As the planet warmed during the last three decades, rising temperatures reduced the yield of corn and wheat crops, and contributed to a modest increase to the price of food, researchers have found.

Although the effects of climate change aren't devastating — they're estimated to be responsible for about a 6 percent rise in food prices since 1980 — scientists say future changes to crops could be more adverse as the planet continues to warm.

"If we don't adapt, I think we are just beginning to see the effects of climate change on agriculture," said David Lobell, a Stanford University scientist who led the research published Thursday in the journal Science.



Cap-and-trade debate

During the 2010 debate over cap-and-trade legislation, which Congress ended up not passing, American Farm Bureau Federation President Bob Stallman said his organization "must aggressively respond to extremists who want to drag agriculture back to the day of 40 acres and a mule."

The skepticism may be due in part to the fact that, with respect to the rest of the world, the United States has experienced less warming during the last century.

As part of the new study, in fact, researchers found no effect on U.S. crop production from climate change. But the effects were quite significant elsewhere. Russia, in contrast, lost an estimated 15 percent of wheat production due to climate change.

"My message to American farmers would be to be careful not to think that what you're experiencing is going on in the world," Lobell said. "In a sense our findings help me understand why farmers are so skeptical about climate change, because they haven't been seeing it themselves. But when you look around the world it's very apparent."

Warmer Texas forecast

With this spring's exceptional drought, skeptical Texas farmers may be getting a preview of what regular droughts will be like at the end of the century, said Bruce McCarl an agricultural economist at Texas A&M University.

A warmer Texas that's prone to more severe droughts - as is forecast by climate models for the end of this century - would spell trouble for the state's agriculture industry if it fails to prepare, he said.

"The signs appear to be that Texas is going to be one of the areas that's treated a little more roughly than other areas," McCarl said.

The effects of a warming climate on crops are fairly complex.

In the United States higher temperatures would tend to lower yields, although this is not universal, as places such as North Dakota could see extended growing seasons, scientists said.

Droughts also have a negative effect on crops such as corn and wheat. Some crops would benefit from increased carbon dioxide levels, however.

Food prices shoot up

The new study comes as food prices have risen dramatically around the world due to a variety of reasons, said Wallace Tyner, a Purdue University agricultural economist.

Tyner said the price of corn has risen from about $2.50 a bushel in 1980 to more than $7 today. He said attributing 6 percent of that increase, about 15 cents, to climate change seems reasonable.

But there are other, much more significant factors. In the last two years, he said, Chinese imports of soybeans and biofuels have been the primary drivers of rising food costs. About 40 percent of U.S. corn production now goes toward producing ethanol, rather than food, he said.

In the long run, however, Tyner sees climate change playing a more significant role in food pricing, especially if farmers are slow to adapt.

"The general gist of what they're arguing in the paper is correct, and maybe even understated," he said.