Global Sequestration Potential of Increased Organic Carbon in Cropland Soils

Abstract

The role of soil organic carbon in global carbon cycles is receiving increasing attention both as a potentially large and uncertain source of CO2 emissions in response to predicted global temperature rises, and as a natural sink for carbon able to reduce atmospheric CO2. There is general agreement that the technical potential for sequestration of carbon in soil is significant, and some consensus on the magnitude of that potential. Croplands worldwide could sequester between 0.90 and 1.85 Pg C/yr, i.e. 26–53% of the target of the “4p1000 Initiative: Soils for Food Security and Climate”. The importance of intensively cultivated regions such as North America, Europe, India and intensively cultivated areas in Africa, such as Ethiopia, is highlighted. Soil carbon sequestration and the conservation of existing soil carbon stocks, given its multiple benefits including improved food production, is an important mitigation pathway to achieve the less than 2 °C global target of the Paris Climate Agreement.

Soil carbon sequestration is an elusive climate mitigation tool

“…Zomer et al (26) have estimated that, over the next 20 years, with the full adaptation of best practices, 18 to 37 Gt C could be technically sequestered (a factor of three to six less than the total loss through historical agriculture discussed above). As for soil carbon sources, land clearing is reported to release carbon at about the same rate (26), whereas global soil warming may cause a feedback release of between 100 and 600 Gt (23). These estimates are uncertain in value but not sign.…”

Managing for soil carbon sequestration: Let’s get realistic

“…Smith et al () estimate 1.6 Pg C/year as the maximum potential for enhanced agricultural management to mitigate CO 2 emissions to the atmosphere, whereas Zomer, Bossio, Sommer, and Verchot () estimate potential storage of 0.90–1.85 Pg C/year in croplands. At 2.45 Pg C/year, a recent new estimate by Lal () is slightly more optimistic.…”

Can plants help us avoid seeding a human‐made climate catastrophe?

“…133 Gt C from soils in the process (Sanderman, Hengl, & Fiske, 2017), and application of crushed rock to farmland could exploit existing logistic infrastructure. Potential also exists for increasing carbon sequestration in agricultural soils through changes in land management practices (Minasny et al, 2017;Zomer, Bossio, Sommer, & Verchot, 2017), including addition of biochar formed by pyrolysis of biomass (Woolf, Amonette, Street-Perrott, Lehmann, & Joseph, 2010), with possible benefits for food security. However, as with most large-scale CO 2 removal proposals, complex cultural, economic and political constraints raise uncertainties over their effectiveness (Amundson & Biardeau, 2018).…”