Hey Mr. Green,

Q: I am trying to do what I can to be environmentally friendly. We hardly use the air conditioner. We got a Nissan Leaf. We recycle as much as possible. But I really want to travel and I'm unsure about how to go without creating an incredible footprint. I am not sure that buying Renewable Energy Credits is the best idea, as offsetting doesn't seem to be a legitimate way to reduce one's carbon footprint. I’d like to go to Spain, but I won't if it dumps a bunch of carbon dioxide into the atmosphere. I know boats often use fossil fuels that are quite dirty. Am I stuck waiting for electric planes, or can you suggest a better way to travel? 

—Chris in Pekin, Illinois 

The emissions from your flight could be offset with a bit of effort or expense: The average international flight requires about a gallon of jet fuel to move one passenger 76.3 miles, according to the International Council on Clean Transportation. Your fuel consumption on the 8,400-mile round trip to Spain would emit anywhere from around 2,300 to 3,100 pounds of carbon dioxide equivalent emissions, depending on the efficiency of the plane (there’s quite a range) and the greenhouse-gas effect of contrails and other high-altitude emissions. 

It might not be terribly hard for you to offset those travel-related emissions. You’d only have to shave about 1,400 kilowatt-hours from your electricity use—15 percent of the household average use in Illinois. (In areas that emit less CO2 to generate electric power, you’d have to reduce your electricity a lot more—which seems unfair.) If you can’t cut that much, you could always hook up with a clean energy company like Arcadia Power—which you pay to put clean power into the grid to offset your dirty power—or rent or purchase a solar system.

Cruise ships use more and dirtier energy than jets and would be feasible only if you had beaucoup bucks and time was not an issue. Your final option—swimming to Spain—might not be feasible because it’s a tad slow, which makes it the most expensive option, since you’d have to charter a boat for quite a spell. Even swimming at a respectable speed for 10 hours a day, it would take six months or so just to get from New York to Spain. You’d also need at least 8,000 calories a day, or the equivalent of around 20 pounds of potatoes just to keep moving.