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Climate‐carbon cycle model CLIMBER2‐LPJ is run with consistent fields of future fossil fuel CO 2 emissions and geographically explicit land cover changes for four Special Report on Emissions Scenarios (SRES) scenarios, A1B, A2, B1, and B2. By 2100, increases in global mean temperatures range between 1.7°C (B1) and 2.7°C (A2) relative to the present day. Biogeochemical warming associated with future tropical land conversion is larger than its corresponding biogeophysical cooling effect in A2, and amplifies biogeophysical warming associated with Northern Hemisphere land abandonment in B1. In 2100, simulated atmospheric CO 2 ranged from 592 ppm (B1) to 957 ppm (A2). Future CO 2 concentrations simulated with the model are higher than previously reported for the same SRES emission scenarios, indicating the effect of future CO 2 emission scenarios and land cover changes may hitherto be underestimated. The maximum contribution of land cover changes to future atmospheric CO 2 among the four SRES scenarios represents a modest 127 ppm, or 22% in relative terms, with the remainder attributed to fossil fuel CO 2 emissions.
Sitch et al. (Fri,) studied this question.