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Climate change could be slowed by planting crop varieties that reflect more sunlight, claim food scientists

Guardian Environment 15th January 2009

Food crops could be used to keep the Earth's temperatures down and slow global warming, say scientists. By growing plants that can reflect more of the sun's radiation back into space, parts of Europe and North America could be cooled by 1°C in the summer, the equivalent of stopping billions of tonnes of carbon dioxide from entering the atmosphere over the next century.

Growing agricultural plants such as maize or barley already cools the climate because they reflect more sunlight back into space than natural vegetation. Different varieties of the same plant can vary in how much light they reflect, a property called albedo, so selecting for higher-albedo crops would enhance the cooling effect from agriculture.

Using the same climate models as the Intergovernmental Panel on Climate Change, Andy Ridgewell led a team of scientists at the University of Bristol to calculate how different varieties of crops would affect global temperatures. "It would be an optimistic scenario that, farming everywhere, people were happy to plant a slightly different variety of crop."

The results, published today in the journal Current Biology, showed that, in the most optimistic scenario with all the world's crops replaced by the most reflective varieties, the world would cool by an average of 0.1C, equivalent to almost a fifth of the warming since the Industrial Revolution.

Over the next century, selecting more reflective crops could have a cooling effect equivalent to preventing 195bn tonnes of CO2 from entering the atmosphere.

Ridgewell says that farmers should seriously consider selecting crop varieties based on their climate effects, in the same way that specific varieties are fine-tuned to optimise crop yield. "The same crops are grown in the same location – all we're talking about is planting a variety of wheat or maize that you already grow, a variety that has slightly increased reflectivity," he said,

"We're very mindful of the biofuel minefield and particularly the way food supply and poverty in large regions of the world is – you could not displace any food production. We're not even talking about changing from wheat to maize or rice to something else."

To encourage them to grow these reflective crops, farmers could be rewarded with carbon credits. Ridgewell calculated that, with current carbon prices, farmers could earn 23 euros per hectare for the CO2 they prevent from reaching the air.

He added that temperatures could fall even further with careful breeding of crops. "We see no reason why, in the future, 2°C might not be achievable but it might require a lot of selective breeding or genetic modification to get that impact." This means selecting plants that have waxier leaves or leaves arranged to reflect more sunlight.

Keith Allott, head of environment group WWF-UK's climate change programme, said: "Like it or not, we are already committed to significant levels of warming because of the carbon dioxide already in the atmosphere. Ideas such as this might have some value in helping to reduce some of the local impacts, but need to be evaluated extremely carefully to make sure there are no other adverse impacts on the local or regional environment. But we shouldn't kid ourselves – the only way to make sure that we keep global warming below very dangerous levels is to secure a very rapid reduction in carbon emissions by moving to clean energy and stopping deforestation."

Ridgewell said that, unlike other proposed geo-engineering schemes to cool the planet, such as dumping iron in the oceans or sending mirrors into space to reflect away sunlight, altering the crops grown by farmers was much simpler. "These would require whole new infrastructures at a cost of trillions of dollars," he said. "We came up with [the crops] idea thinking agriculture is already global-scale and coordinated, to some extent. In a way, you could just go with that and subvert the existing infrastructure to come up with a climate benefit.

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