There are two questions people usually think about when it comes to air travel: can I free my schedule for the trip and how much is the ticket? The reason this happens is because these are the only two criteria directly impacting the person in question. However, there are a few other….
A British physicist called David MacKay was frustrated by the amount of hand waving and vague assertions of “huge amounts of this” and “gigantic amounts of that” which people frequently mention when discussing energy use. He decided to put an end to it so he prepared a framework for people to intelligibly discuss the issues: it comes in form of a brilliant book called Sustainable Energy – Without the Hot Air. The reason the book is brilliant is its basic idea which is to list key energy sources and uses, provide simple models to get rough estimates and in doing so, allow people to get a feel for where we are in terms of energy use and what it means to be sustainable. One of the chapters of the book has something to say about air travel considerations other than time and money.
A Boeing 747, he says, has a reach of 14 000 km, carries a bit over 400 people and uses 240 000 litres of fuel to do it. Its fuel contains 10 kWh of energy per litre. That comes down to 240 000 L / 400 passengers or roughly 600 L, which in turn means 600 L * 10 kWh = 6 000 kWh of energy per passenger. As most passengers tend to come back to where they came from, the right figure is really 2 * 6 000 kWh = 12 000 kWh. Now, the average trip might be shorter than that, but then the plane is never more than 80% full and there are other considerations…in short, the figure is about right. So, if you take one such trip per year, your daily energy footprint comes down to 12 000 kWh / 365 days which roughly equals 30 kWh/day. Allow me to repeat that: 30 kWh/day is the daily energy cost of a single intercontinental flight per year.
The average energy consumption in Great Britain is 125 kWh per day per person (250 kWh in the USA, but we will not go into that now). This is the equivalent of keeping 70 incandescent light bulbs always on. It would take a world-class cyclist 10 days of non-stop cycling to release that much mechanical energy. More importantly, this means that the average person (taking one long flight per year) spends no less than a quarter of all the energy he or she spends in a year on a single long-distance plane trip. Think about this for a second: the trip might last 10 days, i.e. 3% of the year, but it takes 25% of all energy spent during the year. However, unlike shelter, food, medical services etc, it is not something people couldn’t usually do without. In today’s world of cheap flights it is heresy to say so, but squandering the last remains of our energy resources – the same ones we use for food production for 7 billion people – the human race as a whole is demonstrating aspects of extreme psychopathic behaviour. Please note that this is not a phrase: by definition, psychopathic behaviour is “characterized primarily by a lack of empathy and remorse, shallow emotions, egocentricity, and deceptiveness”.
The other part of the story is the effect a plane trip has on the environment, most prominently on climate change. We have already seen that a Boeing 747 uses 600 L of fuel per passenger to travel 14000 km or roughly 4 L of fuel per 100 km. This is roughly twice the fuel efficiency of an average single-occupant car. In other words, if instead of taking a plane trip from London to Shanghai, all passengers travelled in pairs in 200 cars, the net CO2 output would be almost identical. If this kind of wastefulness isn’t shocking enough, because they emit CO2 at higher altitudes, CO2 from air travel has about three times as much impact compared to CO2 emitted at ground level. It is worth keeping in mind that in difference to 14 000 km of car travel which usually takes up to a year for the average driver to accumulate, this all takes place in a matter of half a day. Emitting 130 g of CO2 per person per km, the total CO2 output per passenger in one flight is 130 g * 14 000 km or roughly 2 tons. What other decision could you make that could produce 2 tons of harmful waste in a single day?
Hoping for technology to step in and save the day is mostly wishful thinking: while the global fleet does evolve more or less continuously, there hasn’t been a significant improvement in plane efficiency in decades (figure 17 in this article) and there is nothing radically new on the horizon. It appears unlikely we will ever see a 50% improvement in aeroplane fuel efficiency. With the possible exception of the Hummer, air travel is the definite, undisputed champion of environment-hostile modes of mass of transportation.
Reasoning about air travel such as the above tends to trigger certain types of reactions. One of them is “Well, how do you expect us to travel the world?”, but it is merely a childish false assumption of entitlement, stemming from the completely wrong assumption that if it can be bought and is legal, you have an absolute and moral right to buy/spend it. It is easy to see that a number of features of modern life are not nearly low footprint enough to be deliverable to a population of 7 billion and air travel is definitely among those. At the moment, it is mostly the developed and to a degree developing countries which enjoy the benefits of modern western lifestyles and the system has already hit a resource and energy availability wall. There is no way to scale our air travel infrastructure to serve the significantly larger population which does not yet have access to it. The point is that, to answer the hypothetical question, you are not expected to travel the world at all because there is no sustainable, practical way to do so, at least not yet. Short and medium distance trips can be handled by train which is a very resource efficient mode of transportation, but there is no suitable replacement for flights across oceans and the conclusion it leads to (in a sustainable world, the only kind of world with a future) is that we should reduce and nearly stop such travelling, rather than default to air travel, a system doomed to run out of fuel within a few decades.
“It makes no difference if I fly or not.” “The future is not my responsibility.” The personal impact argument is another way of saying that no raindrop accepts the blame for the flood. Airlines, travel agencies and other business push with all their might to create demand for flights and then they do everything they can to meet that demand. If there is less demand, there will be less travel overall, less flights, less resources being used and less pollution. The fact that a flight is not going to be cancelled because there is one passenger less does not make the contribution worthless. Individuals make statements like that all the time: people who cycle around town, who use the train, who don’t eat fruit out of season… it has a fair chance of adding up to a significant impact: reducing the number of passengers by as little as 5% may halve an airline’s profits or even create losses: an empty plane flight will still incur over 75% of flight costs and margins are thin. But that is just the start: people thinking the same way about sustainability can organize themselves, coordinate to raise awareness, lobby for legislation change, make it more difficult for airlines to externalize their costs etc. Other generations will come after us and we should find some satisfaction in being able to say, each and every one of us, that we did the best we could, the right thing. The fact that we are not forced to do so by law or force is no alibi. If anything, the fact that most of our laws deal only with the present and all but ignore the rights of future generations is no reason to abuse the situation. A tragedy of the commons is a recurring theme in nature. However, we are the only species we know of with significant capabilities of predicting the results of our actions. If in spite of that we still succumb to our immediate desires, sacrificing the future along the way, we will have trampled over that which fundamentally makes us human.