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Though the scientific and moral case against flying is robust, the reaction to making it has made me lose faith in the power of individual action. I think the only solution is a carbon price: see why in my new introduction.

Does it matter if you kill someone if they won’t die for thirty years and you don’t know who it is? Most people, and lawyers, would argue that it does. Killing is surely wrong except with exceptional mitigating circumstances, not just “well, they’re only Africans, and I happen to like going to the Canaries.” And, talking of the future, what about climate-saving technology? Well, in many sectors this is a big possibility, but not so with air travel: electricity, hydrogen, new aircraft shapes and radical improvement of current designs are all off the cards for the foreseeable future. Kerosene is going to be the only economically viable plane fuel for years to come which, when its continued use is highly unethical, can’t be good news.

In depth

I’m not morally obliged to prevent the potential death of some African. Stabbing someone in the street is one thing, but the possible death of a non-specific individual thousands of miles away who probably hasn’t even been born yet? Give me a break.

It is true that you can’t point to a tonne of carbon given off by a plane, demonstrate that it was those CO₂ molecules which caused the 0.0001°C global mean temperature rise which wouldn’t have otherwise happened which resulted in that natural disaster which killed those specific people and that therefore your holiday contributed to one hundredth of the death of that particular individual. But the fact that this argument is based on statistical ethics, rather than the direct attribution one could make about a gunshot, doesn’t make the moral imperative any less strong.

Everyone can agree with the premise that “killing is bad”. More carefully put, “human deaths should be avoided where doing so will not cause insurmountable negative consequences to the well-being of those still alive”.

There is then, surely, an obligation upon us to prevent future death. It would be morally reprehensible to conspire to set a nuclear bomb in Africa with a thirty-year timer, even though you might not know exactly which few million people would be standing nearby when it went off.

Citing the law as a reasonable moral thermometer, future murder is just as illegal as murder committed in the present. If you were to set a trap on a busy high street with some kind of time delay on it, if it went off and killed someone you could still be charged with murder or at least gross negligence manslaughter for leaving a hulking great dangerous trap lying about the place where it might kill someone.

Randomised murder is also illegal; if you discharge a gun into a crowd, it is reasonably within your contemplation that someone will die as a result of your actions even if you don’t know exactly who, and so you could expect a murder charge to follow swiftly.

Thus, it doesn’t seem unreasonable that future, randomised death caused by someone’s actions shouldn’t be attributable to them. Your carbon emissions will cause a change in global mean temperature which will lead to loss of life. It might be rash to bring some fraction of a murder prosecution against frequent fliers, but the analogy holds if you look at the spirit of the law rather than the letter: killing is immoral, so flying is immoral.

I will continue to use planes and, as soon as there is a green alternative, I will embrace that. Aircraft are constantly getting more efficient, so soon it won’t be anything like as immoral as you claim. You don’t know what technological advances will be made in the future.

This is incorrect on two counts. Firstly, the possibility that it will be less damaging in the future is no reason to make an action less morally dubious now, when it certainly is damaging. Secondly, though, there is no technological solution.

Cars, for example, have alternatives on the table; electric models, hybrids, hydrogen fuel cells, all currently in development, some better than others, and it’s not totally inconceivable that there will be a car which can be driven with a clear environmental conscience with currently envisaged technology.

Aircraft have no such alternatives. A plane powered by batteries would be too heavy to take off. Hydrogen carries less than half as much energy per unit volume as kerosene, which would mean planes would need to have a larger fuselage to carry enough for a journey, increasing drag1. It would also need to be stored at extremely low temperatures, requiring pressurised and insulated fuel tanks1. And, all this impracticality aside, hydrogen produces only water vapour when burnt; a boon at ground level in cars and such, but detrimental to the environment when released at high altitude—scientists are currently unsure whether or not it would be similar or worse in its effects to the carbon dioxide it would replace.

As for increasing efficiency of current designs, the evidence that this is possible is minimal. The first issue is the sheer reductions in fuel consumption necessary to make a significant difference. Given that a plane flight can use up years of sustainable carbon budget, if you want to have anything left to light your home or drive to work, fuel usage is going to have to drop by factors of ten or so to become reasonably practical. This would be a massive improvement, and even fairly small efficiency savings are unlikely to be realised.

Aircraft have been the same basic shape for seventy years2, and this means that seventy years of models in wind tunnels, prototypes in the air and, more recently, extensive computer modelling have not produced any serious rethinks in their shape. This means there are almost certainly no major efficiency savings in this mature field3.

There has been a 70% reduction in fuel consumption by jet engines in the last forty years, but the progression towards the optimum turbofan engine is pretty much over4. We just can’t squeeze much more efficiency out of the current designs.

There are those who think that fuel economy can be improved massively with an overhaul of current thinking. For example, some proponents argue that ‘blended wing’ designs, where the fuselage and wings of an aircraft are made into one giant aerodynamic wedge, will improve fuel efficiency by some 30% (useful, but still nothing like enough to be significant), but these designs are decades from widespread commercial implementation1. Replacement engines, like scramjets, are still in the highly experimental stages of development5, and it is likely that supersonic aircraft are up to five times worse than their subsonic counterparts in environmental impact anyway. Thus, the most optimistic predictions for substantial improvements in efficiency are decades away from mass production.

There are proposals to make air traffic control more efficient, or tug planes to and from “starting grids” near to runways rather than making them taxi6, but these are again ways to save a few percent on a flight’s total emissions; all worthwhile savings which will allow more flights in future, but nothing World-changing.

Even BAA Heathrow admit that “aviation is growing at a faster rate than technology can reduce emissions and at present there is currently no significant alternative to burning kerosene” 7.

So, in a field dominated by refinements of current designs and strategies rather than a radical rethink of air technology, it looks highly unlikely that anyone will produce the kind of ten-plus-fold increases in efficiency which taking frequent flights and complying with a reasonably strict carbon budget would require. Shaving off inefficiencies here and there might allow us to take a few more flights in future, but all it might mean is that we’ll be cutting 85% rather than 90% of air travel.