GWP*is a model, not a metric

Abstract To aggregate different greenhouse gases, the UNFCCC common reporting formats, IPCC inventory guidelines, and Paris Agreement rulebook use an emission metric that has been around for more than 30 years: Global Warming Potential (IPCC, 1990). A ‘metric’ establishes ‘equivalence’ between amount of CO2 emissions other gases (such as CH4), which can be used to design cost-effective mitigation strategies (Fuglestvedt et al., 2003). As with many established concepts, there no shortage critical views on GWPs (Denison 2019; Plattner 2009;Shine, 2009). More recently, a method relates rate changes short-lived like methane suggested, referred GWP* (Smith 2012;Allen 2016;Allen 2018;Cain 2019;Smith 2021). This usefully approximate temperature implications time series. Rather mistakenly, though, it suggested replace widely GWPs. The most recent WG1 report 2021) presents GWP both metrics in underlying Chapter, although Summary Policymakers instead refers related methods “approaches”. Here, we examine how falls short key criteria useful applied real-world actions. We show exhibit wrong sign terms climate effects single year emissions, based feature variability would undermine stability any legal framework.