Will carbon farming save the planet?

Could sequestering CO2 in soil help us to reverse the effects of climate change, and if so, how does it need to be implemented if it is to have the required effect?

Dave Reay wants to get to net-zero. This means that, by the time he dies, he will have sequestered the equivalent of a lifetime of carbon emissions. Reay – who is professor of carbon management and education at the University of Edinburgh – hasn't flown for 15 years, is vegetarian and tries to live by the principles he set out in his 2005 book, Climate Change Begins at Home. But to achieve net-zero, he's now turning to the soil: "It's always been in my mind to have a piece of land and to manage it to soak up carbon. A place where I can apply all of my research."

That piece of land is a small 74 acre (30 ha) farm in Kintyre on the west coast of Scotland. It's mainly grass and sheep, but together with a neighbouring farmer, Reay plans to gradually reduce the amount of livestock and plant more trees; and to quantify the amount of carbon in the soil, trees, and even the "blue carbon" – the CO2 that is sequestered in coastal ecosystems – in the seaweed on the shore of his farm. His aim is to work out how you can increase the uptake of carbon while securing a livelihood as a small landowner.

Reay is open that the real excitement for him will be the research rather than farming, but is convinced that we need to get to grips with how we quantify and manage the land in this way. Because much of the agricultural sector is about to enter a whole new paradigm, he says, where the "primary purpose is not producing food, but taking carbon out of the atmosphere".

Welcome to carbon farming. Capturing airborne carbon in the soil was made a formal part of the response to climate change in 2015 by the UN's Lima-Paris Action Agenda. The commitments included several on agriculture, notably the "4 per 1,000" initiative, which aims to increase the amount of carbon in agricultural soils, grassland and forest soils by 0.4% every year. Employing practices such as no-till cropping, stubble retention and agroforestry, through to integrated whole-farm planning, would be enough, 4 per 1,000 argues, to halt the increase in the CO2 concentration in the atmosphere related to human activities.

Another report – Natural climate solutions for the United States – published last year by American Association for the Advancement of Science, claims that changing forestry and agricultural management practices could provide sequestration of the equivalent of 21% of US annual emissions. In the UK, the Royal Society's 2018 Greenhouse Gas Removal report recommends active support for soil carbon sequestration, forestation and habitat restoration be built into new UK agricultural and land-management subsidies. And the Intergovernmental Panel on Climate Change is currently preparing a special report on land, food and climate; a source close to it says mitigation options clearly include storing more carbon in agricultural land.

Affording the time

Little of this is new. People have been advocating for it for at least 50 years, suggests Pete Smith, professor of soils and global change at the University of Aberdeen, and a leading expert on greenhouse-gas-removal technologies. So why all the noise now? Because "we need affordable solutions that buy us time while we are decarbonising the rest of the economy".

Smith believes the extent of what could be achieved by 4 per 1,000 has been "oversold to a certain extent". Food security expert Tim Benton, professor of population ecology at the University of Leeds, echoes this: "Soil carbon sequestration is incremental [and] important, but likely to offset only a small percentage of emissions."

Smith estimates that, if carbon farming was implemented properly worldwide, it could soak up 2-5 gigatonnes of CO2 a year – about 10% of global emissions. However, that benefit would only last us between 20 and 50 years before global soils were saturated. At that point attention should turn to protecting them; keeping that carbon in the ground. This is what Smith means by carbon farming "buying us time". We can use it to compensate for the gap before the mass adoption of electric vehicles, renewables and carbon capture and storage.

None of this detracts from 4 per 1,000 being a good initiative, Smith hastens to add, especially because it's getting people to buy into increasing soil carbon stocks "even if you're not interested in climate change".

The first thing we need to do, Smith says, "is switch off the emissions". That means keeping the carbon where it is and restoring and protecting global peatlands, rather than draining them. Next, we should turn to croplands and degraded pastures that have been depleted by mismanagement and overuse, and try to get their stocks up. He suggests there are around 60 different ways for farmers to increase carbon uptake on their land, and all of these have "co-benefits", such as soil health, reducing feed costs or run-off, that mean the motivation for doing them needn't even be emissions related.

What carbon farming does, though, says Reay, is put a whole new spin on techniques that have been around for years. "It's incentivising [farmers] to trap carbon out of the atmosphere as part of [their] work as a farmer, and be rewarded."

Farming policy has generally not been directed towards climate change. In the UK, the sector accounts for 10% of greenhouse gas emissions – possibly as high as 25% if you include the supply chain – and there's been little change since 2008, according to the Department for Environment, Food and Rural Affairs. The agriculture bill currently going through parliament, which is designed to replace the Common Agricultural Policy post-Brexit, puts the emphasis on subsidies being paid out on the basis of farmers delivering public goods. The expectation is that the bill will bolster support for farmers to increase carbon uptake, while also cutting emissions from their normal activities.

Jeremy Smith MRICS, a rural surveyor at Savills in Exeter, is cautious: "The wording of the paper is, essentially: direct subsidy is going and ecosystems services are coming to the fore – public money for public goods. But the devil is in the detail, and no one knows the details."

Smith says there's little doubt that soil health is still overlooked: "It's not seen as an investment in the farm in the same way as a building or machinery is." But there are signs of change. The Dartington Hall Trust Land Use Review, on which Smith advised, is looking at benchmarking soil health as part of the landlord-tenant relationship, with penalties or rewards for degrading or improving it.

The Trust combines five food and farming enterprises in an agroforestry system known as "silvoarable". One tenant rotates their arable crop between rows of trees, farming "horizontally", while the tree crop licensees farm it "vertically" to maximise the space available for crop production.

"Taking away the [current] subsidy opens up new possibilities for ecosystem services, because you're not beholden to one set of rules," says Smith. And there are arguments for some land being used for ecosystem services over food production – compare the arable potential of the south-east of England to the south-west, for example.

"Most farmers are running a business, so the idea of being paid to reduce carbon is attractive," says the Soil Association's head of horticulture, Ben Raskin. But it also doesn't make sense to reward farmers based solely on location, he adds. For example, if you farm on sandy soils your carbon uptake might be 2-3%, versus 30-40% if you're in a region with peaty soil. "We need to reward practices that we know sequester carbon, such as agroforestry, and also bring other benefits."

Wood works

Agroforestry, for example, gives farmers three bites of the cherry. It pulls carbon from the air, provides a cash crop from the timber, and delivers wider benefits for other crops and livestock.

The challenge for carbon farming at the moment is putting figures on it. "There is a lot of debate about what practices deliver what benefits, and how you maintain those for best effect will vary from site to site," says Raskin. It's difficult to measure. Farmers have to do a lot of sampling to prove what they've achieved in soil carbon sequestration, and people have so far been unwilling to pay for it on the voluntary carbon markets.

And that's the crux of it. What holds carbon farming back is ultimately the same thing that's hindering the adoption of many emissions reduction approaches: we still don't have a carbon price. "If you've got a price, then you've got an incentive," says Smith. "That would be a game changer."

• This article originally appeared in the June 2019 edition of Modus