CO2's Crop Benefits Questioned

From tomorrow's Science magazine:

Increases in atmospheric carbon dioxide that accompany global climate change may be less of a boon to crop agriculture than previously thought, according to a new analysis. The Intergovernmental Panel for Climate Change, for instance, has concluded that the fertilizing effect of higher carbon dioxide levels could offset crop losses brought about by higher temperatures and lower soil moisture in a warmer global climate. But the IPCC's data come from old experiments on crops grown in greenhouses and shelters that don't properly capture real field conditions, say Stephen Long and colleagues. Their analysis of open-field experiments concludes that higher carbon dioxide levels will only enhance crop yields half as much as the older greenhouse experiments suggested. Carbon dioxide increases may not stimulate the growth of crops like corn and sorghum in the tropics at all, they note. The findings “may move impacts on agriculture higher up on the list of pressing concerns about climate change,” David Schimel writes in a related Perspective.