to elephants, accounts for about 550 units. Even these crude numbers allow us to make simple evaluations. For instance, if humans carried deforestation to the ultimate, in other words, if we incinerated the whole terrestrial biosphere and put this carbon in the atmosphere, we would approximately double the amount of carbon dioxide in the earth's atmosphere.

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