Pollution from ships, in the form of tiny airborne particles, kills at least 60,000 people each year, says a new study. And unless action is taken quickly to address the problem - such as by switching to cleaner fuels - the death toll will climb, researchers warn.
Premature deaths due to ultra-fine particles spewed out by ships will increase by 40% globally by 2012, the team predicts.
Ships release an estimated 1.2 million to 1.6 million metric tons of tiny airborne particles each year. Less than 10 micrometres in diameter and invisible to the human eye, most come from the combustion of shipping fuel which releases the ultra-fine soot. This includes various carbon particles, sulphur and nitrogen oxides.
Tiny airborne particles are linked to premature deaths worldwide, and are believed to cause heart and lung failures. The particles get into the lungs and are small enough to pass through tissues and enter the blood. They can then trigger inflammations which eventually cause the heart and lungs to fail.
There is also some evidence that shipping emissions contain some of the carcinogenic particles found in cigarette smoke.
The smaller the particle, the more dangerous it is. According to one study carried about by Aaron Cohen, currently an adviser to the World Health Organization European Center for Environment and Health, particles smaller than 2.5 micrometres across are responsible for 0.8 million deaths worldwide each year - or 1.2% of premature deaths (Journal of Toxicology and Environmental Health, part A, vol 68, p 1301).
Particles released by ships fall into this category, with most measuring less than 2.5 microns across. So James Corbett of the University of Delaware in the US and his colleagues decided to determine what portion of premature deaths can be linked to soot emissions from the shipping industry.
The researchers used two independent inventories of the emissions produced by the global shipping industry. They fed these into computer-run climate models to predict where the emissions are carried by the winds. Using population data from the World Health Organization, they then overlaid the location and concentration of the shipping emissions and population density.
Finally, they used equations which relate concentrations of the microparticles to the incidence of premature deaths to arrive at an estimate of the total number of deaths that can be attributed to shipping emissions. The equations were previously compiled by epidemiologists who compared the incidence of heart and lung failures in areas with high levels of particles, to the death toll in "cleaner" areas (Journal of the American Medical Association, vol 287 p 1132).
Using data from the two emissions inventories and two climate models, "our best estimate is 60,000 deaths" worldwide each year, says Corbett, adding that the number may be "conservative".
The deaths are concentrated in densely populated regions and ones that are close the major shipping lanes - mostly Europe, Asia and the Eastern US (see map, above right).
"The figure does not surprise me," says Mike Moore, who leads the UK Natural Environment Research Council's programme on environment and human health. "If anything, I would have thought it might be bigger," he told New Scientist.
What is more, the number is set to increase. Corbett and colleagues ran a simulation of what the picture may look like in 2012 given current estimates of the growth in trade. They found a 40% rise in premature deaths.
"It appears from this study that a significant number of the deaths are related to fuel quality," Corbett told New Scientist. He and his team ran separate analyses to study the effects of organic carbon particles and sulphite.
The analyses showed that organic carbon particles and sulphite were responsible for roughly 40,000 deaths per year - or over 60% of the total deaths linked to shipping emissions. Emissions of all of these particles could be limited by using more refined fuels in the shipping industry, which typically is powered by diesel fuel.
Corbett says the onus is now on the policy makers. "We leave judgement of what to do and how fast to do it to the policy process," he says. "Our aim was to provide a robust estimate on a global scale so that policy makers would have evidence that human impacts are occurring and so they could decide if the evidence was enough to justify strong and immediate action."
Earlier this year, another study on shipping emissions found that the sulphur particles cause a local cooling by generating contrails in the sky.
Journal reference: Environmental Science and Technology (DOI: 10.1021/es071686z)
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