New Satellites Help Quantify Carbon Sources and Sinks



Deforestation and forest degradation account for between 7% and 30% of total anthropogenic carbon emissions [Canadell et al., 2007; Denman et al., 2007]. This wide range of values results from three major uncertainties: rates of deforestation, carbon stocks (biomass and soils) in forests prior to deforestation, and changes in carbon stocks within forests (i.e., both increases from growth and decreases from degradation). Historically, rates of deforestation and reforestation, together with estimates of forest biomass, have been used to calculate the net flux of carbon between terrestrial ecosystems and the atmosphere [Woodwell et al., 1983; Detwiler and Hall, 1988; Hall and Uhlig, 1991; Fearnside, 2000; DeFries et al., 2002; Achard et al., 2004; Houghton, 20037]. This net flux is the difference between the sinks of carbon in growing and recovering forests and the sources from burning and decay associated with deforestation. Satellite imagery, particularly from Landsat, has long been used to sample deforestation rates [DeFries et al., 2002; Achard et al., 2004; Skole and Tucker, 1993; Hansen et al., 2008]. Obtaining estimates of biomass, reforestation, and forest growth and degradation, however, has proven more difficult.