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Study determines effect of global warming on wheat yields

Extreme heat can cause wheat crops to age faster and reduce yields, a U.S.-led study shows, underscoring the challenge of feeding a rapidly growing population as the world warms.

Scientists and farmers have long known that high heat can hurt some crops and the Stanford University-led study, released on Jan. 30, revealed how the damage is done by tracking rates of wheat aging, or senescence.

Depending on the sowing date, the grain losses from rapid senescence could reach up to 20 per cent, the scientists found in the study, published in the journal Nature Climate Change.

Lead author David Lobell and his colleagues studied nine years of satellite measurements of wheat growth from northern India, tracking the impact of exposure to temperatures greater than 34 C to measure rates of senescence.

They detected a significant acceleration of aging that reduced the grain-filling period. The onset of senescence imposes a limit on the time for the plant to fill the grain head.

“What’s new here is better understanding of one particular mechanism that causes heat to hurt yields,” Lobell told Reuters in an email. He said that while there had been some experiments showing accelerated aging above 34 C, relatively few studies considered temperatures this high.

“We decided to see if these senescence effects are actually occurring in farmers’ fields, and if so whether they are big enough to matter. On both counts, the answer is yes.”

Climate scientists say that episodes of extreme heat are becoming more frequent and more prevalent across the globe, presenting huge challenges for growing crops.

Wheat is the second most produced crop in the world after corn and the United Nation’s Food and Agriculture Organization says global food production must increase by 70 per cent by 2050 to feed a larger, more urban and affluent population.

Learning to adapt

Lobell said his team’s findings could help refine steps to adapt crops and growing times as the planet warms.

“Heat-tolerant varieties will be key. Whether this means faster growing in order to escape extreme heat, more capable of coping with extreme heat, or a combination of both is hard to say,” he said.

“One challenge with sowing earlier is that there is a summer crop, usually rice, which has to be harvested before wheat is sown. That is why in many places wheat is actually sown well after the optimum window climatically.”

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 2 C higher than average, with much of the losses caused by temperatures above 34 C.

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