Multi-centennial climate change in a warming world beyond 2100

Abstract. Sustained anthropogenic perturbations are anticipated to influence Earth's climate system well beyond the 21^st century. Despite growing interest in climate change after 2100 and improved computational resources, multi-century climate projections remain limited in number. Here, we examine a set of 10 ensemble simulations extending the Community Earth System Model 2 large ensemble (CESM2-LE) from 2101 to 2500 under the shared socio-economic pathway (SSP)3-7.0 scenario, which involves the reduction of fossil and industrial CO₂ emissions to zero by 2250. By the year 2500, substantial forced changes are projected in both the spatial and temporal characteristics of variability and mean states. Post-2100, El Niño-Southern Oscillation variability is expected to diminish, while the tropical intraseasonal variability will notably strengthen. The mean state changes include a global mean temperature rise of 12 °C and a 23.5 % increase in global precipitation compared with historical observations. Additionally, substantial soil carbon release from permafrost thawing is projected over Siberia and Canada, resulting in a shift of land from a carbon sink to a carbon source after the 22^nd century. The ocean experiences a rapidly diminished capacity to absorb anthropogenic CO₂ after the 21^st century, while nevertheless continuing to act as a carbon sink, with an increased contribution from the Southern Ocean to total carbon uptake. The model also projects a considerable decline in low-latitude marine primary production, which is linked to a considerable depletion of PO₄ in the local mesopelagic domain. At urban scales, the extended simulations reveal substantial projected changes in the amplitude and phasing of precipitation seasonality, with the same holding for the partial pressure of CO₂ in seawater at regional scales, demonstrating that post-2100 changes are not simply amplifications of projected 21^st century changes. Taken together, these new simulations highlight the far-reaching impacts of multi-centennial climate change on both human societies and global ecosystems.