Petrol-wise, Kerosene-foolish?

A guest post by Bernardo Malfitano.

Michael recently sent me two recent articles featured on the Drudge Report which talk about comparing the emissions and environmental impact from different modes of transportation. I sent him an email explaining how tricky it is to make such comparisons, and apparently he would like me to contribute this analysis directly to his blog. I'm really honored. So, um, hi everyone!

First of all, so that we're clear, let me say I am probably much more of an environmentalist than most of Michael's readers. I think recycling is important (even if it is more expensive than just dumping old stuff and making new materials from scratch), and I think we're responsible for putting way too much CO2 into the atmosphere, which is probably causing climate change. That having been said, this post is about misleading use of numbers in the media, and about misguided environmental policy, not about anthropogenic climate change, so I'm sure we can all agree.

The most obviously ridiculous article is about how some politicians in the UK want to tax airlines (and thus effectively tax travelers) for the CO2 their flights generate. These politicians hope that this will motivate airlines to get more efficient jets, by making it more expensive to fly less-efficient jets:

Mrs Beckett urged Brussels to speed up plans to enforce the levy on airlines to encourage them to fly more fuel-effecient planes and deter people from travelling by air.

I am astounded that these politicians fail to realize that flying less-efficient jets is ALREADY more expensive for airlines: More fuel per mile per passanger means higher ticket costs and fewer passengers. When has Boeing or Airbus ever released an airliner that needs MORE fuel than its predecessors? No airline wants airplanes that make their tickets more expensive. Better fuel economy = more passengers. You don't need a law to make it so.

The average jet pumps close to a tonne of carbon dioxide into the atmosphere for each passenger it carries from London to New York.

This number is also either misguided or misleading, probably both. Of course you burn a lot of fuel, and generate a lot of CO2, when crossing the Atlantic. It's thousands of miles! If somehow you could drive that route, you'd be generating similar amounts of CO2. Jets only sound like they burn too much fuel and generate too much CO2 when we forget that they fly for thousands of miles, and that any car (over the period of a few months that it takes us to drive that far) would generate similar amounts. So you might as well say that traveling is bad for the environment. No point in taxing jet flight any more than travel via train or highway.

(And sure, buses use less fuel per passenger than planes or cars, but their hydrocarbon emissions tend to be pretty horrendous - they're the kinds of emissions that cause LA to look like this).

The best way to compare the environmental impact of different modes of transportation is the way airlines compare the efficiency of commercial jets: Gallons of fuel per passenger per mile. How much fuel is needed for each passenger in the vehicle, for each mile of the trip? Since most fuels are pretty similar, and since most engines these days do a very good job of converting almost all of it into CO2 ans H2O, this gallons-per-seat-mile metric allows you to compare the relative efficiencies of transport by any car, any airplane, etc.

A 767 can use less than 0.01 gallons of fuel per seat mile, while a large business jet like a Gulfstream V needs 0.04 gallons. Both these numbers assume the jets are full (375 people in the 767, eighteen in the G5). A fairly efficient thirty-MPG sedan with one person in it will use 0.0333 gallons per mile per person, not much less than a full Gulfstream. (And most cars do NOT get 30mpg driving around town. If you get 25mpg, you just match the Gulfstream). Even a twenty-MPG SUV with five people in it will use 0.01 gallons, about the same as an efficient airliner, and much better than a Prius or Insight with a single occupant.

The bottom line is, when you travel by airliner, you're burning as much fuel as you would be if you took a group road trip and drove that distance. And if you fly in business jets, you're using 3 or 4 times as much fuel, about the same as when driving alone. A bunch of people generate less CO2 and use less fuel by riding in a Suburban than they would if they each drove a Honda Insight. And whether you drive or fly a distance, the impact of your trip is about the same - it would just take you a heck of a lot longer to drive that far.

This very important number - how many passengers are travelling in the vehicle - is often forgotten when the environmental impact of cars is discussed. The fact that the fuel consumption in a (full but still roomy) business jet is comparable to the fuel consumption of a normal car (with one person in it) is completely ignored by this article about celebrities who drive hybrids but fly bizjets:

Julia Roberts: ...Chicago to LA, 1,749 miles in a private jet.

Gas guzzled: 2,100 gallons of jet fuel.

Julia would have to drive 30,000 miles, or roughly once around the earth and then some to even out her consumption in the air.

Yes, the airplane needs twenty times more fuel to fly a mile than the Prius does to drive a mile. Big deal. But how many people can fly in the airplane? And how many people usually ride with Julia in her Prius?

Of course, riding a bizjet by yourself is ridiculously wasteful. But don't those people usually have entourages anyways?