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In Europe, one in seven particles of toxic nitrogen oxides (NOx) come from shipping exhaust, a 30 percent increase from a decade ago when the ratio was one in nine. All of the resulting smog and acid-rain-producing pollution contributes to shipping’s threat to global health which, as one recent estimate found, “leads to up to 60,000 premature deaths per year,” says Folkert Boersma, an atmospheric scientist who led a new study surveying Europe’s shipping pollution.
From 2005 to 2012, Boersma and his colleagues used NASA’s Aura satellite to scan the air above Europe’s shipping lanes, measuring the levels of NOx. They found that over the past decade, European shipping emissions have experienced wild swings. Changing industry tactics, the global economic crisis, and pollution control legislation on land have all contributed to shipping’s increasing share of the NOx pollution pie.
Before the economic crisis, from 2005 to 2008, European shipping NOx emissions climbed about 15 percent, the scientists found, reflecting a growth in world trade. But in 2008, the global recession shook the shipping industry, sending it, and its emissions, into a sharp decline.
The recession and the resultant drop in trade led to a sharp 12 percent cut in emissions, partly because of decreased demand, but also because of the shipping industry’s adoption of the practice of “slow steaming.”
To save money during the recession, ships dialed back their speeds. As Boersma found, ships in the Mediterranean slowed down by more than 30 percent, going from a running speed of 20 to 25 knots to about 16 to 19 knots. “The slower they go, the cooler their engines run, and the less NOx they produce,” Boersma says. This slow steaming led to a roughly 45 percent drop in average ship NOx emissions.
Yet despite the still-ongoing strategy of slow steaming, “ship emissions are responsible for more and more air pollution in Europe,” says Boersma.
One reason is because land-based NOx emissions in Europe decreased by about four percent annually from 2005 to 2012, due to pollution control policies. “Air pollution on land is cleaning up much faster than air pollution on the sea,” says Boersma.
But since the shipping industry instituted slow steaming for economic and not environmental reasons, ship emissions could climb once more if fuel prices drop.
“The shipping sector should do more to clean up their act, to come into step with the enormous measures being imposed on land-based sources of air pollution,” Boersma says. “Even if slow-steaming was initially done for economic reasons, now that it’s seen to have environmental benefits, my hope is that the shipping sector will continue to do it, since it could help put [the industry] in a more positive light.”