Using the CSIRO global climate model (CCAM) coupled with a terrestrial carbon cycle model, we carried out two simulations using the protocol of C4MIP (Coupled Carbon Cycle Climate Model Intercomparison Project) Phase I to study the influences of increasing atmospheric CO₂ concentration and changes in sea surface temperature over the last 100 years on CO­₂ between atmosphere and 11 biomes. It was found that the inter-annual variation of net ecosystem prediction of global terrestrial biosphere is significantly correlated to the variation of land surface temperature from 1980 to 1999, and the increase in net ecosystem production can be largely explained by the increase in net primary production from CO₂ fertilization from 1970 to 1999 in our model. The response of net ecosystem production to CO₂ fertilization is strongest in tropical rainforest and not significant in tundra. Our estimates of net ecosystem production of global terrestrial biosphere in 1990’s agree well with the results from an inversion study by Allison et al. [this volume].