Looking after our soils to help address climate change
The December 2022 guest blog is written by Pete Smith, Professor of Soils and Global Change at the Institute of Biological and Environmental Sciences at the University of Aberdeen, and looks at the vital role soils play in supporting life on Earth, providing us with clean air and water, the food we eat, pharmaceuticals, building materials, and supporting biodiversity.
Soils are under our feet all of the time, but we rarely turn our thoughts downwards to consider the role that they play in supporting life on Earth. Well managed soils are responsible for providing us with clean air and water, the food we eat, pharmaceuticals, building materials, supporting biodiversity, and they underpin some of our most treasured landscapes. Another important role that soils play, that few of us consider, is their contribution to climate change, and their potential to help address it.
Climate change is predominantly caused by the ever-increasing concentration of greenhouse gases in the atmosphere, the most abundant of which is carbon dioxide. What most people don’t realise is that soils contain vast reserves of carbon, some 1500 thousand million tonnes of carbon in the top metre of soil, which is about twice that found as carbon dioxide in the atmosphere, and three times more that in all trees and vegetation on Earth put together!
Historically, soils in managed ecosystems have lost a portion of this carbon (about 130 thousand million tonnes) through land use change, some of which has remained in the atmosphere - this is equivalent to about a quarter of cumulative emissions from fossil fuel combustion since preindustrial times. So, soils have contributed to climate change, but could they also be part of the solution?
Part of the carbon that has been lost to the atmosphere could be regained through careful soil management, in a process called soil carbon sequestration. Globally, this has a large, cost-competitive potential to help in the fight against climate change, though obviously, cutting fossil fuel greenhouse gas emissions must be the priority. So, what does this careful soil management look like?
Well, peatlands, for example, are particularly rich in carbon. They hold more carbon per unit area than the world’s most productive forests! Of the 4.3 thousand million tonnes of carbon held in UK ecosystems, 2.7 is held in our peatlands. Yet around 80% of our peatlands are degraded – emitting to the atmosphere up to a massive 30-odd tonnes of carbon dioxide per hectare per year – the equivalent of the emissions of 6 or 7 family cars driving around for a year! A priority for the management in peatlands is, therefore, to a) protect our remaining pristine peatlands, and b) restore our degraded peatlands, by actions such as ditch blocking to let then again rewet, so they stop degrading and emitting carbon dioxide.
But most of our land is not peatland. What can we do on this land? Well, we can use forms of farming that try to put back what we take from the soils when we remove food crops or timber from the land, recently termed “regenerative agriculture”. This generally entails keeping to soil covered with plants and/or mulch for as much of the year as possible, returning crop residues, manures and composts to the soil, disturbing the soil less, and including things like trees and grasses in agricultural landscapes. Through these types of management, cropland that has lost carbon historically, can begin the regain carbon, thereby locking carbon dioxide out of the atmosphere and playing a role in tackling climate change.
However, this is no magic bullet. Unlike peatlands, which can continue accumulating carbon for centuries of millennia, our non-peatland soils can only store so much, so they saturate after a few decades. And we mustn’t forget that any carbon gained can easily be lost if soils don’t continue to be managed carefully. Nevertheless, soil carbon sequestration can be useful to meet short- to medium-term targets, making it a viable option for reducing the short-term atmospheric CO2 concentration, and buying us time to decarbonise all sectors of the economy to meet our net zero targets.
So next time you are out and about, spare a thought for our undervalued soils!
About the author:
Professor Pete Smith, FRS, FRSE, FNA, FEurASc, FISoilSci, FRSB
Pete Smith is Professor of Soils and Global Change at the Institute of Biological and Environmental Sciences at the University of Aberdeen (Scotland, UK) and Science Director of the Scottish Climate Change Centre of Expertise (ClimateXChange). His interests include climate change mitigation, soils, agriculture, food systems, ecosystem services modelling and nature-based solutions.
He is a Fellow of the Royal Society of Biology, a Fellow of the Institute of Soil Scientists, a Fellow of the Royal Society of Edinburgh, a Foreign Fellow of the Indian National Science Academy, a Fellow of the European Science Academy, and a Fellow of the Royal Society (London).