A new report from researchers at the University of Minnesota Institute on the Environment has found that climate variability historically accounts for one-third of yield variability for corn, rice, wheat and soybeans worldwide — the equivalent of 36 million metric tons of food each year. 

The report, "Climate variation explains a third of global crop yield variability," was published in the journal Nature Communications. Researchers looked at newly available production statistics for corn, rice, wheat and soybean from 13,500 political units around the world between 1979-2008, along with precipitation and temperature data. The team used these data to calculate year-to-year fluctuations and estimate how much of the yield variability could be attributed to climate variability.

About 32-39% of year-to-year variability for the four crops could be explained by climate variability. That's equivalent to 22 million metric tons of corn, 3 million metric tons of rice, 9 million metric tons of wheat and 2 million metric tons of soybeans per year. 

The links between climate and yield variability differed among regions. Climate variability explained more than 60% of yield variability in some of the most productive regions — including the Midwest — but far less in low-yielding regions. 

"This means that really productive areas contribute to food security by having a bumper crop when the weather is favorable, but can be hit really hard when the weather is bad and contribute disproportionately to global food insecurity,” says paper-author Deepak Ray, senior scientist for the Global Landscapes Initiative at the University of Minnesota. “At the other end of the spectrum, low-yielding regions seem to be more resilient to bad-weather years but don’t see big gains when the weather is ideal."

Some regions, such as parts of Asia and Africa, showed little correlation between climate variability and yield variability.  

The research team is now looking at historical records to see whether the variability attributable to climate has changed over time, and if so, what aspects of climate are most pertinent.

“Yield variability can be a big problem from both economic and food supply standpoints,” Ray said. “The results of this study and our follow-up work can be used to improve food system stability around the world by identifying hot spots of food insecurity today as well as those likely to be exacerbated by climate change in the future.”