Soot and Short-Lived Pollutants Provide Political Opportunity David G

opinion & comment

COMMENTARY: Soot and short-lived pollutants provide political opportunity David G. Victor, Durwood Zaelke and Veerabhadran Ramanathan Cutting levels of soot and other short-lived pollutants delivers tangible benefits and helps governments to build confidence that collective action on climate change is feasible. After the Paris climate meeting this December, actually reducing these pollutants will be essential to the credibility of the diplomatic process.

ver the past two decades there cut emissions of SLCPs, governments could has been an increasing amount of go a long way towards rebuilding credibility Oscientific research showing that a in the broader global effort to manage climate reduction in black carbon (BC, also known BC change — an effort that must include CO2 and as soot), tropospheric ozone, methane and 16% other long-lived gases as well. CO2 hydrofluorocarbons (HFCs) can slow near- 29% Policy confusion term climate change significantly more than HFCs 1–6 previously thought . All of these compounds 13% Oddly, over the past few years some are short-lived climate pollutants (SLCPs) that papers and policy advocacy from climate persist in the atmosphere for days to a decade scientists may have inadvertently confused

and a half — as opposed to CO2 and other policymakers about the huge opportunity CH4 long-lived gases with atmospheric lifetimes of (including O3) in SLCPs. Even those studies highlighting hundreds to thousands of years, which have 42% the important role that SLCPs can play in historically dominated scientific and political slowing climate change in the near-term attention on climate change. make the obvious but important point The fresh scientific insights about SLCPs that SLCPs alone can’t stop warming are opening up a new political front in the forever1–6,9. Other studies are rooted in a battle to mitigate climate change. With Figure 1 | Avoided sea-level rise at 2100 due curious political logic that imagines that available technologies, it is possible to cut to aggressive mitigation of long-lived CO2 and countries can’t focus on more than one thing these pollutants drastically; reductions of short-lived climate pollutants (SLCPs). Such at a time — and thus efforts to cut SLCPs 30% for methane, 75% for black carbon, and aggressive actions can reduce the rise in sea levels might somehow make it harder to address

nearly 100% for the most potent HFCs are by 35 cm (uncertainty range is 17–70 cm) from long-lived pollutants such as CO2 (ref. 10). achievable. This would avoid up to 0.6 °C of the projected sea-level rise of 112 cm (49–210 cm) Still others are based on the questionable

warming by mid-century, while also slowing under a business-as-usual scenario for emissions reasoning that reduction in CO2 emissions the rise in sea levels (Fig. 1), the melting (Representative Concentration Pathway (RCP) from uptake of renewable technologies of glaciers, and the retreat of the Arctic ice 6.0). The pie chart shows percentage contribution will automatically result in reductions in cap1–6. These are not hypothetical cuts; in just of each pollutant. Mitigation of the SLCP methane emissions of SLCPs11, so we need not bother two decades, California, for example, has would lead to reductions in tropospheric ozone, with separate efforts. cut its emissions of black carbon and several another SLCP, and hence the pie chart includes While shifting to clean energy will of 7 pollutants that produce ozone by half . both. As a long-lived pollutant, CO2 plays a course sweep up some air pollution that Carbon dioxide causes long-term warming substantial role (blue section), but reduction in otherwise would have been emitted, the of the planet as a whole — a highly diffused SLCPs (shown in darker colours) would lead to current investment in energy infrastructures problem that most countries don’t yet take a larger degree of avoided sea level. (Under a has locked high emissions into place for seriously enough, in part because the main more intensive business-as-usual RCP8.5 level, some time to come12. In fact, the better benefits of action arise decades after today’s reductions in CO2 would increase the share of CO2 political logic runs in the opposite direction: politicians have left office. SLCPs, on the other mitigation to 50%). All of the simulated values cutting black carbon and tropospheric ozone hand, will reduce the rate of warming within shown in the pie chart are taken from ref. 17. pollution, which is what many countries are a decade of implementing mitigation actions. most focused on achieving, will also lead to

Moreover, an even more compelling case for significant CO2 mitigation. reducing these pollutants is their huge impact pollutants, potential action on SLCPs is better As a practical matter, very little that the on the local ravages of air pollution, which aligned with political realities — especially in scientific community does will alter the already kills seven million people every year8 the emerging countries whose participation is outcome of the Paris talks. But after Paris, the and degrades more than a hundred million vital for any global scheme to manage climate opportunities for action on soot and other tons of crops2,3. Compared with long-lived dangers. And by successfully acting now to SLCPs will be of paramount importance as

