Slowing cargo vessels near coastlines by 10 to 15 miles per hour could dramatically cut ships’ air pollution, according to a new study. But only a few U.S. ports have initiated such efforts.
A speed limit of 14 mph, down from the current cruising speeds of 25 to 29 mph, would cut nitrogen oxides – a main ingredient of smog – by 55 percent and soot by almost 70 percent, according to the University of California, Riverside study. It also would reduce carbon dioxide – a potent greenhouse gas and key contributor to climate change – by 60 percent.
With 100,000 ships carrying 90 percent of the world’s cargo, air pollution is a heavy burden for people living near ports, so slowing ships could improve their health, researchers say.
In the study, the ships traveled at speeds already used at the ports of Los Angeles/Long Beach and New York-New Jersey as part of voluntary programs.
“Vessel speed reduction does significantly reduce emissions, and that's why we have had a vessel speed reduction program in place at our port for several years,” said Arley Baker, a spokesperson for the Port of Los Angeles. “It’s both a feasible and practical way to reduce vessel emissions.”
But setting a speed limit on cargo ships has been an elusive goal for port cities because shipping traffic is regulated internationally.
All ocean-going vessels, when they are within 10 nautical miles of a U.S. port, must slow down, to typically 14 mph. The voluntary programs in Los Angeles/Long Beach and New York-New Jersey slow them farther out, up to 40 miles offshore.
A ship’s fuel consumption and emissions increase exponentially with speed, so burning low-grade oil at traditional cruising speeds emits more air pollution than slower ships, according to the study, led by environmental engineer David Cocker.
"Speed reductions, which are known to reduce emissions, would need to be maintained over a very long-term period in order to produce regional air quality benefits," said James Corbett, a professor of marine policy at the University of Delaware, who has studied the impact of the shipping industry on human health. Corbett was not involved with the new study.
The new study measured the emissions of two container vessels traveling between California's Ports of Los Angeles and Long Beach and the Port of Oakland. Emissions were measured near the ports and in international waters.
In international waters, ships burn heavy fuel oil. As it burns, large amounts of particulate matter, sulfur oxides and nitrogen oxides are released.
Studies worldwide have linked particulate matter – soot – to deaths from respiratory disease and heart attacks. Particulates specifically from ocean-going vessels have been linked to an increased number of premature deaths, according to a 2007 study by Corbett published in the journal Environmental Science and Technology.
In addition, the shipping industry is responsible for 3 percent of the world's carbon dioxide emissions, according to the International Maritime Organization, a United Nations agency responsible for marine safety and pollution. Shipping emissions are expected to grow 2 to 3 percent every year over the next three decades [PDF] as shipping traffic grows, according to the IMO.
The industry has dodged tax strategies and international treaties, such as the Kyoto Protocol. The International Maritime Organization has failed to set a cap on greenhouse gas emissions at international meetings in previous years. Under the World Port Climate Initiative, some of the world’s leading ports have committed to reducing their greenhouse gas emissions.