Mitigation of short-lived climate pollutants slows sea-level rise

Under present growth rates of greenhouse gas and black carbon aerosol emissions, global mean temperatures can warm by as much as 2 C from pre-industrial temperatures by about 20501,2. Mitigation of the four short-lived climate pollutants (SLCPs), methane, tropospheric ozone, hydrofluorocarbons and black carbon, has been shown to reduce the warming trend by about 50% (refs 1,2) by 2050. Here we focus on the potential impact of this SLCP mitigation on global sea-level rise (SLR). The temperature projections under various SLCP scenarios simulated by an energy-balance climate model1 are integrated with a semi-empirical SLR model3, derived from past trends in temperatures and SLR, to simulate future trends in SLR. A coupled ocean–atmosphere climate model4 is also used to estimate SLR trends due to just the ocean thermal expansion. Our results show that SLCP mitigation can have significant effects on SLR. It can decrease the SLR rate by 24–50% and reduce the cumulative SLR by 22–42% by 2100. If the SLCP mitigation is delayed by 25 years, the warming from pre-industrial temperature exceeds 2 C by 2050 and the impact of mitigation actions on SLR is reduced by about a third. Anthropogenic greenhouse gases (GHGs), including CO2, have added 3Wm−2 forcing from the pre-industrial times to the year 2005 (ref. 5). This extra forcing will not only cause a large warming of our planet6,7, but will also contribute to SLR (refs 8,9). Even if the world tries to limit global warming through significant reduction of the CO2 emissions10, for example, a reduction by about 50% by 2050 and 80% by 2075, the CO2 concentrations will still peak at 440 ppm later this century, bringing the total GHG forcing to 4Wm−2 (ref. 7). The committed equilibrium warming associated with this forcing, if fully realized without the cooling effect of anthropogenic aerosols, would be about 3.2 C (2–4.8 C; ref. 7) and could potentially lead to significant changes in Earth’s cryosphere and SLR. Faced with such possibilities, numerous studies1,2,11,12 have focused on non-CO2 climate warming agents, particularly the so-called SLCPs, which contribute as much as 40% to radiative forcing1,5. As the lifetimes of these SLCPs are in the range of a week (black carbon), to amonth (ozone), to a decade (methane and hydrofluorocarbons (HFCs)), an emission reduction of these SLCPs would lead to a reduction in their atmospheric concentrations and their radiative forcing within weeks to a few decades. Recent studies1,2,13 have estimated that the mid-century warming could be reduced by about 0.6 C, leading to a delayed onset of the 2 C warming by several decades. Model studies show that even under aggressive mitigation of GHGs, sea level will continue to rise for centuries owing to the oceanic inertia14. The objective of this