Understanding Miocene Climatic Warmth

The mid-Miocene Climatic Optimum (MMCO), 17-14.50 million years ago, is studied using general circulation models (GCMs). This period of time is characterized by enhanced warming in the deep ocean and in the mid-to-high latitudes. Previous GCMs fail to accurately represent the warmer climate of the MMCO, providing evidence that other warming feedbacks are missing in the models. This study focuses on cloud feedbacks by modifying the Community Earth System Model (CESM 1.0) to explore the MMCO climate. We implement modifications in pre-industrial (284.7 ppm CO2) and modern slab ocean cases (367.0 ppm CO2, 400 ppm CO2, and 800 ppm CO2). One modified case showing the most potential implements an aerosol de- pendent ice nucleation mechanism and a theory based cloud phase separation. This modified case allows the model predicted aerosol concentrations to interact with the cloud microphysics and provide more realistic cloud water contents. The data shows an increase in surface temperature and increase in upper atmospheric cloud fraction when compared to the control case. Preliminary results suggest that this model is able to capture the mid-to-high latitude warming trends and weaker equator to pole temperature gradient.