Physical Society Colloquium

How the physics of clouds affects Snowball Earth and the runaway greenhouse

Dorian Abbot

Geophysical Sciences
University of Chicago

The physics of clouds has a huge impact on the climate of a planet. On Earth, if the clouds forgot that part of their job is to reflect solar energy, we would suffer a runaway greenhouse and end up like Venus. If instead clouds forgot that part of their job is to absorb infrared radiation emitted by the surface and contribute to the greenhouse effect, we would enter global glaciation. Although they are very important for climate, clouds are very difficult to model and represent the largest source of uncertainty in climate modeling. This results both from insufficient resolution to resolve cloud-scale circulation and incomplete understanding of cloud microphysics. Cloud simulation is therefore the main reason our current models aren't better, and is a critical area to attack if we want to create generalized models that could be easily applied to different planets (the clouds might not be water clouds in this case). In this talk I will discuss how we can use the models we have to gain insight into cloud behavior in climates vastly different from modern Earth. The two examples I will focus on are the Snowball Earth episodes that occurred 600-800 million years ago and the runaway greenhouse of tidally locked super-Earths at the inner edge of the habitable zone of M-stars.