Soils constitute the largest terrestrial organic C pool (~1,500 petagrams* (Pg, 1015 grams ) C to a depth of 1 m; 2,400 Pg C to 2 m depth), which is three times the amount of CO2 currently in the atmosphere (~830 Pg C) and 240 times the current annual fossil fuel emissions (~10 Pg). Thus, increasing net soil C storage by even a few per cent represents a substantial C sink potential (1).
Soil C sequestration is one of a few strategies that could be applied in large scales and potentially at low cost; as an example, the French government has proposed to increase soil C concentration in a large portion of agricultural soils globally by 0.4% per year in conjunction with the Conference of the Parties to the UN Framework Convention on Climate Change (UNFCCC) negotiations in December 2015. This would produce a C sink increase of 1.2 Pg of C per year (1).

1) Paustian, et al. Climate Smart Soils, Nature, 532, 49-57 (2016).