ICON-Sapphire: simulating the components of the Earth system and their interactions at kilometer and subkilometer scales

State-of-the-art Earth system models typically employ grid spacings of O(100 km), which is too coarse to explicitly resolve main drivers of the flow of energy and matter across the Earth system. In this paper, we present the new ICON-Sapphire model configuration, which targets a representation of the components of the Earth system and their interactions with a grid spacing of 10 km and finer. Through the use of selected simulation examples, we demonstrate that ICON-Sapphire can (i) be run coupled globally on seasonal timescales with a grid spacing of 5 km, on monthly timescales with a grid spacing of 2.5 km, and on daily timescales with a grid spacing of 1.25 km; (ii) resolve large eddies in the atmosphere using hectometer gridspacings on limited-area domains in atmosphere-only simulations; (iii) resolve submesoscale ocean eddies by using a global uniform grid of 1.25 km or a telescoping grid with the finest grid spacing at 530 m, the latter coupled to a uniform atmosphere; and (iv) simulate biogeochemistry in an oceanonly simulation integrated for 4 years at 10 km. Comparison of basic features of the climate system to observations reveals no obvious pitfalls, even though some observed aspects remain difficult to capture. The throughput of the coupled 5 km global simulation is 126 simulated days per day employing 21 % of the latest machine of the German Climate Computing Center. Extrapolating from these results, multi-decadal global simulations including interactive carbon are now possible, and short global simulations resolving large eddies in the atmosphere and submesoscale eddies in the ocean are within reach.Financial support. This research has been supported by the Deutsche Forschungsgemeinschaft (grant nos. 390683824 and 274762653), Horizon 2020 (COMFORT (grant no. 820989), CONSTRAIN (grant no. 820829), ESiWACE (grant no 675191), ESiWACE2 (grant no 823988), ESM2025 – Earth System Models for the Future (grant no. 101003536), EUREC4A (grant no. 694768), NextGEMS (grant no. 101003470), Nunataryuk (grant no. 773421)), the Bundesministerium für Bildung und Forschung (NextG-Climate Science-EUREC4A-OA), and the Bundesministerium für Verkehr und Digitale Infrastruktur (grant no. 4818DWDP1A)