As UN climate talks in Marrakesh enter their final few days, leaders have a lot on their minds. Political support for a green agenda will wane in America next year. Barack Obama has led international environmental-protection efforts; Donald Trump plans to oppose them. The switch comes just as a new report from the World Meteorological Organisation, a UN body, confirms that this year is virtually certain to be the hottest ever recorded—stealing the title from 2015. This will mean that 16 of the 17 most sweltering years ever tracked have occurred since the millennium.