Yadvinder Malhi, Director of the Oxford Centre ofr Tropical Forests, gives a talk for the Oxford Martin School. We live in a new epoch, the Anthropocene, the Age of Us, of which climate change is just one aspect. The defining feature of this age is that sum of human activity (how many we are and what we are doing) has become large compared to the natural processes of the biosphere. The atmospheric waste products of our activity being the main driver of climate change. How can we measure how “large” we are, and how has our impact on the planet varied throughout human history?