Farmers count cost of climate change: $5bn in lost crops

American researchers have estimated that the impact of climate change on the productivity of cereal farms around the world has cost the global economy US$5bn over 20 years.

Rising temperatures between 1981-2002 have resulted in harvests of wheat, corn and barley being 800 million tonnes less than they might otherwise have expected to have been, say academics from the Carnegie Institution and Lawrence Livermore National Laboratory.

According to the researchers their paper, published this week in online science journal Environmental Research Letters, brings home the fact that the effects of climate change are already being felt and its impact is economic as well as environmental.

"Most people tend to think of climate change as something that will impact the future," said Christopher Field, co-author on the study and director of Carnegie's Department of Global Ecology in Stanford, California.

"But this study shows that warming over the past two decades has already had real effects on global food supply."

The study is the first to estimate how much global food production has already been affected by climate change. The researchers compared yield figures from the UN's Food and Agriculture Organization with average temperatures and rainfall in the major growing regions.

They found that, on average, global yields for several of the crops responded negatively to warmer temperatures, with yields dropping by about 3-5 percent for every degree Fahrenheit the mercury crept up the thermometer.

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

"Though the impacts are relatively small compared to the technological yield gains over the same period, the results demonstrate that negative impacts are already occurring," said Mr David Lobell, lead author of the study and a researcher at Lawrence Livermore National Laboratory.

The researchers focused on the six most widely grown crops in the world: wheat, rice, maize, soybeans, barley and sorghum. These crops account for over half of the total food consumed by humans and almost three quarters of the feed given to livestock.

The main value of this study, the authors said, was that it demonstrates a clear and simple correlation between temperature increases and crop yields at the global scale.

But they also argued that it showed that investment into climate adaptation in agriculture would save the global economy billions of dollars, as well as millions of lives.

Sam Bond




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