"We could easily see this robust transfer of carbon out of the atmosphere and into land-based ecosystems that occurred in the 1990s slow down in the future," says the paper's lead author, David Schimel, of the National Center for Atmospheric Research (NCAR).
Fossil-fuel burning, cement manufacture, and deforestation gave off about 7 billion tons of carbon per year during the 1980s and 8 billion tons annually during the 1990s, about half of it ending up in the earth's atmosphere, according to the study. In the 1980s the amount of carbon released to the atmosphere from deforestation about equaled that taken up by land ecosystems into various "sinks." During the 1990s the balance tipped, and 1.4 billion tons more carbon ended up in the land-based biosphere than in the atmosphere, despite continuing deforestation.
Land-use changes in the Northern Hemisphere have been partly responsible for carbon uptake during the 1990s. In the United States, trees and other growth expanded on abandoned agricultural land, while a reduction in fires allowed forests to spread. Enhanced plant growth spurred by increasing carbon dioxide and nitrogen deposits--a process more noticeable in Europe and Asia--also helped clear the air of CO2 buildup.
"Forests can only replace farms for so long," explains Schimel.
"Eventually new trees and grasses reach maturity and soak up less
carbon dioxide. Similarly, there's a limit to how much forests can
fill in and spread, even with successful fire suppr
National Center for Atmospheric Research/University Corporation for Atmospheric Research