Hey Mr. Green,

I have thought a lot about reducing my carbon emissions by minimizing flying. I wonder, which is a lower-impact option for transatlantic transportation, flying coach or sailing on a cruise ship, either on a repositioning cruise or on the Queen Mary? 

—Valerie in Berwyn, Illinois

You're correct that one of the best things you can do to reduce your carbon emissions is to minimize flying altogether. When you do need to travel, considering just efficiency and cost alone, the plane is your best option between the two. The Queen Mary 2, for example, gets about 20.5 miles per gallon per passenger when traveling at its full speed (though at lower speeds it is considerably more efficient, getting around 45 passenger miles per gallon per passenger). An Airbus A380, in comparison, gets 74 miles per gallon per passenger; the Boeing 737 Max8 gets 110 miles per gallon per passenger. The cost of traveling by ship is considerably higher than by plane as well, though you can save some with a repositioning ticket. In general, air efficiency can depend on many variables, including different routes.

There are other factors to keep in mind when deciding whether to sail on a cruise ship, such as sewage treatment, air pollution, and food waste. Seek out cruise lines that demonstrate transparency and initiative in cleaning up their act. Friends of the Earth released a report card grading cruise lines in 2016.