As trade has been globalized over the last several decades, most manufacturing has been moved to "low cost" countries in Asia, particularly China. That means goods have to be moved over long distances across the world's oceans. This happens with huge container ships, and there are about 90,000 such ships worldwide. New research indicates that each of the biggest ships emit as much as 50 million cars. That means the 15 largest ships combined may be emitting more than all the world's car put together. Part of the problem is that ships typically run on high sulfur bunker fuel oil.
Some 70 percent of shipping emissions are generated within 250 miles of the world's coastlines. The U.S. government has announced its intent to impose a 230-mile low emissions shipping buffer zone around U.S. coasts. Governments need to seriously attack shipping emissions in addition to ground transportation if they really want to make a dent in greenhouse gases levels.
[Source: The Guardian]