Extreme flooding and droughts take a major toll on the global supply of wheat, accounting for about 40 percent of the fluctuations in annual yields, a recent study has found.

The research gives new weight to scientists’ warnings about the effect of runaway climate change on food production. Climate change is expected to exacerbate these extreme weather patterns, the researchers noted, making crops even more vulnerable in the decades to come. Wheat supplies roughly 20 percent of all dietary calories worldwide.

The study by the European Commission’s Joint Research Centre analyzed harvest and climate data in wheat-producing countries between 1980 and 2010. It found that excess rain and cloud cover ― also prompted by climate change ― have an even bigger effect on the grain than drought. The wetter climate breeds pests and diseases that wipe out plants and shrink the annual harvest.

Vincent Kessler / Reuters Cloud cover and excess rain are causing major fluctuations in global wheat harvests.

“There are indications that the results and effects of global warming, and especially the recent acceleration of global warming, are already visible as a signal,” Matteo Zampieri, an Italian climatologist and irrigation expert working for the European Union, told HuffPost Tuesday. “They are emerging in a statistically significant way.”

The findings were published last month in the journal Environmental Research Letters, and the researchers are now expanding the study to examine corn and rice. Climate has an even bigger effect on corn, accounting for as much as 50 percent of its yield variability, they found.

Rice requires a more sophisticated analysis, Zampieri said. The grain is often grown in deliberately flooded paddies, making it less sensitive to weather fluctuations. But water scarcity ― yet another impact of global climate change ― would likely decrease rice production as well.

As food production drops, prices will go up. Studies have already found that manmade global warming has driven up the cost of food by as much as 20 percent over the past few decades. Beef prices alone skyrocketed 34 percent from 2010 to 2014 amid historic droughts in cattle-ranching states like California and Texas.

Another factor will be the world’s growing population. More people will mean more competition for water and other resources ― making it more important than ever for crop yields to reach their potential, Zampieri said.