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 simulation spans 200 years, including a 100-year control run (1950–2050), a 65-year historical run (1950–2014), and a 35-year SSP2-4.5 scenario run (2015–2050), marking the first global km-scale coupled simulation of this length.
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 completing the historical simulation, the experiment was continued under the SSP2-4.5 scenario.
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.
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.