Greater rate of climate zone change in CMIP6 Earth System Models due to stronger warming rates

Köppen-Geiger climate classification is a valuable tool to define climate zones based on the annual cycles of temperature and precipitation. In this study, we use the high-emission scenario global climate models from the Coupled Model Intercomparison Project phase 6 (CMIP6) and phase 5 (CMIP5) along with observations and apply the Köppen-Geiger climate classification. We aim to address the ecological consequences of climate change and compare the two generations of models. Compared to their predecessors, CMIP6 models show slightly improved performance in representing the reference period (1976-2005) observed climate zones. CMIP6 models project a 42-48% change in climate zones by the end of the century, depending on which ensemble subset is used. The projected change rates based on CMIP6 are above the global average for Europe (81-88%) and North America (57-66%). The reductions in the areas of cold and polar climate zones are more pronounced in CMIP6 models compared to CMIP5. Using an ensemble subset of CMIP6 models that are consistent with the latest evidence for equilibrium climate sensitivity limits the changes in climate zones, and their results converge towards the results based on CMIP5. CMIP6 models also project a greater rate of climate zone change throughout the century than CMIP5. The greater change rate observed in CMIP6 is essentially dominated by the stronger projected warming rates of these models, whose plausibility is a matter of concern.