Inevitably, the concept of comparability is subjective, so can mean quite different things to different people. This presents a challenge to reaching agreements in a complex multilateral negotiation. Moreover, because there is an array of possible indicators and metrics of comparability, analytical work that tries to shed light on this subject can, itself, be confusing and add to the problem. However, there are a number of important basic points that need to be understood as one interprets different indicators. For example, initial intuitions when comparing proposed targets for two countries and judging whether they are comparable (or fair or tougher or easier to achieve) can often be quite misplaced. The paper uses a number of simple country A, country B-type thought experiments and examples of country data for a range of indicators and metrics in an attempt to provide guidance for how one might consider comparability and be aware of the traps.

Keywords: climate change policy; comparability; economic costs; emission targets; indicators; metrics