The warming climate is likely to put stress on crops and livestock alike and could cause serious food shortages for half the world’s population, U.S. researchers predicted on Thursday.

The worst effects will be in the regions where the poorest people already live — the tropics and subtropics, the researchers wrote in the journal Science. But temperate regions will see very warm average temperatures, they added.

“In temperate regions, the hottest seasons on record will represent the future norm in many locations,” David Battisti, a University of Washington atmospheric sciences professor, and Rosamond Naylor, director of Food Security and the Environment at California’s Stanford University, wrote in their report.

The two combined direct observations with data from 23 global climate models.

They found a greater than a 90 percent probability that by 2100, growing-season low temperatures in the tropics and subtropics will be higher than the highest current temperatures.

“We are taking the worst of what we’ve seen historically and saying that in the future it is going to be a lot worse unless there is some kind of adaptation,” Naylor said.

There have been some recent tastes of what is to come, such as a heat wave that struck Europe in summer 2003 and resulted in deaths and reduced food production, they said.

Record temperatures hurt key crops including maize and fruit and accelerated crop ripening by 10 to 20 days. Livestock were stressed, the soil was dryer and more water was used in agriculture, they said.

Italy experienced a record drop in maize yields of 36 percent from a year earlier, and in France maize and fodder production fell by 30 percent, fruit harvests declined by 25 percent and wheat harvests declined by 21 percent, they wrote.

“I think what startled me the most is that when we looked at our historic examples there were ways to address the problem within a given year. People could always turn somewhere else to find food,” Naylor said. “But in the future there’s not going to be any place to turn unless we rethink our food supplies.”

Battisti said 3 billion people live in the areas that will be worst affected. The researchers urged investment in development of crop varieties that can withstand higher heat.

“You are talking about hundreds of millions of additional people looking for food because they won’t be able to find it where they find it now,” he said.

“The stresses on global food production from temperature alone are going to be huge, and that doesn’t take into account water supplies stressed by the higher temperatures.”
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