Soil Carbon: Growing food to mitigate climate change.

Climate change is the most urgent threat humanity faces, and yet there is a surprisingly simple way to remove carbon dioxide from the atmosphere. It’s photosynthesis. Through growing plants, atmospheric C0₂ can be removed and sequestered into the soil where it has an essential role in soil health. Globally, soils have lost most of their carbon through industrial agriculture and deforestation, but we have the ability to put it most of it back. The policies and practises that would enable this to happen would also improve food security, soil fertility and secure the rights of small farmers against the onslaught of globalisation.

CO₂ in the atmosphere is a massive problem, but it’s important to note that carbon isn’t the problem. Carbon is an essential building block of life. Plants take up CO₂ from the atmosphere and convert it to biomass as they grow where it becomes part of their living structure until they die and decompose. Plants also exude a form of carbon out of their roots where it becomes part of the soil structure in the form of soil organic matter (SOM). (1) The science is well established on the importance of SOM in the soil. (2,3) It helps the soil retain water, prevents erosion, feeds micro-organisms and increases nutrient availability. The carbon contained in plant biomass and within the soil is part of the carbon cycle which moves carbon from the atmosphere to biomass to soil and back to the atmosphere through the natural process of photosynthesis, respiration and decomposition. There is more carbon stored in the soil that there is in the world’s biomass and in the atmosphere, (4) which makes understanding its movement and keeping it in the soil a vital part of climate change mitigation.

Soils globally have lost between 50-66% of their carbon (5) through deforestation, conventional tillage and chemical use. The carbon that used to be in the soil is now in the atmosphere warming the planet, leaving us with depleted soils, yet we have the ability to put it all back. (6) By increasing soil carbon year on year, we would be sucking it out of the atmosphere and putting it back in the soil where it belongs. Land use and land cover change are the second biggest emitter of anthropogenic CO₂ after the burning of fossil fuels (7) when you add to that the environmental cost of methane emissions from cows, oceanic deadzones from run-off, and the energy consumed in the manufacture of chemical herbicides, pesticides and fertilizers, it’s clear that our food producing systems have to change. (8)

Much of the CO₂ currently in the atmosphere came from the terrestrial pool of carbon and to reverse this we need to change our agricultural systems from carbon sources to carbon sinks. Carbon is released through the burning of forests, the draining of peatland and conventional tilling and spraying of soils.(9) Deforestation and land use change has been driven by agricultural expansion. (10) Commodity crops like palm oil, cotton, soy and corn also have driven deforestation and draining of peatlands without contributing much to the global food supply as they are grown to feed animals, biofuels or grown for beauty products and processed snacks. (11) Key to changing this is first to stop deforestation and preserve the carbon in the biomass of trees. Equally important is to halt the conversion of areas with high SOM into cropland. Secondly, we must afforest all marginal and degraded lands to sequester CO₂. But most importantly, we must change the way we farm and farm to increase soil carbon by building up organic matter in the soil. (12) This requires no new technology and can be implemented immediately with the adoption of agroforestry, (13) diversification of crops and regenerative agricultures. (14)

The techniques for building up soil organic matter are simple, it involves returning organic wastes to the soil, increasing the amount of perennial species, using cover crops, diversifying grazing lands to included deep rooted herbaceous plants, reducing tillage and eliminating chemical fertilisers. The benefits of this will be healthier, more fertile soils and greater drought resilience. By reducing livestock numbers and integrating them with perennial cropping, methane emissions will drop, and livestock will be restored to their useful role within ecosystems of providing manure, cleaning up waste and controlling vegetation.  Livestock grazing is a part of regenerative agriculture and in some parts of the world they have a major role to play. Grazing lands are an important resource: they cover 3.7 billion hectares of the earth’s surface. (15) Grasslands have co-evolved with grazing animals and are believed to have been a force for global cooling in the past. (16) These grazing systems, if correctly managed, can sequester carbon (17) but there will be little alternative but to reduce red meat consumption for the majority of the western world (18). Facing climate change requires a transformation in the way we operate but holds the promise of changing farmers from climate wreckers into climate heroes and ecosystem restorers.

Changing the way we farm requires no new technology as it is a biotic (biological) method of carbon sequestration, as opposed to an abiotic (engineered) one. All that’s needed is a shift in policy away from supporting industrial agriculture and towards supporting regenerative agriculture. Small, diverse family farms still dominate most of the global south and feed more of the worlds population than industrial agriculture (19). In spite of this, they are facing a constant battle against the forces of globalisation and industrialisation. (20). Much of the western world subsidises conventional agriculture leading to overproduction and dumping of exports on poor countries. (21) Instead we need policies and financing that support farmer led efforts to stay on their land, go organic, build soil carbon and sell in local markets. (22). Similarly, studies have shown that the best way to protect forest is to secure the indigenous and community rights of the people living there. (23) Steps towards a global initiative to increase soil carbon were taken at the Paris climate talks in 2015. France tabled the 4 per 1000 initiative, (24) a proposal to increase soil carbon by 0.4% every year which would be enough to halt the increase in GHG emissions from anthropogenic sources. New Zealand signed the initiative but has put very little resources into researching or promoting soil carbon. There is still a lot we don’t know about how to keep carbon in the soil. How much carbon different soils can hold and how stable it is depends on the underlying geological material, the temperature, precipitation, vegetation and human management (25). It’s also the case that it will only be a temporary solution, as the trees planted today will eventually die and decompose which will release the CO₂ they’ve stored back in the atmosphere. But it can buy us some desperately needed time as we transition the economy onto renewable energy and circular use of materials.

