Conflicting hypotheses are investigated for the observed atmospheric CO₂ increase of 20 ppm between 8 ka BP and pre-industrial time. The carbon component of the Bern Carbon Cycle Climate (Bern CC) model, which couples the Lund-Potsdam-Jena Dynamic Global Vegetation Model to an atmosphere-ocean-sediment component, is driven by climate fields from time-slice simulations of the past 21 ka with the Hadley Centre Unified Model or the NCAR Climate System Model. The entire Holocene ice core record of CO₂ is matched within a few ppm for the standard model setup, and results are broadly consistent with proxy data of atmospheric ¹³CO₂, mean ocean δ¹³C, and pollen data, within their uncertainties. Our analysis suggests that a range of mechanisms, including calcite compensation in response to earlier terrestrial uptake, terrestrial carbon uptake and release, SST changes, and coral reef buildup, contributed to the 20 ppm rise. The deep sea δ¹³C record constrains the contribution of the calcite compensation mechanism to 4–10 ppm. Terrestrial carbon inventory changes related to climate and CO₂ forcing, the greening of the Sahara, peat buildup, and land use have probably influenced atmospheric CO₂ by a few ppm only. The early Holocene CO₂ decrease is quantitatively explained by terrestrial uptake and calcite compensation in response to terrestrial uptake during the glacial-interglacial transition. The recent hypothesis by Ruddiman [2003] that anthropogenic land use caused a 40 ppm CO₂ anomaly over the past 8 ka, preventing the climate system from entering a new glacial, would imply an anthropogenic emission of 700 GtC and a decrease in atmospheric δ¹³C of 0.6 permil. This is not compatible with the ice core δ¹³C record and would require an upward revision of land use emission estimates by a factor of 3 to 4.