Reuters, March 19, 2007


[Rachel's introduction: Global warming is always portrayed as a problem that lies in the future. Now a new study reveals that for the past 20 years global warming has been reducing the grain harvest in the U.S. by 44 million tons per year.]

By Timothy Gardner

NEW YORK -- Global warming has cut about US$5 billion worth of the world's most commonly grown grains over 20 years, according to a new study.

Warming temperatures from 1981 to 2002 cut the combined production of wheat, corn, barley and other crops by 40 million tonnes per year, according to the peer-reviewed study published in Environmental Research Letters on Friday.

"Most people tend to think of climate change as something that will impact the future," Christopher Field, a co-author on the study and ecology expert at the Carnegie Institution in Stanford, California, said in an e-mail response to questions.

"This study shows that warming over the past two decades has already had effects on global food supply," he added.

Not every scientist agrees that agriculture is suffering from warmer temperatures.

A draft UN report obtained by Reuters on Thursday said warming is expected to turn the planet a bit greener by spurring plant growth, but crops and forests may wilt beyond mid-century if temperatures keep rising. That report, by the Intergovernmental Panel on Climate Change, will be released on April 6.

Field said the Carnegie study was the first to estimate how much global food production has already been affected by climate change. It was funded by the Carnegie Institution and the Lawrence Livermore National Laboratory, which is managed by the University of California for the US government.

Average global yields for several of the crops suffered from warmer temperatures, with yields dropping by about 3 to 5 percent for every 1 degree Fahrenheit increase, the study said.

Average global temperatures increased by about 0.7 degree F during the study period, with even larger changes in several regions.

If the past is an indication, agriculture will also suffer going forward, Field said. "We expect future warming to continue to be a drag on yields, essentially like driving with the parking brake engaged."

The cereal crops hit by global warming account for at least 55 percent of non-meat categories consumed by humans, according to the study. They also contribute more than 70 percent of the world's animal feed.

Farmers can adapt to warmer temperatures through changing crop planting times, the varieties they grow, or the locations used for each crop, Field said. He said in the past farmers have been very adaptable to environmental challenges, but adaptation to warming can take years.