Earlier this year, a report from climatologists around the world made it clear that climate change is happening now and that it is almost entirely a result of human behaviour. This is not a controversial conclusion and it is not hard to explain how the report’s authors arrived at it. First, independent observations — from the ocean to the atmosphere, from poles to tropics — all show rapid and significant warming over the past century, particularly over the past few decades. Human activity has simultaneously caused a 50 per cent increase in carbon dioxide concentrations, a more than doubling of methane concentrations, and the appearance of multiple synthetic gases, all of which are potent greenhouse substances. Who is responsible? Over the past 170 years, carbon dioxide emissions have been led by the United States, followed by China, Russia, and the UK in eighth place.