NPR logo The Smoggy Seas: Cargo Ships Bring Pollution, Health Risks

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The Smoggy Seas: Cargo Ships Bring Pollution, Health Risks

Cargo ships berth in Qingdao, a port city on China's east coast. AFP/Getty Images hide caption

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AFP/Getty Images

Cargo ships berth in Qingdao, a port city on China's east coast.

AFP/Getty Images

"Made in China" labels have multiplied over the past decades — and so have the trade ships docking in East Asian ports.

More shipping containers go through Shanghai than any other port in the world — and most of the world's 10 busiest ports are in China. Asian ports loaded or unloaded almost 50 percent of shipped goods in 2013, according to a U.N. report.

But the increased trade comes at a price. The growing fleet of shipping vessels visiting East Asia is pumping greenhouse gases and other pollutants into the air, causing more than 10,000 premature deaths annually, according to a study published Monday in Nature Climate Change.

"Air pollution kills as many people as tobacco," says Dr. Carlos Dora, coordinator of the World Health Organization's interventions for healthy environment unit, who was not involved in the study. "It's not only a health issue, it's a major health issue." Dora praised the paper for showing the cost of pollution in lives.

Previous studies have examined the emissions of ships in Europe and North America, but included relatively scant data from other global regions. A team of researchers from China and the U.S. decided to take a closer look at all of the vessels passing through East Asian waters.

Ships automatically send location information to satellites at regular intervals. By calculating the distance traveled within regular periods of time, the scientists were able to estimate speed, which significantly affects emissions. Once the scientists collected the data on ships' routes and speed, they fed the data into a model, which simulated how particles mingle in the air and how ship emissions would mix with the atmosphere.

As they expected, the team found exhaust from East Asian shipping vessels had greatly increased over the past decade. The pollution accounted for 16 percent of global shipping carbon dioxide emissions, compared to 4 percent to 7 percent in 2002-2005. What's more, ships emit 60 percent of their pollution within 20 nautical miles of shore, well within the reach of East Asian coastal populations.

"Definitely shipping is an issue for people who live within 100 miles of the coast, and even more so within 10 miles of the coast," says Duke University's Drew Shindell, a climate scientist who oversaw the modeling part of the study.

Two of the polluting particles that Shindell investigated were carbon dioxide and sulfur. The greenhouse gas carbon dioxide is produced by burning fossil fuels and warms the atmosphere, contributing to climate change.

Sulfurous particles, which come from the ship's fuel, initially cool the atmosphere, but only for about a week, so they don't compensate for the carbon dioxide's warming effect. The particles stick around long enough to harm humans, though. Their tiny size allows them to infiltrate human lungs and pass into the bloodstream, where they thicken blood vessels and increase the risk of lung cancer, respiratory disease and stroke.

Using previous medical studies to calculate the relationship between pollutants and death, the scientists were able to attribute 14,500 to 37,500 premature deaths per year to pollution from East Asian vessels.

"This really changed my thinking," says Dr. Brian Christman, a pulmonology professor at Vanderbilt University School of Medicine who was not involved in the study. He said before reading the paper, he'd assumed trucks were polluting, but that ships were "wonderful." Young children and the elderly are most vulnerable to death from pollution, says Christman, though anyone inhaling pollutants deeply on a regular basis could be harmed. "It kind of gives you the heebie-jeebies," Christman says, "because we all have to breathe."

Shipping emissions have sometimes been a blind spot for environmental regulation, according to the University of Delaware's James Corbett, who wrote a review of the paper. Though on land many countries have low-sulfur fuel standards for cars, vessels in international waters are still allowed to have relatively dirty fuel. Shipping emission regulations were left out of the international Paris climate summit (COP21) of last year.

That's not to say nothing can be done. Corbett says East Asian countries can regulate emissions along their own coastlines, as North America and much of Europe have. And he says the International Maritime Organization, or IMO, could institute stricter international regulations on ships.

Depending on the outcome of a review this year, the IMO may significantly reduce the level of sulfur allowed in fuel, beginning in 2020, says IMO spokesperson Natasha Brown.

Shindell says he hopes the IMO passes regulations, but, ultimately, humans may also need to re-evaluate what needs to be shipped — and what can be homegrown.