Just 2 degrees of global warming will be enough to cramp food production in Earth's temperate and tropical regions as soon as the 2030s, according to a sobering study published this week.

"Our research shows that crop yields will be negatively affected by climate change much earlier than expected," lead author and University of Leeds professor Andy Challinor says in a statement. "Furthermore, the impact of climate change on crops will vary — both from year to year and from place to place — with the variability becoming greater as the weather becomes increasingly erratic."

The study, published in the journal Nature Climate Change, is based on a new dataset created from 1,700 previously published studies. That makes it "the largest dataset to date on crop responses," according to the researchers, whose work is included in newest installment of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report, which is due out at the end of March.

Their research suggests an extra 2 degrees Celsius (3.6 degrees Fahrenheit) will likely begin shrinking harvests of staple crops like rice, corn and wheat within 20 years. In 2007, the IPCC suggested temperate climates like those in Europe and North America could handle a couple degrees of warming without a negative effect on harvests, but Challinor says that forecast now needs an update.

"As more data have become available, we've seen a shift in consensus, telling us that the impacts of climate change in temperate regions will happen sooner rather than later," he says.

Climate change is now expected to reduce average crop yields from the 2030s onward, with the worst effects coming in the century's second half. By then, yearly staple harvests may routinely shrink by more than 25 percent. Median food yields are expected to fall by up to 2 percent per decade for the rest of the century, even as demand is projected to rise 14 percent each decade until 2050.

The new study is part of a growing awareness that a hotter world will also be hungrier. Last fall, for example, charity group Oxfam reported climate change could raise the number of undernourished people by 20 percent — from 870 million to more than 1 billion — before 2050. "If the remainder of the 21st century unfolds like its first decade," Oxfam warned, "we will soon experience climate extremes well outside the boundaries of human experience, ever since agriculture was first developed."

The new findings are also part of an increasingly ominous outlook for climate change in general, according to a leaked draft of the upcoming IPCC report obtained by the Independent newspaper in London. By the end of this century, for example, the report predicts "hundreds of millions of people will be affected by coastal flooding and displaced due to land loss," especially in Southeast Asia. It also warns that a 2.5-degree rise above pre-industrial temperatures could lead to global economic losses of between 0.2 and 2 percent, which translates to about $1.4 trillion.

While the idea of worsening world hunger can be demoralizing, Challinor notes there's still time to adapt thanks to research like this. "Climate change means a less predictable harvest, with different countries winning and losing in different years," he says. "The overall picture remains negative, and we are now starting to see how research can support adaptation by avoiding the worse impacts."

Russell McLendon is science editor at MNN. Follow him on Twitter and Google+.

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