Earth system model simulations show different carbon cycle feedback strengths under glacial and interglacial conditions

Markus Adloff1,2,a, Christian H. Reick1, and Martin Claussen1,2 1Max Planck Institute for Meteorology, Bundesstraße 53, 20146 Hamburg, Germany 2Meteorological Institute, Centrum für Erdsystemforschung und Nachhaltigkeit (CEN), Universität Hamburg, Germany anow: School of Geographical Sciences, University of Bristol, University Road, BS8 1SS, United Kingdom Abstract. In Earth system model simulations we find different carbon cycle sensitivities for recent and glacial climate. This result is obtained by comparing the transient response of the terrestrial carbon cycle to a fast and strong atmospheric CO2 concentration increase (roughly 1000ppm) in C4MIP type simulations starting from climate conditions of the Last Glacial Maximum (LGM) and from Pre-Industrial times (PI). The sensitivity β to CO2 fertilization is larger in the LGM experiment during most of the simulation time: The fertilization effect leads to a terrestrial carbon gain in the LGM experiment almost twice as large as in the PI experiment. The larger fertilization effect in the LGM experiment is caused by the stronger initial CO2 limitation of photosynthesis, implying a stronger potential for its release upon CO2 concentration increase. In contrast, the sensitivity γ to climate change induced by the radiation effect of rising CO2 is larger in the PI experiment for most of the simulation time. Yet, climate change is less pronounced in the PI experiment, resulting in only slightly higher terrestrial carbon losses than in the LGM experiment. The stronger climate sensitivity in the PI experiment results from the vastly more extratropical soil carbon under those interglacial conditions whose respiration is enhanced under climate change. Comparing the radiation and fertilization effect in a factor analysis, we find that they are almost additive, i.e. their synergy is small in the global sum of carbon changes. From this additivity, we find that the carbon cycle feedback strength is more negative in the LGM than in the PI simulations. Citation: Adloff, M., Reick, C. H., and Claussen, M.: Earth system model simulations show different carbon cycle feedback strengths under glacial and interglacial conditions, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-67, in review, 2017.   This article appeared on the Earth System Dynamics website at http://www.earth-syst-dynam-discuss.net/esd-2017-67/]]>

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