Scientists close in on missing c...( at combine worldwide wind patterns with...)

at combine worldwide wind patterns with measurements of carbon dioxide taken just above ground level. The models indicate that northern forests absorb about 2.4 billion tons per year. However, ground-based studies have tracked only about half that amount, leaving scientists to speculate about a "missing carbon sink" in the north.

Stephens and his collaborators set out to test how well the models captured carbon sinks, focusing in particular on estimates produced by a recent international study into global carbon exchange known as TransCom. They turned to flasks of air collected by research aircraft over various points of the globe for the past 27 years. The air samples had been analyzed by several labs around the world, which used them to investigate various aspects of the carbon cycle, but this was the first time that a team of scientists analyzed them to obtain a picture of sources and sinks of carbon on a global level.

The research team compared the air samples to estimates of airborne carbon dioxide concentrations generated by the computer models. The scientists found that most of the models significantly underestimated the airborne concentrations of carbon dioxide in northern latitudes, especially in the summer, when plants take in more carbon. The aircraft samples show that northern forests absorb only 1.5 billion tons of carbon a year, which is almost 1 billion tons less than the estimate produced by the computer models.

The scientists also found that intact tropical ecosystems are a more important carbon sink than previously thought. The models had generally indicated that tropical ecosystems were a net source of 1.8 billion tons of carbon, largely because trees and other plants release carbon into the atmosphere as a result of widespread logging, burning, and other forms of clearing land. The new research indicates, instead, that tropical ecosystems are the net source of only about 100 million tons of carbon, even though tropic
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21-Jun-2007

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