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2015-12-08 13:38:45
Dec 7th 2015, 15:44 by A.W. | WASHINGTON, DC
THE winter holidays are around the corner, and that means a spike in air
travel. A year ago, according to America s Bureau of Transportation Statistics,
the number of miles travelled on the county s airlines jumped 10% between
November and December, before declining 16% over the following two months. So
as you book trips to see friends and family (or to travel for business but let
s hope not), how guilty should you feel about the extra carbon you are causing
to be spewed into the atmosphere?
The answer depends on whether you consider your actions as an individual or as
a representative of the offending species.
By the former criterion, Gulliver has good news for you: environmental damage
caused by flying is a lot less than it would have been a few decades ago.
According to a study by Michael Sivak at the University of Michigan, picked up
by Mother Jones, the average amount of energy consumed per mile, per passenger,
fell by 74% on domestic flights in America between 1970 and 2010.
There are two main reasons for the drop. First, aircraft manufacturers are
obsessed with making their planes more fuel efficient, and they are doing
pretty well. As they have added thrust, reduced wind resistance and shed
weight, they boosted the fuel efficiency of new planes by nearly 50% between
1968 and 2014. Second, flights are fuller than they used to be. According to
the Bureau of Transportation Statistics, since 2002 (admittedly not the fairest
baseline, since 9/11-related fears were still fresh, but that s where the data
begin) the average flight has gone from 70% of capacity to 85%. More passengers
means less fuel consumed per passenger.
As a result, on average a commercial jet now requires only half as much fuel to
move someone one mile as a car does, according to the Michigan research.
(Driving has become more efficient, too just not nearly as fast as flying has.)
Of course virtually no one flies just one mile. The average domestic flight is
914 miles about 100 times longer than the typical car journey. Since longer car
trips generally take place on fast-moving highways while short flights consume
a bigger proportion of their fuel on takeoff and landing, driving is more
efficient for trips between 300 and 500 miles.
For all of that, in the aggregate travellers have more than undone the gains in
fuel efficiency by flying a whole lot more than they used to. The Department of
Transportation reports that on domestic routes, passenger miles rose from 31
billion in 1960 to 565 billion in 2010 a far greater change than the
improvements in fuel efficiency or the drop in marginal emissions per
passenger.
Of course, you can t help what others are doing. And if you still feel guilty
about the emissions you are contributing, diminished though they may be, you
can assuage your guilt by buying carbon offsets. According to the offset
calculator on the ClimateCare website, just $12.40 buys enough offsets to
compensate for a round-trip flight from Los Angeles to New York. The offset
system does have its flaws. Not least of which is that it does exactly what it
s intended to do: make people feel less guilty about activities that harm the
planet. For those that really care, there is always the train.