Extreme heat hurts wheat yields as world warms
Lobell said extreme heat wasn't the only reason for lower yields. "But in hot places it is important enough to be among the top few reasons for why heat hurts," he added.
A 2010 study by scientists in Australia found wheat output fell by up to half during a growing season where temperatures were two degrees Celsius higher than average, with much of the losses caused by temperatures above 34 degrees Celsius.
Another study published in the journal Nature Climate Change last week said geo-engineering could help lower temperatures and boost crop yields, although it had drawbacks.
Ken Caldeira of the Carnegie Institution for Science, at Stanford University, and his colleagues found that shielding the Earth with aerosol particles lobbed into the stratosphere could dramatically increase yields of corn, wheat and rice.
Using two computer models, the researchers estimated corn production would rise by 14 percent, wheat by 21 percent and rice by 8 percent. This contrasts with suggestions in the scientific community that geo-engineering would threaten food and water supplies for billions of people.
But Caldeira noted that it could result in localized drops in crop productivity, and the shading effect would not stop ocean acidification, which could affect marine productivity.
(Additional reporting by Deborah Zabarenko in Washington; Editing by Miral Fahmy)