Our previous theoretical model for a global carbon cycle considering CO2-fertiiization effects of land biota is utilized to forecast future atmospheric CO2 concentrations. Three typical CO2-emission scenarios prepared by the IPCC Working Group I i.e. IS92a, IS92e and IS92e are used. A comparison between the present and IPCC predictions for the case of IS92a shows that our model forecasts somewhat lower future atmospheric CO2 concentrations than the IPCC Working Group. In addition, it is found that predicted atmospheric CO2 concentrations to about 2020 depend only very weakly on the adopted emission scenarios and that the atmospheric CO2 concentration around this year will be about 440 ppmv.