Worldwide slowdown in plant carbon uptake
Recent droughts stifled growth of terrestrial vegetation
By Sid Perkins
Deep and extended droughts are responsible for a recent slowdown in the amount of carbon dioxide that land plants pulled from the atmosphere as they grew, a new study suggests.
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Satellite data suggest that between 1982 and 1999, the world’s net primary production — the amount of carbon pulled from the air as CO2 and stored in living plants each year — rose about 6 percent, says Maosheng Zhao, an ecologist at the University of Montana in Missoula. A rise in carbon storage matches what many scientists expected in a warming world with higher atmospheric concentrations of CO2, he notes. But new analyses by Zhao and Montana colleague Steven Running, reported in the Aug. 20 Science, indicate that the amount of carbon pulled from the atmosphere by the growth of terrestrial vegetation dropped about 1 percent during the first decade of this century.
Changes in carbon storage during the decade varied by region, analyses of satellite images reveal. In general, warmer temperatures boosted growth in high-latitude regions and at higher elevations. But in the Amazon, which accounted for about two-thirds of the change in carbon storage, increased warmth boosted evaporation and induced water stress, thereby trimming carbon storage. In 2005, an intense drought in the Amazon caused many trees to die, says Zhao.