Pity Carnival cruises. Not only has its public relations office had to deal with passengers falling deathly ill of noroviruses, but now it has to fight charges that it releases too much carbon.

The UK’s Daily Telegraph finds CO2 emissions per passenger from a Boeing 747 are just a third of the emissions per passenger on a cruise. That's technically any cruise, not just Carnival's. And the article casually mentions that the Eurostar rail service, per passenger, emits just 1/36th that amount.

The paper based its calculations on Carnival's annual environmental report—which may be why it was singled out by name—which says that on average, it emits 401 grams of CO2 per passenger per kilometer.

(If you haven’t done the math yet, that’s an average of 132 grams of CO2 per Boeing passenger. And 11 grams of CO2 emitted on average per Eurostar passenger.)

Maybe playing the numbers game doesn't explain it all. Consider the travel time involved, the maximum number of passengers, and what they can do to pass the time going from Point A to Point B:

A Eurostar seats 750 people, promises to take passengers to another country within 2.5 hours, and lets them feast someplace called a Gastro-pub, "Europe’s longest champagne bar" and a farmers market.

A Boeing 747 can seat nearly 600 passengers and fly them from San Diego, California to Mexico within hours. Amenities—do chips and soda count?

A fully-booked Carnival cruise can leave San Diego with up to 3,400 people and take up to two weeks to reach its final destination south of the border. Granted even driving would be faster, but Carnival's site promises to keep passengers entertained, offering spa treatments, lobster every day, gambling in the casino at night, or taking lessons from a virtual golf coach.

If the ball falls overboard, it's sleeping with the fishes.