Understanding and preparing for the impacts of anthropogenic climate change are some of the most urgent scientific challenges of our time. Remarkable progress has been made in the last half century in our ability to simulate Earth’s climate using state-of-the-art models and project future climate changes under specific emission scenarios. However, simulation does not equal understanding. Confidence in climate model projections requires an understanding of the mechanisms underlying the modeled responses, which helps to ensure the responses are not the result of structural and parameter uncertainty. In this talk I will discuss progress toward closing the gap between simulating and understanding climate change. I will present examples from the pioneering work of Nobel Prize winning scientist Dr. Syukuro Manabe and from our more recent work on the response of the atmospheric circulation to climate change.