Global warming's silver lining � more crops � not a certainty www.azstarnet.com �

CHICAGO — Scientists had thought that there was one potential upside to global warming: more food to feed the world.
Years of laboratory tests led them to believe that more carbon dioxide in the atmosphere could fertilize food crops such as corn, soybeans, wheat and rice, offsetting the plant-damaging effects of higher global temperatures and less rainfall.
But a new study with field tests in Illinois and other spots around the globe is challenging that assumption, suggesting that any increase in crop yields due to the buildup of greenhouse gases would be modest or nonexistent.
Lower-than-expected yields could have dire consequences for the world's food supply, the study's authors concluded. They called for more research into plant varieties that could withstand the assault.
The prevailing scientific wisdom has been repeatedly cited in government projections on food supplies and by Bush administration officials who oppose limits on emissions of heat-trapping gases.
Authors of the new University of Illinois study, published Friday in the journal Science, said their findings are more accurate because they mimic predicted atmospheric changes in farm fields.
The researchers set up plots surrounded by rings of tubes that spray carbon dioxide and ozone over the crops.
They found that corn yields didn't increase at all when the air over the plots contained the amount of carbon dioxide projected to be lingering in the atmosphere by 2050. Increases in wheat and soybean yields were about half of what was previously thought.
Supreme Court weighs issue
The new study, financed in part by the U.S. Department of Agriculture, comes a few days after the U.S. Supreme Court agreed to consider whether carbon dioxide should be regulated as an air pollutant.
If the high court agrees with a coalition of states and environmental groups that sued the government, automakers could be forced to build cars that emit less pollution.
Many scientists say there is more than enough evidence to suggest immediate action is needed. Forty senators sent a letter to President Bush on Thursday, calling for government-imposed limits on heat-trapping gases, which come mostly from the burning of coal and oil.