Towards a Methodology of Specifying States’ Mitigation Obligations in line with the Equity Principle and Best Available Science: Assessing the Role of Integrated Assessment Models

What level of greenhouse gas emissions reduction is an individual state required to achieve for it to live up to its legal obligations? This question is looming over increasingly more courtrooms around the world. A critical sub-question in this context concerns the temperature pathway that is to be pursued and at what likelihood level. While this is a paradigm question of equity, scientific disciplines such as climate econometrics are the law’s key ally in gaining information about the assumptions, selection choices and the robustness of anti-bias measures in relevant pathway models. Of prime importance in this context are recent studies, inter alia, by the Potsdam Institute for Climate Impact Research which have revised Nordhaus’ famous DICE Model and arrived at a significantly lower economically optimal warming outcome. This paper investigates how these findings align with the best available science principle and the equity principle enshrined in the Paris Agreement.