GISS Lunch Seminar
Speaker: Clare Singer (CalTech)
Title: How clouds shape our climate

Abstract:
Clouds are a dominant feature of Earth's climate, controlling surface temperatures by reflecting sunlight back to space and infrared radiation back to the surface. Cloud response to climate change is a major source of uncertainty for future climate projections. This is mainly due to their small scales, which makes clouds, and their interactions with radiation, impossible to resolve in global models. In this talk, I will present two projects focusing on different aspects of modeling and understanding clouds. First, I will talk about errors that arise in GCMs from ignoring 3D scattering of photons by clouds. I will show how we can use high-resolution simulations of clouds and full 3D radiative transfer on small domains to calculate this bias explicitly and then scale up the result to make a global estimate of the 3D cloud radiative effect. In the second part of the talk, I will switch gears and focus on subtropical marine stratocumulus clouds and what controls stratocumulus-cumulus regime transitions (SCT). I will introduce a bulk boundary layer model that includes prognostic cloud fraction. I will first use it to explore spatial SCT in climatology and compare it against satellite observations across the North East Pacific. Finally, I will use it to study SCT under extreme CO2 forcing and highlight key mechanisms governing stratocumulus breakup and compare results with large-eddy simulations.