By David Wren

The company that keeps its Sunshine pleasure ship at Union Pier Terminal in downtown Charleston is defending its use of scrubbers to comply with global emissions standards that begin in 2020.

Under the International Maritime Organization mandate, shipping lines will be required to use fuel that contains no more than 0.5% sulfur — or install equipment that reduces sulfur dioxide emissions — starting in January.

The coming demand for low-sulfur fuel — and potential shortages — means it will be more expensive than today’s bunker fuel, which contains 3.5 percent sulfur. Some analysts predict fuel prices will rise by one-third, and the higher costs will be passed throughout the transportation chain.

Some ship operators, Carnival Cruise Line included, have gone a different route by installing pollution-control devices called scrubbers that help filter sulfur dioxide from smokestack emissions so the vessels can use the higher-sulfur fuel yet remain compliant with the new rule.

The scrubbers aren’t cheap — they run as high as $5 million apiece — but Terry Thornton, Carnival’s senior vice president, told The Post and Courier they’re more cost-effective in the long run than buying expensive low-sulfur fuel.

That plan has run into opposition from environmentalists, who have called for a moratorium on scrubbers. They cite evidence in a criminal pollution case against Carnival that showed the devices failed multiple times, leading to significant air pollution.

Such pollution is one reason environmental and historic preservation groups and some Charleston residents are going to court to fight the development of a new cruise passenger terminal at Union Pier. Tommie Robertson told The Post and Courier in June that black smoke from the ship stacks have made her sick while sitting on the porch of her Laurens Street home.

Last month, a webcam operator in the Bahamas posted video of a Carnival ship belching black smoke while docked in Nassau, prompting environmentalists to again call on Carnival to switch to low-sulfur fuel rather than rely on ineffective equipment.

Carnival has responded to the controversy with a new website that argues scrubbers aren’t just the best way to reduce sulfur dioxide but also a host of other airborne pollutants.

Scrubbers “have the proven capability to outperform low-sulfur fuel alternatives,” the website states, adding they provide “overall cleaner air emissions in a way that is safe for ocean environments.”

Thornton said the technology has long been proven in land-based uses, such as reducing pollution at factories.

“The challenge has been fitting it into the space we have on our ships,” he said. “Our existing ships were never designed for the space this technology requires.”

To date, Carnival has invested $500 million in scrubbers and installed more than 220 of them on its fleet. The Sunshine has been operating with scrubbers for months and is “fully compliant,” Thornton said, with the new rules. The same is true for the Ecstasy, which called Charleston its home port until the Sunshine replaced it in May.

“We’ve made tremendous investments in all the technology that’s needed to meet those requirements,” he said of the IMO regulation.

That’s not likely to satisfy environmentalists. In a May 14 letter to the IMO’s secretary general, 10 environmental groups called on the maritime agency to take action.

“As Carnival Corp.’s criminal debacle has shown, (scrubbers) are not the answer to delivering air pollution reductions for the shipping sector,” the groups wrote, asking that scrubbers be banned pending a study in which the IMO “reviews the technology’s marine and air pollution impacts.”