Climate change curbs crops: Study

Global maize (corn) production, for example, is estimated to be about 3.8 per cent 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,” emphasises 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 that 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, who was not involved with the work.

The study notes that the United States – which produces about 40 per cent 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.

Unpicking a trend

Crop yields depend on many things, from the vagaries of the market to the price of fertiliser and the availability of new technologies. However, the authors assumed that most of these factors are not linked to the weather, making it possible to extract a model of how temperature and precipitation is linked to national yields. Although warm temperatures can extend growing seasons, excessive heat generally restricts crop growth, and promotes pests and water loss. |

Additional rainfall, meanwhile, is beneficial up to a point.

The authors used their modeling results to estimate the effect that temperature and rainfall trends had on each nation’s food production from 1980 to 2008.

They estimate that, despite the fertilising effect of increased carbon dioxide in the atmosphere, the negative effect of climate change on plant growth has cut wheat production by 2.5 per cent, but boosted that of rice by 2.9 per cent and soya beans by 1.3 per cent. It has also, they calculate, bumped up food commodity prices worldwide by about 6.4 per cent over 30 years.

A study published by Nature in 19942 concluded that the fertilising effect of carbon dioxide would probably counteract the negative effects of warming at low latitudes for a few decades to come. “We don’t see that,” says Lobell.

Nature News