Uncertainty of Climate Response to Natural and Anthropogenic Forcings Due to Different Land Use Scenarios

The A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS) climate model (CM) of intermediate complexity is extended by a spatially explicit terrestrial carbon cycle module. Numerical experiments with the IAP RAS CM are performed forced by the reconstructions of anthropogenic and natural forcings for the 16th to the 20th centuries and by combined SRES (Special Report on Emission Scenarios) A2--LUH (Land Use Harmonization) anthropogenic scenarios for the 21st century. Hereby, the impact of uncertainty in land--use scenarios on results of simulations with a coupled climate--carbon cycle model is tested. The simulations of the model realistically reproduced historical changes in carbon cycle characteristics. In the IAP RAS CM, climate warming reproduced in the 20th and 21st centuries enhanced terrestrial net primary production but terrestrial carbon uptake was suppressed due to an overcompensating increase in soil respiration. Around year 2100, the simulations the model forced by different land use scenarios diverged markedly, by about 70 Pg (C) in terms of biomass and soil carbon stock but they differed only by about 10 ppmv in terms of atmospheric carbon dioxide content.