Multi-centennial climate change in a warming world beyond 2100

Changes in the climate due to human influences are expected to extend well beyond the 21st 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 (ENSO) variability is expected to diminish, while the tropical intraseasonal variability will notably strengthen. Global mean surface temperature and precipitation are projected to continue rising even after CO2 emissions cease. In addition, 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 22nd century. The ocean experiences a rapidly diminished capacity to absorb anthropogenic CO2 after the 21st 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 dissolved inorganic phosphate in the local mesopelagic domain. The extended simulations predict substantial changes in the amplitude and timing of precipitation seasonality at the urban scale, with variations across different locations. Similarly, seasonal variations in the partial pressure of CO2 in seawater along different latitudinal bands are projected to experience distinct changes. These findings suggest that post-2100 changes will not simply be an extension of the trends projected for the 21st century. Taken together, these new simulations highlight the far-reaching effects of multi-centennial climate change on both human societies and global ecosystems.