I've been trying to fly less and less because it seems the right thing to do. But I can't quite counter this thought:

The EU Emission Trading System (ETS) covers commercial aviation. So passenger flight emissions will comply with the goals that the EU has set out (neutral 2050, 55% 2030). The ETS had some startup problems, but works okay now, and EU is serious about it (e.g. fit for 55).

If I don't fly, the airline can sell "my" emissions to a different industry and it'll get emitted somewhere else. It's not this granular, but you get the idea: there's a ceiling/cap and probably everything under that ceiling will be emitted somewhere.

So does my choice to fly or not fly affect actual, total emissions given the new regulations?

Feels like I'm missing something... but maybe I'm not and ETS just works (good enough, for aviation). Can someone confirm or disconfirm this reasoning?

  • It's more of a moral issue -- if you fly, you're contributing to the climate problem. If the airline sells your emissions to someone else, it's the buyer's fault, not yours.
    – Barmar
    Dec 26, 2021 at 22:47
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    @Barmar Since you say it's a moral issue, can you answer it from a consequentialist angle? What immoral consequences are there from flying within the EU ETS system?
    – J.H.
    Dec 26, 2021 at 23:40
  • I'm not a philosopher, but I was thinking of personal ethics -- you'll feel bad for helping the airlines contribute to climate change.
    – Barmar
    Dec 27, 2021 at 5:15
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    @usr-local-ΕΨΗΕΛΩΝ Are you suggesting that OP is obliged to fly in order to support those working in the airline industry? If so, then note that most of that money doesn't actually go to the staff, someone who gets laid off as an eventual result can get another job (possibly in the industry where you're spending the flight money instead), the government can support them, or you can just give that money directly to poor people instead if you feel strongly about it.
    – NotThatGuy
    Dec 28, 2021 at 14:56
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    @usr-local-ΕΨΗΕΛΩΝ Many people will continue flying as long as they're able and it's affordable enough, and this should overshadow the few people who might reduce how often they fly to prevent any potential economic disaster. Even the most frequent flier shouldn't have to worry in the slightest about an economic disaster if they just suddenly stop flying altogether today. I'm not commenting on the ETS - this may or may not have been a consideration there, and I'm not commenting on what all of humanity should do, I'm simply commenting on individual action.
    – NotThatGuy
    Jan 3 at 16:10

4 Answers 4


You probably need to look at it from the point of view of supply and demand in classical market theory.

If there was very limited demand for flying, the industry would not be able to afford any ETS on the auction market, so it would stop emitting. Rather, to put it differently, if customers were unwilling to pay any extra costs for emissions from flying, the industry would not be able to buy emissions permits and would rather sell off its allocations.

On the flip side, if customers were willing to pay any price to continue on flying, the industry would just buy off permits from other industries and continue flying.

In aggregate, if no one was ready to pay extra to pollute - across industries -, consumption would recenter on low-emission activities and goods.

Things that somewhat muddle this issue is how aggressive the EU would be to retire allocations and auctionable capacity if demand and prices for CO2 was low. Would it consider that say $40 a ton indicated low demand for CO2 and reduce the cap the following year or decision phase? At the cost of shutting down industries? Conversely, if all capacity is fully purchased, what happens if someone can't buy capacity on the market? Do they just pay a fine, after the fact? If so, the tolerance of high prices by customers would cover that.

Looking at it from an abstract economic viewpoint, rather than overmuch on current and future ETS specifics, the willingness to "pay any price" to participate in carbon intensive activities would reduce the price elasticity of demand which is not what you want to happen if you want to reduce actual emissions rather than push numbers around.

Any time you participate in those purchases you contribute, in a small way, to push up that aggregate demand.

If this seems somewhat uncertain it's because the ETS itself seems to have been somewhat of a moving target, in the size of its initial allocations and industrial and national allowances. This isn't unique to the ETS, of course, as emission costs begin to bite, it remains to be seen if governments will keep turning the screws.

Also, the airline can sell "my" emissions to a different industry and it'll get emitted somewhere else. That's a hypothesis in your question that is far from evident.

  • are all emissions used up and capped? In other words, if there is 2GT of CO2 allowed, are they all used up? Is there a hard limit and no more CO2 gets emitted? If not, any use you make would not necessarily be emitted somewhere else.

That's actually a surprisingly hard thing to figure out with ETS. What were the total limits and were they all used up? What happened after that? So far, much of the discussion seems to be be about allocations (not paid for) vs. auctions (which polluters have to buy). Nowhere is it mentioned that hard limits were reached, past which people could not pollute any more.

Meaning your 1 extra ton of flying CO2 means 1 incremental extra ton of CO2. No more, no less. And that is certainly true if no hard limit was reached past which no one else could pollute. This is as things sit today, not as they may be 10 years down the line, but these is the context affecting a decision to fly or not today.

Furthermore what we can see is that most industries did cut down over time, even with the (to date) rather toothless ETS.

With the exception of the airline industry (my bolding).

Aviation emissions halt rise

Aviation activities covered by the EU ETS are estimated to have emitted just 28.9mn t CO2e in 2020, down by 39.3mn t CO2e from 68.2mn t CO2e in 2019.

This marks the first time in seven years that aviation emissions under the scheme have declined, and wipes out a cumulative rise of 14.7mn t CO2e between 2014-19. Only flights that take off and land within the European Economic Area are covered by the system.

BTW, while I am not fully convinced this is a Politics question, the degree to which future EU-decided ETS policies is likely to affect your question makes it at least somewhat relevant.

