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Tuesday, January 13, 2009

Global warming will be a killer for agriculture, UW scientists say

Forget ice melting and sea-level rise. Global warming's most pressing threat may be heat that wilts crops across much of the globe, says a UW scientist.

When searing heat waves blasted Western Europe in 2003, more than 50,000 people perished and harvests of corn, wheat and fruit fell by up to a third.

Imagine those temperatures being the norm over much of the world, and you'll have an idea of what the future is likely to hold for agriculture — and humanity, says a new report from scientists at the University of Washington and Stanford University.

"I'm not worried about Greenland sliding into the sea. I'm not worried about sea levels going up," said UW atmospheric-sciences professor David Battisti. Those changes will take several hundred years to unfold, he said, but the effects on agriculture will begin showing up within the next several decades.

"This is probably the most compelling reason why we need to deal with global warming."

If the buildup of greenhouse-gas emissions isn't halted or slowed, the odds are higher than 90 percent that average growing-season temperatures will be higher than in recorded history across a big swath of the planet by the end of the century, says the analysis published today in the journal Science. The hardest-hit areas will be the tropics and subtropics, which encompass about half the world's population and include Africa, the southern United States, and much of India, China and South America.

"We are headed for a completely out-of-bounds situation for growing food crops in the future," said report co-author Rosamond Naylor, director of Stanford's Program on Food Security and the Environment.

There is time to adapt to the rising temperatures through development of heat-resistant crops, the scientists say.

High temperatures cause plants like rice, corn and wheat to grow faster but reduce plant fertility and grain production. With average growing-season temperatures expected to rise more than 6 degrees F in many places, crop yields will fall 20 to 40 percent, the report estimates. The effects will be aggravated by increased evaporation and loss of soil moisture.

Even in the United States, where warming caused by greenhouse-gas emissions is projected to increase some crop yields through the middle of this century, harvests will most likely fall by 2100 as the heat intensifies.

But worldwide, the impacts will be felt most keenly by subsistence farmers and the poor, Battisti pointed out.

"You're talking about hundreds of millions of additional people looking for food because they won't be able to find it where they find it now."

France and Italy were able to turn to other nations to fill their food gaps in 2003, but a 1972 drought in the former Soviet Union showed how easily worldwide grain supplies can be disrupted, the report says. After the Soviets secretly began buying vast amounts of wheat, global prices more than tripled.

In a warmer future, there will be fewer places to turn for help when the cupboards are bare, Battisti said. "In a sense, there will be no place to hide from this."

The scientists reached their conclusions by combining climate data with projections from 23 global climate models used by the Intergovernment Panel on Climate Change, winner of the 2007 Nobel Peace Prize.

Michael Glantz, a political scientist who studies the social impacts of climate and climate change, said the study raises some good points, but that the developing world faces so many immediate problems it's difficult to worry about what will happen in five decades or more.

"When I think about 2100 and climate-change impact on food security, I just glaze over," said Glantz, who directs the Consortium for Capacity Building at the University of Colorado, Boulder.

But Cary Fowler, director of the Rome-based Global Crop Diversity Trust, says the report is a wake-up call for the need to develop new heat-resistant crop strains.

"This research shows we're about to enter a whole new game," said Fowler, whose group receives funding from the Bill & Melinda Gates Foundation and operates the "doomsday" seed vault on the remote Norwegian island of Spitsbergen.

It can take two decades or more to breed a new crop strain, but investments in agricultural research have been stagnant for the past several decades, Naylor pointed out.

The Gates Foundation is helping fund an effort in Africa to develop hardier crop strains. That work hasn't focused specifically on heat tolerance, said Gary Toenniessen, of the Rockefeller Foundation, a partner in the project. But it is helping developing agricultural-research capacity where it will be needed most in the future.

Spurred partly by Battisti's work, the Global Crop Diversity Trust has launched a program to screen existing seed collections for traits like heat and drought resistance, Fowler said. It's also developing a computerized database to share the information.

"Plants can be adapted to a range of temperatures," Fowler said. "This really is a problem that we can solve."

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