Monday, June 14, 2010

Intensive farming 'massively slowed' global warming

Andy Coghlan in New Scientist: Fertilisers, pesticides and hybrid high-yielding seeds saved the planet from an extra dose of global warming. That, at least, is the conclusion of a new analysis which finds that the intensification of farming through the green revolution has unjustly been blamed for speeding up global warming.

Steven Davis of the Carnegie Institution of Washington in Palo Alto, California, and colleagues calculated how much greenhouse gases would have been emitted over the past half-century if the green revolution had not happened. The study included carbon dioxide and other gases such as methane emitted by rice paddies. It found that, overall, the intensification of farming helped keep the equivalent of 600 billion tonnes of CO2 out of the atmosphere – roughly a third of all human greenhouse-gas emissions between 1850 and 2005.

The emissions were avoided because the green revolution boosted crop yields – for instance by promoting hybrid varieties that had higher yields, and through widespread distribution of pesticides and fertilisers. This meant that more food could be produced without having to slash vast swathes of forest to expand farmland.

"I think our results show the danger of focusing on one part of a complex system," says Davis, in response to environmentalists' claims that intensive agriculture has boosted emissions of greenhouse gases because it involves making and adding more fertiliser and agrochemicals.

"While it's certainly true that emissions from the manufacture of fertiliser have grown as a result of the green revolution," says Davis, "we show that these and other direct emissions from agriculture are outweighed by the indirect emissions avoided by leaving unmanaged lands as they are." And by enabling farmers to produce more on existing farmland, the green revolution spared 1.5 billion hectares – an area one-and-a-half times that of the US – from being turned over to agriculture….

Aerial photo of farms in Grant County, Washington, USA. View is looking roughly south, just east of George, Washington. You can see the square patterns of land ownership and the circular patterns caused by irrigation sprinklers. Shot by Joe Mabel, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 3.0 License.

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