Is EasyJet as green as it says?easyJet claims that its flights are a greener way to travel than motoring solo in a Toyota Prius. Really.

easyjet greener than a prius?Specifically, it says its flights emit less carbon dioxide per person than that bestselling hybrid car. Can it be true? It's a jaw-dropping statement given the prevailing wisdom about air travel – that it's one of worst things you personally can do in terms of global warming, and air travel by 2050 may become one of the largest contributors to heating the planet. One vacation splurge by plane can produce one and half times the global warming pollution created by a WHOLE YEAR of weekday commuting, says the Union of Concerned Scientists, which urges vacations by motor coach or train.
"The effects of aircraft emissions on the current and projected climate of our planet may be the most serious long-term environmental issue facing the aviation industry," states a report on the Federal Aviation Administration's web site.

So is easyJet's green claim legit?

I set out to truth-squad the bargain European carrier's claim by contacting Clark Williams-Derry, a statistics guru at Sightline Institute, a Seattle-based nonprofit sustainability think tank.

"The short answer is...surprisingly enough, it's not completely crazy! Really," Williams-Derry responded. But it's also very misleading.

To summarize his points:
  • easyJet's claim isn't crazy.
  • But by focusing on carbon dioxide only, the company is missing some important factors that make air travel worse environmentally than it otherwise appears.
A typical, long-haul airplane flight emits less carbon dioxide per passenger mile than a real-world Prius, Williams-Derry said. Here are estimates he drummed up for a report a few years back to compare the number of pounds of carbon dioxide spewed per passenger mile:

Prius solo driver: 0.42.
Airplane short-haul flight: 0.60.
Airplane medium-haul flight: 0.45.
Airplane long-haul flight: 0.38.

"That comes as a surprise to most people, who are used to hearing that airplanes have a big climate impact," Williams-Derry said. "And they do -- but mostly because airplane flights are long, not because planes are particularly inefficient at consuming fuel per mile."

You might wonder why there's such a big difference in the amount of carbon dioxide emitted on short flights vs. long flights. Here's why: A lot of fuel is used in taxiing and takeoff, Williams-Derry said, and a lot less fuel per mile is used at the high altitudes that long-distance flights reach. There's less air friction up there. So measured per mile, long-haul trips are more efficient than shorter ones. Super-long trips get less efficient, though, because the plane carries more fuel, and it takes fuel to carry fuel.

But easyJet has mostly short- and medium-haul flights. So that raises questions, Williams-Derry said: Why are easyJet's emissions lower than the industry average? And how does the company document the difference? easyJet's press office didn't respond to four e-mail requests for an interview.

The answer to the first question, however, according to easyJet's web site, is that its planes are newer and the company has more efficient ground operations. The planes may also be more full than average -- and the number of empty seats is one of the biggest single drivers of travel fuel efficiency when measured per passenger. easyJet's web site claims that in a warming world, "efficient low-cost airlines are the solution, not the problem."

Williams-Derry volunteered that his estimates may be debatable, or off somewhat.

But his basic conclusion was confirmed by Thomas K. Tomosky, senior applications manager at TRX Travel Analytics, who referred me to his web site's "sample enterprise report."

"You can see that a Prius and a 737 jet flying for a 600-mile trip produce about the same amount of CO2," Tomosky said. "So, easyJet's claim is probably true."

"It may be counter-intuitive to come to this conclusion," Tomosky said, "but you have to consider the fact that a 737 can carry up to 189 passengers. So, does it seem reasonable to you that 189 Prius trips emits as much CO2 as one 737 trip? If so, there is the equivalence."

Another expert agreed it's not totally cuckoo. Scientist Andrew Heymsfield of the National Center for Atmospheric Research in Boulder checked with a colleague on my behalf. The answer is that the airline's green claim is sort of correct: Typically, if an airplane is full of passengers, the per-passenger emissions of CO2 are comparable - or less - than the emissions of a car traveling the same distance. One way to check this is to look at the price of the airline ticket and compare it to the cost of fuel to drive the same distance. If you pay about the same for the airline ticket, and the airline is making money, then the fuel costs must be less for the flight than for the drive.

But it's not a matter for green bragging rights, experts say. Nope. Not when you consider the rest of the story.

Carbon dioxide makes up only one-third of a plane flight's total climate impact, explained Andrew Dessler, a professor in the Department of Atmospheric Sciences at Texas A&M University. Another third comes from water vapor emitted by planes directly into the upper troposphere, where it can lead to the formation of thin cirrus clouds (and these clouds provide additional warming). The final third comes from emitting oxides of nitrogen into the upper troposphere, which forms ozone. Ozone is a greenhouse gas.

Once you consider these extra factors, Williams-Derry estimates that the emissions spewed per passenger mile really look more like this:

Prius real-world solo driver: 0.56.
Airplane short-haul flight: 0.90.
Airplane medium-haul flight: 1.05.
Airplane long-haul flight: 0.97.

So airplanes generally are worse than a Prius. That said, estimates for these added factors can vary considerably -- there's no one value that everyone accepts, as far as Williams-Derry can tell.

easyJet's web site makes some other green pronouncements – like, it's a myth that aviation CO2 is more damaging.

"Nobody thinks that it's the CO2 emitted at high altitude that creates special problems," responded Williams-Derry. "It's stuff like ozone, which is warming if emitted in the upper troposphere, where airplanes fly. So they're correct, CO2 at altitude is a myth, but it's like they're arguing that underpants gnomes don't exist: nobody (at least nobody reasonable) ever said they did."

In the end, easyJet is "kinda cheating" when it claims it's greener than a Prius based strictly on carbon dioxide emissions, Williams-Derry said. Added with the company's aviation CO2 myth claim and some other points in its myths vs. reality leaflet, "this seems to be veering into greenwashing."

As Dessler of Texas A&M concluded: "I think it is clear the total climate change due to flying is much larger than from driving a Prius."

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