As Russian wheat withers under a record-breaking heat wave, driving up grain prices on global commodity markets, a new study shows rice production, too, has suffered in recent decades from rising temperatures.
Experts say it may be the latest warning of how climate change in some key farming regions could threaten world food supplies.
In the new study in the Proceedings of the National Academy of Sciences, researchers examined six years of data from 227 farms in six major rice-producing countries in Asia. They looked at how rice production varied depending on the weather, and extrapolated those effects over the past quarter-century.
They found that "higher nighttime temperatures lead to lower yield," says lead author Jarrod Welch at the University of California, San Diego (UCSD).
Hot nights in Louisiana
In the southern U.S. state of Louisiana, the nation's third-largest producer of rice, hot nighttime temperatures have made the plants susceptible to a bacterial disease. Rice farmer Clarence Berken says yields are off by 25 to 30 percent in some of his fields.
"Especially in a year like this year, when [the price] for our crop is about half of what it was two years ago, and input costs have basically stayed the same," he says, "it's really something that's worrisome."
There may be more to worry about in the future for Berken and rice farmers around the world, because nighttime temperatures are predicted to rise faster with climate change than daytime temperatures. Welch says the negative impact on productivity could make rice more expensive in the future.
"The numbers of people that depend on rice are astronomical," he says. "Something like 3 billion people eat rice every day. Six hundred million or so depend on it as their staple food. And those 600 million are among the world's poorest billion."
All major crops affected
Rice consumers aren't the only ones put at risk by rising temperatures. Last fall, another major study looking at U.S. maize, soybean and cotton production showed that yields go down for each day a crop is exposed to temperatures above a certain threshold. Depending on how fast the climate warms this century, the study predicted crop yield declines from 30 to 80 percent.
The current run-up in wheat prices caused by Russia's heat-damaged harvest may be a glimpse into the future, according to Lester Brown, head of the Washington-based think tank, the Earth Policy Institute.
"This has been sort-of a textbook lesson in the effect of rising temperature on grain yields," he says. "If you're an agronomist, if you're someone concerned about future food security, you have to worry about that projected possible rise in temperature."
But many U.S. farmers like Clarence Berken in Louisiana are not convinced that we're headed for a hotter future.
"We've had heat waves in the past, and that will come and go," he says. "I think it's more cyclical than anything else."
He adds that whatever the future holds, the Louisiana State University research station is constantly developing new rice varieties that help him adapt to changing conditions.
"It used to take 10 years to come out with a variety. And now we've cut that basically in half," he adds. "The research station does an excellent job of doing those kinds of things that basically have kept us in business."
"There are limits"
Research into improving crop yields has always been the key to meeting the world's food needs, says Nina Fedoroff, a plant scientist at Penn State University and former advisor to the U.S. State Department.
But she says it's unequivocal that the climate is getting hotter, and "there are limits to what our current crops can do."
She says today's commercial crops have evolved in a temperate climate and there is only so much breeders can do to adapt them to a hotter, drier environment.
"The breeding for drought resistance, for example, will not create crops that are significantly more productive than the ones we have today. They will be crops that suffer less of a beating when there's a spell of high temperature," she says.
Scientists will need to create crops that are significantly more productive because the world's population is expected to grow nearly 50 percent by mid-century. Fedoroff says major changes – perhaps including the introduction of entirely new crops and methods of production – will be needed to meet the challenges.
Scientists have made huge productivity gains before, and they could do it again. But Fedoroff notes that despite the urgent needs, crop research remains seriously underfunded.
"In principle, the doom and gloom doesn't have to happen," she says. "In practice, will we actually rearrange our priorities enough to prevent it? I don't know."