Air travel continues to grow despite its environmental cost.

The number of passengers travelling by plane increases every year, although everybody knows that aviation damages the environment. This creates serious problems, but there are some possible solutions.

The first problem is pollution. Aeroplanes burn a very large quantity of fuel and produce carbon dioxide high in the atmosphere, where the effect is even stronger. One return flight from Europe to Asia produces more emissions than a person produces in a whole year by driving a car, so the damage of this industry is enormous.

The second problem is that it is very difficult to change this technology. Cars can use electricity, and factories can use solar or wind energy, but a battery is too heavy for a big aeroplane flying ten hours. So we cannot simply replace the fuel with a clean alternative in the next few years.

One solution is to make flying more expensive. At the moment aviation fuel is not taxed in many countries, although petrol for cars is taxed heavily. If governments removed this advantage, tickets would cost more and fewer people would fly for a weekend.

Another solution is to develop fast trains. For a journey of five hundred kilometres, a modern train takes almost the same time as a plane if we count waiting at the airport, and it pollutes much less. If governments invest in railways and make tickets cheaper, many short flights will disappear.

In conclusion, air travel produces a large quantity of emissions and has no clean alternative today, but taxing fuel fairly and building good railways can reduce the number of flights.

Passenger aviation continues to expand despite widespread awareness of its environmental cost. The problem is more difficult than it is usually presented, and this determines which responses are realistic.

The first difficulty is technical rather than moral. Jet fuel has an exceptionally high energy density, and no available alternative comes close at the range and payload commercial aviation requires; batteries are far too heavy for long flights and are likely to remain so. Unlike electricity generation or road transport, where clean substitutes already exist and merely need deploying, aviation has no mature replacement waiting. Emissions released at altitude also have a greater warming effect than the same quantity at ground level, so the sector's impact exceeds its share of fuel burned.

The second point is that the burden is remarkably concentrated. A small minority of the world's population takes the majority of flights, and a large share of the population has never flown at all. This matters because the environmental cost is borne by everyone while the benefit accrues to comparatively few, and because it changes what a fair remedy looks like.

The most defensible solution follows from that concentration: a frequent flyer levy that rises with each additional flight taken in a year. This leaves an annual family holiday largely unaffected while pricing the repeated discretionary trips that generate most emissions, which a flat tax would not.

Removing the fuel tax exemptions that aviation enjoys in many countries would also correct an obvious distortion, since road fuel is taxed heavily while jet fuel frequently is not. Investment in high-speed rail addresses the short routes where a genuine substitute exists, and where door-to-door journey times are already comparable.

In conclusion, aviation is difficult to decarbonise and its costs fall on people who mostly do not fly. Since supply-side solutions remain distant, pricing that targets frequency and substitution on short routes are the credible responses.

Aviation occupies an awkward position in climate policy, and pretending otherwise produces weak answers. In most sectors the technology to decarbonise already exists and the obstacle is cost or politics. In aviation it does not, which means the usual reassurance that innovation will resolve the problem is considerably less available here than elsewhere.

The constraint is energy density. Jet fuel stores an enormous amount of energy per kilogram, and that ratio is what makes long-range flight possible at all; batteries are roughly an order of magnitude worse and the gap is a matter of chemistry rather than engineering effort. Synthetic and biological fuels exist but remain scarce and expensive, and would compete for land and renewable electricity needed elsewhere. Meanwhile emissions released at cruising altitude produce warming effects beyond carbon dioxide alone, so the sector's contribution exceeds what its fuel consumption suggests. Abatement here is genuinely hard, not merely unpopular.

The second feature of the problem is its distribution, and it is decisive for policy. Flying is extraordinarily concentrated: a small minority takes the great majority of flights, while a large share of humanity has never flown once. The costs, however, fall on everyone, and disproportionately on populations least able to adapt to a changing climate. Any remedy that ignores this — a flat ticket tax, for instance — is regressive, pricing an infrequent traveller out of a rare holiday while barely registering with someone flying twenty times a year.

The remedy that follows is a levy scaled to frequency rather than to the flight itself, rising with each additional trip within a year. This targets exactly the demand that is genuinely discretionary and leaves occasional travel largely untouched, which makes it both more effective per unit of restriction and far easier to defend publicly than an across-the-board increase.

Two further measures address obvious distortions. Aviation fuel escapes taxation in much of the world while motorists pay heavily on every litre — an exemption with no principled justification that makes flying artificially cheap relative to alternatives. And on routes under roughly five hundred kilometres, high-speed rail is already competitive on door-to-door time; substitution here is achievable now and removes a meaningful share of flights without asking anyone to travel less.

In short, the problem is a sector with no near-term clean substitute whose costs are borne overwhelmingly by people who do not use it. Because supply-side answers are decades away, the realistic lever is demand — applied to frequency rather than to travel as such, which is what makes it both proportionate and fair.