Credit: iStockphoto/Daniel Loiselle

Estimating the total health effects of reducing atmospheric aerosols is a tough task. The tiny particles cause major public health problems but many also cool the planet, potentially staving off warming-related illnesses. A study now attempts to calculate the optimal public health policy for aerosol reduction, using the case of emissions from shipping.

Jakob Löndahl, of Sweden's Lund University, and colleagues compared the number of deaths attributed to the aerosols generated by global shipping with those that could potentially occur under various warming scenarios1. Whereas previous analyses hint that aerosols from shipping could cause about 63,000 deaths annually, Löndahl's team estimated that the cooling effect of these aerosols reduces global average temperature by about 0.05 degrees Celsius, preventing around 20,000 climate-change-related deaths per year.

But the total effect on health of cooling aerosols is highly uncertain, say the researchers, whose estimates are a first attempt at the problem. Reducing aerosol sources that both warm the atmosphere and are unhealthy to inhale — such as black carbon — would have a much clearer outcome, they say.