The first version of the ICON Earth System Model

A team of researchers around Dr. Johann Jungclaus from the Max Planck Institute for Meteorology (MPI-M) has published a paper in the Journal of Advances in Modeling Earth Systems documenting the ICON Earth System Model Version 1.0, the first coupled ocean-atmosphere-land model based on the ICON system.

The article describes the coupled ICON model and explores its performance by evaluating a set of standardized climate change experiments following the protocol of the Coupled Model Intercomparison Project (CMIP). The authors used a model configuration at moderate resolution, which allows them to compare the results with MPI-M’s predecessor model MPI-ESM, and other models participating in CMIP. One CMIP experiment is the “historical” simulation running from the beginning of industrialization in the mid 19th century to present. To account for internal variability in the climate system, the authors executed an ensemble of five simulations and found that ICON-ESM performs well in reproducing the observed trajectory of climate change (Figure 1), although some discrepancies remain, such as an overestimation of warming in the Northern Hemisphere in the late 20th century (Figure 1b).



Figure 1: Time series of surface temperature relative to the respective 1850-1899 averages over a) the globe, b) the northern hemisphere, and c) the southern hemisphere for (red-orange) the ICON-ESM historical ensemble, and observational data by (blue) the Goddard Institute for Space Studies Surface Temperature product, (black) the blended Hadley Centre/Climate Research Unit global temperature data set, and (light blue) the National Oceanographic and Atmospheric Administration NCDC historical merged land ocean surface temperature data set. The simulated surface temperature is constructed using sea surface temperatures over the ocean and surface air temperatures over land. (from: Jungclaus et al., 2022, CC BY-NC-ND 4.0)


ICON stands for “ICOsahedral Nonhydrostatic” and provides a novel framework for modelling based on innovative design principles. For example, the numerical grids are created by subsequently dividing the faces of an icosahedron (hence “icosahedral”) and avoid problems known from previously used geographical grids, such as singularities at the poles. Moreover, ICON’s numerical concepts are designed to run with very high efficiency at modern computational infrastructure, such as the new “Levante” computer at the German Climate Computing Centre (DKRZ). Over the last years, scientists at MPI-M, the German Meteorological Service (DWD), and other institutions in Germany and Switzerland have developed the component models for atmosphere, ocean, land and the biogeochemical cycle. While the performance of those models had already been explored individually, coupling the sub-system together to form the first ICON Earth System Model (Figure 2) “was a challenging endeavor that required numerous sensitivity experiments to be carried out by a dedicated team of scientists and programmers from all three departments of MPI-M and the partner institutions” says Dr. Johann Jungclaus.



Figure 2: Schematic representation of the model components (coloured boxes) and the coupling software YAC (gray) of the ICON-ESM. The lines indicate interaction between components and the triangular structures in the background illustrate the models’ numerical grids, where the atmosphere features coarser resolution (160km), compared to the ocean (40km). (Credit: Y. Schrader)


The authors emphasize that ICON-ESM V1.0 is only the first important milestone, from where future development steps promise to open new perspectives in Earth system modelling. Examples of further innovations are configurations with highly variable grid resolution or ultra-high-resolution coupled simulations that aim to serve as “digital twins” of Earth. In particular, the goal of ongoing collaboration between DWD and MPI-M is the development of a system for “seamless” predictions from weather to climate scales.


Original publication:

J.H. Jungclaus, S.J. Lorenz, H. Schmidt, V. Brovkin, N. Brüggemann, F. Chegini, T. Crüger, P. De-Vrese, V. Gayler, M.A Giorgetta, O. Gutjahr, H. Haak, S. Hagemann, M. Hanke, T. Ilyina, P. Korn, J. Kröger, L. Linardakis, C. Mehlmann, U. Mikolajewicz, W.A. Müller, J.E.M.S Nabel, D. Notz, H. Pohlmann, D.A. Putrasahan, T. Raddatz, L. Ramme, R. Redler, C.H. Reick, T. Riddick, T. Sam, R. Schneck, R. Schnur, M. Schupfner, J.-S. von Storch, F. Wachsmann, K.-H. Wieners, F. Ziemen, B. Stevens, J. Marotzke, M. Claussen  (2022). The ICON Earth System Model version 1.0. Journal of Advances in Modeling Earth Systems, 14, e2021MS002813.



Dr. Johann Jungclaus
Max Planck Institute for Meteorology
Email: johann.jungclaus@we dont want