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© 2015 Macmillan Publishers Limited. All rights reserved opinion & comment diplomats grapple with the many topics that tangible reductions in climate stress and are review of INDCs and other policy pledges. the meeting won’t resolve — including the not merely new excuses for inaction. After Paris the questions will quickly reality that the efforts agreed in Paris, on their become: what has been achieved? what own, won’t come anywhere close to stopping Ending the downward spiral more is feasible? These questions need to warming at 2 °C or other widely discussed Fixing the global problem of climate be answered long before 2020 — when goals. Reductions in SLCPs, precisely because change requires effective international the Paris agreement is expected to take these pollutants are short-lived, can help cooperation. Making that a reality requires full effect — and technical input will be to rapidly slow the rate of warming, by as that the community of climate change essential. A robust system of assessment much as 50% by mid-century1,4. Both for scientists understands that credibility is the and peer review for pledges is needed — vulnerable developing countries and for pivotal challenge for international political a system that can learn from the success natural ecosystems, immediate efforts to slow action on climate change. International of the Montreal Protocol, where experts warming are essential yet unattainable with cooperation has few serious enforcement evaluate national programs in a fair mitigation strategies that focus only on CO2 mechanisms; agreements, such as the manner and root their analysis in a sober and other long-lived gases. accords taking shape in Paris, have an assessment of what is feasible16. impact only if national governments Third, the opportunities for action New vision and their citizens believe they align with on SLCPs will, in many countries, need The opportunity for science to help realign national interests and implement them funding. The World Bank needs to launch the politics of global warming arises because through national measures. Despite a planned (but not yet implemented) a new vision is emerging that recognizes overwhelming scientific evidence of climate financing mechanism that could cut that effective action must happen on many dangers, the credibility of international black carbon from cooking stoves and fronts and in many forums, not just the climate change negotiations has plummeted other sources while also expanding its United Nations Framework Convention after decades of inaction. Spiralling mechanism for financing cuts in methane on Climate Change (UNFCC)13. Several downwards, this inaction has led industries (www.pilotauctionfacility.org). In the of those fronts are ripe for action on to lose confidence that they should invest future, climate credits may even help SLCPs. Important other forums include in technologies to cut emissions. And this, finance some of these projects. The HFC the Montreal Protocol — a treaty designed in turn, has delayed advances in needed amendment under the Montreal Protocol and successfully relied upon over the past technologies and made political action to is also due to finish in 2015 — a process 30 years to address the depleting ozone cut warming gases even harder. Practical that will unlock funding from that treaty’s layer, while also producing significant near-term cuts in SLCPs can reverse the financial mechanism. The new funds climate benefits14, notably because the spiral — they can create fast, tangible that will be agreed on in Paris should chlorofluorocarbons it phased out were both and multiple benefits that are politically include specific mandates for action ozone depleters and strong warming gases15. attractive to the world’s biggest emitters. In on SLCPs. Diplomatic talks aimed at an agreement turn, that success can give those emitters As in many other areas of international on phasing down HFC production and more confidence to do more to tackle the diplomacy — such as the global talks consumption are far advanced. Other politically harder problem of CO2, which is on trade that are mired in more than a forums include the Climate and Clean Air essential for stopping warming in the long decade of gridlock — serious action on Coalition to Reduce Short-Lived Climate term. Efforts of many types will be needed, climate change has proved to be long, slow Pollutants (CCAC), a voluntary coalition with scientists and diplomats working and difficult. While near-term gains are of governments, non-governmental in tandem. achievable, they are most likely to occur organizations (NGOs) and business First, in the run-up to Paris, governments if they are decentralized and will work on associations developing practical plans to have made pledges to reduce emissions many different fronts, not just through a reduce black carbon from cooking stoves, through a process known as intended single treaty negotiation under the UN. brick kilns16, and diesel vehicles; it is also nationally determined contributions Success in these efforts requires working focusing on methane and HFCs. Bilateral (INDCs). From these pledges serious first on problems that are politically programs on climate change — such as collective action can emerge — once tractable and can build credibility. Action that between the US and China — also countries see what others will pledge, they, on SLCPs raises the odds that, this time, include a heavy focus on HFCs, soot and in turn, can adjust what they promise. SLCPs the world will develop the confidence to other SLCPs. Even unilateral action has are an ideal area for this upward ratcheting get serious on climate change. ❐ played a role — most notably by the EU and of effort because they have such strong California, where deep cuts in SLCPs are resonance with what countries already see as David G. Victor is in the School of Global Policy being implemented. in their national interest — such as cutting and Strategy, University of California at San This new approach lets countries — as local air pollution under their national Diego, 9500 Gilman #0519, La Jolla, California well as companies and NGOs — pursue many laws. The INDCs submitted so far don’t pay 92093-0519, USA and the Global Agenda Council strategies for mitigation, trying new ideas much attention to SLCPs or offer practical on Governance for Sustainable Development, and seeing what is technologically feasible information on the kinds of cuts in SLCPs World Economic Forum, 91-93 route de la Capite, and gets political traction, which has been the that are feasible, although Mexico’s INDC CH-1223 Cologny/Geneva, Switzerland. Durwood missing ingredient in most diplomatic efforts does include soot, Chile announced that Zaelke is at the Institute for Governance and to address climate change. It promises to be it would follow suit and China is notably Sustainable Development, 2300 Wisconsin Avenue, less brittle than relying just on the UNFCCC making major efforts to cut air pollution. It NW, Washington DC 20007, USA. Veerabhandran to deal with the reality that so many different will be essential in the after-Paris period to Ramanathan is at the Center for Clouds, Chemistry countries and issues cannot be glued together fill in this missing information and expand & Climate Scripps Institution of Oceanography, into a single, integrated global agreement. the pledges to cut SLCPs. University of California, San Diego, 9500 Gillman But success requires demonstrating that Second, the community of scientists Drive #0221, La Jolla, California 92093-0221, USA. decentralization and flexibility can produce and engineers can play a pivotal role in the e-mail: [email protected]; [email protected]

