Putting a speed limit on cargo ships as they sail near ports and coastlines could cut their GHG emissions by up to 70 percent, according to scientists writing in the journal Environmental Science & Technology.
More than 100,000 ships carry 90 percent of the world’s cargo, David R. Cocker III and colleagues write in the journal. Engines on these vessels burn low-grade oil that produces large amounts of air pollution. While cargo ships make up less than 5 percent of the total ocean-going fleet, they emit more than 21 percent of the CO2 from the international shipping industry, according to the journal.
Some 70 percent of ship-related emissions occur within 216 nautical miles of the coastline, the authors write, and between 74 and 83 percent of all vessels are within 200 nautical miles of land at any given time. Because fuel consumption and smokestack emissions increase exponentially with speed, the authors explored how speed limits could reduce pollution.
The research found that slowing container ships to about 14 mph reduced emissions of carbon dioxide by about 60 percent and nitrogen oxides by 55 percent compared to emissions at traditional cruising speeds of 25 to 29 mph. Soot emissions fell by almost 70 percent.
The authors conclude that imposing these speed limits on vessels near ports and coastlines could significantly reduce pollution and protect the health of people living in those areas.
The authors received funding from the California Air Resources Board — which has proposed speed limits on cargo ships — and the EPA.
Some port authorities have launched voluntary speed limits, according to the study. The Los Angeles and Long Beach San Pedro Bay ports have a voluntary program, slowing ships to 12 knots in certain zones.
This vessel speed reduction program helped the Port of Los Angeles cut its cumulative emissions as much as 76 percent while container volumes increased 6 percent between 2005 and 2011, according to the Port of Los Angeles’ 2011 Inventory of Air Emissions.