Few would have predicted at the start of 2006 that a slide show lecture on the science of climate change would become a cinema blockbuster.

Al Gore’s film An Inconvenient Truth, in which the former vice president of the US explains the scientific evidence for climate change, quickly became the third highest grossing documentary of all time, behind Fahrenheit 911 and the March of the Penguins. It was a measure of how far the issue of global warming had invaded public consciousness.