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The crops spread across large fertile regions of North America and Europe  would send a small percentage of the sun's light and heat back into space.

Different strains of crops such as wheat have significantly different levels of reflectivity, or albedo, say scientists. Selecting those that reflect the most could make summers in Europe more than 1% cooler, they claim. Varieties of wheat or barley with waxy leaves for instance could increase the amount of light reflected.

Lead researcher Dr Joy Singarayer, from the University of Bristol, said: "Our current studies on crop reflectivity are at an early stage, but our initial results are really encouraging, as they suggest that simply by choosing to plant specific strains of crops, we could alter the reflectivity of vast tracts of land and significantly reduce regional temperatures.

"The concept of using increased reflectivity to manipulate our climate is, in fact, an ancient one - humankind has for centuries painted settlements white to reflect the sun and keep cool. We could now realise the opportunities to do this on a much bigger scale via our agricultural plantations."

The findings were outlined in London at the Royal Society discussion meeting "Geoengineering - Taking Control of our Planet's Climate".

Arable land makes up more than 10% of global land use, said the scientists. Particularly dense agricultural regions covered Europe, North America and Southern Asia.

A global climate computer simulation was used to assess the potential for planting crops with high reflectivity.

The study found that a 20% increase in crop albedo could provide Europe with an average summertime cooling of more than 1%. This was a fifth of the change needed to offset a doubling of atmospheric carbon dioxide levels in the next century.

Under a more moderate global warming scenario, the method could offset up to half of the predicted summer warming over Europe.

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http://iopscience.iop.org/1748-9326/4/4/045110/pdf/erl9_4_045110.pdf