Differentiating (historic) responsibilities for climate change

Following the conclusion of the official work of the Ad Hoc Group for the Modelling and Assessment of Contributions to Climate Change (MATCH), this article considers the politically more sensitive aspect of the Brazilian proposal, namely the issue of differentiating (historic) responsibility for, and not merely (causal) contribution to climate change. Its aim is (1) to highlight the fact that, while related, the two issues ('contribution to' and 'responsibility for') are fundamentally different and should not be confused, and (2) to propose a methodology for calculating shares of responsibility as opposed to the shares in causal contribution arrived at through the MATCH results. Two conceptions of responsibility ('strict' or 'limited') are applied in order to operationalize the notion of 'respective capabilities' given in Article 3.1 of the UNFCCC. The key message resulting from the calculations is that causal contribution-while an important indicator of (environmental) relevance to the problem-must not be confused with the moral responsibility for it. The rather large difference between the responsibilities at the two extremes of the scale under both conceptions gives pause for thought as to what sorts of burdens can justly be demanded in any application of the UNFCCC <italic>principle of common but differentiated responsibilities</italic>, whether in the context of the Brazilian proposal or beyond.