Assessing the impact of Laurentide Ice Sheet topography on glacial climate

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.climate-of-the-past.net/home.html.Simulations of past climates require altered\ud boundary conditions to account for known shifts in the Earth\ud system. For the Last Glacial Maximum (LGM) and subsequent\ud deglaciation, the existence of large Northern Hemisphere\ud ice sheets caused profound changes in surface topography\ud and albedo. While ice-sheet extent is fairly well\ud known, numerous conflicting reconstructions of ice-sheet topography\ud suggest that precision in this boundary condition is\ud lacking. Here we use a high-resolution and oxygen-isotope-enabled\ud fully coupled global circulation model (GCM)\ud (GISS ModelE2-R), along with two different reconstructions\ud of the Laurentide Ice Sheet (LIS) that provide maximum and\ud minimum estimates of LIS elevation, to assess the range of\ud climate variability in response to uncertainty in this boundary\ud condition. We present this comparison at two equilibrium\ud time slices: the LGM, when differences in ice-sheet topography\ud are maximized, and 14 ka, when differences in maximum\ud ice-sheet height are smaller but still exist. Overall, we\ud find significant differences in the climate response to LIS\ud topography, with the larger LIS resulting in enhanced Atlantic\ud Meridional Overturning Circulation and warmer surface\ud air temperatures, particularly over northeastern Asia and\ud the North Pacific. These up- and downstream effects are associated\ud with differences in the development of planetary\ud waves in the upper atmosphere, with the larger LIS resulting\ud in a weaker trough over northeastern Asia that leads to the\ud warmer temperatures and decreased albedo from snow and\ud sea-ice cover. Differences between the 14 ka simulations are\ud similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference\ud in maximum LIS elevation in the LGM simulations. These\ud results suggest that such uncertainty in ice-sheet boundary\ud conditions alone may significantly impact the results of paleoclimate\ud simulations and their ability to successfully simulate\ud past climates, with implications for estimating climate\ud sensitivity to greenhouse gas forcing utilizing past climate\ud states