A Cruise To Guilt Island

A complicated patchwork of federal and domestic laws governs what cruise ships can discharge and where. For the past few years, environmental groups have been pushing a piece of legislation called the Clean Cruise Ship Act, which would bring all the regulations under one umbrella and strengthen policies on oily bilge water, sewage and gray water.

If you're shopping around, check whether your boat comes equipped with an advanced wastewater treatment system. You might also see whether the ship can plug into the local power grid when docked, rather than continuing to run its engines, a process known as "cold ironing." Cruise ship companies tout plenty of other environmental initiatives, from laundry facilities that reuse water from air-conditioning systems to kitchens that serve local and sustainably sourced food.

What about greenhouse gases? According to Carnival Corp., the company's ships emit 1.17 pounds of carbon dioxide per passenger mile. So let's say you've decided to take Carnival's week-long Western Caribbean cruise, a total of 1,826.5 miles. Your personal emissions would come to 2,137 pounds of CO2, or just about a ton. In 2006, fossil-fuel-related CO2 emissions in the United States were 21.8 tons per capita, or about 119.5 pounds per person per day. So a seven-day cruise produces about 18 days' worth of carbon dioxide.

In contrast, a round-trip flight on a regional jet from Miami to Grand Cayman would emit about 312.3 pounds of CO2 per person, assuming an industry-standard 80 percent occupancy. That's a lot less than a cruise, but then it's not an apples-to-apples comparison, since a cruise ship provides transportation, accommodation and entertainment. The overall emissions of a plane trip would still be lower if you could keep your carbon footprint during your week on Grand Cayman at less than double what it would be at home.

The Green Lantern thanks Marcie Keever of Friends of the Earth and Jackie Savitz of Oceana.