Abstract:

The “Pattern effect” refers to the dependence of Climate sensitivity, i.e. the amount of global-mean warming per doubling of atmospheric CO2, to regional warming patterns. For example, a pattern with amplified warming in regions of deep convection – such as has been observed in recent decades – will lead to more outgoing radiation, more negative radiative feedbacks, and ultimately a lower climate sensitivity. Conversely, a pattern with amplified warming in the equatorial Pacific cold tongue – such as models simulate in the future – would lead to higher climate sensitivity.

The magnitude of the pattern effect has not yet been constrained by observations, and GCMs show substantial uncertainty. This uncertainty is so substantial that a recent assessment concluded that the observational record of Earth’s energy budget cannot constrain the upper bound of ECS. The lack of observational constraints on the pattern effect presents one of the largest roadblocks to improved projections of future warming.

In this talk I will discuss recent advances in understanding the origin of the pattern effect; the ability of climate models to simulate it; its impact on both historical and future energy budgets; as well as prospects for better constraining it.