The dubious climate gains of turning soil into a carbon sink
4 min read
“There’s more known about space travel than there is about soil health,” says Tom Gregory, gulping down a cup of tea and glancing out from his farmhouse kitchen at a valley of green fields.
Ten years ago, he and his wife Sophie set up their organic dairy farm in Chard, Somerset. Five years ago, they realised it was not working. The proof was in the earth; by most indicators the farm’s soil had got worse since they began their organic endeavours.
Like many others around the world, Gregory has responded by turning to so-called regenerative agriculture: improving soil quality by better stewardship such as reduced tilling and planting more diverse temporary pasture.
Big food companies are taking an interest in such practices, and not just for ecological reasons. As well as boosting crop yields and potentially cutting fertiliser usage, regenerative agriculture can help increase carbon sequestration — storing carbon in the soil and keeping it out of the atmosphere.
The Gregorys’ farm is part of a regenerative
According to Sachet, in rare cases some companies want to switch to different calculation tools in order to maximise the amount of carbon they can report as removed.
Earthworm uses computer models “as a proxy”, he says, because that’s what companies are being asked to use by the Science-Based Targets initiative (SBTi, an arbiter of corporate net zero plans) and investors. But he acknowledges that “there is bit of a caveat on the accuracy of those methodologies” and that Earthworm also uses satellite imaging to verify the farmers’ claims.
Ron Hovsepian, the outgoing chief executive of US-based Indigo, disagrees. He argues the computer models, augmented with random soil sampling, are scientifically robust. Indigo is one of several companies that have sprung up to help farmers make money selling soil carbon credits on the voluntary markets. The company has “given birth to over 133,000 tonnes of carbon sequestration”, says Hovsepian, and is now helping food and drink giants such as Nestlé and Anheuser-Busch InBev reduce their scope 3 emissions through soil carbon sequestration.
A more fundamental challenge than measuring carbon is the finite capacity of soil to store it, according to scientists and environmentalists.
Keith Paustian, a soil scientist at Colorado State University, says switching from conventional to regenerative farming can increase the amount of carbon stored in soils, provided the farmer does not revert to industrial practices like using synthetic fertilisers and intensive ploughing.
During this time, a food company can use the negative emissions from the soil sequestration to offset their positive ones, he explains. But after a while, usually around 20 years, the soils reach their capacity and once that happens the net emissions rise again.
Carbon stored in the land is also “not very reliable when it comes to the climate benefits”, says Sam van den Plas, policy director at Carbon Market Watch, which scrutinises carbon pricing schemes. “The carbon may be released at a later date and within a timeframe that it still contributes to global warming.”
Paustian adds that it is not like sequestering carbon deep underground, “where if you don’t have cracks in the rock, it’s going to stay there”. Carbon stored in soil remains biologically active. Paustian says the technology to measure carbon is good enough; the real issue is that without set standards it is easy for those involved in soil carbon credits to “cut corners”.
For van den Plas this is “comparable to what you have in the more classic voluntary carbon market offsetting schemes”, where the monitoring and verification of emission reductions is “fraught with difficulties”.
Smith, the University of Aberdeen professor, says carbon sequestration can buy food suppliers “time to decarbonise the rest of their supply chains” but it does not eliminate their emissions permanently.
“There’s an over-focus on carbon,” agrees Sachet. “Because financial actors are the ones behind it, they have managed to translate the environmental crisis into one metric, which is carbon.” The limitations in measuring carbon stored in soil mean companies “need to stay humble in their claims”, he adds.
For many farmers, regenerative agriculture is more to do with the health of their land than of their bank balances. In Somerset, Tom Gregory scoffs at the idea of selling carbon from his farm on the voluntary markets. “I could not be less interested,” he says. His wife Sophie adds that “the whole carbon scene is quite cowboy-ish.”
The Gregorys are dubious about payments linked directly to the amount of carbon sequestered in general, whether those payments come from within the supply chain or from selling on carbon markets. They believe farmers should be paid for their stewardship of the land. “We’re doing it for the soil,” says Sophie, “not so much the carbon.”
