Earth Protect Blog

Warming has already lowered yields of wheat and corn.

Nicola Jones

Farmers have produced less food during the past three decades than they would have done were climate change not happening, according to a study published today1. Global maize (corn) production, for example, is estimated to be about 3.8% lower than it would have been in a non-warmed world — the equivalent of Mexico not contributing to the maize market.

"These things are happening now," emphasizes David Lobell, an Earth system scientist at Stanford University in California and a co-author on the study.

The results come as a surprise to many. "I've been operating under the assumption we wouldn't be able to detect changes until the 20s or 30s of this century," says Gerald Nelson, an agricultural economist with the International Food Policy Research Institute in Washington DC, who was not involved with the work.

National crop yields are still rising as a general trend. But the fact that they are lower than a theoretical maximum is important when considering the huge challenge of feeding the world's booming population, the authors say.

Bigger changes may lie ahead. The study notes that the United States — which produces about 40% of the world's soya and maize — has so far been shielded from yield declines because its crop-growing regions haven't warmed in summer over the past 30 years, perhaps because of natural variability or the cooling counter-effect of aerosols. "There has been a perception that a perfect storm of conditions led to higher food prices in recent years. But that wasn't the case at all, because this major producer wasn't being detrimentally affected," says Lobell. "The US may have been lulled into a sense of complacency."

The study also shows that temperature has so far had a much greater effect on crop yields than precipitation. So it might be more important to breed heat tolerance into future generations of crops than to make them capable of surviving with less water. 

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