Scientists trace global warming to a buildup of carbon dioxide and other gases in the atmosphere. But they have reasoned that warmer temperatures would spur tree growth, which in turn would make the trees draw more carbon dioxide out of the atmosphere. The growth of inland Alaska white spruce has declined, however, with warming temperatures, researchers from the University of Alaska Fairbanks said in the June 8 issue of the journal Nature.

The problem is that in this region, which is semiarid, climbing temperatures have produced drought stress on the trees since the 1970s, they said. Their study used climate records and analysis of tree rings. White spruce is one of the most common trees in the northern forests of western North America, they said. So the idea that warming will make those forests pull carbon dioxide from the atmosphere may be incorrect and could lead scientists to underestimate future concentrations of the gas, they said.