Climate Physics: from Lava Planets to Global Warming

Global warming has become a matter of increasing concern in recent decades. In parallel, astronomers have discovered thousands of exoplanets with varied atmospheres, some of which could harbour life. Despite tremendous public and academic interest in both topics, it is not widely appreciated that the same 19th century atmospheric physics governing anthropogenic climate change also governs planetary habitability. Even lava planets, arguably the strangest extrasolar worlds yet discovered, can be understood using the same undergraduate physics. In this talk, I will give examples of neat bits of climate physics that operate on exotic worlds, but which have analogs right here on Earth: molecular dissociation on ultra hot Jupiters, rock vapour winds on lava planets, salt clouds on sub-Neptunes, and hemispheric ice sheets on temperate rocky planets. The complex interplay of such phenomena, however, makes it challenging to predict the global climate of a planet: although near-term forecasts of global warming are increasingly precise, we struggle to predict the Earth’s climate in the distant future or distant past, let alone the climates on distant worlds. Hence, we need empirical measurements. Observing hundreds of exoplanets with telescopes is a perfect complement to detailed atmospheric measurements in the Solar System. Extrasolar worlds therefore offer a path to uncovering some of the trends and underlying patterns in planetary climate.

Nicolas Cowan is an Associate Professor of Physics and of Earth & Planetary Sciences at McGill University. He is the Canadian PI of the Ariel mission and holds a Canada Research Chair in Planetary Climate and an Arthur B. McDonald Fellowship. Cowan uses telescopes and mathematical models to study the climates of exoplanets. He has pioneered remote sensing techniques to map the atmospheres and surfaces of these distant planets. In parallel, he combines geochemistry, geophysics, and climate physics to understand planetary habitability. These observational and theoretical lines of research are converging on the study of habitable, and possibly inhabited, planets orbiting nearby stars. Cowan was born in Córdoba, Argentina, but grew up in Québec. As an undergraduate, Cowan studied Physics at McGill and spent a summer cycling across Canada. He moved to Seattle to enjoy the outdoors and pursue a PhD in Astronomy at the University of Washington… he also met his wife and became a father! After stints as a postdoctoral fellow at Northwestern University and professor at Amherst College, he returned to Montréal, and McGill, in 2015. He was granted tenure in 2019. In his spare time, Nic finds, cleans, and climbs rocks with his son.