What Role for Short-Lived Climate Pollutants in Mitigation Policy?

Parallel strategies must focus on long- and short-lived pollutants, but not at the cost of reducing pressure for action on CO2. Short-lived climate pollutants (SLCPs) include methane (CH4), black carbon (BC), tropospheric ozone, and hydrofluorocarbons (HFCs). They are important contributors to anthropogenic climate change, responsible for as much as one-third of the current total greenhouse forcing (1). An emerging strategy, which we refer to as hybrid climate mitigation (HCM), emphasizes reducing SLCPs in parallel with long-lived carbon dioxide (CO2) so as to achieve climate goals, as well as health and food security benefits, associated with some of the SLCPs. Proponents of HCM argue that we should focus substantial effort on reducing SLCPs now, as we wait for sufficient political will to reduce CO2 emissions (2–4). But others (5) worry that any strategy involving SLCPs risks delaying efforts to reduce CO2, the main greenhouse gas most important for long-term warming if emissions continue as projected.