Thread by @giulio_mattioli

Aviation accounts for 3.5% of climate change impact, and it's one of the sectors where emissions are increasingly most rapidly.

But where do aviation emissions come from?

The answer is in this new paper led by Frédéric Dobruszkes - THREAD doi.org/10.1016/j.jtra…

[Little pedantic note before we start. For various good reasons the analysis in this paper refers to "fuel burnt", not CO2 emissions. But there is an almost perfect equivalence between the two so it doesn't matter in the end]

More than half of flights globally (54.5%) are over distances of less than 1,000km. The kind of flights you could imagined substituting with trains

The problem is that these flights account for *just 17.9% of fuel burnt*. Why? Because they're short

https://x.com/yl_oswald/status/1846894010838790194

This also means that *a small number of long flights accounts for a whole lot of fuel burnt*

Just 5% of flights are over 4000km, but they account for a 39% of fuel burnt

The 9% of flights over 3000km accounts for *nearly half* of fuel burnt (47%)!

https://x.com/yl_oswald/status/1846894010838790194

Which flights are we talking about in practice?

Nearly 75% of fuel burnt from long-haul flights (<4,000km) is from flights to/from Europe, Asia, or North America.

The most important macro-region pairs are:

Europe-NA = 8.9%
Europe-Asia = 7.4%
NA-Asia = 6.7%

We also find *huge* inequalities in aviation emissions across world regions.

In the Indian subcontinent, people burn 5.5kg of aviation fuel per year per capita

In Europe it's 96kg (47% of which for long-haul) and in Oceania-Pacific it's 230kg! (59% of which for long-haul)

There's more bad news. If we look at trends in travel activity (seat-km) between 1996 and 2018, we find little growth (+28%) in flights <500km, which account for very little emissions.

But growth rates are over 100% for longer-haul segments (+212% for the 1000-4000 segment!)

And +168% for the long-haul >4000 segment that accounts for such as disproportionate share of fuel burnt.

So why don't we hear so much about those few long-haul flights, if they account for so many emissions?

Well, they create a bit of a policy conundrum. You can't really substitute them with rail, and you can't really decarbonise them with technology...

https://x.com/giulio_mattioli/status/1576874528093143040

...so the only real option to reduce emissions from long-haul flights over 3000-4000km is to... reduce levels of travel activity in those segments. Or at least make sure that they don't keep increasing at the 150%/200% rate that we've seen over the last 20 years.

But that proposition tends to be politically controversial (I am looking forward to people insulting me in the replies BTW 😘)

There are more possible reasons for the silence surrounding those very polluting long-haul flights.

They tend to be much more lucrative for the airlines. So expect pushback from those quarters, if the question is raised.

On the other hand, we think that there are some reasons why measures targeted specifically at the long-haul segment might be easier to introduce:

1. *Very* few people fly long-haul with any regularity. So expect little pushback there.

2. So targeting long-haul flights would maximise the ratio between the emission reduction achieved and the number of trips & people affected.

In other words, it would be a very efficient way of reducing emissions - see this interesting paper about it

https://x.com/ZiaWadud/status/1808097280311824709

3. Long-haul flights are also more likely to be perceived as a "luxury", and many holiday trips could be substituted with trips to similar destinations that are close

IMPORTANT CAVEAT: some people with migration background and/or family abroad may arguably need to fly such long distances to maintain their relationships. That is indeed a thorny issue. See our research on that here

https://x.com/giulio_mattioli/status/1572158721412710401

and here doi.org/10.1016/j.tbs.…

4. Targeting long-haul flights might exploit divisions within the airline industry. We know that airlines that do long-haul are keen on measures vs. short-haul and viceversa. See work by @InfluenceMap on this
influencemap.org/report/Airline…

@InfluenceMap END

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