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 anthropogenicand natural forcings for the 16th to the 20th centuries and by combined SRES (Special Report on EmissionScenarios) A2--LUH (Land Use Harmonization) anthropogenic scenarios for the 21st century. Hereby, theimpact of uncertainty in land--use scenarios on results of simulations with a coupled climate--carboncycle model is tested. The simulations of the model realistically reproduced historical changes in carboncycle characteristics. In the IAP RAS CM, climate warming reproduced in the 20th and 21st centuriesenhanced terrestrial net primary production but terrestrial carbon uptake was suppressed due to anovercompensating increase in soil respiration. Around year 2100, the simulations the model forced bydifferent land use scenarios diverged markedly, by about 70 Pg (C) in terms of biomass and soil carbonstock but they differed only by about 10 ppmv in terms of atmospheric carbon dioxide content.