Why does our planet have ice caps at the poles? What conditions are necessary for ice caps to form and to be maintained? Earth has not always had ice at the poles - in fact a warm ice-free earth may be its common natural state. Professor Mills and his research group have recently proposed that our planet’s present state, with ice at the poles, may be a fortunate combination of circumstances. In this talk he will explain why the temperature of planets changes over time, how present climate change compares to previous variations, and what the long-term future might look like.