Significant contribution of internal variability to recent Barents-Kara sea ice loss in winter

The Arctic has experienced a rapid sea ice loss in the Barents and Kara Seas in winter during the last few decades. Such sea ice loss has been attributed to anthropogenic warming and internal variability, but their relative contribution remains unclear. Using machine-learning methods and large ensemble simulations, we successfully reproduce Barents-Kara sea ice trends as the joint impact of anthropogenic and internal atmospheric variability components. Results show that the loss of Barents-Kara sea ice extent over the recent 20 years (1997-2017) is significantly enhanced by atmospheric internal variability (>50%) acting on top of anthropogenic warming. Overall, this study highlights that internal variability plays a more important role in recent winter Arctic sea ice loss than previously thought, and promotes similar machine-learning methods for attributing sea ice trends in other polar regions and seasons.