In 2008, Mark Lynas published Six Degrees, a book which charts the changes our planet will go through as, degree by degree, it warms over the coming decades. It imagined the likely future, of rivers ten times the size of the Amazon gushing off the ice sheet into the north Atlantic, vast pumping systems keeping the water out of most of Holland, devastation in the Nile delta, and Pakistan crippled by drought brought on by disappearing Himalayan glaciers. The scenarios imagined in Six Degrees might to some sound sensationalist, but on 27th August 2017, Hurricane Harvey devastated the Houston metropolitan area with unprecedented flooding. Lynas remembered that in Six Degrees, Houston was swamped in chapter 3, which described three degrees of global warming. Now it was happening for real, on the evening news - but too soon, two chapters and two degrees too soon. This new book completely redrafts our possible future from the one Lynas laid out in 2008. Back then, looking forward was seeing through a glass darkly. Today, a decade's-worth of additional cutting-edge science has shed much light and the news is terrifying. In a world where America has withdrawn from the Paris Climate agreement and this urgent issue seems to have disappeared from the political agenda in Britain, Six Degrees: the 2020 Report is a sobering and vital call to arms.