Sequestering carbon by regenerating soil, planting trees, and changing land use

Robin Stott, a doctor and ardent environmentalist has been campaigning on climate change for the past 20 years. He offers some thoughts on the potential benefits of simultaneously enriching soil and sequestering carbon.

Regenerating soil

Carbon regeneration of soil will bring benefits to human and planetary health such as the ready availability of non-polluted, locally grown food, a move to a diet richer in vegetables and fruit, an increase in rewarding rural jobs, and the psychological benefits of having easy access to a much more biodiverse natural environment. But I’m concentrating here on how it can sequester carbon.  My objective is to show how a transformation of our agricultural system and land use can help us in the UK get to carbon net zero by 2030 and when applied worldwide will be a major factor in tackling climate heating. 

The agricultural soil carbon story is important because of the need to use natural systems to sequester carbon if we are to get nationally, or indeed globally, to carbon net zero in time to avoid exceeding 1.5 degrees warming. Our UK contribution should be to aim for carbon net zero by 2030 at the latest.

I don’t think we can remove all fossil fuels from the UK economy by 2030, but even the Committee on Climate Change say we could and should reduce emissions sufficiently by 2050 to enable the UK to be carbon net zero by then. As I understand it, they also suggest we should have achieved a 50% reduction from 1990 levels by 2030. 

So to get to carbon net zero by 2030 ( assuming we don’t manage to increase the rate of our decarbonisation, which I hope we will do) we have to sequester a lot of carbon. The best book I know of which looks at all forms of sequestration is Countdown by Paul Hawken and Tom Steyer.

In their book they look at the whole range of sequestration possibilities, including many of nature’s way of sequestering. In this context, they look at the capacity of soil to sequester and say that globally much of the soil we have now which has been ploughed and artificially fertilised has depleted soil carbon levels to between 1 and 2%. With regenerative agriculture the percentage can increase to between 5 and 8% over 10 to 20 years, by which time the soil will become carbon replete. According to them, each percentage increase represents 8.5 tons of carbon sequestered per acre: so between 25 and 60 tons per acre over 10 -20 years. 

As the name implies, regenerative agriculture rehabilitates soil, which is otherwise depleting at an alarming rate. I am assuming the UK soil is similar to that elsewhere. 

I think Hawken and Steyer get the figure of 8.5 tons per 1% increase, a figure they quote on page 194 of their book, from research done at the Rodale Institute in the USA. A figure from an Australian group is 5 tons of carbon per 1% increase. In looking at the UK potential I use this lower figure of 5 tons/acre/1% percent increase. And I assume that our depleted soil now has 2% carbon per acre and that we will get to 6% of carbon per acre over 10-20 years through regenerative practice, which means 20 tons of carbon sequestered/acre. 

To get to carbon net zero by 2030, how much carbon do we need to sequester? 

The figures are:

  • In 1990 the base line year, the UK emitted 600 million tons of CO2. In 2018 it was 364 million tons. 
  • The committee on climate change say we need to be half the 1990 amount by 2030—that is, 300 million tons. To be net zero we would need to sequester this 300 million tons of CO2, (which is approximately 100 million tons of carbon.) 
  • Of course, as Greta Thunberg and many others have pointed out, we don’t include air and ship fuel in our figures and take no account of the industry we have exported.
  • Domestic shipping is estimated at around 2 million kg of oil per year.135 kilograms of oil produces 118 kgs of carbon: 2 million tons of carbon 
  • Domestic airlines 33 million tons CO2, about 10 million tons carbon
  • The UK is estimated to “export”150 million tons of CO2: about 50 million tons carbon. (The difference between the CO2 we emit in manufacturing our exported goods compared with the CO2 emitted in manufacturing the goods we import.) 
  • Adding these amounts to the million tons of carbon we are still emitting within the UK, we need to be sequestering 160 million tons of carbon in that year to be genuinely net zero by 2030.
  • Let’s say we are sequestering 20 tons of carbon per acre in regenerative agriculture over 10 years. To sequester 160 million tons of carbon we would need around 8 million acres of regenerative agriculture. 
  • The UK has 23 million acres of agricultural land. If we converted around a third of land to regenerative agriculture we would achieve carbon net zero. 

This assumes we don’t do anything else and because of the time factor is an underestimate. But assuming we also promote the other natural sinks, in particular tree planting (which I look at below), I think it’s a reasonable statement.

As an inducement to farmers to move rapidly to regenerative agriculture I suggest the government remove all present agricultural subsidies and pay farmers instead £50 for each ton of sequestered carbon. To assess how much each farmer should be paid we wouldn’t have to monitor carbon in soil, which at scale will be difficult. We would instead need to check whether farmers are genuinely farming in a regenerative way, which means:

  • Are not ploughing
  • Are using cover crops (this could be done with aerial surveys)
  • Are using natural fertilisers not artificial fertilisers or pesticides (examine their accounts)
  • And if they have livestock are mob grazing and grass feeding, so none of their land is being used to grow grain for cattle feed.  

Then we would use the well documented carbon sequestration numbers to assess how much money each farmer would receive.

Planting trees

Planting trees will help. The US Department of Agriculture estimates that a tree sequesters 88lb of carbon per year. A more conservative estimate is 48lb per year. I use this lower figure.

  • There are 2204lb per metric ton: 46 trees are needed to sequester 1 metric ton each year. 
  • 46 million trees would sequester 100 million tons. 
  • So if two in three people in the UK planted a tree, that would be a substantial step forward.

Changing land use

An additional benefit comes from examining the present pattern of land use: about two thirds of agricultural land is presently used for grass feeding livestock, and a further fifth for growing grain to supplement this. When livestock is dominantly grass fed, this land will come available to grow food for humans or to rewild.

Robin Stott is a a doctor and environmentalist.

Competing interests: None declared.