Carbon Flux to the Atmosphere from Land-Use Changes - Richard A. Houghton and Joseph L. Hackler
In the attempt to "balance" the global carbon cycle (that is, reconcile the known sources and sinks of carbon), two major unknowns have been the flux between the atmosphere and the oceans and the flux between the atmosphere and terrestrial ecosystems. To address the latter, several investigators have attempted to estimate the flows of carbon between the atmosphere and both temperate and tropical ecosystems. The database presented in this section provides estimates of regional and global net carbon fluxes, on a year-by-year basis from 1850 through 2000, resulting from changes in land use (such as harvesting of forest products and clearing for agriculture), taking into account not only the initial removal and oxidation of the carbon in the vegetation, but also subsequent regrowth and changes in soil carbon. These estimates indicate that the global total net flux from 1850 through 2000 was 156 petagrams (1 Pg = 1015 grams) carbon. For the year 1999, the global total net flux was estimated to be 2.1 Pg carbon; for comparison, the estimated 1999 carbon flux to the atmosphere from fossil-fuel combustion and cement production has been estimated at 6.5 Pg carbon (Marland et al. 2002).