Department Seminar: Nicole Feldl

Title: The Lapse Rate Feedback: How climate feedbacks and atmospheric energy transport conspire to shape polar-amplified warming

Abstract: Arctic amplification of climate change is widely attributed to the sea-ice albedo feedback, with its attendant increase in absorbed solar radiation, and to the effect of the vertical structure of atmospheric warming on Earth’s outgoing radiation. The latter lapse rate feedback is subject, at high latitudes, to a myriad of local and remote influences whose relative contributions remain unquantified. In this talk, I summarize results from idealized modeling experiments in which polar feedbacks are systematically modified to understand the role of ice, moisture, and seasons on polar amplification. I additionally present diagnostic analyses across the ensemble of comprehensive ocean-atmosphere models, partitioning the distinct controls on the high- latitude lapse rate feedback into “upper” and “lower” contributions originating from dynamically distinct regions: the high-latitude lower troposphere and the rest of the atmosphere. This decomposition elucidates how the positive high-latitude lapse rate feedback over polar oceans arises primarily as an atmospheric response to local sea ice loss and is reduced in subpolar latitudes by an increase in poleward atmospheric energy transport. The separation of the locally driven component of the high-latitude lapse rate feedback further reveals how it and the sea-ice albedo feedback together dominate Arctic amplification as a coupled, season-spanning, ocean-mediated mechanism.