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Climate change is likely to have more dramatic effects on global agriculture than previously predicted, leaving around half the world's population facing serious food shortages, according to a new analysis.

Harvests of maize, rice and other staple crops could drop by up to 40 per cent by the end of the century because of higher temperatures during the growing season, the study found.

The research, conducted by a US team, aimed to create a more global picture of the fate of agriculture under climate change than previous analyses.

The researchers calculated the difference between historical and projected average temperatures each season throughout the world, using data from 23 global climate models that contributed to the 2007 Intergovernmental Panel on Climate Change's scientific synthesis.

In Science today (9 January) they say that the highest temperatures of the growing season experienced by the tropics and subtropics over the last 100 years will, by the end of the twenty first century, be the lowest.

They predict that, for every rise in seasonal temperature of one degree Celsius, yields of major grain crops will drop by 2.5–16 per cent. 

"When you're in the tropics or subtropics, an extreme temperature change today might be a half a degree averaged over the summer," lead author David Battisti, professor of atmospheric sciences at the University of Washington, told SciDev.Net.

But average seasonal temperature increases could be three or four degrees by the end of the century. "The stresses on agriculture due to [these] temperature increases just haven't been seen yet."

Battisti said the predicted temperature stresses could reduce crop yields by as much as 20–30 per cent across the tropics and subtropics.

And the outcome could be worse than the study predicts, as many of the regions assessed are projected to become drier, which would add to the temperature stress, said Battisti.

"The population will double in the next fifty years in the tropics and subtropics — that's a very hard place to be. How do you adapt to that, especially with the lack of resources there?"

Battisti and co-author Roz Naylor, at the US-based University of Stanford, call for major investment in adaptations to develop crops that are tolerant to heat and heat-induced water stress, and irrigation systems suitable for diverse environments. A key first step, they argue, is investment in infrastructure.

"We need to worry about the next 30 years, not 2100. If you're going to do any adaptation at all, you have to have an infrastructure."

Claudia Ringler, senior research fellow in the Environmental and Production Technology Division at the International Food Policy Research Institute, praised the study for stressing the projected increases in temperature in addition to "the more common emphasis on drought".

But she added: "The dire picture in the paper assumes no adaptation. Adaptation will certainly happen … Significant improvement in agricultural production is possible in the lagging regions, such as Sub-Saharan Africa, within the time span of the projection".

Link to full paper in Science

Link to commentary in Science

References

Science 323, 240 (2009)

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