Each degree of global warming will cut into harvests of the world's staple crops, according to a new study that takes a broad view of the agricultural research field.

Wheat, corn, rice and soybeans make up two-thirds of humans' caloric intake. Each crop reacts differently to rising temperatures, and the effects vary from place to place. On average, though, the world can expect 3.1 to 7.4 percent less yield per degree Celsius of warming, according to the research.

The findings draw from a meta-analysis of more than 70 studies of models, statistical regressions and experiments. Twenty-nine researchers published the paper this week in Proceedings of the National Academy of Sciences.

It bolsters other predictions about degraded food supply by the Intergovernmental Panel on Climate Change. The United Nations predicts the world's population will grow to 9.8 billion by 2050 from 7.6 billion today. Warmer conditions could make it harder to grow enough food for so many mouths, and the crops that do grow could offer fewer nutrients (Climatewire, Aug. 2).

The Paris climate agreement has committed the international community to less than 2 degrees Celsius of warming by the end of the century. The United States plans to quit the accord.

But American agriculture could suffer disproportionately from warmer conditions, especially when it comes to corn, according to the study.

Corn proved most sensitive to rising temperatures. Evidence suggests global corn harvests could decline 7.4 percent per degree Celsius of warming.

The effect emerges consistently across the world's major corn producers, with the United States' harvests suffering most: 10.3 percent less corn per degree of warming.

China, Brazil and India would also suffer — though the warming impact on France could be modest enough that statistical modeling suggests a slight improvement is possible.

Wheat showed a more consistent response, declining at a global average of 6 percent per degree, according to the paper.

Rice, a main food source for developing countries, could decline an average of 3.2 percent. Some research pointed toward an even greater impact — as much as 6 percent — while statistical regressions suggested almost no impact.

And soybeans, the world's fourth-most important commodity crop, could yield 3.1 percent less per degree. Although soybeans offered the most uncertain results, the researchers estimated American harvests could decline an average of 6.8 percent per degree, while Chinese harvests might not see any statistically significant changes.

The researchers only studied the direct effect of rising average temperatures, but indirect effects could change things, too. Water stress and drier soils might drag down harvests. So could more frequent heat waves. Climate change could also affect pests, weeds and diseases.

All of those factors present challenges that farmers have overcome before. But the researchers write that yields in some parts of the world have already started stagnating.

“Further increases in temperatures will continue to suppress yields, despite farmers' adaptation efforts,” they wrote.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.