In this talk Professor Tim Palmer CBE, Co-Director of the Programme on Modelling and Predicting Climate, gives a talk for the Oxford Martin School. Tim Palmer will address three related questions. Firstly, what are the physical reasons why predictions of climate change are necessarily uncertain? Secondly, how can we communicate this uncertainty in a simple but rigorous way to those policy makers for whom uncertainty quantification may seem an unnecessary complication. Finally, what is needed to reduce uncertainty about future climate change? For the latter, I will argue that the sort of inspiration and ambition that led to the Large Hadron Collider is now needed for the development of climate-change science.