CMIP6 GCMs Projected Future Koppen-Geiger Climate Zones on a Global Scale

This study compared the future global climate zones based on four radiative forcings ranging from low-end (SSP1-2.6) to high-end (SSP5-8.5) using the Köppen-Geiger climate classification. To reduce uncertainties in future projected precipitation and temperature, multimodel projections comprising 25 general circulation models (GCMs) were sourced from the recent Coupled Model Intercomparison Project phase six (CMIP6) and used to create a Multi-Model Ensemble. The changes in historical climate zones on CMIP6 simulations were divided into six periods considering data availability (1954–1964; 1964–1974; 1974–1984; 1984–1994; 1994–2004; and 2004–2014). Furthermore, the climate zone reproducibility of 25 CMIP6 GCMs was compared with the reference data sourced from Global Precipitation Climatology Centre precipitation and Climatic Research Unit temperature. The future climate zones were projected into seven periods using monthly precipitation and surface temperature under four main SSP scenarios. Consequently, the climate variables from GCMs were overestimated compared to the reference data, and the composition of the climate zones was less complex. While temperature discrepancies of 1–2°C may not drastically alter the Köppen-Geiger climate zone classifications, precipitation-based classifications are significantly impacted by the observed errors. Thus, it is crucial to recognize that despite the advancements in GCMs, they still possess limitations in accurately predicting “real” future climate changes. The projected future climate zones are simpler compared to the historical periods across six continents, with tundra and ice caps expected to disappear. This study highlights potential risks by projecting future climate zones based on varying greenhouse gas concentration levels, stressing the importance of using these projections with caution given the inherent uncertainties and limitations of GCMs.