CMIP6 Earth System Models Project Greater Acceleration of Climate Zone Change Due To Stronger Warming Rates

Warming climate and precipitation changes induce notable shifts in climate zones. In this study, the latest generation of global climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and the previous generation CMIP5 under high-emission scenarios are used together with observations and applied to the Koppen-Geiger climate classification. The aim is to shed light on how projected warming and changes in precipitation will influence future climate zones and their associated ecosystems while revealing differences between the two model generations. Compared to CMIP5 models, CMIP6 models exhibit slightly improved performance in replicating the observed Koppen-Geiger map for the historical (1976-2005) period and similar inter-model agreement for the future. The models show major changes in climate zones with a range of projections depending on which ensemble subset is used: 37.9%-48.1% of the global land area is projected to change climate zone by the end of the century, with the most pronounced changes expected over Europe (71.4%-88.6%) and North America (51.2%-65.8%). CMIP6 models project a higher rate of areal climate zone change (km(2)/year) throughout the 21st century, which is mainly driven by their greater global land warming rates. Using a likely equilibrium climate sensitivity subset of CMIP6 models that is consistent with the latest evidence constrains the climate zone shifts, and their projections better match the results of CMIP5 simulations. Although the high warming rates of some CMIP6 models are less credible, the risks associated with them are greater, and they heighten the need for urgent action to preserve terrestrial ecosystems.