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.

Figure 1

Soil organic carbon (SOC) in the top 30 cm, currently (T₀), on all available cropland soils globally (i.e. those not excluded from the analysis as high SOC soils or sandy soils). Maps were produced based upon a geospatial analysis of datasets from the SoilsGrids250 database, using ESRI ArcGIS software (version 10.3; www.esri.com).

Figure 2

Annual increase in soil organic carbon (SOC) in the top 30 cm, on all available cropland soils globally (i.e. those not excluded from the analysis as high SOC or sandy soils) under the medium scenario (i.e. an increase in percent SOC of 0.27 over 20 years). Maps were produced based upon a geospatial analysis of datasets from the SoilsGrids250 database, using ESRI ArcGIS software (version 10.3; www.esri.com).

Figure 3

Increase in SOC (%) over time under two cropland sequestration scenarios (Eq. (1)). SOC₀ in the shown cases is 0.60% and 0.71% for the high and medium graphs, respectively; note that the values for SOC₀ are exemplary only and do not affect SOC sequestration rates. If the SOC content in the 0–30 cm depth layer of all available cropland increased 0.27% (medium scenario) to 0.54% (high scenario), then from 0.56 to 1.15 t C/ha/yr would be sequestered (Table 1), which translates to 0.90 to 1.85 Pg C/yr globally, for at least the minimum of 20 years that sequestration can be expected to continue.