In the global push to combat greenhouse gases, an industry whose smokestacks once passed under the radar is drawing the increased attention from scientists and coastal environmental regulators for its contributions to air pollution.
Maritime shipping's carbon dioxide emissions represent as much as 5 percent of the global total—roughly double those of aviation—and are anticipated to rise by as much as 75 percent in the coming two decades, barring some significant change.
That change may soon be pulling into port: ships powered by cleaner-burning liquefied natural gas.
Global shipbuilders and fleet operators are turning to liquefied natural gas as the potential maritime fuel source of the future. That's because maritime emissions, which were not covered under the 1997 international Kyoto agreement to reduce greenhouse gases, are now facing increased scrutiny in coastal areas around the world.
Liquefied natural gas is not only cleaner than diesel, but it's also cheaper—especially in markets like North America, where shale-rock energy exploration has unlocked an abundance of natural gas.
In September, the United Arab Shipping Company ordered 10 ultra-large container ships that are "LNG ready," or capable of being easily retrofitted to run on liquefied natural gas.
"That is seriously big news in the maritime industry," wrote Lars Petter Blikom, a liquefied natural gas expert for Det Norske Veritas, a Norwegian-based international maritime classification society. "It is a potential game changer for container shipping."
More big news came in June, when TOTE became the first U.S. company ever to win the Next Generation Shipping Award, a prestigious industry design honor given out annually by the Oslo, Norway-based maritime forum Nor-Shipping.
TOTE, a subsidiary of Seattle's Saltchuk Resources, won for its partnership with San Diego-based shipbuilder General Dynamics to build the world's first two container ships powered primarily by liquefied natural gas.
Sized to carry 3,100 containers each, the 764-foot ships will pump out 71 percent less carbon dioxide, 99 percent less soot, 98 percent fewer sulfur oxides, and 91 percent fewer nitrogen oxides.
The ships will run between Jacksonville, Fla., and San Juan, Puerto Rico—areas where new environmental rules are mandating emissions reductions.
"For us, the reason, first and foremost, is environmental," Anthony Chiarello, president and CEO of TOTE, told Popular Mechanics. "Having an environmentally friendly solution was the driver from the beginning."
Mike Corkhill, editor of LNG World Shipping, wrote in December that in the North and Baltic Seas, new emissions rules are part of why shippers "are set to make a major commitment to liquefied natural gas as a ship fuel years ahead."
Danish officials had previously estimated that natural gas-fueled vessels in Northern Europe could burn as many as 4 million tons per year of liquefied natural gas by 2020. The latest data, Corkhill wrote, "now indicate that that figure could be too low."
Whether liquefied natural gas will eclipse diesel isn't certain. A lack of infrastructure, for example, could stem the flow of natural gas to ports.
The current trends, however, favor natural gas.
TOTE told Popular Mechanics that it had fielded "more than a dozen calls" from natural gas suppliers offering to get the fuel it needs to Jacksonville, Puerto Rico or anywhere else.
Lured by the expected long-term low cost of natural gas, ferry systems in British Columbia, Washington state and Staten Island, N.Y., are exploring conversions of their fleets to natural gas-power as a way of warding off fare increases.
In October, New Orleans-based Harvey Gulf International Marine launched the first U.S.-flagged vessel to run primarily on natural gas. It will be first of six to 10 offshore supply vessels the company will use to tend to offshore platforms in the Gulf of Mexico.
Blikom, of Det Norske Veritas, wrote in April of what he believed the future may look like: "In 2040 a ship burning oil will be a rare sight on the seas, but quite popular in museums."