3.2.3.2 Short-lived climate pollutants

Outside of the UNFCCC, intergovernmental efforts to manage SLCPs are an important dimension of global climate mitigation efforts, especially because they can have short-term benefits. SLCPs, including methane, tropospheric ozone and black carbon, can have disproportionate regional impacts on particular tipping systems. For example, black carbon deposition is particularly effective at melting snow and ice. Hence the mitigation of specific SLCPs can have a disproportionate benefit in preventing specific ESTPs. Mitigating SLCPs can also contribute to limiting global warming pressure on most ESTPs. According to Szopa et al., 2021, across the Shared Socioeconomic Pathway climate scenarios, “the collective reduction of methane, ozone precursors, and hydrofluorocarbons (HFCs) can make a difference of 0.2°C with a very likely range of [0.1 to 0.4]°C in 2040 and 0.8°C with a very likely range of [0.5 to 1.3]°C at the end of the 21st Century”.

On global and regional levels, several institutions address SLCPs. A focal arena is the Climate and Clean Air Coalition (CCAC), a state-led transnational partnership established under UNEP in 2011, which has become a key actor in global policy advocacy and knowledge exchange on SLCPs. In addition, other international fora have made concrete steps to mitigate specific SLCP s. For instance, in the Northern hemisphere, black carbon emissions are integrated into the targets to reduce particulate matter pollution under the Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone. In 2015, the Arctic Council agreed on the Framework for Action on Enhanced Black Carbon and Methane Emission Reductions. In 2016, the Montreal Protocol on Substances that Deplete the Ozone Layer was complemented with the Kigali Amendment on the phase-out of HFC s. Further, under the Paris Agreement, some countries have included SLCP mitigation targets or policies in their NDCs, and various global cooperation efforts, including the Global Methane Pledge (Sun et al., 2021), have been launched to address methane emissions. Elevated action on SLCPs is essential because the effects are felt more rapidly than those of CO₂ abatement. 

Other short-lived pollutants, such as sulphates and particulates, can have cooling effects, and their elimination would increase warming (also on short time scales) (IPCC, 2018). For example, reducing sulphate emissions from shipping for health reasons has a climate trade-off (Sofiev et al., 2018). While this creates challenges for policy design, it cannot justify the intentional release of sulphates or other particulates (even sea salt) in efforts to compensate for warming effects through deliberate geoengineering. In addition to the ethical differences between deliberate interventions and unexpected side effects (Morrow, 2014), we discuss the practical and political uncertainties of geoengineering below.