ICON‐A is the new icosahedral nonhydrostatic (ICON) atmospheric general circulation model in a configuration using the Max Planck Institute physics package, which originates from the ECHAM6 general circulation model, and has been adapted to account for the changed dynamical core framework. The coupling scheme between dynamics and physics employs a sequential updating by dynamics and physics, and a fixed sequence of the physical processes similar to ECHAM6. To allow a meaningful initial comparison between ICON‐A and the established ECHAM6‐LR model, a setup with similar, low resolution in terms of number of grid points and levels is chosen. The ICON‐A model is tuned on the base of the Atmospheric Model Intercomparison Project (AMIP) experiment aiming primarily at a well balanced top‐of atmosphere energy budget to make the model suitable for coupled climate and Earth system modeling. The tuning addresses first the moisture and cloud distribution to achieve the top‐of‐atmosphere energy balance, followed by the tuning of the parameterized dynamic drag aiming at reduced wind errors in the troposphere. The resulting version of ICON‐A has overall biases, which are comparable to those of ECHAM6. Problematic specific biases remain in the vertical distribution of clouds and in the stratospheric circulation, where the winter vortices are too weak. Biases in precipitable water and tropospheric temperature are, however, reduced compared to the ECHAM6. ICON‐A will serve as the basis of further development and as the atmosphere component to the coupled model, ICON‐Earth system model (ESM).
[1] The present paper addresses the origin of natural variability arising internally from the climate system of the global carbon cycle at centennial time scales. The investigation is based on the Max Planck Institute for Meteorology, Coupled Model Intercomparison Project Phase 5 (MPI-MCMIP5) preindustrial control simulations with the MPI Earth System Model in low resolution (MPI-ESM-LR) supplemented by additional simulations conducted for further analysis. The simulations show a distinct low-frequency component in the global terrestrial carbon content that induces atmospheric CO 2 variations on centennial time scales of up to 3 ppm. The main drivers for these variations are low-frequency fluctuations in net primary production (NPP) of the land biosphere. The signal arises from small regions scattered across the whole globe with a pronounced source in North America. The main reason for the global NPP fluctuations is found in climatic changes leading to longterm variations in leaf area index, which largely determines the strength of photosynthetic carbon assimilation. The underlying climatic changes encompass several spatial diverse climatic alterations. For the particular case of North America, the carbon storage changes are (besides NPP) also dependent on soil respiration. This second mechanism is strongly connected to low-frequency variations in incoming shortwave radiation at the surface.Citation: Schneck, R., C. H. Reick, and T. Raddatz (2013), Land contribution to natural CO 2 variability on time scales of centuries,
This work documents the ICON‐Earth System Model (ICON‐ESM V1.0), the first coupled model based on the ICON (ICOsahedral Non‐hydrostatic) framework with its unstructured, icosahedral grid concept. The ICON‐A atmosphere uses a nonhydrostatic dynamical core and the ocean model ICON‐O builds on the same ICON infrastructure, but applies the Boussinesq and hydrostatic approximation and includes a sea‐ice model. The ICON‐Land module provides a new framework for the modeling of land processes and the terrestrial carbon cycle. The oceanic carbon cycle and biogeochemistry are represented by the Hamburg Ocean Carbon Cycle module. We describe the tuning and spin‐up of a base‐line version at a resolution typical for models participating in the Coupled Model Intercomparison Project (CMIP). The performance of ICON‐ESM is assessed by means of a set of standard CMIP6 simulations. Achievements are well‐balanced top‐of‐atmosphere radiation, stable key climate quantities in the control simulation, and a good representation of the historical surface temperature evolution. The model has overall biases, which are comparable to those of other CMIP models, but ICON‐ESM performs less well than its predecessor, the Max Planck Institute Earth System Model. Problematic biases are diagnosed in ICON‐ESM in the vertical cloud distribution and the mean zonal wind field. In the ocean, sub‐surface temperature and salinity biases are of concern as is a too strong seasonal cycle of the sea‐ice cover in both hemispheres. ICON‐ESM V1.0 serves as a basis for further developments that will take advantage of ICON‐specific properties such as spatially varying resolution, and configurations at very high resolution.
Based on the Max Planck Institute Earth System Model simulations for the Coupled Model Intercomparison Project Phase 5 and on simulations with the submodel Cbalone we disentangle the influence of natural and anthropogenic vegetation changes on land carbon emissions for the years 1850 until 2300. According to our simulations, climate‐induced changes in distribution and productivity of natural vegetation strongly mitigates future carbon (C) emissions from anthropogenic land‐use and land cover change (LULCC). Depending on the assumed scenario, the accumulated carbon emissions until the year 2100 are reduced between 22 and 49% and until 2300 between 45 and 261%. The carbon storage due to climate‐induced vegetation change is generally stronger under the presence of LULCC. This is because the natural vegetation change can reestablish highly productive extratropical forests that are lost due to LULCC. After stopping anthropogenic vegetation changes in the year 2100 the refilling of depleted C pools on formerly transformed land takes (dependent on the scenario) time scales of centuries.
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