Evidence provided by the scientific community strongly suggests that limits should be placed on greenhouse gas emissions. This means that states, firms, and individuals will have to face potentially serious burdens if they are to implement these limits. Which principles of justice should guide a global regime aimed at reducing greenhouse gas emissions originating from human activities, and most notably from CO2emissions? This is both a crucial and difficult question. Admittedly, perhaps this question is too ambitious, given the uncertainties and (...) complexities characterizing the issue of climate change. Yet, rather than listing them all at this stage, let us address the question in a straightforward manner, introducing some of these complexities as the need arises. (shrink)