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\begin{document}

\title{The ICON Earth System Model Version 1.0 1}



\author[1]{Johann Jungclaus}%
\author[1]{S J Lorenz}%
\author[1]{H Schmidt}%
\author[1]{V Brovkin}%
\author[2]{N Brüggemann}%
\author[1]{F Chegini}%
\author[1]{T Crüger}%
\author[1]{P De-Vrese}%
\author[1]{V Gayler}%
\author[1]{M A Giorgetta}%
\author[2]{O Gutjahr}%
\author[1]{H Haak}%
\author[3]{S Hagemann}%
\author[4]{M Hanke}%
\author[1]{T Ilyina}%
\author[1]{P Korn}%
\author[1]{J Kröger}%
\author[1]{L Linardakis}%
\author[1]{C Mehlmann}%
\author[1]{U Mikolajewicz}%
\author[1]{W A Müller}%
\author[1]{J E M S Nabel}%
\author[2]{D Notz}%
\author[5]{H Pohlmann}%
\author[1]{D A Putrasahan}%
\author[1]{T Raddatz}%
\author[1]{L Ramme}%
\author[1]{R Redler}%
\author[1]{C H Reick}%
\author[1]{T Riddick}%
\author[1]{T Sam}%
\author[1]{R Schneck}%
\author[1]{R Schnur}%
\author[4]{M Schupfner}%
\author[1]{J.-S Von Storch}%
\author[4]{F Wachsmann}%
\author[1]{K.-H Wieners}%
\author[4]{F Ziemen}%
\author[1]{B Stevens}%
\author[2]{J Marotzke}%
\author[2]{M Claussen}%
\affil[1]{Max Planck Institute for Meteorology}%
\affil[2]{Universität Hamburg}%
\affil[3]{Helmholtz Zentrum Hereon}%
\affil[4]{DKRZ}%
\affil[5]{Deutscher Wetterdienst}%


\vspace{-1em}



  
  \date{May 18, 2024}


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\begin{abstract}
* This work documents ICON-ESM 1.0, the first version of a coupled model
based 19 on the ICON framework 20 * Performance of ICON-ESM is assessed
by means of CMIP6 DECK experiments 21 at standard CMIP-type resolution
22 * ICON-ESM reproduces the observed temperature evolution. Biases in
clouds, winds, 23 sea-ice, and ocean properties are larger than in
MPI-ESM. Abstract 25 This work documents the ICON-Earth System Model
(ICON-ESM V1.0), the first cou-26 pled model based on the ICON
(ICOsahedral Non-hydrostatic) framework with its un-27 structured,
icosahedral grid concept. The ICON-A atmosphere uses a nonhydrostatic
dy-28 namical core and the ocean model ICON-O builds on the same ICON
infrastructure, but 29 applies the Boussinesq and hydrostatic
approximation and includes a sea-ice model. The 30 ICON-Land module
provides a new framework for the modelling of land processes and 31 the
terrestrial carbon cycle. The oceanic carbon cycle and biogeochemistry
are repre-32 sented by the Hamburg Ocean Carbon Cycle module. We
describe the tuning and spin-33 up of a base-line version at a
resolution typical for models participating in the Coupled 34 Model
Intercomparison Project (CMIP). The performance of ICON-ESM is assessed
by 35 means of a set of standard CMIP6 simulations. Achievements are
well-balanced top-of-36 atmosphere radiation, stable key climate
quantities in the control simulation, and a good 37 representation of
the historical surface temperature evolution. The model has overall
bi-38 ases, which are comparable to those of other CMIP models, but
ICON-ESM performs 39 less well than its predecessor, the Max Planck
Institute Earth System Model. Problem-40 atic biases are diagnosed in
ICON-ESM in the vertical cloud distribution and the mean 41 zonal wind
field. In the ocean, sub-surface temperature and salinity biases are of
con-42 cern as is a too strong seasonal cycle of the sea-ice cover in
both hemispheres. ICON-43 ESM V1.0 serves as a basis for further
developments that will take advantage of ICON-44 specific properties
such as spatially varying resolution, and configurations at very high 45
resolution. 46 Plain Language Summary 47 ICON-ESM is a completely new
coupled climate and earth system model that ap-48 plies novel design
principles and numerical techniques. The atmosphere model applies 49 a
non-hydrostatic dynamical core, both atmosphere and ocean models apply
unstruc-50 tured meshes, and the model is adapted for high-performance
computing systems. This 51 article describes how the component models
for atmosphere, land, and ocean are cou-52 pled together and how we
achieve a stable climate by setting certain tuning parameters 53 and
performing sensitivity experiments. We evaluate the performance of our
new model 54 by running a set of experiments under pre-industrial and
historical climate conditions 55 as well as a set of idealized
greenhouse-gas-increase experiments. These experiments were 56 designed
by the Coupled Model Intercomparison Project (CMIP) and allow us to
com-57 pare the results to those from other CMIP models and the
predecessor of our model, the 58 Max Planck Institute for Meteorology
Earth System Model. While we diagnose overall 59 satisfactory
performance, we find that ICON-ESM features somewhat larger biases in 60
several quantities compared to its predecessor at comparable grid
resolution. We empha-61 size that the present configuration serves as a
basis from where future development steps 62 will open up new
perspectives in earth system modelling. 63%
\end{abstract}%



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