Two Theories of Responsibility for Past Emissions of Carbon Dioxide

David A. Weisbach
Michelle Hayner

We consider the claim that individuals or nations who emitted carbon dioxide in the past should be held responsible for those emissions. We examine two theories of responsibility for past emissions that are often conflated: (i) that emissions in the past by individuals in one nation have wrongfully harmed, or will wrongfully harm, individuals in other nations, and (ii) that individuals or nations who emitted in the past used more than their fair share of the limited ability of the atmosphere to absorb carbon dioxide. These two theories have distinct philosophical bases. A theory of responsibility for harm caused to others is based on conventional theories of corrective justice or efficiency, such as the Polluter Pays Principal. The difficulty with these theories is measuring relative harm. There are few estimates of the harms from the 1°C of temperature change experienced so far from past emissions because it is difficult to distinguish the resulting harms from normal variations in the climate. The second theory, a theory of responsibility for excess use, would require a level of compensation several orders of magnitude larger than a theory based on harm. Responsibility for excess use, however, is more difficult to ground in widely-accepted theories of justice. It is, we argue, a theory of equal ownership of all limited resources which few theories of justice would support.