- A Los Angeles resident is planning a vacation to Seattle. Which way to get there and back generates the least amount of global-warming carbon dioxide?
The plane, but in this case, just barely. The roundtrip flight would generate the equivalent of 0.93 tons of CO2, compared to the SUV's 1.18 tons. Jet fuel and gasoline both generate about 20 pounds of CO2 per gallon burned, according to Tuft University's Climate Initiative.
- Consider the same vacation, but this time for a family of four and a third travel choice. Which generates the least CO2?
The 30-mpg car would generate the least CO2. But even the SUV beats the plane in this match-up because it's carrying four people at the same mileage and CO2 emissions.
- Does it really matter whether I take a plane or train or drive? That plane's going to fly even if I'm not on it.
If you're not on board next Tuesday, Southwest probably isn't going to ground the plane or Amtrak cancel its run. But your day-by-day decisions -- and those of everyone else -- absolutely drive overall market demand. Carriers hate empty seats and constantly fine-tune the number of departures in response.
- While jet fuel and vehicle gasoline both generate about the same amount of CO2 per gallon burned, the mile-for-mile effect of jets is more than twice that of autos and trucks.
True. For a clue to the difference, think about what happens to those jet trails six to eight miles up in the air. They coalesce into clouds, which trap the earth's heat, even though they also reduce the sun's incoming warmth. Known as radiative forcing, this problem's not driven strictly by the CO2, but by all the other things jets emit, including water vapor and nitrogen oxides. Still, the end result is that a single ton of high-altitude aircraft CO2 does as much damage as 2.7 tons of ground-level vehicle C02.
- When you do fly, it's easier on the environment if you take non-stop flights.
True. Just as your car's gas mileage plummets if you jackrabbit off a stoplight, planes use more fuel -- and create more CO2 -- taking off than at cruising speed. Really long flights of more than 10,000 miles, say New York to New Zealand, generate 40 percent less C02 per mile than those under 1,500 miles. Assuming your legs still work once you arrive.
- Given the role gas mileage plays into the drive-or-fly decision, would it be better to take the smaller car instead of the van or SUV?
No mystery about this answer. You may arrive with frayed nerves, but the smaller car's probably better for the planet. Just as backpackers know that every item they carry has a cost, make some hard choices before hitting the road. Bigger vehicles easily swallow all the kids' toys, all the clothes, and all the gear you might use. But choosing to leave behind some of that stuff could make for a more relaxing trip -- and a little practice at living lighter when you get back home.
- How do passenger trains stack up against commercial airlines?
All three of the above choices apply. According to the U.S. Department of Energy, Amtrak's passenger trains are 18 percent more efficient per passenger mile than commercial flights. Secondly, among the dozens of products refineries extract from a single 42-gallon barrel of crude oil, 7.9 gallons of diesel are produced but only 4.1 gallons of jet fuel. It's true that refineries can adjust the overall product mix, but it takes less crude to generate a gallon of diesel than jet fuel. (Gasoline, by the way, accounts for almost half of a barrel's yield.) Finally, until trains can fly they won't contribute to heat-trapping cloud formations as much as planes do.
While Amtrak's limited route choices may make the train an impractical choice in many parts of the U.S., vacationers along the East Coast still have plenty of options. Trains' green edge over planes also might mean rethinking hopping on one of Europe's cheap city-to-city flights when a rail connection exists.
- When one must fly, does it help to buy so-called carbon offsets?
Yes -- if you do your homework and choose a reputable vendor. The idea of carbon offsets is simple: the money you pay is used to
fund projects worldwide that reduce or slow the production of global-warming gases.
Buying an offset for that Los Angeles to Seattle roundtrip flight, for example, would cost only $5.14.
Just remember that the first step in fighting global warming is reducing your overall energy
demands everywhere you can. Carbon offsets definitely help, but none of us can buy our way out of the problem. (If you're interested in how the
Sierra Club's Outings program handles offsets, click here.)
- How do commercial airplanes, trains, and cars rank from most to least efficient per passenger mile?
B is the right answer: Trains are the most efficient, followed by cars, and then planes. You get partial credit if you guessed A since you realized that planes are the least efficient. According to the DOE, passenger trains use 2,978 British thermal units per passenger mile, while cars use 3,496 BTUs/passenger mile, and airplanes use 3,959 BTUs/passenger mile. However, if you include personal trucks and SUVs along with cars, the nation's vehicle fleet uses 4,329 BTUs per passenger mile, which is worse than airplanes. You could vacation Easy Rider style on a motorcycle, which uses 2,272 BTUs for every passenger mile. Or consider a bicycle trip: just as breezy as the Harley but gasoline free.
- Are ship cruises a more environmentally friendly way to travel?
CO2 emissions are almost the least of a cruise ship's environmental problems. According to Climate Care, a UK firm that sells carbon offsets, large cruise ships can emit up to three times as much CO2 as airliners. A larger issue, however, has been proper disposal of the sewage and garbage generated by mega-cruisers, which carry as many as 3,000 passengers at a time. After a spate of lawsuits and unfavorable publicity six to eight years ago, cruise lines have reduced such discharges, at least within three miles of shore. Still, environmental critics and congressional allies continue to press for tighter controls.