受氣候暖化影響 榖類作物每年產量減

Warming temperatures since 1981 have caused annual losses of about US$5 billion for six major cereal crops, new research has found. This is the first study to estimate how much global food production already has been affected by climate change. From 1981 to 2002, fields of wheat, corn and barley throughout the world have produced a combined 40 million metric tons less per year because of increasing temperatures caused by human activities.

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

"Most people tend to think of climate change as something that will impact the future, but this study shows that warming over the past two decades already has had real effects on global food supply," said Christopher Field, co-author on the study.

Lobell and Field studied climate effects on the six most widely grown crops in the world – wheat, rice, soybeans, barley, maize or corn, and sorghum, a genus of about 30 species of grasses raised for grain. Production of these crops accounts for more than 40 percent of global cropland area, 55 percent of non-meat calories and more than 70 percent of animal feed.

Using global yield figures for 1961-2002 from the United Nations Food and Agriculture Organization, Lobell and Field compared yields with average temperatures and precipitation over the major growing regions. They found that, on average, global crop yields respond negatively to warmer temperatures for several of the crops. The importance of this study, the authors say, is that it demonstrates a clear and simple relationship at the global scale, with yields dropping by approximately three to five percent for a one-degree Fahrenheit increase.