It could be much more difficult than we thought to feed everyone in a warmer world. Satellite images of northern India have revealed that extreme temperatures are cutting wheat yields. What’s more, models used to predict the effects of global warming on food supply may have underestimated the problem by a third.

In India’s breadbasket, the Ganges plain, winter wheat is planted in November and harvested as temperatures rise in spring. David Lobell of Stanford University in California used nine years of images from the MODIS Earth-observation satellite to track when wheat in this region turned from green to brown, a sign that the grain is no longer growing.

He found that the wheat turned brown earlier when average temperatures were higher, with spells over 34 ºC having a particularly strong effect. He then inferred yield loss, using previous field studies as a guide.

This revealed a much stronger effect of temperatures on yield than previous studies. Lobell’s data predicted that yield losses in the Ganges plain will be around 50 per cent greater from an average warming of 2 ºC than existing models.

“It surprised me a little how much crop models underestimate the observed effects,” says Lobell. They might have especially underestimated the impact of hot spells. » Read more: Wheat will age prematurely in a warmer world