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Yields of crops such as rice, maize and wheat — relied upon by billions of people for their staple diet — could decline by as much as a third in tropical areas as temperatures rise due to climate change, according to two new scientific studies.

Research at the International Rice Research Institute (IRRI) in Manila, Philippines suggests that yields could fall by 10 per cent for every one degree Celsius of warming, possibly due to disruption of the flowering process. The latest report from the Intergovernmental Panel on Climate Change estimates average warming of 3°C in the tropics over the next century.

Klaus Toepfer, Executive Director of United Nations Environment Programme (UNEP), speaking at the climate change negotiations in Morocco said, “I would urge governments and delegates at this week’s climate change [conference] to remember the billions of people living at or near the poverty line whose lives face ruin as a result of global warming.”

“Food crops grown in the tropics are at or near their thermal limits, making it difficult for them to withstand further rises in temperature,” says John Sheehy, a crop ecologist at IRRI. His team is looking into ways of genetically modifying strains of the crops to make them more heat tolerant.

Although climate change is likely to benefit agricultural production in some regions — temperate areas such as Siberia and Canada may experience extended growing seasons, for example — overall these gains are unlikely to offset the losses in the tropics, which will particularly impact on the world’s poorest people.

A separate study by GRID Arendal — a UNEP collaborative centre in Norway — reveals that key cash crops, such as coffee and tea, will also be vulnerable to the effects of global warming over the coming decade.

New environmental maps of Uganda show that the total area for growing Robusta coffee would be dramatically reduced if local temperatures rose by just 2°C. If this happened, farmers might be forced to abandon existing plantations and seek cooler sites. Dr Svien Tveitdal, Managing Director of GRID Arendal said “only higher areas would remain, as the rest would become too hot to grow coffee”.

The coffee maps form part of a series of graphics designed to convey the complex impacts of climate change in a simple form.

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