Department Lecture - Colin Goldblatt (Victoria)

Colin Goldblatt (Victoria)
Wednesday, April 21, 2021 - 4:00pm to 5:00pm
Virtual via Zoom

Earth's long term climate stabilized by clouds

The Sun was dimmer earlier in Earth history, but glaciation was rare in the Precambrian: this is the ``Faint Young Sun Problem''. Most solutions rely on changes to the chemical composition of the atmosphere to compensate via a stronger greenhouse effect, whilst physical feedbacks have received less attention. 

We perform Global Climate Model experiments, using two versions of the Community Atmosphere Model, in which a reduced solar constant is offset by higher \ce{CO2}.  Model runs corresponding to past climate show a substantial decrease in low clouds and hence planetary albedo compared to present, which contributes 40\% of the required forcing to offset the faint Sun. Through time, the climatically important stratocumulus decks have grown in response to a brightening Sun and decreasing greenhouse effect, driven by stronger cloud-top radiative cooling (which drives low-cloud formation) and a stronger inversion (which sustains clouds against dry air entrainment from above). 

We find that systematic changes to low clouds have had a major role in stabilizing climate through Earth's history, which demonstrates the importance of physical feedbacks on long-term climate stabilization, and a smaller role for geochemical feedbacks. 

About this Series:

Weekly talks given by leading thinkers in the areas of geology, geophysics, geobiology, geochemistry, atmospheric science, oceanography, climatology, and planetary science. Lectures take place on Wednesdays from 4pm EST unless otherwise noted. For more information please contact: Maggie