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 Commissions 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.