Estimates of the potential for additional soil carbon sequestration vary widely. According to studies on European cropland (Smith et al., 2000a), US cropland (Lal et al., 1998), global degraded lands (Lal, 2003a) and global estimates (Cole et al., 1996; IPCC, 2000a), global soil carbon sequestration potential is estimated at 0.9 ± 0.3 Pg C/year (Lal, 2003b), between one-third and one-fourth of the annual increase in atmospheric carbon levels. Over the next 50 years, the level of carbon sequestration suggested by Lal (2003b) would restore a large part of the carbon lost from soils historically. Estimates based only on Europe and North America by Smith et al. (2000b) suggest a lower potential (one-third to one-half of historical soil carbon loss over 100 years). Soil carbon sequestration rates have a limited duration and cannot be maintained indefinitely.
The estimates for carbon sequestration potential in soils are of the same order as for forest trees, which could sequester between 1 Pg C/year (the lower figure of IPCC, 1996) and 2 Pg C/year (Trexler, 1988, cited in Metting et al., 1999), between one-third and two-thirds of the annual increase in atmospheric carbon levels.
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