Understanding Heat-transfer Regimes in Past, Present and Future Climates

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The Earth's climate is a product of heat transfer, as the warming effect of heat energy gains, including the latent heat released in precipitation, must over time be balanced by equal heat losses to achieve a persistent climate state in any given region. An atmospheric column can transfer heat energy through its top and bottom by radiation, for instance when it cools by emitting infrared radiation to space, and by evaporation and thermal conduction at the Earth's surface. Lateral heat transfer is also critical, as in the tropics the Earth receives more energy from the sun than it radiates back to space and the opposite is true near the poles. Thus the tropics must export heat energy to the poles to balance the budgets of both regions. Work under this award seeks to understand atmospheric heat transfer in low, middle, and high latitudes, considering both changes in heat transfer over the the seasonal cycle and differences in heat transfer between warmer and colder climates. For example simulations of modern climate show strong seasonal variations in latitudinal heat balances, with radiation largely balancing local evaporation and surface heat conduction in the middle latitudes of the Northern Hemisphere in summer, while lateral heat transfer is more prominent in other seasons. The situation is quite different in simulations of the "snowball earth" climate, where lateral transfer is prominent throughout the year over most of the globe. The underlying mechanisms that determine atmospheric heat balances in different climates, and drive changes in heat balances during transitions between climate states, are explored through analysis of existing simulations and through novel simulations using a variety of model configurations.Heat transport plays an essential role in maintaining Earth's climate, and research on the topic has societal value given the need to better understand how the climate system works and how it is likely to change under the influence of greenhouse gas increases and changes in aerosol pollution. The project also provides support and training for a graduate student and an undergraduate, the latter recruited through a campus-wide program dedicated to increasing participation of underrepresented minorities in scientific research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.