Sunday, March 22, 2009

Is it more energy efficient to fly or to drive to your destination?

DW asked a question of me that was asked at Crunchy Chicken. Is it selfish to fly for tourism/pleasure?

Here's my take on this question. But first, it has to be framed in the "right" way.

Here's my way of asking the question, giving it two parts, each of which I will simplify into just talking about CO2 emissions at the vehicle.
1) Is it better for the environment for my family to drive or to fly to our vacation destination? Or not to go at all?

2) Is it better for the environment for me to drive or fly to a work meeting?

Let's start with 2) because it's a single person on travel and I often do not have the choice about going if I want to keep my job.

I was going to use this graphic, but it sucks. It's not clear how to account for three passengers or a ULEV vehicle.

Let's calculate based on estimates from various sources rather than a graphic. According to, my business travel this week is likely to cost about 1080 kg CO2. I've read their documentation, and it seems light, but relatively well-done. It's certainly not a research article, but I don't think it's meant to be. I'm going to trust that it is approximately right.

The personal-vehicle travel, round-trip distance is about 3900 km (2400 miles). If I took my Prius, according to, it would cost about 0.6 tonnes (metric tons) of CO2. It would also take me about 36 hours round-trip. If I took the business vehicle, an older Ford SUV, it would cost about 1.6 tonnes of CO2.

So, clearly, it would be best for the environment if I didn't go. It would probably also be best for the marriage if I didn't go (at least until I lost my job). Next best would be to drive the Prius. However, the above estimate only accounts for the CO2 cost of driving. I would need to spend at least one night each-way in a hotel. I don't want to go into the details of how much CO2 that would cost, but it would add a bit to the total trip cost. Driving the Prius may even come out to more than the air travel due to dining out for at least six meals, additional energy costs at the hotel, etc., etc., etc. I could mitigate some or a lot of that additional CO2 cost by camping and buying food from a grocer or farmer, but does anyone really think that would happen during a business trip? Perhaps if I knew the route well enough.

Now, let's answer 1). The three of us are planning a trip to Los Angeles this late Spring. Do we fly or do we drive? The round-trip driving distance is about 1600 km (1000 miles). The CO2 cost is about 0.2 tonnes of CO2, assuming 10% city and 90% freeway driving. The estimate is almost certainly for a single driver, so let's assume that with the passengers, we double the weight of the driver, which only accounts for about 5% of the total weight (10% with the passengers). So, we would not change the total emissions by an appreciable amount.

The cost to fly? claims that for three passengers, the cost would be about 1.3 metric tons of CO2 (a little over 0.4 per passenger).

So, again, it's cheaper in CO2 for us to drive our Prius. Now, the Prius is not a very common vehicle, so each person would need to do the calculation for their vehicle, but unless you drive an SUV, you are likely to put less greenhouse gas mass into the atmosphere if you drive. Also, an airplane puts the greenhouse gases into just about the worst place possible in terms of environmental damage.

Now, back to the original question. Is flying to a vacation destination selfish? Yes, of course it is. Now, that doesn't mean I think everyone needs to instantly stop traveling, but I do think people should be aware of their actions (admission is the first step or something like that). If you have to go on a long trip, you might also consider taking the train, which is much more efficient than flying.

Considering the amount of driving people in the USA do, I think we should focus on decreasing emissions from our personal vehicles (by using them less, by technology, by whatever means necessary) before we worry too much about that 10% or less effect our air travel has. Where do I get the 10%? Well, most people don't travel 1,000 miles by air for every 10,000 miles they drive. I suspect the number is much smaller. But, the total greenhouse gas emissions from air travel accounts for about 10% of transportation costs. So, not really pulling a number from my...thin air, the total amount of air travel-caused emissions is 10% or less for most people.

Driving three blocks to get groceries or coffee twice a week is much more of a selfish thing to do. I'm as guilty as everyone else.

Hi, My name is Moses and I'm a CO2 emitter.


Jennifer said...

You should get help for that. Carbon Emitters Anonymous meets weekly, I think.

Grumpator said...

I agree that it is more important to focus on reducing our regular CO2 emissions than it is to fret over our vacations. Much like saving up the money for a vacation, I can feel much less guilty about flying somewhere if I know I've done my best to limit unnecessary emissions throughout the year. Though, unlike saving up the cash, you don't want it to be an even trade.

Does that make sense? I haven't emitted enough CO2 today, so I may be in withdrawal.

Kerry said...

For those of us not great at unit conversion, can you tell how many metric tonnes 1080kg is so we can get a better sense of your first comparison?

I am Moses. said...

Jennifer: I am getting help, but the multi-step program seems to require that I blame it on someone else. Instead, I'm just quitting cold turkey.

Grumpator: It does make sense. I suspect that exposing ourselves to people different from ourselves may be more important to the future of our global civilization than completely cutting out the 10-20% of travel-based emissions that are contributed by air travel.

Kerry: A metric tonne is 1000 kg.