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Ever since humans learned to wrest food from soil, creatures like the corn earworm, the grain weevil and the bean fly have dined on our agricultural bounty. Worldwide, insect pests consume up to 20 percent of the plants that humans grow for food, and that amount will increase as global warming makes bugs hungrier, according to a study published Thursday in the journal Science.
That could encourage farmers to use more pesticides, which could cause further environmental harm, scientists said.
For every degree Celsius (two degrees Fahrenheit) that temperatures rise above the global historical average, the amount of wheat, corn, and rice lost to insects will increase by 10 to 25 percent, the study says. Temperate agricultural regions, like those in the United States and Western Europe, would be particularly hard hit.
The international Paris Agreement is designed to keep warming below two degrees Celsius, but the world’s countries are far off track from meeting that goal.
By eating such a large amount of crops in the field, “insects have consumed something like one out of every eight loaves of bread before it even gets made,” said Curtis Deutsch, a professor of chemical oceanography at the University of Washington and an author of the study. “If we warmed four degrees, which is what climate models typically predict for the end of this century, then that amounts to insects eating two of our eight loaves of bread instead of one.”
Higher temperatures speed many insects’ metabolisms, making them eat more. Their life cycles also get faster, causing them to reproduce more quickly. Both effects would diminish crop yields even as the human population continues to increase, putting additional strains on the global food supply, the study says.
To arrive at their estimates, Dr. Deutsch and his colleagues used statistical models to simulate the effects of global warming on insect feeding and reproduction. They focused on wheat, corn and rice crops because they account for 42 percent of the calories directly consumed by humans.
Other factors could help mitigate crop losses. Beneficial insects could also thrive in a warmer climate, said Michael Hoffmann, a professor of entomology and executive director of the Cornell Institute for Climate Smart Solutions, who was not involved in the study. Those insects could end up “offering some suppression of the pests, so that the damage may not be as great as they are suggesting,” Dr. Hoffmann said.
Still, higher temperatures can spell bad news for thirsty crops regardless of insect activity. A study last year in the journal Nature Communications found that the pressures from increased summer temperatures could lead to a significant decline in agricultural yields. This summer’s European heat wave, which is in keeping with patterns of climate change, reduced Germany’s grain production by roughly 20 percent.
That study found that improved irrigation could offset at least some of the losses. But it is less clear if insecticides could help stave off multiplying pests.
“The one out of eight loaves of bread that we currently lose already reflects what we can do to manage crop losses to insects,” said Dr. Deutsch. Pesticides could help where they’re not already in use, but in other regions, “there’s a real question as to whether or not they’re already at their maximum effectiveness,” he said.
In addition, pesticides can unintentionally harm other organisms, and some have been linked to human health problems. Their manufacture, transport and use also contribute to global warming.
Dr. Deutsch said the real solution was to drastically reduce the level of greenhouse gases that humans emit. “If you want to solve a big problem with a million tendrils, you have to go to the root of it,” he said. “Otherwise, you’re manufacturing a million Band-Aids. I don’t think that’s feasible. It’s also much harder.”
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