Flying and Offsetting

Guy Lipman
Jun 25 · 10 min read

A post arguing why we should reduce flying, but any flying you need to do should be offset using carbon offsets, and indeed ‘over-offset’, in order to properly eliminate your harm.

In the past, I never thought much about whether it makes sense to buy carbon offsets on my flights. But as I started work on my PhD (on reducing emissions from electricity) I started to get asked by friends what I thought, and decided to read and think about it.

As I’ve been talking to people about it, I’ve realised that a lot of other people have thought deeply about the issue, and passionately feel differently to me. A lot of the questions I raise are ones of perception of risk, and of values — in which two smart people can reasonably reach different conclusions. This blog post isn’t intended to try and convince anyone that they’re wrong. Instead, it is intended to share what I think and why, and perhaps give some food for thought to people who are starting to think about the questions involved.

Are increasing levels of greenhouse gases in the atmosphere harmful?

I’m not a client scientist, so there’s a point to which I’m relying on other scientists for this bit. But the basic idea I understand is that as the level of greenhouse gases in the atmosphere increases, the planet heats. We are past the point where that heating is causing harm (and the more it heats from current levels, the more harm that is likely to occur).

I accept this (though I’d obviously love it not to be the case) and I assume my readers do too.

Does flying cause emissions?

I don’t think there is any question that flying leads to emissions of greenhouse gases. My understanding is that it currently accounts for 2–5% of total global emissions. This proportion is likely to grow, partly due to globalisation and partly because it will prove easier to reduce emissions in other sectors.

This may not seem such an enormous level, but I believe it is still something we should be taking extremely seriously. First, this level of flying is largely discretionary, and there is a huge variation between who flies and how much. Second, there is a strong social dimension, in which we form views of how much flying is appropriate for work and leisure from the behaviour of those around us. Third, it is not the case that flying less is an alternative to addressing climate change in other ways: in fact, for what we spend on flying (even without the environmental cost being priced in) we could do a lot to improve our environment.

Should flying be banned?

Some people feel there can be no excuse for flying ever. While I respect people who decide not to fly for this reason, I wouldn’t be in favour of a ban. Perhaps I’m somewhat biased, living in London but having most of my family in Australia. But I’m also aware that flying isn’t the only harmful activity, and I’d generally rather let people make their own choices (taking into account those harms).

What else can be done to reduce flying?

Despite not believing we should ban flying, I do think there is quite a bit we can do to discourage flying.

We can definitely support government policy that seeks to ensure that fliers pay a cost that reflects the harms done (though I appreciate that determining the appropriate cost and applying it on an international level aren’t trivial). But even without this, there’s no reason that we shouldn’t at least try to take into account that cost ourselves (more on this below). Also, we can work at a social level to discourage flying. For example, we should fight the tendency to think of frequent fliers as more productive. I support initiatives like Flying Less (which supports reductions in academic flying).

Can we really spend money to lower levels of greenhouse gases in the atmosphere?

There are a lot of projects to which you can contribute money, that work to lower levels of greenhouse gases. These include directly removing greenhouse gases from the air (including growing trees), reducing emissions from industrial processes, improving energy efficiency and decarbonising energy supplies. There are a number of organisations like Gold Standard, Carbon Footprint or Carbon Fund that put your money towards projects like this, and advise you how many tonnes of greenhouse gases they believe your money has eliminated. Cool Earth work to increase rainforest growth. There are also organisations like Chooose that buy emissions certificates in order to reduce the emissions by other companies. Finally, you might invest in research and development that improves our ability to reduce greenhouse gases further down the line. If you look at these organisations, you’ll see that most of their projects are in the developing world — however as greenhouse gases operate at a global level, it doesn’t matter where we eliminate them.

Are these projects guaranteed to work?

Not much in life is guaranteed to work, so I wouldn’t see the absence of a guarantee as a reason to reject any of these projects. But it is sensible to think of the risks when choosing organisations and projects (and many organisations that invest in these projects undergo auditing to maximise the chance that the projects genuinely reduce emissions).

The most obvious risk is that the project may not succeed technically. The trees might burn down. The users may fail to take up the offered technology. The project manager may be cheating the investors. Most project managers care a lot about these risks, and I believe that the risks are low for the better organisations. There is also a risk of bad side-effects — perhaps a hydroelectric project will lead to a landslide. However, a good project manager will be mindful of these risks, and indeed will often choose projects in which side-effects are likely to be good rather than bad (eg reduced soot in homes).

The next kind of risk is often referred to as additionality — the risk that the emissions would have been reduced even without this project. For example, I might invest in a project, but had I not invested, someone else would have invested in it, have I really made a difference. In this case, I’d argue I may still have made a difference if the other investor uses their money for other projects that do good. Again, most project managers (and their auditors) consider additionality when choosing projects to invest in.

Another kind of risk is when these projects come up against national or market targets. For example, the UK has a national emissions target in its legislation. If my project reduces emissions, it can be argued that it just frees up others to emit more. While this is possible, these limits are regularly revised — by helping achieve a target one year, it is more likely that the target will be lowered in future. Many project managers also have a policy of investing in projects in locations that do not have such strict targets. A related risk is that by investing in projects sponsored by the aviation industry, the aviation industry might be perceived as less harmful (and less likely to have a carbon price applied).

As a result, yes, we should take into account these risks (and good project developers already do), but they shouldn’t deter us from investing in the better projects that are available.

Can you offset the harm of flying by investing in these schemes?

This is probably the most controversial question in this whole post — a lot of people passionately believe the answer to be no.

