各地农民感受到全球变暖的影响

SCOTT SIMON, host: This is WEEKEND EDITION from NPR News. I'm Scott Simon.

The United Nations says world food prices are still near record highs. Grain prices in particular continue to move higher, poor people around the world who feel price increases most, suffer an especially disproportionate(不成比例的） burden.
Global prices are driven by many factors, for example, the strength of the U.S. dollar. A new study finds that global warming is also having a measurable effect on world grain prices.
NPR's Richard Harris has the story.

RICHARD HARRIS: Many studies have projected that higher temperatures and altered rainfall from global climate change will ultimately take a toll on four of the most important crops in the world: rice, wheat, soy and corn, which some call maize. The new study finds that the effects are already starting to be felt.

Wolfram Schlenker at Columbia University is co-author.

Professor WOLFRAM SCHLENKER (Environmental Economics, Columbia University): We find that for two crops, which is maize and wheat, there has actually been a decline in yields (生产量，投资效益）, if you account for the trend in climate especially a warming trend that we've observed over the last 30 years.

HARRIS: The scientists looked specifically at places where there are warming trends, and sure enough, they found these staple crops(主要作物） weren't doing quite as well.

For rice and soy, declines in some places were offset by productivity boosts elsewhere in the world, so there was no overall change. But they did see a change for wheat and corn. Schlenker says the losses caused by warming thus far are still smaller than the gains made though improved agriculture.

Prof. SCHLENKER: We're not saying yields have gone down, just to make this clear. What we're saying is that yields are lower than they would have been without the climate trend. So yields have still been going up over the last 30 years.

HARRIS: The study is published online by Science magazine. It shows that these crops have declined about 5 percent over what they would have been in the absence of warming. That sounds small, until you consider that these crops are worth globally about a trillion dollars a year. Five percent of a trillion dollars...

Prof. SCHLENKER: So it's still $50 billion more in expenditures on food, which I think is quite sizeable.

HARRIS: And that number is probably just the beginning. Gerry Nelson at the International Food Policy Research Institute says as the planet heats up in the coming decades, the 5 percent loss today could easily grow to 20 percent.

Mr. GERRY NELSON (Senior Research Fellow, International Food Policy Research Institute, Washington, D.C.): Definitely do not consider shrugging that off. We can expect to see higher prices that are going to cause problems around the world.

HARRIS: And most of those problems hit people who can afford it the least.

Mr. NELSON: Who gets hurts most are people those who spend most of their money on food and who spend most of their money on eating commodities directly rather than as we do in the U.S. where the food price that we pay that's actual commodities is relatively small.

HARRIS: A doubling of wheat prices might only add a dime（十美分） to the cost of a $2 loaf of bread（长面包）, he says. But double the price of rice and people who fill their food bowl with that grain every day will really feel it.

Americans are also insulated from this effect for another reason. The new study found that the effects of warming have not been felt evenly around the world.
Again, Wolfram Schlenker.

Prof. SCHLENKER: Well, the one big exception we actually found is the United States. So this is the one place that doesn't have a big temperature trend.

HARRIS: America's breadbasket has not warmed, so thus far American grain farmers have been fortunate. Professor Gene Takle at Iowa State University says farmers in the Midwest have instead dealt with a long-term trend of additional rainfall in that area.

Professor GENE TAKLE (Atmospheric Science and Agricultural Meteorology, Iowa State University): Farmers are very good at adapting to climate change, adapting to anything. And when the ranges of climate are not too extreme, they can and they are adjusting.

HARRIS: Midwestern farmers have adapted to the added wetness by spraying more pesticides to control fungus（霉菌）, by planting more per acre and by buying bigger machines to cope with the wetter fields, he says. And Takle says the farmers will surely be able to adapt to at least some degree of warming, which is likely sooner or later.

Prof. TAKLE: But that's a real critical issue of what is the range of temperature or climate conditions to which we can adapt, and when do we exceed those?

HARRIS: Many other farmers around the world are already beginning to struggle with those higher temperatures.

Richard Harris, NPR News.