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

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 CO2 over preindustrial conditions of 2.77 K, maintaining the previously identified highly nonlinear global mean response to increasing CO2 forcing, which nonetheless can be represented by a simple two‐layer model.

Equilibrium Climate Sensitivity Estimated by Equilibrating Climate Models

“…We find that the longwave clear sky feedback does moderately increase in many models as the temperature or the forcing level increases, mainly in the tropics and Northern Hemisphere middle latitudes (Figures a, S4, and S5). This is in accordance with the proposed argument that the tropics govern the global feedback evolution because the water vapor feedback increases with warming (Andrews et al, ; Block & Mauritsen, ; Jonko et al, ; Meraner et al, ), possibly following the rising tropical tropopause (Meraner et al, ; Mauritsen et al, ).…”

Realistic Quasi‐Biennial Oscillation Variability in Historical and Decadal Hindcast Simulations Using CMIP6 Forcing

“…We use the MPI-ESM-HR (Mauritsen et al, 2019;Müller et al, 2018) together with the historical simulations using CMIP5 (Taylor et al, 2012) and CMIP6 (Eyring et al, 2016) forcing. MPI-ESM-HR uses the European Centre Hamburg version 6.3 (ECHAM6.3) as the atmospheric component with a resolution of T127L95 (~100 km in the horizontal with 95 vertical levels) and the Max Planck Institute ocean model as the oceanic component of TP0.4 (0.4°nominal) resolution.…”

“…The historical simulations with MPI-ESM-HR are analyzed in Müller et al (2018) and Mauritsen et al (2019). In the following, we describe the MiKlip decadal prediction system employing the MPI-ESM-HR climate model.…”

Effects of a stochastic multicloud parameterization on the simulated Asian‐Australian monsoon rainfall in an AGCM

“…The model used in the present work is ECHAM6.3.02, which is a subversion of the state-of-the-art ECHAM6.3. It is the atmospheric component of coupled models, such as the Nanjing university of information science and technology Earth System Model version 3 (NESMv3; Cao et al, 2018), and the basis of MPI-ESM1.2 of Max-Planck-Institut für Meteorologie (Mauritsen et al, 2019). In brief, the terminology "ECHAM6.3" is used to represent the model version (ECHAM6.3.02) in this study.…”

“…In brief, the terminology "ECHAM6.3" is used to represent the model version (ECHAM6.3.02) in this study. A new representation and implementation of the radiative transfer scheme RRTMG is incorporated into ECHAM6.3 (Mauritsen et al, 2019). The convection scheme used in ECHAM6.3 adopts a mass flux scheme of Tiedtke (1989) combined with modified penetrative convection (Nordeng, 1994).…”