Global warming blights world’s corn

STANFORD (US) — Corn—long believed to tolerate hot temperatures—is a likely victim of global warming, according to historical crop yield data from Africa.

Combined data collected from 20,000 trials in sub-Saharan Africa with weather data recorded at stations scattered across the region from 1999 to 2007, shows a temperature rise of a single degree Celsius causes yield losses for 65 percent of the present maize-growing region in Africa—and only if the crops received the optimal amount of rainfall.

Under drought conditions, the entire maize-growing region suffers yield losses, with more than 75 percent of areas predicted to decline by at least 20 percent for 1 degree Celsius of warming.

The research is reported in the journal Nature Climate Change.

“The pronounced effect of heat on maize was surprising because we assumed maize to be among the more heat-tolerant crops,” says Marianne Banziger, co-author of the study and deputy director general for research at the International Maize and Wheat Improvement Center (CIMMYT).

“Essentially, the longer a maize crop is exposed to temperatures above 30 Celsius, or 86 Fahrenheit, the more the yield declines,” she says. “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.”

Similar sources of information elsewhere in the developing world could improve crop forecasting for other vast regions where data has been lacking.

“Projections of climate change impacts on food production have been hampered by not knowing exactly how crops fare when it gets hot,” says David Lobell, assistant professor of environmental earth system science at Stanford University, and the study’s lead author. “This study helps to clear that issue up, at least for one important crop.”

While the crop trials have run for many years throughout Africa in order to identify promising varieties for release to farmers, nobody has examined the weather at the trial sites and studied the effect of weather on the yields.

“These trials were organized for completely different purposes than studying the effect of climate change on the crops,” Lobell says. “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.”

The data recorded at the yield testing sites does not include weather information. Instead, the researchers used data gathered from weather stations all over sub-Saharan Africa. Although the stations were operated by different organizations, all data collection was organized by the World Meteorological Organization, so the methods used were consistent.

Lobell then took the available weather data and interpolated between recording stations to infer what the weather would have been like at the test sites. By merging the weather and crop data, the researchers could examine climate impacts.

“It was like sending two friends on a blind date—we weren’t sure how it would go, but they really hit it off,” Lobell says.

Previously, most research on climate change impacts on agriculture has had to rely on crop data from studies in the temperate regions of North America and Europe, which has been a problem.

“When you take a model that has been developed with data from one kind of environment, such as a temperate climate, and apply it to the rest of the world, there are lots of things that can go wrong” Lobell says, noting that much of the developing world lies in tropical or subtropical climates.

But many of the larger countries in the developing world, such as India, China, and Brazil, which encompass a wide range of climates, are running yield testing programs that could be a source of comparable data.

“We’re hoping that, with this clear demonstration of the value of this kind of data for assessing climate impacts on crops, others will either share or take a closer look themselves at their data for various crops.

“I think we may just be scratching the surface of what can be achieved by combining existing knowledge and data from the climate and agriculture communities. Hopefully this will help catalyze some more effort in this area.”

The work was funded by the Rockefeller Foundation.

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