New working paper on the implications of alternative warming metrics for national climate targets here (pdf).
Commonly-used greenhouse gas (GHG) accounting metrics do not correctly compare the relative warming impacts of short-lived gases, like methane, and long-lived gases, like carbon dioxide (CO2). A new metric which corrects this shortcoming, GWP* (GWP-star), has been the subject of recent debate in the literature and has raised interest in policymakers. However, it has to date not been demonstrated for application to national GHG target-setting. Here we explore the implications of using GWP* in Ireland, which is the fourth highest per-capita emitter of agricultural methane globally and to date a “climate laggard”. The government plans an acceleration in GHG mitigation efforts, setting the target of halving GHGs within the next decade, while also increasing agricultural outputs, particularly in dairy and beef production, while seeking to acknowledge the distinctive warming characteristics of biogenic methane. We examine the feasibility and consistency of these targets under GWP*. We find that with rising methane emissions, CO2 emissions would need to fall to zero by 2030 to offset the warming impact under GWP*. Furthermore, the incumbent metric under-represents the powerful mitigation lever that reducing methane emissions presents, leading to sub-optimal mitigation pathways. Finally, the mitigation pathways required for CO2 under the incumbent and newly proposed metric are dramatically different, therefore scientific and global policy consensus is needed on GWP* before it can be practically applied at a national level.