Jet stream response to future Arctic sea ice loss not underestimated by climate models

Abstract Previous studies using an emergent constraint have suggested that climate models underestimate the winter jet stream response to sea ice loss, casting doubt on the quality of mid-latitude climate projections. However, the robustness of this emergent constraint has been questioned. Here, we propose a more robust emergent constraint based on lower stratospheric winds. Using coordinated sea ice loss experiments with bespoke versions of two state-of-the-art climate models along with a multi-model archive, we identify a strong relationship between these winds and the jet stream response. The new emergent constraint reduces the uncertainty in the response by 62% and indicates that the real-world response closely matches the multi-model mean—suggesting no systematic underestimation, in contrast to earlier studies. Our results underscore the importance of reducing lower stratospheric wind biases and increase confidence in climate model projections of a future poleward shift of the jet stream in response to global warming.