Food crops already feel the heat as the world warms, study finds

Jeff Vanuga; USDA Natural Resources Conservation Service Crops

A Stanford study found that human-caused global warming reduced the combined production of wheat, corn and barley—cereal grains that form the foundation of much of the world's diet—by about 44 million tons per year between 1981 and 2002.

Chris Field

Chris Field

Over a span of two decades, warming temperatures caused annual losses of roughly $5 billion for major food crops, according to a study published March 16 in the online journal Environmental Research Letters.

The study found that between 1981 and 2002, human-caused global warming reduced the combined production of wheat, corn and barley—cereal grains that form the foundation of much of the world's diet—by about 44 million tons per year.

"Most people tend to think of climate change as something that will impact the future," said study co-author Christopher Field, professor of biological sciences at Stanford and director of the Carnegie Institution's Department of Global Ecology. "But this study shows that warming over the past two decades has already had real effects on global food supply."

In the study, Field and co-author David Lobell of the Lawrence Livermore National Laboratory compared yield figures from the United Nations Food and Agriculture Organization (FAO) with average temperatures and precipitation in major growing regions. The researchers focused on the six most widely grown crops in the world—wheat, rice, maize (corn), soybeans, barley and sorghum, a genus that includes about 30 grass species raised for grain. These crops occupy more than 40 percent of the world's cropland and account for at least 55 percent of non-meat calories consumed by humans, according to FAO, and contribute more than 70 percent of the world's animal feed.

The researchers found that, on average, global yields for some crops responded negatively to warmer temperatures, with yields dropping between 3 and 5 percent for every 1 degree Fahrenheit increase. Average global temperatures increased by about 0.7 degrees Fahrenheit during the period of the study, with 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," Lobell said. "We assumed that farmers have not yet adapted to climate change—for example, by selecting new crop varieties to deal with climate change. If they have been adapting—something that is very difficult to measure—then the effects of warming may have been lower. A key moving forward is how well cropping systems can adapt to a warmer world. Investments in this area could potentially save billions of dollars and millions of lives."

The study was supported by the Lawrence Livermore National Laboratory and the Carnegie Institution of Washington.

This article is based on a press release written by the Carnegie Institution of Washington.