Non-CO2 Greenhouse Gas Mitigation in the 21st Century

It is important to understand how the reduction of other greenhouse gases than CO2 can reinforce existing climate policy. This particularly includes methane (CH4), nitrous oxide (N2O), fluorinated gases (F-gases) and various aerosols (micro particles). Together, these comprise a bit more than a quarter of the total greenhouse gas emissions. Prior studies showed that policy strategies aimed at all greenhouse gases lead to the lowest policy costs and the highest climate benefits. This study shows that many possible mitigation measures exist to reduce non-CO2 GHGs at relatively low costs. Moreover, a stronger focus on non-CO2 species with a short atmospheric lifetime could lead to advantageous climate effects in the short term. However, these benefits are temporary when reaching ambitious climate goals (e.g. as the Paris goals), since short-lived non-CO2 species are expected to be reduced in any such scenario. Timely reduction of non-CO2 emission does offer permanent health benefits because of improved air quality. In that respect, combining climate and air quality policy is most effective (with an estimated 11 million avoided deaths worldwide between now and 2030). Reducing soot (BC) emissions is a very cost-effective measure in terms of health. It is a less suitable climate policy measure since it leads to small or even negative climate benefits. Lastly, this research examines the consequences of the use of GWP-metrics in climate policy (this is used to compare greenhouse gases based on their climate impacts). The use of the 100-year GWP (current policy) is shown to be effective because it allows for sufficient reduction of non-CO2 emissions.