Continental shelf area inundation drove reduced temperature seasonality in East Asia during the last deglaciation

East Asia (EA) has experienced a decreasing trend in the summer-to-winter temperature difference (temperature seasonality) in the context of ongoing global warming. However, the impacts of natural external forcing remain unclear. The last deglaciation, marked by substantial global warming, provides a paleoclimate context for understanding the roles of natural forcing in EA temperature seasonality changes. Here, using transient simulations (iTraCE), we demonstrate that EA experienced greater winter warming compared to summer during the last deglaciation, supported by paleo-climatic reconstructions. Sensitivity experiments indicate that the inundation of continental shelf area due to rising sea-level played a critical role in driving these differential warming trends. Further quantifications highlight the contributions of greater heat capacity instead of reduced surface albedo of the expanded ocean area. Resulting atmospheric responses expanded the seasonality change to EA landmass by cloud‒radiation feedback and temperature advection processes. These findings provide insight into the potential climatic impacts of sea-level rise under ongoing global warming.