Sequestering CO₂ in the soil is probably our greatest hope for reversing climate change. It also gives us a chance to fix many of the flaw of our food production system. Its a chance to build a system around the local farmers who have a passion for protecting the environment, building a local food economy, cleaning the waterways and shifting to a healthier diet. There are many gaps in our understanding of soil carbon and time is running out, but its a project that can be started immediately and it places understanding natural systems at the centre of its vision.

Notes:

1. More about soil micro organisms and how they create healthy soil.
2. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/soil-organic-matter
3. https://www.noble.org/news/publications/ag-news-and-views/2001/august/what-does-organic-matter-do-in-soil/
4. Carbon Sequestration for Mitigation and Adaption. D. Ussir, R. Lal. Springer, 2017
5. Soil Carbon Sequestration to Mitigate Climate Change. R Lal 2004. Geoderma, vol 123 https://doi.org/10.1016/j.geoderma.2004.01.032
6. Increasing soil carbon by 0.4% per year in the top 30-40cm of soils would halt the increase in atmospheric Co2. https://4per1000.org
7. IPCC (2014) Climate change 2014: synthesis report. Contribution of working groups I, II and III to the fourth assessment report of the Intergovernmental Panel on Climate Change. In: Pachauri RK, Meyer L, Team CW (eds) Intergovernmental Panel on Climate Change, Geneva, Switzerland, p 151
8. The links between food and climate change https://www.grain.org/article/entries/4357-food-and-climate-change-the-forgotten-link
9. https://www.carbonbrief.org/worlds-soils-have-lost-133bn-tonnes-of-carbon-since-the-dawn-of-agriculture
10. “Areas that have been converted to cropland from forests have seen a reduction of soil C from 24 – 54%. Worldwide, agriculture has cleared or converted 70% of grasslands, 50% of the savannah, 45% of deciduous forest, and 27% of the tropical forest biome.” Ramankutty N, Evan AT, Monfreda C, Foley JA (2008) Farming the planet: 1. Geographic distribution of global agricultural lands in the year 2000. Glob Biogeochem Cy 22(1).
11. The hidden costs of industrial agriculture. https://www.ucsusa.org/food_and_agriculture/our-failing-food-system/industrial-agriculture/hidden-costs-of-industrial.html#.XFpK6NKP6Uk
12.  “Increasing the C pool of the pedosphere by 10% over the 21st century (+250 billion tons) can create a drawdown of 110 ppm of atmospheric CO2 abundance.” Sequestering carbon in soils of agroecosystems. R Lal. Food Policy. Volume 36, Jan 2011.
13. “We showed that agroforestry systems play an effective role in global carbon sequestration, involved in carbon capture and the long-term storage of atmospheric carbon dioxide,….the process is critical to mitigating or deferring global warming.” Andrea De Stefano. Agroforestry systems may play a vital role in mitigating climate change. Penn State. https://www.sciencedaily.com/releases/2018/02/180201115554.htm
14. A short definition of regenerative agriculture: https://thecarbonunderground.org/wp-content/uploads/2017/02/Regen-Ag-Definition-7.27.17-1.pdf
15. “Grazing lands are the largest and most diverse resource on earth. More than half the worlds land surface is grazed, the estimated total is between 3.4 billion ha (FAO) and 3.7 billion ha (Lal 2004). Improved management of the worlds grazing lands have huge potential for carbon sequestration”. Follett RF, Reed DA (2010) Soil carbon sequestration in grazing lands: societal benefits and policy implications. Rangeland Ecology & ManagementVol. 63, No. 1, Global Grazinglands and Greenhouse Gas Fluxes (Jan., 2010), pp. 4-15 (12 pages)
16. Global Cooling By Grassland Soils of the Geological Past and Near Future. G Retallack. Annual Review of Earth and Planetary Sciences, 2003. DOI: 10.1146/annurev-earth-050212-124001
17.  http://www.fao.org/fileadmin/templates/cpesap/C-RESAP_Info_package/Links/Module_5/Livestock_grazing_and_soil_carbon_sequestration.pdf
18. The 5 largest meat and diary companies together account for more emissions than Exxon, Shell or BP. https://www.fcrn.org.uk/research-library/how-big-meat-and-dairy-are-heating-planet
19. https://www.grain.org/article/entries/4929-hungry-for-land-small-farmers-feed-the-world-with-less-than-a-quarter-of-all-farmland
20. https://foodfirst.org/publication/five-global-threats-to-the-survival-of-family-farms-in-the-international-year-of-family-farming/
21. https://www.reuters.com/article/us-foundation-food-subsidies/developing-countries-blast-rich-world-farm-subsidies-at-rome-talks-idUSKCN0HV1NK20141007
22. http://www.fao.org/newsroom/en/news/2008/1000947/index.html
23. “Strengthening the rights of forest communities presents a vital tool for decreasing CO2 emissions and tackling climate change.”https://www.wri.org/publication/securing-rights-combating-climate-change
24. http://www.4per1000.org/
25. Carbon Sequestration for Mitigation and Adaption. D. Ussir, R. Lal. Springer, 2017 DOI 10.1007/978-3-319-53845-7