evidence: Some people mistakenly believe water vapour is a driver of Earth’s current warming. But as I explain below, water vapour is part of Earth’s hydrological cycle and plays an important role in the natural greenhouse effect. Its rise is a consequence of the atmospheric warming caused by our emissions arising especially from burning fossil fuels. [...] Water vapour is a powerful greenhouse gas. Since the 1970s, its rise likely increased global heating by an amount comparable to that from rising carbon dioxide. We are now seeing the consequences. In many ways, water vapour is the most important greenhouse gas as it makes Earth habitable. But human-induced climate change is primarily caused by increases in the long-lived greenhouse gases carbon dioxide, nitrous oxide, methane and chlorofluorocarbons (CFCs).