Growing swarms of hungrier and hyperactive insects may wipe out big percentages of the world's three most important grain crops—wheat, corn and rice—even if the world manages to cap global warming at 2 degrees Celsius, the upper-end target of the Paris climate agreement, scientists warn.

The biggest crop losses are expected in temperate areas where global warming will increase both insects' population growth and their metabolic rates. That includes the major breadbaskets of North America and Europe.

Altogether, the potential scale of the damage is so high, it could threaten global food security, according to research published Aug. 30 in the journal Science.

"We're turning the dial up in the temperate zones, and insects, for the most part, thrive in a warmer climate," said co-author and sustainability researcher Josh Tewksbury, director of Future Earth at the University of Colorado. "It gets better and better for them."

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For people accustomed to the pace at which today's crop-destroying insects migrate, the rapid and widespread changes fueled by global warming may come as a shock. Farmers will need to adapt, Tewksbury said. That could mean overhauling crop rotations, more genetic research and rethinking pesticide use to avoid severe damage.

"Get ready, because the fight is coming to you," he said.

The researchers project that, globally, crop yield losses for wheat, corn and rice will increase 10 to 25 percent for every degree of global warming. If global temperatures rise 2 degrees Celsius over the 1971-2000 average, they project that the rise in insect pest activity would increase wheat yield losses by a median of 46 percent, corn by 31 percent, and rice by 19 percent.

Those three food crops are staples for about 4 billion people, and account for about 42 percent of direct calories consumed by humans worldwide, according to the UN Food and Agriculture Organization.

University of Washington climate researcher and co-author Curtis Deutsch explained the impact this way:

"Insect pests currently consume the equivalent of 1 out of every 12 loaves of bread (before it ever gets made). By the end of this century, if climate change continues unabated, insects will be eating more than 2 loaves of every 12 that could have been made," he wrote.

'This Sets Off Alarm Bells'

The researchers relied on fundamental insect physiological data, based on decades of lab studies and field research, that show how warmer temperatures accelerate the metabolism of insect pests like aphids and corn borers at a predictable rate. That makes them hungrier, and warmer temperatures also speed up their reproduction in most regions.

By 2050, growing-season temperatures will probably be warmer than anytime during the past century, according to the study. The temperature increase alone is expected to reduce crop yields as heat waves intensify and ground dries out more quickly. But most previous projections for the impact of global warming on crops "rarely considered impacts on insect pests," the study's authors say.

Currently, the world loses about 30 percent of its crops to pests, weeds and various pathogens, said Western Sydney University environmental researcher Markus Riegler, who wasn't involved in the research but wrote a related article on the findings. The losses projected by the new study are staggering, he said.

"This sets off alarm bells," Riegler said.

Clues to the amount of damage insects can do in a warmer world are also contained in ancient fossils from an era of abrupt climate change linked to rapidly climbing CO2 levels about 56 million years ago, he said. In a study looking at about 5,000 fossils from that era, a separate group of researchers found that plant damage from insects correlated with rising and falling temperatures, reaching a maximum during the warmest periods.

The results suggest that insects will cause a lot more damage to all plants as the climate warms, and they highlight the need start protecting crops now. Farmers, industries, policy-makers, and wider society must all be involved because the actions needed include big changes to food systems, Riegler said.

"I'm concerned about the loss of political progress toward stopping global warming, and this highlights one of the big risks of no action." With 800 million people already suffering daily hunger, now is the time to act to ensure future global food supplies, he said.

What Can Farmers and Governments Do?

There are steps that farmers and policymakers can start taking, beyond reducing the greenhouse gas emissions that are fueling climate change, Riegler said.

"We are going to have to be smart about how we manage insect pests. We'll need integrated pest and crop management and really think about what plants to plant when and where and in what sequence," he said.

"We also have to improve quarantine procedures. That will be an additional twist," he said, explaining that insects pests traveling via growing international commerce will more easily find footholds in new areas.

And there needs to be more emphasis on protecting natural genetic diversity, because there are opportunities to work with plants that have natural resistance to pests, he added.

That requires thinking in a systematic, global way, Tewksbury added.

"The answer is not finding new bugs that kill bugs, or just using more pesticides," Tewksbury said. "We need a science-based approach that takes into account the natural evolution of the plants and what insects co-evolved with them. Our lack of attention to that knowledge is going to come back to bite us."

A global database of crop pathogens would be a good place to start, said North Carolina State University ecologist Rob Dunn, who was not involved in the study. Widely shared global information would help identify changing pest problems early, giving time to find a solution before it becomes a crisis.