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Food harvests dragged lower by global warming

By Martin Leggett - 05 May 2011 18:11:0 GMT
Food harvests dragged lower by global warming

There have already been plenty of indicators that global warming may be acting as a drag on world food production - lowering yields and pushing up food prices. Now a Stanford University research team has modeled in detail how the planetary warming of the last 3 decades has hit the world's 4 main food crops. The results, published today in Science Express, show that an area of corn (maize) equal to Mexico's annual output has been lost - and that France's wheat harvest would be entirely swallowed by the lowered wheat yields. And these reduced harvests can be pinned onto the effects of climate change.

Harvest that are lower than what they could-have-been have helped to push an extra $50 billion onto the world's food bill, despite some benefit for crops from higher CO2 levels. But the numbers coming from the research do vary widely with crop and region. Whilst wheat and maize show bigger 'missed yield increases' from rising temperatures, soya beans and rice show no effect yet on their yields. And the US appears to have gotten away with no major losses in potential yields - its major crop-growing regions have yet to see the warming experienced by many other parts of the world.

In order to pull out these numbers, the scientists - led by David Lobell, an assistant professor of environmental Earth science at Stanford University - merged published crop yield data sets from the UN's Food and Agriculture Organization with those from the Universities of Delaware and Wisconsin, as well as McGill University. Together they covered three decades of harvests for the 'big four' food crops - soya, corn, wheat and rice - which account for three-quarters of human calorie-intake.

They then zeroed in on the main crop-producing areas, and looked at how rainfall and seasonal temperatures have evolved since 1980. By stripping out the known changes due to global warming  over that period - and recalculating the harvests using a 'climate stable' crop model - the team came up with crop-yield numbers that would have applied, if global warming hadn't intervened.

Although overall crop harvests have increased in the face of greenhouse gas-fueled warming, the study showed that climate change has left wheat down 5.5% and corn 4%, compared to what would have happened without global warming. Losses in wheat were greatest for Russia, India and France, whereas China and Brazil were the biggest losers with corn.

But the US Corn Belt seems to have been shielded from serious climate effects so far, and has even seen a slight cooling trend. That has been very beneficial globally - the US produces 40% of the world's corn and wheat, and by holding onto its high harvests, food price rises have been somewhat blunted. That luck may not hold, however.

The modest global warming seen to-date (around 0.13 degrees Celsius per decade) is likely to accelerate over the coming century - and models have even the US Corn Belt in the firing line. Lobell said ''The climate science is still unclear about why summers in the Corn Belt haven't been warming. But most explanations suggest that warming in the future is just as likely there as elsewhere in the world.''