Sea ice and atmospheric circulation shape the high-latitude lapse rate feedback

Nicole Feldl,Stephanie Hay,Hansi K A Singh,Paul J Kushner,Stephen Po-Chedley

doi:10.1038/s41612-020-00146-7

Abstract

Arctic amplification of anthropogenic 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 longwave radiation. The latter lapse rate feedback is subject, at high latitudes, to a myriad of local and remote influences whose relative contributions remain unquantified. The distinct controls on the high-latitude lapse rate feedback are here partitioned into “upper” and “lower” contributions originating above and below a characteristic climatological isentropic surface that separates the high-latitude lower troposphere from the rest of the atmosphere. This decomposition clarifies 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 mechanism operating across the seasonal cycle.

Highlights

In climate simulations forced by increasing concentrations of atmospheric CO2, changes in the rate at which temperature decreases with altitude act as an important negative feedback in the global climate system[1,2,3]
To quantify the relative importance of the physical mechanisms known to shape the high-latitude lapse rate feedback, we have partitioned the effects of local surface processes and remote atmospheric energy transport
We have clarified how the positive lapse rate feedback over the Arctic Ocean is tied to sea ice retreat and represents the changing seasonal dynamics of sea ice

Summary

Introduction

In climate simulations forced by increasing concentrations of atmospheric CO2, changes in the rate at which temperature decreases with altitude (i.e., changes in the lapse rate) act as an important negative feedback in the global climate system[1,2,3]. The lapse rate feedback, defined as the radiative feedback associated with atmospheric warming that is vertically nonuniform, is negative at low latitudes. This negative feedback arises because moist convection leads to greater warming in the upper than in the lower troposphere, which increases outgoing longwave radiation and counteracts further surface warming. The lapse rate feedback is influenced by regions in which the lower troposphere exhibits greater warming than the upper troposphere, leading to a smaller increase in outgoing longwave radiation relative to uniform warming and a positive feedback. The distinct, competing tropical and high-latitude processes that shape the meridional structure of the lapse rate feedback have been recognized as major contributors to polar-amplified surface warming[6,7,8,9]

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Conclusion