Promise and limitations of soils to minimize climate change

Excerpt

The atmospheric abundance of carbon dioxide (CO₂) has increased by 36% from 280 ppm in ~1750 to 381 ppm in 2006 with an annual rate of increase during the 2000s at 1.93 ppm (World Meteorological Organization 2006; Canadell et al. 2007). Principal sources of CO₂ since 1850 have been fossil fuel combustion contributing ~330 Pg C and land use change contributing 158 Pg C. The latter, attributed to deforestation and the attendant biomass burning and soil tillage along with erosion and other degradation processes, includes an estimated emission of 78±12 Pg C from world soils (Lal 1999). Of the total annual emission of approximately 9.4 Pg C y^-1 during the 2000s (including 7.5 Pg C y^-1 from fossil fuel combustion and 1.9 Pg C y^-1 from land use conversion), 4.1 Pg C (44%) is absorbed annually by the atmosphere, 2.2 Pg C (23%) by the ocean, and 2.7 Pg C (33%) by land-based sinks (Canadell et. al. 2007). The capacity of the land-based sink is progressively decreasing in proportion to total emissions (table 1; Canadell et al. 2007), probably due to gradual increase in extent and severity of soil degradation.

About 56% of the anthropogenic emissions of CO₂ are being …