A high-resolution ice-core record of atmospheric CO2 concentration over the Holocene epoch shows that the global carbon cycle has not been in steady state during the past 11,000 years. Analysis of the CO2 concentration and carbon stable-isotope records, using a one-dimensional carbon-cycle model,uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial-scale changes of atmospheric CO2 concentrations.