The IMO 2020 sulphur cap: a step forward for planetary health?
Authors: John S Ji
Journal: The Lancet Planetary Health (2020)

As the year 2020 commences, people around the world can breathe cleaner air because of the implementation of the International Maritime Organization's (IMO's) sulphur cap. The IMO is a UN specialised agency responsible for global maritime regulations, and effective as of Jan 1, 2020, its Marine Environmental Protection Committee mandated a limit to the fuel used for emissions of 0·5% mass by mass sulphur. Previously, the limit was 3·50% mass by mass for ships operating outside Emission Control Areas.1IMOThe 2020 global sulphur limit—frequently asked questions.http://www.imo.org/en/MediaCentre/HotTopics/GHG/Documents/2020%20sulphur%20limit%20FAQ%202019.pdfDate accessed: December 31, 2019Google Scholar Cleaner marine fuel is a positive step forward for global environmental health, ensuring cleaner coastal air, reducing ecological damage, and ultimately saving lives.2Wan Z Zhu M Chen S Sperling D Pollution: three steps to a green shipping industry.Nature. 2016; 530: 275-277Crossref PubMed Scopus (109) Google Scholar Marine fuel is considered the lowest grade of fuel, often made up of heavy fuel oil and diesel oil. It emits high amounts of fine and ultrafine particulate matter, sulphur oxides (SOx), nitrogen oxides (NOx), metals, polycyclic aromatic hydrocarbons, and soot.3Wu D Li Q Ding X et al.Primary particulate matter emitted from heavy fuel and diesel oil combustion in a typical container ship: characteristics and toxicity.Environ Sci Technol. 2018; 52: 12943-12951Crossref PubMed Scopus (49) Google Scholar The associated health hazards are numerous; a study estimated that ship-related pollution is responsible globally for about 400 000 premature deaths from lung cancer and cardiovascular disease, and 14 million childhood asthma cases each year. Lowering of pollution via the sulphur cap can reduce estimated ship-related premature mortality and morbidity.4Sofiev M Winebrake JJ Johansson L et al.Cleaner fuels for ships provide public health benefits with climate tradeoffs.Nat Commun. 2018; 9: 406Crossref PubMed Scopus (204) Google Scholar The most direct beneficiaries of the reduction of ship-sourced sulphur oxide emissions are populations living close to ports and coasts. The busiest mega-ports are in Asia; the top-ranked ports by container volume are Shanghai, Singapore, Shenzhen, Ningbo, and Guangzhou. Few of the top ports in the world are outside of Asia: Rotterdam in the Netherlands is ranked 11th, and Los Angeles in the USA is ranked 17th.5WSCTop 50 world container ports.http://www.worldshipping.org/about-the-industry/global-trade/top-50-world-container-portsDate: 2019Date accessed: December 31, 2019Google Scholar Cities with the busiest marine trades are also some of the world's most populous, and air pollution reduction will have large population-weighted effects. Furthermore, although regulating shipping emissions is not a focus of the Paris Agreement—possibly owing to difficulties in allocating emissions to specific countries and policing compliance—it is undoubtedly central to the climate change agenda of greenhouse gas mitigation. However, few planetary health issues could be as simple as that. Ironically, the immediate reduction of SO2 contributes to global warming if CO2 is not concurrently reduced. Atmospheric SO2 is part of the global cooling mechanism through conversion into sulphuric acid aerosols, which block incoming solar radiation and reflect the sun's heat. In fact, spraying sulphur into the atmosphere has been proposed as a form of geoengineering to cool the planet by scattering solar radiation and thereby reducing the amount of surface heating by shortwave radiation.6Laakso A Korhonen H Romakkaniemi S Kokkola H Radiative and climate effects of stratospheric sulfur geoengineering using seasonally varying injection areas.Atmos Chem Phys. 2017; 17: 6957-6974Crossref Scopus (20) Google Scholar The reduction of sulphur might affect the complex interplay of SO2 and CO2 in global warming. Gaseous SO2 in the atmosphere lasts for only a few days, whereas the warming effect of CO2 lasts centuries. SO2, along with NO2 also have the indirect effects of ocean acidification and fertilisation, which affect the exchange of CO2 between the atmosphere and the oceans.7Fuglestvedt J Berntsen T Eyring V Isaksen I Lee DS Sausen R Shipping emissions: from cooling to warming of climate—and reducing impacts on health.Environ Sci Technol. 2009; 43: 9057-9062Crossref PubMed Scopus (91) Google Scholar Ship owners are expected to bear high costs. Compliance with the sulphur cap limit is achievable in two main ways: by burning fuel that has a sulphur concentration within the cap limit, or by installing emission abatement technology (scrubbers) on board. There is a cascading effect on the entire supply chain. Retrofitted scrubber installation costs millions of dollars per ship. However, a high proportion of the global fleet is fitted with open-loop systems, in which the exhaust gas is sprayed with seawater and the treated wastewater is then discharged into the sea. There are concerns that sulphur cap regulation might inadvertently convert air pollution into water pollution when wastewater is not treated properly and is illegally discharged.8Laville S Thousands of ships could dump pollutants at sea to avoid dirty fuel ban.https://www.theguardian.com/environment/2018/oct/29/thousands-of-ships-could-dump-pollutants-at-sea-to-avoid-dirty-fuel-banDate: 2018Date accessed: December 31, 2019Google Scholar Disagreement between stakeholders adds another hurdle for sulphur cap implementation. The ship-owners association in the Philippines has indicated that domestic ships are not ready to comply with the new regulation, and other parties called for delays because of concern that compliant fuels might not be readily available in necessary quantities worldwide.9Liang LH Filipino Shipowners Association says domestic owners not ready for IMO 2020.https://www.seatrade-maritime.com/regulation/filipino-shipowners-association-says-domestic-owners-not-ready-imo-2020Date: 2019Date accessed: December 31, 2019Google Scholar An economic slowdown might drive businesses into bankruptcy. Maritime shipping is still the most carbon-efficient form of transporting goods—far more than road or air. To inform the IMO's decision-making for the improvement of human health, policymakers should integrate new epidemiological studies on the dose-response relationship of air pollution and health, remote sensing exposure assessment of pollutants such as black carbon or ultrafine particles, modelling of the joint effect of chemical mixtures, and perhaps cost–benefit analyses. For scientists, this policy change might be considered a natural experiment and an opportunity for planetary health research. I served as the Asia Editor of The Lancet in 2017.