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Antarctic Climate and its Sensitivity: Orography, Moisture Transport, and Natural Variability of the Coupled Atmosphere-Ocean-Ice System

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Date and time Mar 04, 2019
from 04:10 PM to 05:00 PM
Location MP606
Host Robert Fajber

Hansi Singh

Pacific National Laboratories
https://atmos.washington.edu/~hansi/

Antarctic Climate and its Sensitivity: Orography, Moisture Transport, and Natural Variability of the Coupled Atmosphere-Ocean-Ice System

 
Over the last 50 years as our planet has warmed in response to rising  anthropogenic greenhouse gas emissions, the Arctic has warmed at roughly three times the global rate and its sea ice cover has receded dramatically.  In the Antarctic, on the other hand, sea ice cover has expanded, and surface warming is relatively muted over much of the continent and the surrounding ocean.  In this talk, I present some recent work regarding the unique relationships between atmosphere, ocean, land ice, and sea ice in the Antarctic, and how these impact the sensitivity of the Antarctic to climate forcings. I show that Antarctic climate sensitivity is intrinsically much lower than that of the Arctic, whether it is forced through greenhouse gas emissions (without any accompanying changes in ocean heat uptake or convergence) or through increased subpolar ocean heat uptake alone.  I show that some of this insensitivity is due to the orography of the Antarctic continent, which rises to nearly 3 km above sea level, rendering it thermodynamically and dynamically isolated from the surrounding ocean and sea ice.  I further discuss the impact of Antarctic orography on the polar hydrologic cycle and its response to greenhouse warming from a moist entropy perspective, with some implications for interpretation of water isotopes from ice cores.  Finally, I present evidence that natural variability in the coupled atmosphere-ocean-ice system, combined with low intrinsic sensitivity to climate forcings, can result in paradoxical transient behavior, such as the expansion of Antarctic sea ice cover (from 1979 to 2015) even as atmospheric greenhouse gases increased and the rest of the globe warmed.
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