The Nature Conservancy:

Photo © Mark Godfrey

Let's say you live in New York and you're looking into vacationing in San Francisco...which is 2,582 miles away. Sounds like fun!

But you're environmentally conscious — which we know you are — and let's say you'd like to get to the City by the Bay in the greenest way possible. (Except walking and biking, of course. We're assuming you don't have weeks or months to make the journey...or a high tolerance for blisters.)

So: plane, train or automobile? The answer is…train, according to a number of websites we've found that calculate CO₂ and total greenhouse gas emissions. Use our findings — and the links below — as a jumping-off point for tallying the emissions your own journeys might generate.

Plane. What's the opposite of green? Flying anywhere, by all accounts.

For instance, the carbon calculator at carbonplanet.com — which takes into account factors such as the curvature of the Earth and the different emissions levels for short-haul versus long-haul flights — says that a round-trip economy ticket on a N.Y.-S.F. flight that's 80 percent full would generate 2.5 tons of CO₂.

But what does that figure mean? According to the U.S. Climate Technology Cooperation Gateway, 2.5 tons of CO₂ equals:

The emissions generated by six months of driving a passenger car of average gas mileage;
The carbon sequestered for a year in 1.89 acres of pine or fir forest;
The emissions from generating the electricity used by an average U.S. household for 3.5 months.

Even worse, the CO₂ and other greenhouse gas emissions from flying are released directly into the stratosphere, which carbonplanet.com says gives them roughly three times the global warming potential that the same emissions would have if they had been released on the ground (where they reside for a while before moving upward in the atmosphere).

And if you like luxury seating while flying, know that it comes at a price to the environment. Because business-class and first-class seating take more aircraft space, passengers who use them are responsible for more of the global warming effect of their flights — twice as much for business class, and three times as much for first class.

Car. But if long trips on planes are bad for climate, taking the car generally isn't much better.

The Nature Conservancy's carbon calculator allows you to calculate the tons of CO₂ emitted by vehicles of different gas mileages for different periods of time — so you can easily hack it to determine the CO₂ a long car trip would generate. And it shows that only vehicles that get more than 40 miles per gallon of gas would be more efficient than an economy coast-to-coast flight:

Below are roughly the tons of CO₂ vehicles of different efficiencies would generate on a 5,164-mile trip by one person with no passengers:

A hybrid vehicle (or one that gets above 40 miles per gallon): 2.3 tons of CO₂. (That's still 80 percent below the carbon dioxide emitted by the average U.S. vehicle annually.)
A "small" vehicle (one that gets 30-40 miles per gallon): 3.4 tons of CO₂.
A "mid-size" vehicle (one that gets 20-30 miles per gallon): 3.9 tons.
A "large" vehicle (one that gets 10-20 miles per gallon): 4.5 tons.

Good news for the conscientious, though. If you're making the trip with your own vehicle and you check its air filter and tire pressure monthly, our carbon calculator says you can shave up to one-half ton of CO₂ off those amounts.

Train. But if you have three days to get there and you'd like to see the country, consider the train. Travel by rail is recommended by many websites as definitely the greenest way to get from coast to coast…as well as for shorter journeys.

According to the train advocate blog The Man in Seat Sixty-One as well as the websites of Amtrak and Eurostar (which pioneered train service between London and Paris via the "Chunnel"), trains emit between 4 percent and 15 percent of the CO₂ emissions of a plane per passenger, depending on the efficiency of the train and the length of the trip. (Not that it matters for U.S. domestic trips, but Eurostar has also pledged to reduce its own CO₂ emissions by 25 percent by 2012 — and to offset every traveler's emissions for free beginning in November 2007.)

But you can't take the train everywhere? you say. Yes, you can (almost). The Man in Seat Sixty-One offers tables that show you how to get from anywhere to anywhere — from Albania to Zimbabwe to Vietnam to California — without using a plane. All aboard!

Want more tips?
Visit our Enviro-Tips archive.

Looking for even more to do?
Tell a friend about the Great Places Network, so they can help save the last great places too!

The Nature Conservancy is a non-profit, tax-exempt charitable organization under Section 501(c)(3) of the Internal Revenue Code. Donations are tax-deductible as allowable by law.

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