End of the day, the only certainty is that when you fly and emit a ton of CO2 a ton of CO2 has been emitted.

  • Thanks! I take your points about supply & demand and price elasticity. I filtered out two reasons not to fly: 1. Caps are decided by politicians, not climate scientists. This means cap levels may not be what climate science demands but what industry & electorate (can) support. By not flying you keep carbon price lower, making it less likely cap will be put too high to actually reach the goals. 2. Caps can be violated and fines/regulatory capacity may not be adequate to prevent this. Not flying reduces carbon price, reducing incentive to emit more than your bought capacity. Is that correct?
    – J.H.
    Dec 27, 2021 at 1:30
  • Not flying also reduces the degree to which airlines can compete on carbon auctions with "more essential" industries like steel or cement manufacturing for example. Because, at the end of the day, while most of us do not need to fly, we do need certain material inputs. A high degree of competition would drive up the costs of those goods, stoking inflation and possibly motivating the politicians to loosen up. Dec 27, 2021 at 1:34
  • Alright, yep, clear. So now, what's the risk of the caps being set too high or unregulated emissions happening due to these kinds of political factors? Is there relevant research/estimations? Is there evidence that this risk is (in)significant and should or should not influence my behavior?
    – J.H.
    Dec 27, 2021 at 2:07

If fewer people are flying, there are fewer flights, which means less emissions.

That's it.

The whole idea of emission allowances is just a way to make people responsible for their emissions (and emission trading is just economics). It doesn't change the underlying fact that fewer flights = less emissions.

To strictly prove that your choice to not fly would reduce emissions could be quite difficult from a consequentialism point of view. There are just too many stakeholders and too many moving parts. Consequentialism can often be an easy excuse to do whatever you want if you insist on such proof.

Going in the opposite direction, it would also probably be difficult to prove that you not flying won't reduce emissions. This would require that both:

  • they would sell your emission and
  • there wouldn't be any other eventual reduction in emissions as a result

When you have 2 options and it's not clear whether either would achieve your goal in the context of all other moral agents, it usually makes most sense to go with whatever the best option would be given the fewest assumptions. That is: flying creates emissions, so don't fly.

If you're looking for a more concrete reason to not fly within the context of the EU ETS:

  • If there's a significant reduction in the number of people choosing to fly, they may reduce the emission allowances for flights at the next available opportunity. This should have a much more direct impact on the amount of emissions.

  • Also, there may be a more direct reduction already built into the allowances. For example, there's a special reserve for distribution to fast-growing aircraft operators and new entrants. If there are fewer flights, there may be fewer fast-growing operators and fewer new entrants, meaning less of this reserve is likely to be spent.

Keep in mind that others also still have to pay to buy those emissions. That can still serve as an incentive to not emit. If emissions are expensive enough, then it will eventually simply be cheaper to invest into renewables or to lose out on some profit by reducing energy usage. Now you not flying could increase tradable emissions supply, and therefore decrease the price, but keep in mind that the difference here is only emissions you would've already otherwise been spent by flying, and the ETS could make provisions to reduce tradable emissions supply as explained above (and this would increase the price).

You seem to be thinking of this as a zero-sum game: whatever emissions aren't spent by one person would be spent by another.

But even if emissions will always be spent regardless, the simple fact of the matter is: the more we decrease our emissions, the greater the benefit to humanity as a whole.

The incentive for anyone and everyone to decrease emissions is the fact that many people will suffer and die if we don't.

By flying you're contributing to increasing emissions, therefore you are part of the problem.

If you don't fly and other people counteract that, you're not part of the problem (at least not in that very specific way).

Don't be part of the problem.


If the trading system is properly designed, and airline tickets behave like typical goods in Econ-101, then removing yourself from the market shifts the demand curve, making it slightly cheaper for others to fly, but the new supply-demand equilibrium would still be at a "lower" point in terms of "quantity".

Note the "you" in the question must be plural, to avoid issues of granularity. I.e. 1 fewer passenger doesn't mean 1 fewer aircraft-flight, but 100 fewer might.

Elaborating further, with arbitrary fake numbers:

Suppose 250 people skip the flight, and cause one fewer aircraft-flight from airline A.

Then the carbon-permit cost for airlines B,C,D... would in theory get a little cheaper. Thus tickets on B,C,D might get a little cheaper. Thus they might sell slightly more tickets.

Thus the net effect would be discounted a little bit, so in carbon terms, it could maybe be as if only 200 people made the choice not to fly, instead of 250.


ETS is a "cap and trade" system. You seem to be focusing on the "trade" part, and ignoring the "cap".

Cap and trade is intended to reduce total carbon emissions by putting a limit on the total emissions from all entities participating in the system -- that's the cap.

But it also recognizes that there are considerable short-term costs to reducing emissions. The trade system allows entities to make tradeoffs. Some may be willing to spend money to reduce their emissions, and they can subsidize these expenses by selling credits to other entities that need more time.

None of this is really intended to influence the behavior of individual customers of these businesses. The goal isn't for airlines to reduce the number of passenger-miles that they fly (although that would reduce carbon emissions significantly). The hope is for them to find ways to reduce the carbon emissions per flight (e.g. replace aging airplanes with more modern, efficient ones). And if they're able to do that, they can sell carbon credits to someone else who hasn't been able to reduce their emissions yet.

Either way, total emissions should theoretically go down, because the total number of carbon credits available is supposed to be more than historic emissions, and will be reduced further over time. Someone will have to cut back on emissions to meet these goals.

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