WASHINGTON, June 11 -- A study published on Monday in the Proceedings of the National Academy of Sciences showed that warmer temperatures by the end of this century may increase the likelihood of simultaneous low yields across multiple high-producing regions, which could lead to price hikes and global shortages.

The research led by the University of Washington (UW) showed dramatic increases in the variability of corn yields from one year to the next.

Corn, the most widely grown crop in the world, is used in food, cooking oil, industrialized foods, livestock feed and even automobile fuel.

While most rice is used domestically, corn is traded on international markets. Four countries, the United States, Brazil, Argentina and Ukraine account for 87 percent of global corn exports, with China mostly producing for domestic use.

According to the study, today the probability that all four exporters would have a bad year together, with yields at least 10 percent below normal, is virtually zero.

But results showed that under two degrees Celsius warming, which is projected if people succeed in curbing greenhouse gas emissions, this risk increases to 7 percent.

Under four degrees Celsius warming, which the world is on track to reach by the end of the century if current greenhouse gas emissions rates continue, there's an 86-percent chance that all four corn-exporting countries would simultaneously suffer a bad year.

It suggested that cases like the 2003 heat wave in Western Europe, which devastated crops there, would be more likely to coincide with bad years in other regions.

"Yield variability is important for determining food prices in international markets, which in turn has big implications for food security and the ability of poor consumers to buy food," said the paper's lead author Michelle Tigchelaar, a UW postdoctoral researcher in atmospheric sciences.

According to the study, warmer temperatures will severely decrease average corn yields in the U.S. southeast, Eastern Europe and sub-Saharan Africa, and will increase the variability in the United States and other exporting nations.

"Even with optimistic scenarios for reduced emissions of greenhouse gases, results show that the volatility in year-to-year maize production in the U.S. will double by the middle of this century, due to increasing average growing season temperature," said co-author David Battisti, a UW professor of atmospheric sciences.

"The same will be true in the other major maize-exporting countries. Climate change will cause unprecedented volatility in the price of maize, domestically and internationally," said Battisti.

The study did not take into account precipitation changes, since those are harder to predict, and projections show that changes will be small compared to the natural changes in rainfall from one year to the next.

It also assumed that temperature swings will stay the same as today, though some models project temperatures will become more variable under climate change.

"We took a conservative approach and assumed the weather will be the same, only acting on top of an overall warmer climate," Battisti said.