Although long believed to tolerate hot temperatures, corn is likely to fall victim to global warming, a new study suggests.

A temperature rise of a single degree Celsius would cause yield losses for 65 percent of the present maize-growing region in Africa, provided the crops received the optimal amount of rainfall, according to a study jointly conducted by researchers at U.S. Stanford University and the International Maize and Wheat Improvement Center (CIMMYT).

Under drought conditions, the entire maize-growing region would suffer yield losses, with more than 75 percent of areas predicted to decline by at least 20 percent for one degree Celsius of warming, the researchers said in the study published on Monday by the American Association for the Advancement of Science (AAAS).

A clear negative effect of warming on maize - or corn - production was evident in experimental crop trial data conducted in Africa from 1999 to 2007, the researchers said.

The researchers combined data from 20,000 trials in sub-Saharan Africa with weather data recorded at stations scattered across the region.

"The pronounced effect of heat on maize was surprising because we assumed maize to be among the more heat-tolerant crops," said Marianne Banziger, co-author of the study and deputy director general for research at CIMMYT.

"Essentially, the longer a maize crop is exposed to temperatures above 30 C, or 86 F, the more the yield declines," she said. "The effect is even larger if drought and heat come together, which is expected to happen more frequently with climate change in Africa, Asia or Central America, and will pose an added challenge to meeting the increasing demand for staple crops on our planet."

While the crop trials have been run for many years throughout Africa, to identify promising varieties for release to farmers, nobody had previously examined the weather at the trial sites and studied the effect of weather on the yields, said Stanford agricultural scientist David Lobell, lead researcher in the study.

"Projections of climate change impacts on food production have been hampered by not knowing exactly how crops fair when it gets hot," Lobell said. "This study helps to clear that issue up, at least for one important crop."

"These trials were organized for completely different purposes than studying the effect of climate change on the crops," he said. "They had a much shorter term goal, which was to get the overall best-performing strains into the hands of farmers growing maize under a broad range of conditions."