Atmospheric carbon dioxide and carbon reservoir changes.

The net release of CO(2) from the biosphere to the atmosphere between 1850 and 1950 is estimated to amount to 1.2 x 10(9) tons of carbon per year. During this interval, changes in land use reduced the total terrestrial biomass by 7 percent. There has been a smaller reduction in biomass over the last few decades. In the middle 19th century the air had a CO(2) content of approximately 268 parts per millon, and the total increase in atmospheric CO(2) content since 1850 has been 18 percent. Major sinks for fossil fuel CO(2) are the thermocline regions of large oceanic gyres. About 34 percent of the excess CO(2) generated so far is stored in surface and thermocline gyre waters, and 13 percent has been advected into the deep sea. This leaves an airborne fraction of 53 percent.