Physical Society Colloquium

Climate Models and Climate Sensitivity

Paul Kushner

Department of Physics
University of Toronto

The climate sensitivity parameter measures how much the Earth surface warms for a doubling of atmospheric carbon dioxide concentration, under conditions of radiative equilibrium. It is arguably the most important number to pin down in order to predict the future of Earth's climate under global warming. In this colloquium I will aim to build physical intuition about climate sensitivity, and the climate feedbacks that contribute to it, using simple models. This intuition will help us interpret the relative importance and uncertainty of the feedbacks in comprehensive climate models. I will highlight the relatively simple snow albedo feedback, which is surprisingly uncertain in climate models. This uncertainty has local consequences for North American summertime climate and remote consequences, through long-range spatial correlations, for the atmosphere-ocean circulation of the Northern Hemisphere.