Effects of terrestrial carbon-nitrogen coupling on climate-carbon cycle feedbacks
Peter
Thornton, NCAR, thornton@ucar.edu
(Presenting)
Jean-Francois
Lamarque, NCAR, lamar@ucar.edu
Nan
Rosenbloom, NCAR, nanr@ucar.edu
We demonstrate that the inclusion of coupling mechanisms between terrestrial carbon and nitrogen cycles has significant impacts on the major climate-carbon cycle feedback mechanisms that control the fraction of anthropogenic CO2 emissions taken up by the land biosphere. We use a series of offline simulations with a recently developed land model component of the NCAR Community Climate System Model to show that the land response to increasing CO2 is lower by approximately a factor of four when C-N coupling mechanisms are included. We also show that the sensitivities of land carbon exchange to variability in temperature and precipitation are reduced by inclusion of C-N coupling. Finally, we show that the change over time in the temperature and precipitation sensitivities under a scenraio of increasing atmospheric CO2 is opposite for the C-N vs. C-only model configurations, with decreasing sensitivities over time with C-N coupling, but increasing sensitivity over time for the C-only model. We are now performing fully coupled experiments with this model in the CCSM3 framework.