Developments in the MPI‐M Earth System Model version 1.2 (MPI‐ESM1.2) and Its Response to Increasing CO₂

Abstract

Abstract A new release of the Max Planck Institute for Meteorology Earth System Model version 1.2 (MPI‐ESM1.2) is presented. The development focused on correcting errors in and improving the physical processes representation, as well as improving the computational performance, versatility, and overall user friendliness. In addition to new radiation and aerosol parameterizations of the atmosphere, several relatively large, but partly compensating, coding errors in the model's cloud, convection, and turbulence parameterizations were corrected. The representation of land processes was refined by introducing a multilayer soil hydrology scheme, extending the land biogeochemistry to include the nitrogen cycle, replacing the soil and litter decomposition model and improving the representation of wildfires. The ocean biogeochemistry now represents cyanobacteria prognostically in order to capture the response of nitrogen fixation to changing climate conditions and further includes improved detritus settling and numerous other refinements. As something new, in addition to limiting drift and minimizing certain biases, the instrumental record warming was explicitly taken into account during the tuning process. To this end, a very high climate sensitivity of around 7 K caused by low‐level clouds in the tropics as found in an intermediate model version was addressed, as it was not deemed possible to match observed warming otherwise. As a result, the model has a climate sensitivity to a doubling of CO 2 over preindustrial conditions of 2.77 K, maintaining the previously identified highly nonlinear global mean response to increasing CO 2 forcing, which nonetheless can be represented by a simple two‐layer model.

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Affiliated Institutions

• Sorbonne Université FR
• Lamont-Doherty Earth Observatory US
• International Centre of Insect Physiology and Ecology KE
• Monash University AU
• Physical Sciences (United States) US
• Karlsruhe Institute of Technology DE
• Cooperative Institute for Research in Environmental Sciences US
• NOAA Earth System Research Laboratory US
• University of Reading GB
• University of Colorado Boulder US
• University of Cologne DE
• Université de Versailles Saint-Quentin-en-Yvelines FR
• Stockholm University SE
• Laboratoire des Sciences du Climat et de l'Environnement FR
• Leipzig University DE
• Ludwig-Maximilians-Universität München DE
• CEA Paris-Saclay FR
• Helmholtz-Zentrum Hereon DE
• Centre National de la Recherche Scientifique FR
• Laboratoire de Météorologie Dynamique FR
• Infektionsmedizinisches Centrum Hamburg DE
• Senckenberg Biodiversity and Climate Research Centre DE
• Columbia University US
• Max Planck Institute for Meteorology DE
• German Climate Computing Centre DE
• National Centre for Atmospheric Science GB
• Commissariat à l'Énergie Atomique et aux Énergies Alternatives FR

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