Effects of human land-use on the global carbon cycle during the last 6000 years

Abstract: Humanity has become a major actor within the Earth system, particularly through transforming large parts of the land surface and by altering the gaseous composition of the atmosphere. Deforestation for agricultural purposes started thousands of years ago, which might have resulted in a detectable human influence on climate much earlier than the industrial revolution. This study presents a first attempt to estimate dynamic changes in anthropogenic carbon fluxes over the last 6000 years. A global gridded data set on the spread of permanent and non-permanent agriculture over this time period was developed and integrated within the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM). The model was run with and without human land-use, and the differences in terrestrial carbon pools were calculated as an estimate of anthropogenic carbon release to the atmosphere. The modelled total carbon release during the industrial period (1850-1998) was 162 gigatons of carbon (GtC), of which 36 GtC originated from non-permanent agriculture. For pre-industrial times (6000 BP until AD 1850), human-related carbon release was 79 GtC from permanent agriculture and an additional 35 GtC as a result of non-permanent agriculture. The modelled total carbon release was considerably lower than would be required for a substantial influence on the climate system.