The State Dependency of Climate Sensitivity and Cloud Responses to CO2 Doubling

Abstract

Cloud feedbacks are a large source of uncertainty in paleoclimate studies and in the constraint of climate sensitivity, and it is thought that climate sensitivity depends on climate state because of these feedbacks. Here we evaluate the state dependence of both climate sensitivity and cloud responses to CO2 doubling for a palate of climates with varying solar luminosity and CO2 concentrations, yet near-equivalent global mean surface temperatures. We find that cloud responses to CO2 doubling and climate sensitivity are largely dependent on the magnitude of radiative forcing from doubling CO2 alone, and are therefore independent of climate state. We also determine that the most important responses in clouds occur in the mid-latitude storm tracks, owing to inhibited baroclinic activity as a consequence of a more equable climate under higher CO2 concentrations.