There are at least two kinds of global injustice with regard to global climate change. One is unfair effect of climate change, which adversely affects the more vulnerable to the change, and which is an outcome of environment-threatening footprint of the global better off. The other is unfair distribution of climate burden. When climate change had an unfair and adverse effect, actions had to be taken so urgently that those who had realised the seriousness of climate change set up formal or informal efforts to tackle climate change and have been sharing the climate burden of mitigating and adapting to the change. The fact that only some, not all, people who are responsible for climate change share the climate burden produces global injustice, which deepens when some of those who are not necessarily responsible for the change restrict their right to clean development by reducing GHG emissions. Being concerned with global injustice of unfair distribution of climate burden, this paper asks the following question: who should join the efforts to share the climate burden? To this question of climate obligation, which should be distinguished from climate responsibility and climate justice, I suggest the principle of fairness as a theory of climate obligation by exploring moral foundations of the principle and the basic idea of identifying the obligation bearers in terms of ''retrospective beneficiaries''. The idea of ''retrospective beneficiaries'' is discussed to be advantageous in overcoming typical problems we face in dealing with the distribution of climate burden such as the ignorance problem, the non-existence problem, and the non-identity problem.
