How Green Is Your Airline? (Hint: It's More Than Carbon Emissions)

One airline is advertising that its fleet emits less carbon emissions than a Prius per passenger mile. Obviously there's more to being "green" than low carbon emissions. But let's follow this story.

EasyJet, a low cost carrier (LCC) in Europe, advertises that its fleet produces lower carbon emissions, i.e. CO2, per passenger mile than "the best selling hybrid car." If so, this would be good news after all the bad news we've heard regarding airline carbon emissions. I mean, the Union of Concerned Scientists advises people to take vacations by bus or train to reduce the climate change impact. And the US Federal Aviation Administration, which has as part of its charter to promote the aviation industry, says that the effect of carbon emissions on the climate may be the single greatest long-term threat to the aviation industry. The easyJet advertising also makes me wonder where they got their planes and why no one else has them.

Given all that, you might conclude that easyJet's claim could use some investigating. Clark Derry-Williams of the Sightline Institute here in Seattle did just that. Here's his take on easyJet's claims and aviation carbon emissions in general.

Derry-Williams determined that easyJet's claim isn't completely unfounded. But it is a bit misleading.

If one focuses only on CO2 emissions, then airplanes can be quite efficient. Derry-Williams found that emissions per passenger mile look something like this:

• Prius solo driver: 0.42.


• Airplane short-haul flight: 0.60.


• Airplane medium-haul flight: 0.45.


• Airplane long-haul flight: 0.38.

Here's the misleading part: easyJet assumed that their flights were full, but that the Prius had a solo driver. Just add a single passenger to the Prius, and the carbon emissions per passenger mile drop by half. Make it a family of four, and it's no contest.

Also, easyJet has mostly short haul flights, which should come with the higher carbon emissions. Short haul flights have higher emissions because a disproportionate amount of the fuel is burned in taxi, takeoff, and climb out. They are actually pretty efficient once they are at altitude.

But there's more.

Only about one-third of an aircraft's emissions are CO2. The other two-thirds are water vapor, which causes clouds that help retain warmth like a blanket, and various nitrogen oxides, which decay into ozone, a greenhouse gas. Taking all that into account, Derry-Williams estimated the following emissions per passenger mile.

• 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, how green is your airline? Well, let's think about it a bit.

• They all get their planes from the same two manufacturers. So the equipment doesn't make much difference.


• If you're counting ALL emissions, and not just carbon emissions, the route map doesn't make a lot of difference either.


• The use of biofuels might be a difference, but that will depend on where the energy to make the biofuel came from. Biofuels are no panacea.

The surprise take away here is that an airline's "greenness" comes down to its ground operations. Are they using electric tugs rather than diesel? Are they taxiing on a single engine rather than multiple engines? Have they optimized their dispatch operations to reduce or eliminate waiting time on the tarmac and circling time in the air? These are the places the differences are made. Not in the sky.

Paul Birkeland lives in Seattle, WA, US, and develops Strategic Energy Management Systems for government, commercial, and industrial organizations through Integrated Renewable Energy.

Photo: BiomassAuthority.com