Scientists close in on missing c...( al deforestation is occurring rapidly. ...)

"Our results indicate that intact tropical forests are taking up a large amount of carbon," Stephens explains. "They are helping to offset industrial carbon emissions and the atmospheric impacts of clearing land more than we realized."

Most of the computer models produced incorrect estimates because, in relying on ground-level measurements, they failed to accurately simulate the movement of carbon dioxide vertically in the atmosphere. The models tended to move too much carbon dioxide toward ground level in the summer, when growing trees and other plants take in the gas, and not enough carbon dioxide up in the winter. As a result, scientists believed that there was relatively less carbon in the air above mid-latitude and upper-latitude forests, presumably because trees and other plants were absorbing high amounts.

Conversely, scientists had assumed a large amount of carbon was coming out of the tropics and moving through the atmosphere to be absorbed in other regions. But the new analysis of aircraft samples shows that this is not the case.

"With this new information from aircraft samples we see that the models were overestimating the amount of uptake in the north and underestimating uptake in the tropics," says Kevin Gurney of Purdue University, a co-author of the paper and coordinator of the TransCom study. "To figure out exactly what is happening, we need improved models and more atmospheric observations."

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21-Jun-2007