Accelerating Southern Ocean Sea Ice Decline due to Cloud-Climate Feedbacks

After decades of stability, Southern Ocean sea ice has recently experienced an abrupt decline, with uncertain future behaviour. Using high-resolution climate simulations, we identify a seasonally modulated cascade of feedbacks driving rapid sea ice loss, especially in the Weddell Sea. Anthropogenic warming reduces sea ice, enhancing ocean heat release in warm seasons, which warms and moistens the atmospheric boundary layer in cold seasons. This increases mid-level cloud cover and longwave radiative warming, suppressing spring sea ice formation and activating the sea ice-albedo feedback. Current ocean warming trends indicate this transition threshold is nearly reached. These findings highlight a potential near-term regime shift in Southern Ocean sea ice, emphasising the importance of monitoring ocean-atmosphere interactions and cloud feedbacks to understand implications for regional and global climate change.