Polar Climates, Clouds, and Seasonality in the Paleogene

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Climatic records show that polar regions have demonstrated an amplified response to global climate change through geologic time. Additionally, polar regions have significant influence upon global climate processes and conditions. Clouds also have been cited repeatedly as a critical factor in climatic change. The early Eocene appears to have been a time of warm polar conditions, but climate modeling efforts have been unsuccessful in reproducing these conditions. To date, Eocene seasonality characteristics reconstructed from proxy data have been unsatisfactorily explained by model scenarios of high atmospheric pCO2 or by warm high latitude ocean surface temperatures. However, proxy data interpretations may be explained by the presence of warming clouds at high latitudes. We have hypothesized that polar stratospheric ice clouds may have occurred in the early Eocene and produced a dampened seasonal cycle at high latitudes. Here we propose to test this hypothesis by using an atmospheric general circulation model to test the sensitivity of high latitude climates to the presence of such polar clouds. Of paramount interest will be temperature seasonality of polar climates with and without such clouds. We will examine the polar cloud mechanism for both poles, thereby testing the cloud influence on a water-covered pole surrounded by land masses and on a continentally-capped pole surrounded by ocean.