A Jolt to Complacency on Food Supply

For a look at what climate change could do to the world’s food supply, consider what the weather did to the American Corn Belt last year.

At the beginning of 2012, the Agriculture Department projected the largest corn crop in the country’s history. But then a savage heat wave and drought struck over the summer. Plants withered, prices spiked, and the final harvest came in 27 percent below the forecast.

The situation bore a striking resemblance to what happened in Europe in 2003, after a heat wave cut agricultural production for some crops by as much as 30 percent and sent prices soaring.

Several researchers concluded that the European heat wave was made more likely by human-caused climate change; scientists are still arguing over the 2012 heat blast in the United States. Whatever their origin, heat waves like these give us a taste of what could be in store in a future with global warming.

Among those who are getting nervous are the people who spend their lives thinking about where our food will come from.

“The negative impacts of global climate change on agriculture are only expected to get worse,” said a report earlier this year from researchers at the London School of Economics and a Washington think tank, the Information Technology and & Innovation Foundation. The report cited a need for “more resilient crops and agricultural production systems than we currently possess in today’s world.”

This may be the greatest single fear about global warming: that climate change could so destabilize the world’s food system as to lead to rising hunger or even mass starvation. Two weeks ago, a leaked draft of a report by the United Nations climate committee, known as the Intergovernmental Panel on Climate Change, suggested that the group’s concerns have grown, and that the report, scheduled for release in March in Yokohama, Japan, is likely to contain a sharp warning about risks to the food supply.

The tone is strikingly different from that of a report from the same group in 2007, which discussed some risks, but saw global warming as likely to benefit agriculture in many important growing regions.

In the years since, new scientific research has checked those assumptions.

For one, a group of young scientists has pioneered more sophisticated ways of analyzing the relationship between agriculture and climate. People like David Lobell at Stanford and Wolfram Schlenker at Columbia have used elaborate statistical techniques to get a detailed picture of what heat does to crop yields. Their work suggests that rising heat stress in some major growing areas is already putting a drag on production, and raises the possibility of much more serious effects as global warming continues.

Scientists had long hoped that the effect of heat and water stress on crops might be offset by the very thing driving global warming: the sharp increase of carbon dioxide in the air. The gas is the main food supply for plants, and a large body of evidence suggested that the ongoing rise could boost crop yields.

But a lot of that evidence came from tests in artificial environments like greenhouses. Younger scientists, who insisted on testing crops in open-air conditions more closely resembling the real world, found that the bump in yield, while certainly real, was not as high as expected. And it may not be high enough to offset other stresses from global warming.

None of this work can be called definitive — experts say we need more studies, in more types of crops, under a wider variety of growing conditions. Because the body of science is so incomplete, our forecasts of future food supply are primitive, and that means the Yokohama report will certainly not be the last word.

The scientists writing the intergovernmental panel’s report appear to have taken the recent science seriously. The draft suggests they intend to serve notice on world leaders that the risks could be substantial.

Those political leaders have tended to take the security of the food supply for granted, until a crisis hits.

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