As the globe warms, farmers will face more drought, flooding, and crop-frying heat. But that may be nothing compared with the bugs. A new study finds that higher temperatures will produce more voracious grasshoppers, caterpillars, and other crop-devouring pests, with potentially catastrophic consequences for the world’s food supply.
The study is “a stark warning” for our future food security, says Robert Paxton, an insect ecologist at the Martin Luther University of Halle-Wittenberg in Germany, who was not involved with the work. But he notes that the computer model making the dire predictions omits other factors that might limit the toll.
Scientists became keenly aware of the insect threat 10 years ago. That’s when Curtis Deutsch, a biogeochemist at the University of Washington in Seattle, published a study showing that as temperatures rise, nearly all insects multiply and rev up their metabolisms. “When there’s more thermal energy in the environment,” says Deutsch, “all of the different chemical reactions in the complex soup of biochemistry inside living things start to speed up, and they need to consume more calories.”
To see what kind of damage this increased insect appetite might have on the global food system, Deutsch and his team built a computer program that combined physiological data on hundreds of insect species with climate models. When the planet warmed by an average of 2°C, as models predict will happen by 2100, if not sooner, wheat crops shrunk by 46%, rice by 19%, and maize (or corn) by 31%. Temperate, productive regions like the United States’s “corn belt,” wheat fields in France, and rice paddies in China were especially hard hit, the team reports today in Science.
For wheat and maize, the model predicted that the losses would continue to increase 10% to 25% for each extra degree of warming. Rice yields, however, might start to stabilize after a 3°C increase in temperature, as it is grown in many tropical environments where insects might begin to die off after too much warming.
“The modeling is robust, and the conclusions are sound,” says Paxton, who notes that German farmers are expected to lose one-fifth of their crops this year because of record-setting heat and lack of rainfall. But Paxton and Deutsch agree that the simplified model has left out many factors like how insects’ natural predators will respond to warming, whether the insects’ diets might change, and whether changes in farming techniques could keep the bugs at bay.
Still, Deutsch says it’s important to begin planning for the effects that climate change could have on the global food supply, because the people hardest hit by crop loss will likely be the world’s poorest households. According to recent United Nations estimates, at least 815 million people worldwide already go hungry each day, and maize, rice, and wheat are the main food sources for about 4 billion people.
“If we think about food supply as the pie we all get to eat, some us of get smaller slices than others,” Deutsch says. “If the pie begins to shrink, we need to find ways to stop it from shrinking and to carve it up more evenly so people aren’t left without.”