Linearity of the Climate System Response to Antarctic Topography Change
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A hierarchy of general circulation models is used to investigate the linearity of the response of the global climate system to changes in Antarctic topography. Models range in complexity from an atmospheric dry dynamical core to a slab-ocean global climate model with idealized West Antarctic ice sheet topography changes and experiments were conducted where topography was either lowered or raised. The range of model complexity used allows the mechanisms responsible for different aspects of the response to be identified. The temperature and circulation response to Antarctic topography change is nearly linear in the dry dynamical core. In all other model configurations the atmosphere consistently warms near the surface over the Southern Ocean, and cools in the stratosphere over the continent, whether topography is raised or lowered. The wind response to changes in ice sheet elevation is linear near the surface, but nonlinear in the upper atmosphere. When topography is lowered in the slab-ocean model configuration the warming is due to enhanced southward atmospheric heat transport. When topography is raised, the warming is associated with an increase in cloud fraction at all levels and downwelling longwave radiation over the Southern Ocean. Finally, experiments were conducted with a fully-coupled global climate model using Antarctic ice sheet topography from a West Antarctic Ice Sheet (WAIS) collapse scenario taken from an ice sheet model, as well as topography that represents half of the change between present day topography and WAIS collapse, and the negative of the change between present day and WAIS collapse topography. The response is largely consistent with the more idealized slab-ocean experiments, but the full depth ocean additionally shows warming throughout the water column in the ocean. In summary these results indicate that ice sheet-climate system feedbacks may differ depending on whether the Antarctic ice sheet is gaining or losing mass.
- Atmospheric sciences