Let's start with this stat: planes are roughly comparable to cars in fuel consumption per passenger mile, at least with respect to carbon dioxide output. It makes for an easy comparison; a 60-hour cross-country car trip burns up about the same amount of fuel per passenger, and has the same "carbon footprint," as a five-hour cross-country flight.
I don't think a traveler has to be a member of Greenpeace to reach the end of a 3,000-mile drive and think "Whoa, I burned up some fuel on this trip." However, the same person might step off a plane after 4.5 hours eastbound from Los Angeles to New York and not ponder even for an instant the resultant fuel consumption, greenhouse gas emissions or carbon footprint of their trip. How bad can the damage be when you barely had time to fall asleep?
The truth is that air travel does even more damage than you'd imagine -- so much that many travelers are looking into ways to neutralize the carbon emissions from their flights. A whole host of companies have sprung up to help travelers go "carbon neutral," an increasingly popular term that was declared the 2006 word of the year by the New Oxford American Dictionary.
It remains to be seen whether carbon offsetting is the wave of the future or just a passing fad -- but with evidence mounting about the overwhelming ecological effects of air travel, it's well worth considering how you can do your part for the environment on your next trip.
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A Mile Is a Mile: Quick and Dirty Look at the Science
Air travel has a particularly negative impact on the atmosphere due to two factors, expressed here in as close to lay terms as I can muster: 1) planes emit a stew of other harmful gases in addition to carbon dioxide, and 2) gases released in the upper atmosphere where planes cruise have a much greater impact than gases released on the ground due to something called the "radiative forcing" effect. The sum total of the damage is about 1.9 times that of driving a relatively fuel-efficient car.
Radiative forcing notwithstanding, it's much easier simply to call a mile a mile. Since most of us are doing so little about the problem already, to quibble over the exact radiative forcing effect is a bit like working inside the Beltway, where people would rather argue over how to do something than actually do it. As convenient as it would be out here in the real world to live that way, we can't, so let's use the mile = mile metric.
Thus, if the average American drives 10,000 - 15,000 miles each year, it takes only a trip to Europe for a West Coaster, a trip to Hawaii for an East Coaster or a couple of cross-country flights to do as much damage (or more) as you do during an entire year of commuting and cruising in your car.
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Politics Cedes to Science (Finally)
While global warming has considerable staying power as a hot-button topic among politicians, virtually no reputable scientists and increasingly few citizens see it merely as a political issue any longer. After years in the political wilderness, global warming has come to be accepted as scientific fact by most Americans -- or close enough to fact to act.
Many travelers are willing to do something about it -- but are we willing to stop traveling? In this global economy, and in a country where extended families might live all over the country (my own family has folks in New Jersey, Florida, San Diego and Seattle), forgoing air travel entirely isn't going to happen. And the greater benefits of global travel are multifold and diverse, whether you focus on cultural, political or economic factors. So what can we do about it?
Carbon Offsetting: Solution or Panacea?
For better or worse, the concept of "carbon offsetting" has gained considerable currency in the media as one way to mitigate the environmental impact of many facets of modern living. The concept is fairly simple: for every mile you travel, or rather every ton of carbon dioxide your mode of travel causes to be released into the atmosphere, you pay a small fee to enable other folks to work on solutions to mitigate the damaging ecological effect of your travel.
There are some great things about carbon offsetting:
Unlike a lot of environmental science, the concept is extremely easy to grasp. Spew a bunch of gases into the atmosphere + plant a tree that can chew up those gases = zero sum total.
To let the market help solve some of its own problems is a promising long-term approach; several companies mentioned below are making it very easy to participate, which is a critical component of any popular movement.
For insanely busy working Americans who simply do not have the resources to plant 40 trees every time they fly to Chicago, paying a very reasonable amount to have someone else do this work is both effective and realistic.