GHG accounting needs two metrics: stabilisation temperature and damage

This paper aims to develop and resolve a tension between two motivations for GHG accounting. On the one hand, we want to measure and ultimately reduce our emissions because climate change causes damage, as spelled out in the IPCC's Reasons for Concern framework. On the other hand, international agreements (such as the Paris Agreement) propose to limit warming to a particular level, and we use GHG accounting to measure our progress towards net zero goals set with these limits in mind. We show that these two motivations impose incompatible constraints on our choice of GHG accounting methods and metrics. We then develop a novel dual ledger approach, which incorporates two different metrics—one focused on stabilisation temperature and the other on damage. We argue that progress toward net zero goals should be measured using a metric focused on stabilisation temperature, but that too narrow a focus on stabilisation temperature will lead us to miss other opportunities to reduce climate damage. Since it is important to make use of all the ways we have to reduce damage, we suggest that decision makers also need metrics focused on damage.