Tropical Forests and the Global Carbon Cycle

Science  01 Jan 1988:
Vol. 239, Issue 4835, pp. 42-47
DOI: 10.1126/science.239.4835.42


New data on the three major determinants of the carbon release from tropical forest clearing are used in a computer model that simulates land use change and its effects on the carbon content of vegetation and soil in order to calculate the net flux of carbon dioxide between tropical ecosystems and the atmosphere. The model also permits testing the sensitivity of the calculated flux to uncertainties in these data. The tropics were a net source of at least 0.4 x 1015 grams but not more than 1.6 x 1015 grams of carbon in 1980, considerably less than previous estimates. Decreases in soil organic matter were responsible for 0.1 x 1015 to 0.3 x 1015 grams of the release, while the burning and decay of cleared vegetation accounted for 0.3 x 1015 to 1.3 x 1015 grams. These estimates are lower than many previous ones because lower biomass estimates and slightly lower land clearing rates were used and because ecosystem recovery processes were included. These new estimates of the biotic release allow for the possibility of a balanced global budget given the large remaining uncertainties in the marine, terrestrial, and fossil fuel components of the carbon cycle.