Soil carbon sequestration to combat climate change – a real solution, or just hype?

Guest Post By Jocelyn Lavallee, 2019-2020 Sustainability Leadership Fellow and Postdoctoral Fellow in the Department of Soil and Crop Sciences and the Natural Resource Ecology Laboratory

The intensifying climate crisis is bringing the need for climate solutions to the forefront. We know we need to act fast to pull carbon dioxide (CO2) and other greenhouse gases out of the atmosphere, but what strategies should we use? One potential solution lies under our feet, in soils. Soils naturally store huge amounts of carbon and they have room to store even more.

The soil carbon cycle. Plants take in carbon from the atmosphere and build their biomass through photosynthesis, and when they shed leaves or die, they decompose and their carbon enters the soil. Once there, soil carbon can either be stored for long periods of time or be decomposed further to CO2 that then enters the atmosphere, completing the cycle. Source: Jocelyn Lavallee

This has prompted several large-scale efforts to actively sequester carbon in soils, especially agricultural soils. But this is a contentious topic. Some critics say that these initiatives are too ambitious, promising soil carbon gains that aren’t biophysically possible. Others say that even if we do sequester all the carbon we realistically can in soils, the amount of atmospheric greenhouse gases it would offset are just a small fraction of what needs to be offset to solve the climate crisis. So, are the critics right? Is soil carbon sequestration a viable solution, or is it just hype?

Let’s go through two of the most common critiques and see where we come out.

1) Soil carbon sequestration on a massive scale isn’t feasible.

This argument came about in large part as a reaction to two initiatives that are extremely ambitious in terms of their magnitudes. The ‘4 per mille’ initiative began at the 2015 United Nations Framework Convention on Climate Change (UNFCC) in Paris, with the idea that if we increase soil carbon by 0.4% (4 per 1000) per year in agricultural soils around the globe, we could fully offset the amount of greenhouse gases that human activities emit each year. However, this still leaves out the carbon that we have been emitting for the past 250 years. A more ambitious initiative from Indigo Ag called the “Terraton Challenge” aims to remove one trillion tons of carbon from the atmosphere, essentially getting us back to pre-industrial CO2 levels. They are trying to achieve this through research and innovation of new technologies that can massively accelerate rates of atmospheric CO2 drawdown. Both of these initiatives are aiming very high in terms of how much carbon they want to sequester in soils, aiming either to completely offset all human-caused CO2 emissions, or a very large portion of them. Is that really feasible?

The ‘4 per mille’ initiative. Source:

With our current technology, many scientists say ‘no’. One argument is that the only ways to achieve these very high carbon sequestration rates are by using management practices that aren’t profitable or feasible for most farmers (for example adding lots of costly organic inputs like manure), or by taking land out of agricultural production, which would threaten global food security. A second argument is that building soil carbon at this scale requires other chemical elements like nitrogen that are in short supply. Soil carbon isn’t stored on its own; it’s bound up with nitrogen, phosphorus, and other elements in complex molecules. Storing as much carbon as these initiatives aim to do would require similarly massive amounts of other nutrients that are essential for plants and animals, so sequestering them away would cause an enormous  ecological trade-off.

There are other arguments for why storing these massive amounts of carbon in agricultural soils probably isn’t feasible. Even the folks behind the “4 per mille” initiative have readily admitted that it is a lofty goal that represents more of an aspiration or a concept – that agricultural soils can play a huge role in food security and climate change mitigation – than a specific number. Indigo Ag also understands this issue, which is why their initiative focuses on research and innovation. Maybe we can’t conceivably achieve these large scales right now, but that doesn’t mean it’s impossible. Breakthroughs in research and technology could sow the seeds for unprecedented rates of carbon sequestration in soils.

But given what is currently possible, these high rates of carbon sequestration just aren’t in the cards in the near term. This brings us to our second common critique of soil carbons sequestration:

2) If we consider currently feasible C sequestration rates in soils, then we can only achieve a small fraction of what needs to be done in terms of solving the climate crisis, so why should we bother? In fact, it could even be dangerous to climate mitigation efforts if decision-makers use these soil carbon sequestration initiatives as excuses to slow down or avoid other, more effective solutions to climate change, like the much-needed transition to renewable energy.

It’s right to say that soil carbon sequestration, given current estimates of what’s feasible, only represents a small fraction of the total carbon offsets we need to tackle the climate crisis. The highest estimates are around 20-35% per year, but most are much lower.

That said, there is no single solution to the climate crisis. It’s a big, complex problem that requires big, innovative solutions, and we can’t bank on new technology in any one area to completely solve the problem. Instead, we need a diversified strategy with multiple parts working simultaneously.

Diversified climate solutions. There are many different “natural climate solutions”, including soil carbon sequestration, and these are part of an even further diversified overall strategy that includes other solutions like renewable energy. Source: Griscom et al. (2019) Global Change Biology 25:6, 1889-1890.

It’s detrimental to climate mitigation efforts if decision-makers use any single solution – whether it be soil carbon, or tree-planting, or ecosystem restoration –  as excuses to slow down or avoid other components of the solution to climate change, like the much-needed transition to renewable energy. We must all be aware (and we must make sure that policy makers know) that we can’t focus on any single climate solution, and we certainly shouldn’t rule any out if they are feasible and effective.

Soil carbon sequestration is a viable part of a diversified solution to climate change. And if that’s not reason enough to do it, increasing soil carbon in agricultural soils has other benefits for society! Soil carbon is great for improving soil quality. It helps to store water and nutrients, feeds soil organisms, and supports healthy ecosystems and crops. Using soils as part of the overall climate solution will have great co-benefits for our ecosystems and food security!

This is a lot to take in, but there’s so much more to talk about when it comes to soil carbon sequestration! How can we confirm and measure soil carbon sequestration? How do we know if that carbon is really stable over time, or if it will be lost back to the atmosphere in a few years? For more on how soils store carbon, how we measure it, and why it matters, you can check out some great blogs and articles here, here and here!

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