In recent decades, the Arctic has warmed at a rate significantly higher than other regions, so called Arctic Amplification. Notably, Arctic warming in spring is particularly pronounced, even approaching the level of autumn, which experiences the strongest warming. Previous studies attributed the primary mechanism of spring Arctic warming to the surface albedo feedback triggered by accelerated land snow-ice melt. Consequently, the underestimation of spring warming in CMIP6 simulations was often attributed to insufficient representation of snow-ice processes in land models. However, accelerated snow-ice melt over land in spring is far less extensive than in summer, yet Arctic warming in summer is weaker than in spring. Our research has identified an alternative mechanism for Arctic spring warming. Winter warming over the Barents-Kara Seas reduces the meridional potential vorticity gradient, which decreases the difference between Rossby wave phase speed and group velocity, reduces energy dissipation, and thereby enhances atmospheric blocking events and meridional heat transport. In some CMIP6 models, the initial conditions are set too warm, resulting in weaker winter warming over the Barents-Kara Seas. This leads to an underestimation of Ural blocking events and consequently an underestimation of Arctic spring warming.

Arctic spring warming,CMIP6 simulation,Ural blocking,Barents-Kara Sea