Soybean boom spells bad news for climate

energy / climate change

CHOPPING down the Amazon rainforest to plant soybean crops is more detrimental to the climate than clearing space to graze cows. Fields of soybean reduce rainfall dramatically, over four times as much as pastureland.
Around 13 per cent of the original Brazilian rainforest has been cleared so far, with 85 per cent turned into pasture and 15 per cent into soybean fields. However, these plantations are rapidly expanding thanks to soya's popularity as a food and suitability as a biofuel.
To measure how different land use affects climate, Marcos Costa from the Federal University of Viçosa in Brazil, and colleagues, measured changes in albedo or reflectivity over experimental plots of soybean and pastureland. They then plugged the data into a climate model to investigate the effect of the change in land use.
Clearance of any kind caused a decline in rainfall but soybean dried up the skies much more than pastureland (Geophysical Research Letters, DOI: 10.1029/2007GL029271). When three-quarters of the forest plots were cleared for soybean, there was a 15.7 per cent decrease in precipitation, while the same clearance for pasture produced a 3.9 per cent decrease.
The stronger reflectivity of soybean fields was to blame. "With a higher albedo than pasture - and forest - the soybean crop absorbs less solar radiation, heating the surface less, decreasing convection and cloudiness and, in the end, causing less precipitation," explains Costa.
Carefully planned farming might help to reduce the damage. "Inter-cropping or designing a better spatial arrangement of forest and cropland could produce a better result," says Jon Lovett, an environmental scientist at the University of York, UK.
Soybean may eventually lose some of its popularity. "It could well be that biofuel production from other sources will be cheaper than high-protein soybeans," says Lovett.
Nonetheless, the soybean boom shows no sign of abating for the moment, with the construction of the 1144-kilometre trans-oceanic highway connecting Brazil's Atlantic ports to Peru's Pacific ports, and the paving of the BR-163 highway, making export of agricultural products to international markets much easier.
From issue 2600 of New Scientist magazine, 21 April 2007, page 12