Changes of Köppen climate zones over China in simulated interglacial and future warm intervals

Köppen climate classification provides a threshold-based description of regional hydrothermal conditions and relates to the ecosystem. Comparing its changes under past natural warm intervals and future CO₂-driven warming scenarios helps clarify how climate zones respond to different external forcings. In this study, the Köppen climate type changes over China and related mechanisms are investigated using the multiple Coupled Model Intercomparison Project phase 6 (CMIP6) models under past and future warm conditions of the Last Interglacial (LIG; 127 ka), mid-Holocene (MH; 6 ka), and an idealized future warming scenario with a 1% CO2 increase per year (1pctCO2). The 1pctCO₂ experiment shows the most extensive subtype-level Köppen climate changes, affecting 48% of national terrestrial land, compared to 38% in the LIG and 16% in the MH. Cold climate is the most sensitive type across the three warm intervals. Compared to the preindustrial period, the simulated tropical, arid, and temperate zones contract, but the cold zone expands during the interglacial epochs, related to increased temperature seasonality. In the future, all major types expand, except the polar zone. Temperature dominates these transitions across the three warm periods. Surface energy balance indicates that interglacial climate type shifts are linked to enhanced temperature seasonality due to the surface net shortwave radiation variations, whereas the 1pctCO2 experiment exhibits uniform seasonal warming over China driven by longwave radiation. Simulated interglacial climate type transitions qualitatively agree with site-based proxy reconstructions. These results highlight forcing-dependent climate zone responses, providing a paleoclimate reference for future climate–ecosystem boundary shifts in China.