I’m unable to honestly reach that conclusion. I believe that there is always some level of greenhouse gas elimination that will offset the harm from a flight. Even if there’s a risk that the greenhouse gas elimination does not occur, there is still a level of expected greenhouse gas elimination that will offset the harm from a flight.

I’m sure a lot of the critics of this view will claim that people will use this view as an excuse to fly more, or that they won’t adequately invest in greenhouse gas elimination. I’m sympathetic to these objections, but I am still (as yet) unable to share their conclusion.

Does this mean you are morally good if you fly and offset sufficiently?

This is actually the question I’ve struggled with most myself. On one hand, if you fly and invest in enough greenhouse gas elimination, what harm are you doing? But in another sense, it feels wasteful, kind of like working for a day and then burning your income in front of other people. I’m therefore going to hold back from offering an answer to this question.

What I would say is that I believe you are doing much better if you fly and offset sufficiently, than if you fly and don’t offset.

What level of emissions does flying cause?

The UK Government requires organisations to publish their emissions from flying, and produces conversion factors to help people put an estimate on the emissions from all sorts of activities including flying. These work out at about 0.15kg/km for economy, 0.40kg/km for business class and 0.55kg/km first class. I estimate that these numbers are equivalent to about 135kg/hr economy, 360kg/hr business class, and 495kg/hr first class (assuming an average speed of 800kph). These numbers are scaled up to reflect the fact that emissions at a higher altitude have almost twice the impact of emissions on the ground. The UK Government acknowledge that these estimates are approximate, but I’m happy to accept these.

Note that throughout this post, I talk about kg or tonnes emitted. In fact, there are different greenhouse gases, for example methane has a much greater greenhouse impact per tonne than carbon dioxide. The usual approach is to convert all gases to their equivalent carbon dioxide equivalent. As a result, when I talk about emitting a tonne of greenhouse gases, what I mean is emitting greenhouse gases equivalent to one tonne of carbon dioxide.

Is it sufficient to just offset that same quantity of emissions?

Not all tonnes of greenhouse gases will prove equally cheap to eliminate. There is a chart by McKinsey & Co that shows a range of technologies that cost vastly different costs to eliminate greenhouse gases from the atmosphere — from €-90 to +60 per tonne. It should be noted that the right side of the chart is truncated — there are also technologies that could eliminate more, though at considerably higher cost (ClimeWorks are currently offering carbon capture sequestration at a price of €1000/tonne).

The carbon offsets that people are buying right now are the easiest/cheapest ones. They tend to cost about €10–20 per tonne, even including all the administrative costs. But there is a limited number of cheap opportunities to reduce emissions (as shown by the chart). If everyone who flew bought offsets, more expensive offsets would be needed, and the price would necessarily rise considerably. If more essential activities like home-building were offset, the cost of offsets for flying would rise even more.

I therefore don’t believe that someone who adds a tonne of greenhouse gas to the atmosphere, and then eliminates a tonne cheaply, has sufficiently offset. In a way, it is as if you threw away rubbish in the middle of the park, and then you find some rubbish next to the bin and put it in.

How much do you need to eliminate to offset the harm from flying?

To answer this, we need to think about the cost of the final tonne of greenhouse gas that we’re going to need eliminate — the tonne that wouldn’t need to be eliminated had you not flown. We don’t know exactly how much they are going to cost, but I’d suggest the last tonnes we eliminate are more likely to cost €80–100/tonne. As a result, I’d argue that if you want to sufficiently undo the harm of one tonne of flight emissions, you need to invest this sort of amount, perhaps by paying for the elimination of 5–10 tonnes of greenhouse gases.

Using a price of €100/tonne means you would want to pay around €13/hr for economy, €36/hr for business class and €50/hr for first class. If you wouldn’t be prepared to pay these sorts of amounts to offset your flight, you probably shouldn’t be flying.

I note that this calculation doesn’t take into account the social cost of flying, but there are most likely less costly ways of addressing these.

Can you do other good things with that money instead of offset?

There is an argument that reducing levels of greenhouse gases is one of many good things we can do, and it is fine for people who can, to use their money in a better way. Some will also say that you can use your time and political capital to make up for not paying to eliminate greenhouse gases.

In general, I think people should be able to choose what good things they do, taking into account their values, talents and interests, and that there isn’t an obligation to do good things. However, when it comes to undoing the harm of your choice to fly, it doesn’t feel fair if you harm future generations through your emissions, even if you do something wonderful to help particular people today.

As a result, I’d conclude that if you fly, you should spend money eliminating emissions, but beyond that you have more choice in how you do good in the world.

How does this need to offset interact with a carbon price?

I stated above that it would be good for there to be a carbon price, but in the absence of a carbon price individuals should determine the harm of their flying and pay to offset this harm.

If we do introduce a carbon price, how does this change? I would hope that revenue raised by a carbon price would be spent reducing greenhouse gases, in which case individuals would be justified in reducing the amount they spent investing in projects directly. However, if the money was spent on other things (for example, reducing the tax burden) I don’t believe the obligation to undo one’s damage goes away.

Is offset the best word to describe what is being done?

This is another question that I’m not sure of my answer to. I do believe that some amount of greenhouse gas elimination does offset a tonne of greenhouse gas emission. But I appreciate that some people use the term to imply a 1 to 1 relationship between a tonne of additional emissions released, and a tonne of emissions eliminated, which I don’t believe. The fact that I’m having to write “over-offset in order to offset” (over-offsetting tonnes, in order to offset harm) is awkward. So I’d be open to improving the language we use.

Guy Lipman

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