Tread lightly

Debris along the shoreline in Xcalak, Mexico, off the Great Maya Reef.

The truth behind the carbon footprint of cruise ships

The Great Maya Reef runs the full length of the Yucatan Peninsula and south to the Bay Islands in Honduras. It’s the largest coral reef in the western hemisphere; worldwide, it’s second only to the Great Barrier Reef in Australia. It’s a mecca for divers and snorkelers, and has spawned a thriving eco-tourism industry along the Costa Maya.

Beginning south of the Mayan Riviera, the Costa Maya stretches from the Mayan ruins of Tulum to Xcalak National Reef Park, and encompasses the Sian Ka’an international biosphere reserve. The approach to the biosphere is lined with low-impact hotels, interspersed with boho vegan restaurants and eco-chic retreats.

But as you move down the coast, unspoiled beaches give way to something entirely unexpected. A thick ribbon of rubbish decorates the edge of the shore, just a few hundred feet from the reef. Shards of plastic. Broken disposable cutlery. Bottle caps. The odd shoe.

At the southernmost tip of this peninsula, just 10 kilometres from Belize, lies the tiny town of Xcalak—a formerly robust fishing community that’s slowly rebounding after it was laid flat by hurricane Mitch in 1998.

Xcalak is off the grid. Homes are powered by small wind turbines, and electricity is conserved accordingly. There is no cellphone service; the locals communicate by ham radio. The absence of light pollution is dazzling. The stars are draped across the night sky like a shimmering blanket.

But every morning, more garbage washes ashore. A floating gyre of debris hovers in the lee of the mangroves—in stark contrast to how residents live. We speculated that the trash travelled with the currents up the coast from Central America. But we were surprised and appalled to hear the locals’ account of where it comes from: cruise ships.

These massive floating cities generate no small quantity of trash. By some calculations a cruise ship’s carbon footprint, per passenger, can be three times that of a Boeing 747. As such, you’d expect cruise lines to have some pretty high standards for managing waste. But the story told in Xcalak, over and over again, is that—rather than paying disposal fees at port—many ships opt to discharge it at sea, a few miles offshore.

It’s a shocking claim, but perhaps not far off base.

Waste management at sea is governed by the International Convention for the Prevention of Pollution from Ships, or MARPOL. It regulates the disposal of everything from food waste to drycleaning chemicals. A single cruise ship generates about seven tonnes of solid waste a day.

It’s discouraging to see how much garbage can be legally dumped in the ocean. Glass can be crushed and either recycled or discharged at sea. Paper and packaging materials are incinerated, and the ash can be discharged at sea. But a far greater problem is the wastewater.

Greywater from sinks, galleys, showers and laundry can be legally discharged into the ocean, as long as it does not “deposit solids in the water or leave a sheen on the water.” Bilge water is treated through an oily water separator, and if the oil content is less than 15 parts per million it can be discharged at sea. And the big yuck—cruise ships generate up to 25,000 gallons of sewage a day. Once it’s “treated” by marine sanitation devices, a ship moving faster than six knots can dump it just four miles from shore. Again, the regulations draw the line at an oily sheen or visible chunks. Furthermore, cruise ships may discharge untreated sewage in coastal waters and Canadian internal marine waters at a distance of more than 12 nautical miles from shore, as long as it’s discharged “at a moderate rate,” while the boat’s travelling at least four knots.

And that’s when they’re following the rules.

It’s well known that sewage is harmful to marine life and corals. Coral reefs are extremely fragile ecosystems. Colonies of calcium carbonate formations are built over hundreds of years. More than 500 species of fish, molluscs and crustaceans have been documented in the Great Maya Reef.

Corals are particularly susceptible to oxygen depletion (which is aggravated by nitrogen and phosphorus present in sewage) and ocean acidification caused by absorbing CO2 from the atmosphere. It’s a one-two punch that threatens to wipe out coral reefs altogether— potentially within just a few decades.

There are some signs of change. In 2003, Royal Caribbean (then the second largest cruise line in the world) committed to installing advanced wastewater treatment technology on its entire fleet. A decade later, an environmental report card produced by Friends of the Earth gives Royal Caribbean an “A” for sewage treatment. But the company scores a dismal “F” for its efforts to reduce air pollution, for poor results overall (see sidebar on page 3).

Plasma gasification is a clean alternative to incineration. The process uses plasma energy to destroy solid waste onboard cruise ships at temperatures above 5,000°C. The resulting gases, such as hydrogen and carbon monoxide, are recaptured and burned as fuel. Carnival was the first cruise line to embrace the technology in 2003. According to Friends of the Earth, they’ve made some headway with air pollution, but they’re failing on sewage treatment.

It’s hard to vacation without a carbon footprint. But if you’re visiting a coral reef, tread lightly. They may not be there much longer.