Title: Constraining Earth’s Climate Sensitivity: From Process-Level Studies to System-Level Analysis
Abstract: Developing better constraints on Earth's equilibrum climate sensitivity (ECS) -- the equilibrated response of global-mean surface temperature in response to a doubling of CO2 concentrations -- is one of the central goals of climate science. However, despite decades of work, large uncertainties in Earth's ECS persist, with a typical uncertainty range being 2-4.5C. In this presentation I propose two paths forward for narrowing this uncertainty. First, I show that a combination of high resolution modelling work and basic physics can be used to better understand the key processes responsible for this uncertainty, focusing specifically on precipitation efficiency. Precipitation efficiency exerts a strong control on climate models' sensitivity, and I demonstrate that it increases with warming, primarily because clouds become denser in a warmer world. Second, I take a system-level view of the climate system in order to present ideas about how we can leverage model diversity to better constrain ECS. In particular, I find that there is a strong relationship between climate models' internal variability and their climate sensitivity. I conclude by discussing future applications of these two approaches, including thoughts on how we can untangle the interactions between cloud processes and the large-scale tropical circulation, and the benefits of taking a "frequency-perspective" of the climate system.