Did prehistoric humans prevent a new Ice Age ?
© 2013 EPFL
Humans have altered the Earth’s land surface since the Paleolithic by clearing forests, first to improve hunting and gathering opportunities, and later to produce agricultural cropland. In the Holocene, agriculture was established on nearly all continents and led to widespread modification of terrestrial ecosystems.
To quantify the role that humans played in the global carbon cycle over the Holocene, we developed a new inventory of anthropogenic land-cover change from 8000 years ago to the beginning of large-scale industrialization (AD 1850). Using this data set, we forced the LPJ dynamic global vegetation model to evaluate the impacts of humans on terrestrial carbon storage during the preindustrial Holocene. By three thousand years before the present (ka BP), cumulative carbon emissions caused by anthropogenic land-cover change in our new scenario ranged between 84 and 102 Pg, translating to ~7 ppm of atmospheric CO2. By AD 1850, emissions were 325-357 Pg. Simulated cumulative anthropogenic emissions over the preindustrial Holocene support the hypothesis that anthropogenic activities led to the stabilization of atmospheric CO2 concentrations at a level that made the world substantially warmer than it otherwise would be.