Cleaner, lower-sulphur fuels for ships will halve the number of childhood asthma cases associated with ship air pollution, suggests a new analysis in Nature Communications. However, this comes with trade-offs for climate change as the reduction in aerosols removes the radiative cooling effect they have, suggesting that air-pollution and climate-mitigation policies should go hand in hand.

Ships emit sulphate aerosols, which are detrimental for human health and terrestrial and aquatic environments. At the same time these aerosols also cool the climate through their radiative effects. The International Maritime Organization has proposed to reduce the sulphur content of fuel oils used in shipping to 0.5% by 2020. This should result in increased health benefits, but will also reduce the radiative cooling from ship emissions.

James Corbett and colleagues present a global assessment of the regional health benefits and climate consequences of implementing lower-sulphur standards for marine fuels in 2020. The authors combine high resolution emissions inventories, integrated atmospheric models and health risk functions and find that cleaner fuels will reduce ship-related premature mortality by 34% to 266,300 cases per year from 403,300, globally. Childhood asthma associated with ship air pollution will be reduced by 54% from 14 million cases annually to 6.4 million.

However, the positive health impacts of cleaner fuel standards are accompanied by 80% reduction in radiative cooling of aerosols. Therefore, the authors suggest, international policy efforts should jointly consider reduction of greenhouse gases and air pollution.