Benjamin A. Stephens, UT-Austin

"Investigating a Tropical Atmospheric Trigger for Abrupt Climate Change"

Abstract: Abrupt climate change is known to have occurred in the distant past and may be a possibility in the future. Dominant theories of abrupt change have located the trigger for such change in the North Atlantic ocean, but some evidence suggests that the tropical atmosphere may play an important role, and advisory bodies have recommended further investigation. Using both single-column and general circulation models, both of which partition rainfall between parameterized convection (giving “convective” rain) and cloud microphysics (giving “large-scale” rain), I present findings indicating that the tropical atmosphere could indeed act as a trigger for abrupt change. I first show that different ratios of tropical rainfall partitioning in general circulation models are associated with very different types of large-scale atmospheric circulation, affecting also the response to CO2 forcing. Secondly, I demonstrate that abrupt changes in rainfall partitioning can be induced in a single-column model using physics similar to that of a global model.