Published November 12, 2021 - Last Update November 3, 2023 -

Asking questions is the first step on the road to improvement. Hiding behind the real or virtual walls of your own fortification might feel comfortable at first, but may all too easily lead to distrust and escalation.

The following questions came up in discussions on LinkedIn and in conversations with the media. If you have other questions you can, if you wish, submit them via the Contact page.

1. Are the statements on this website verifiable?

Of course. The website is in fact a summary. Sources are provided along with more facts and more examples of framing in the pdf “Aviation – Solutions versus Framing“.

2. Isn’t the climate impact of aviation larger than just the CO2-emissions?

Absolutely, take for example the effect of contrails. However, the scientific support for the other effects is qualified by the EU as moderate to weak and the margins of uncertainty are large. According to some, the effect is small, according to others, the effect is a doubling of the impact of the CO2-emissions.

A few additional remarks though. If you include other effects for aviation, you must of course do the same for other sources. But, more importantly, even if there were a doubling, this would not affect the choice between modes of transport for intercontinental distances. The only alternative for these routes is passenger ships and these use seven times as much energy per passenger as aircraft do.

For continental distances, the alternative is High-Speed Rail. But in most cases HSR uses at least as much energy per passenger as aircraft do and at those distances the relative effect of contrails, for example, is very limited because of the relatively short time that an aircraft flies at the altitude at which contrails can arise in certain circumstances. For more remarks about other effects, see “Aviation -Solutions versus Framing“.

3. Are hubs and transfer passengers necessary, isn’t it much better to use direct flights only?

That’s definitely true. However, the potential traffic volume between two locations is not always large enough to support a direct flight.

That problem exists for every transport system and the solution is always the same: traffic streams that do not support direct connections are bundled and than routed to hubs where they can be combined with low volume traffic from other places. A hub airport is actually a kind of distribution center.

So, transfer traffic is not so much necessary as it is unavoidable.

4. Because of subsidies, isn’t it true that trains cannot compete with aircraft?

Actually, it is the other way around. Despite subsidies, trains cannot compete with aircraft in most cases. Indeed, fuel for international air traffic is exempt from taxation, but the train too does not pay taxes on fossil fuel used to generate electricity either.

In addition, the infrastructure for the train is heavily subsidized. Within the Netherlands for instance the train passenger pays about 45% of the costs. For HSR the subsidy is probably higher. See “Aviation – Solutions versus Framing”.

The airline passenger pays all costs. Aviation is cheap because flying in itself is a very efficient mode of transport. Furthermore virtually no physical infrastructure is required and aircraft can be deployed very flexibly, making an average load factor of around 85% possible. Relatively few aircraft are therefore needed, which also lowers the cost. Fewer than 30,000 aircraft provide all of the air traffic of the whole world.

As a result, the total energy used per person per kilometer is also rather low. All in all, from an economic point of view as well as from a climate point of view, HSR is only competitive starting at nine million passengers per year and over distances of less than 500 km.

5. For trips shorter than 500 km you should not fly, as the climb to cruising level will cost too much energy?

This is a common misunderstanding, often used in framing. Fact is that specifically on short flights almost all of the energy used for the climb is recovered during the descent. This is a consequence of the law of the conservation of energy. See for more on this the blog-post ‘Knowledge Lost‘.

6. Isn’t aviation growing so fast that aviation will be responsible for perhaps 30% of CO2-emissions in 2050?

That might happen, but then all other human sources of CO2-emissions would have to be reduced by at least 75% and, moreover, aviation would not have to participate in the energy transition. Of course the latter has to happen and the former would be a great achievement. Incidentally, the source of this frame is a clever fake-news item from an action group. So clever in fact that even the New York Times fell for it. See the post ‘New York Times Tackled‘ for an analysis.

7. Isn’t aviation a direct threat to achieving the climate goals?

Not really. With a share of about 2% of the greenhouse gas emissions, aviation is almost irrelevant. And it will remain so, despite the expected growth. Of course, aviation must also participate in the energy transition and that 2% must go to zero, but that is certainly not the biggest obstacle to achieving climate goals. The major challenge for our society is to produce sufficient amounts of emission-free electricity.

The image of aviation as the Big Bad Wolf in the land of climate change is framing and was promoted by a piece in Bloomberg, among others. See the post ‘Bloomberg’s Blooper‘ for an analysis. For the amount of emission-free electricity needed and what this means for the aviation energy transition, see the post ‘Airway to 2050‘.

If you wish, you may submit additional questions by using the Contact page.