That’s the conclusion from a new study in the Proceedings of the National Academy of Sciences (PNAS). Two Stanford researchers looked at the effects of the Green Revolution—the half-century old transition to more intensified agriculture, with more fertilizers and more irrigation—to see what impact the shift might have had on global carbon emissions. Here’s how the British magazine New Scientist reported the findings:
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.
600 billion tonnes of CO2 might seem like a huge figure—it’s equivalent to about a third of the world’s total output of greenhouse gases since 1850—but the analysis is pretty straightforward. The conversion of forests to farmland is a major cause of carbon emissions—when trees are burnt or cut down, the carbon they’ve sequestered is released into the atmosphere. (Deforestation is responsible for about 15% of global carbon emissions.) By raising the crop yield per acre, industrial agriculture means more food can be raised on less land, which means fewer acres need to be converted to farmland. In fact the co-authors of the PNAS paper—Stephen Davis and Jennifer Burney—estimate that the Green Revolution has prevented the need to convert 1.5 billion hectares to farmland—an area equal to one and a half times the size of the U.S.
It’s important to realize, however, that simple carbon accounting doesn’t include the drawbacks of industrial farming, like fertilizer runoff, pesticide accumulation and antibiotic resistance. And advocates for organic farming have long argued that more sustainable practices can still have impressive crop yields, if done right— researchers at the University of Michigan argued in a 2007 study that organic and conventional farms can have similar yields in developed countries, and that organic can still feed the world. But organic farms do tend to require a lot more human labor—fighting pests takes more work if you can’t use chemicals—and in the U.S. at least, farming employment has generally been on a downward slide as farms have consolidated. The PNAS study isn’t a conclusive blow for industrial farming, but it is a reminder that in a growing world with shrinking limits, every choice will come with consequences.