The Net Carbon Emissions from Historic Land Use and Land Use Change

Deforestation from timber harvests and farmland conversions have led to 565 GtCO2 (billion tons of carbon dioxide) being emitted into the atmosphere. Taking into account natural regeneration on forestland, Houghton (2003, 2008) and Houghton et al. (2012) estimate that deforestation has caused a net loss of 484 GtCO2 since 1900 which is about one third of all manmade emissions. However, these estimates do not take into account the substantial investment into fire management, plantations, and replanting since 1950, as well as the effect of carbon fertilization on a younger forest. We compare the outcome of a deforestation scenario with subsequent forest management with what would have happened if the natural forest in 1900 had not been harvested thereafter. Deforestation plus forest management suggests current forests actually hold about 94 GtCO2 more today than they did in 1900. However, natural forests would have held an additional 186 GtCO2. Human activities on forestland have therefore caused about 92 GtCO2 of net emissions since 1900. The effect of manmade land use and land use change is relatively small compared to the 1294 GtCO2 from industrial emissions over the same time period (Marland et al., 2008).