It is now well established that action to avoid dangerous climate change must take place according to the principles of ‘responsibility and capability’, and the UN’s Framework Convention on Climate Change (UNFCCC) subscribes to this view. Morally and in political terms developed countries should lead global mitigation by making significant domestic emissions reductions. But in a world of limited finance, reductions arguably be undertaken wherever they can be made for the lowest cost. Since emissions reductions in developed countries are insufficient to resolve the climate problem and are often more expensive to make than in developing countries, the principles of responsibility and capability might more productively be applied to the financing of global reductions: this would mean that the higher a country’s level of responsibility and capability, the greater its share of global climate finance. Technically, developed countries are already obliged to transfer finance to developing countries, under the UNFCCC, which states that ‘agreed full incremental’ costs in developing countries should be met by finance and technology from developed countries (Article 4.3).