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.
After completion of the historical simulation, the experiment was extended along the SSP2-4.5 scenario pathway until 2050 to estimate near-future climate change using a long-term climate simulation at the kilometer scale. For this purpose, CMIP6 scenario forcings were used. Tropospheric aerosol estimates are based on the MACv2 aerosol forcing, which was subsequently adjusted to ensure compatibility with the CONFESS aerosol forcing used during the historical simulation.
