Earth system science studies the planet as an array of interacting “spheres” that represent components of a single system. Antarctica dominates the cryosphere—the frozen parts of the planet consisting of ice and snow—and thus has a major influence on the overall functioning of the Earth system. Joining the podcast is Prof. Will Steffen, a world leading Earth system scientist and public intellectual who has long operated at the interface of science and policy, including as chairman of the Antarctic Science Advisory Committee in Australia. He is also closely associated with concepts such as the Anthropocene, the Great Acceleration, and the Planetary Boundaries framework. In addition to explaining the centrality of Antarctica in the Earth system, Prof. Steffen discusses the idea of “Hothouse Earth”, evoked in an article published in Proceedings of the National Academy of Sciences USA, which received a great deal of international media attention.