Contemporary debates about climate security should take seriously the historical antecedents in discussions of the role of climate on human civilizations. The revival of geopolitical rivalries draws on some of this earlier literature, but now the crucial point about climate is that policies on fossil fuels determine the future trajectory of climate and hence the hazards and difficulties that policies of climate security must address. The complexities of both responding to climate disruptions and trying to decarbonize energy systems are immense, but both of these need to be tackled urgently in the new Anthropocene circumstances of a climate-disrupted world.