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References 7. Ramanathan, V. et al. Black Carbon and the Regional Climate of 12. Davis, S. J., Caldeira, K. & Matthews, H. D. Science 1. Ramanathan, V. & Xu, Y. Proc. Natl Acad. Sci. USA California (Report to California Air Resources Board, 2013). 329, 1330–1333 (2010). 107, 8055–8062 (2010). 8. Lim, S. S. et al. Lancet 380, 2224–2260 (2013). 13. Keohane, R. O. & Victor, D. G. Perspect. Polit. 9, 7–23 (2011). 2. Integrated Assessment of Black Carbon and Tropospheric Ozone: 9. Schmale, J., Shindell, D., von Schneidemesser, E., Chabay, I. 14. Velders, G. J. M., Andersen, S. O., Daniel, J. S., Fahey, D. W. & Summary For Decision Makers (UNEP and WMO, 2011). & Lawrence, M. Air pollution: Clean up our Skies. Nature McFarland, M. Proc. Natl Acad. Sci. USA 104, 4814–4819 (2007). 3. Shindell, D. T. et al. Nature Clim. Change 3, 567–570 (2013). News (19 November 2014); http://www.nature.com/news/ 15. Ramanathan, V. Science 190, 50–52 (1975). 4. Xu, Y., Zaelke, D., Velders, G. J. M. & Ramanathan, V. air-pollution-clean-up-our-skies-1.16352 16. Sabel, C. F. & Victor, D. G. Climatic Change (in the press). Atmos. Chem. Phys. 13, 6083–6089 (2013). 10. Pierrehumbert, R. T. Annu. Rev. Earth Planet. Sci. 17. Hu, A., Xu, Y., Tebaldi, C., Washington, W. M. & Ramanathan, V. 5. Jacobson, M. Z. S. J. Geophys. Res. 115, D14209–D14232 (2010). 42, 341–379 (2014). Nature Clim. Change 3, 1–5 (2013). 6. IPCC Climate Change 2014: Mitigation of Climate Change 11. Rogelj, J. et al. Proc. Natl Acad. Sci. USA (eds Edenhofer, O. et al.) (Cambridge Univ. Press, 2014). 111, 16325–16330 (2014). Published online: 13 July 2015

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