Scientific evidence suggests that to have a 75 per cent chance of limiting warming in 2100 to 2°C above the pre-industrial level, the cumulative emissions of CO2 over the period 2010–50 should be capped at 657.1 Gt. The objective of this article is to examine the distribution of such an emission budget by applying different ethical perspectives. In particular, the article first analyses the paths for sharing the emission budget, that is, the major families of distributive patterns that vindicate a number of elementary principles and criteria of distribution. Subsequently, it presents and discusses the shares of the emission budget attributed to states, regions and groupings of states according to the paths investigated and it draws some reflections on the implications of such shares for the ethics of mitigation. Finally, it advances some lessons for international climate policy.