“This is tens of billions of dollars a year in lost [agricultural] productivity because of warming,” said David Lobell, an Earth scientist at Stanford University and an author on the report.
Three decades of global warming crimped worldwide yields of corn by about 5.5 percent and wheat by about 3.8 percent compared with what would have been produced had world temperatures remained stable, the report says.
A burgeoning global population also needs more crops — and more grain-fed beef — which contributes to rising food prices much more than climate change, Lobell said. This week, the United Nations also projected that the global population will hit 7 billion in October and 10.6 billion by 2050. Such a huge increase will continue to push food prices higher.
For now, the bread basket of America bucked the trend, as agricultural regions of the United States have not warmed much during their growing seasons since 1980. Climate scientists debate the reasons, with some pointing to particulate pollution over the middle of the United States as a possible cooling counterbalance.
This climate hit adds about 6 percent to the cost of wheat and corn, staples whose prices have skyrocketed in recent years. Although global warming is “a small part of the overall story of why prices are going up,” Lobell said, “it’s not negligible.”
Global corn prices doubled between April 2010 and April 2011, the United Nation’s Food and Agriculture Organization reported Thursday. Wheat prices are up 60 to 80 percent depending on the strain, said Abdolreza Abbassian, an FAO analyst.
Diversion of corn for ethanol also adds to its rising cost, said Wolfram Schlenker, an economist at Columbia University who contributed to the Science report. “We need increasing yields to continue feeding the world,” he said.
Lobell and colleagues compiled temperature, rainfall and crop production data for growing regions around the world from 1980 through 2008. They found a striking increase in temperatures in many growing regions during the growing season.
The team then compiled how much corn, wheat, rice and soybeans were grown in every country in 2008. They compared those figures with projections of how much of each crop could have been grown had global temperatures not risen since 1980.
Production of rice, which thrives in warm temperatures, and soybeans, which are largely grown in regions that did not experience much warming, were not affected by climate change.
The study also found that increased atmospheric carbon dioxide — which many crops absorb for growth — boosted production of rice, wheat and soybeans. But for wheat, this boost was more than drowned out by the negative impact of higher temperatures.