DOI: 10.26050/wdcc/eerie_fesom_hist_v1
title: EERIE: Ocean Eddy-rich Kilometer-scale Climate Simulation with Integrated Forecasting System (IFS) - Finite volumE Sea Ice-Ocean Model (FESOM2.5): historical simulation (Version 1)

description: Project: European Eddy RIch Earth System Models - This project, running from January 2023 to December 2026, will reveal and quantify the role of ocean mesoscale processes in shaping the climate trajectory over seasonal to centennial time scales. To this end EERIE will develop a new generation of Earth System Models (ESMs) that are capable of explicitly representing a crucially important, yet unexplored regime of the Earth system – the ocean mesoscale. Leveraging the latest advances in science and technology, EERIE will substantially improve the ability of such ESMs to faithfully represent the centennial-scale evolution of the global climate, especially its variability, extremes and how tipping points may unfold under the influence of the ocean mesoscale.

Model improvements include new dynamical cores, new components (particularly for sea ice), scale-aware parametrisations and the complementary use of Machine Learning (ML). The technological challenge associated with this ambition is very high. EERIE’s goal is to achieve a simulation speed of up to 5 simulated years per day and to make efficient use (reduction in power consumption by 50%) of the pre-exascale supercomputers now available in Europe. The technological solutions that are to be leveraged in EERIE are the use of reduced numerical precision, Graphic Processing Units (GPUs), ML and reduced Input/Output (I/O). Alongside model improvements, EERIE will develop innovative experimental simulation protocols that are suitable for the mesoscale, to be pioneered on behalf of the global climate modelling community, in preparation for the next Intergovernmental Panel on Climate Change (IPCC) cycle.

(Ref: https://eerie-project.eu/about/)
Summary: The EU project European Eddy RIch Earth System Models (EERIE) aims to advance kilometer-scale Earth System Models (ESMs) to reduce biases associated with low-resolution climate simulations. Its goal is to develop centennial-scale ESMs that explicitly resolve ocean mesoscale processes, thereby improving the representation of long-term climate evolution, variability, extremes, and potential tipping points.
One of these models, IFS-FESOM2-SR, couples the ECMWFs Integrated Forecast System (IFS) atmosphere (9 km resolution) with the FESOM2.5 ocean model (minimum 5 km resolution). The FESOM2.5 ocean model employs an NG5 unstructured triangular grid with 70 depth levels, achieving ~5 km resolution in eddy-rich mid- and high-latitudes and ~13 km in the tropics (Rackow et al., 2025). Its sea-ice component is FESIM (Danilov et al., 2015). The atmospheric model, IFS cycle 48r1 from ECMWF, uses a Tco1279 (~10 km) octahedral grid with 137 vertical levels. The setup follows Rackow et al. (2025) except for deep convection, where the operational IFS scheme is used instead of the modified reduced cloud-base mass flux version.
Following the HighResMIP protocol (Haarsma et al., 2016), the main simulations were preceded by a 50-year spin-up period using 1950 CMIP6 forcing. From the spin-up’s final state, two simulations were launched in parallel: a control run and a historical run using CMIP6 forcings. According to the HighResMIP protocol, the control simulation aimed to assess any potential drift within the simulation, enabling us to exclude the influence of such drift in order to better understand the impact of changes in radiative forcing over time. The historical simulation employed CMIP6 historical forcing spanning from 1950 to 2014, running for a total of 65 years.
In the context of tropospheric aerosols, we employed the CONFESS aerosol forcing, which is available from 1970 onwards and is applied in five-year epochs. For the period preceding 1970 (from 1950 to 1969), we generated epochs by replicating the 1970 aerosol forcing. This generation of aerosol forcing was conducted as part of the EU project DestinE (Destination Earth), from which additional model developments and adaptations are being integrated. These efforts aim to prepare the IFS-FESOM for conducting multidecadal climate simulations.