NEW YORK, 19 NOVEMBER 2008
Dear EarthTalk: How can I determine if it is more eco-friendly
to fly or drive somewhere?
Christine Matthews, Washington, DC .
Most experts agree that driving in a relatively fuel efficient
car usually generates fewer greenhouse gas emissions per capita
than flying - and it only gets better when you carpool. The
simple answer is that driving in a relatively fuel efficient
car (25-30 miles per gallon) usually generates fewer greenhouse
gas emissions than flying. In assessing the global warming
impact of a trip from Philadelphia to Boston (about 300 miles),
the environmental news website Grist.org calculates that
driving would generate about 104 kilograms of carbon dioxide
(CO2) - the leading greenhouse gas - per typical medium-sized
car, regardless of the number of passengers, while flying on a
commercial jet would produce some 184 kilograms of CO2 per
What this also means, of course, is that while even driving
alone would be slightly better from the standpoint of
greenhouse gas emissions, carpooling really makes environmental
sense. Four people sharing a car would collectively be
responsible for emitting only 104 kilograms of CO2, while the
same four people taking up four seats on a plane would generate
some 736 kilograms.
Journalist Pablo PÃ¤ster of Salon.com extends the comparison
further to a cross country trip, and comes to similar
conclusions. (Differences in the math are attributable to the
use of slightly varying assumptions regarding fuel usage and
source equations.) Flying from San Francisco to Boston, for
example, would generate some 1,300 kilograms of greenhouse
gases per passenger each way, while driving would account for
only 930 kilograms per vehicle. So again sharing the drive with
one or more people would lower each individual's carbon
footprint from the experience accordingly.
But just because driving might be greener than flying doesn't
mean it always makes the most sense. With current high gas
prices, it would cost far more in fuel to drive clear across
the United States in a car than to fly non-stop coast-to-coast.
And that's not even factoring in the time spent on restaurants
and hotels along the way. Those interested in figuring out
driving fuel costs can consult AAA's nifty online Fuel Cost
Calculator, where you can enter your starting city and
destination as well as the year, make and model of your car to
get an accurate estimate of what filling 'er up will cost
between points A and B.
Once you've made your decision whether to drive or fly,
consider purchasing carbon offsets to balance out the emissions
you are generating with cash for renewable energy development.
TerraPass, among others, makes it easy to calculate your carbon
footprint based on how much you drive and fly (as well as home
energy consumption), and then will sell you offsets
accordingly. (Monies generated through carbon offsets fund
alternative energy and other projects, such as wind farms, that
will ultimately take a bite out of or eliminate greenhouse gas
Of course, an individual's emissions from riding a bus (the
ultimate carpool) or a train (many of which rely solely on
electric power generated by their own motion) would be
significantly lower. Paster adds that a cross-country train
trip would generate about half the greenhouse gas emissions of
driving a car. The only way to travel greener might be to
bicycle or walk - but the trip is long enough as it is.
CONTACTS: Grist; Salon; AAA Fuel Cost
Calculator; TerraPass .
GOT AN ENVIRONMENTAL QUESTION? Send it to: EARTHTALK, c/o E/The
Environmental Magazine, P.O. Box 5098, Westport, CT 06881;
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