Farmland contributes 4% of carbon emissions

Carbon-rich soil is a bigger contributor to global warming than you might realise...
21 April 2023

Interview with 

Tom Marquand, University of Cambridge


Hands holding soil


When we talk about fighting climate change, you most often hear about efforts to reduce the quantity of fossil fuels we burn. What you don’t hear about so often is the contribution of farmland to greenhouse gas emissions. Nowhere is this subject more relevant, perhaps, than right on our doorstep here in Cambridgeshire. Closeby are the Fens - nearly 4000 square kilometres of marshy, fertile soil. Until the 1600s, this region was a low-lying swamp, and it wasn’t until Dutch engineers were brought in to drain it that it was turned into productive farmland. The soil that emerged as a result was carbon rich, causing microbes in the earth to belch out vastly more co2 and methane than normal soil. This has negative impacts on farming yields as well as the planet, and here to tell us more is Tom Marquand, who’s been conducting a research project into the Fens at the University of Cambridge…

Tom - In general, we have a pretty good understanding of the very basic principle that when you remove water from the soil, you allow air to get deeper into the soil. And that brings with it a lot of oxygen. That's what the microbes need to break down that soil carbon and release a lot of co2. And that's what they're doing right now. That basic picture is well established, what we don't have such a good handle on is the nuances. How does the temperature affect it? How does it vary seasonally? Specifically, if I raise the water table by 10 centimetres, what is the number? How much less co2 is emitted? Those are really important things to have a strong grasp on if you want to make informed policy decisions in the future.

Chris - So you've effectively got the makings of a model of how this sort of environment works and, when we change it or do something to it, what the anticipated outcome would be?

Tom - That's the dream. Yeah. My collaborators and I are not the decision makers, but what we really hope to be able to do is to produce a body of evidence that's really well grounded in cutting edge research that allows the policy makers in the future to make really informed decisions about what the future of the Fens looks like.

Chris - It's an important area, it's a a big area, but it's just one area. The planet's much bigger. Can this be extrapolated from what's going on in the Fens to other environments like it elsewhere? Does it inform the bigger picture?

Tom - Definitely, definitely. I think the Fens are a really great place to start with this bigger picture of soil carbon emissions globally. Human land use accounts for about 4% of our greenhouse gas emissions. So it's a huge contributor overall. And if this is something that we can get more of a handle on, then that would be really useful in the future, all over the world.

Chris - How much emission is coming off the Fens? I've said that it's a lot, but put some numbers on it.

Tom - Yeah. So the East Anglian Fens on their own account for 400,000 tons of carbon being emitted each year and that's being emitted almost entirely as co2. There's very little methane emissions from the Fens and that's something that you see more in a natural wetland than in a drained one.

Chris - And so what would be the ultimate goal then? Is it to work out whether we should re flood some parts of the Fens? Would that mitigate things? Because obviously there's a price to pay in food production if we do remove some of it to cut down some of that carbon footprint. Do we end up reimporting food from elsewhere with an attached carbon footprint, which may have knocked down a rainforest somewhere to grow?

Tom - Definitely. I mean this is the really tricky thing. To some degree, I'm very happy that I am the person putting together the evidence and not the person making the decision. The decisions that will have to be made about the future of the Fens will be really difficult. Ones that have to balance this economic and food security side with an environmental and sustainability side. At the moment, the Fens are losing peat, so we actually can't carry on as we are, even if we really want to. We're going to have to do something, and that's why this matters. It's a massive contributor to our food supply. We don't really want to move that abroad. And I think what most of the people I'm working with and speaking to would really like to see is more sustainable farming practices and a sort of patchwork landscape where maybe some of it can be given over to wetlands and nature reserves for biodiversity and for trapping carbon, and some of it can be farmed in perhaps a more sustainable but still productive way. That's the goal, at least.


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