Boom! Why supersonic planes are a climate nightmare

Notoriously, aviation is one of the trickiest sectors to decarbonise. It isn’t the biggest sector relative to things like road transport, electricity or industry, ranging between 2 to 5% of total global emissions depending on how you calculate it, but every little bit counts (in a bad way), and every sector has to significantly reduce emissions for the world to meet climate goals.

There aren’t many technological alternatives available, either. You can make planes run on an electric motor, or you can run their engines on an alternative lower-emissions fuel. This can be hydrogen, a ‘sustainable aviation fuel’ (say, waste cooking oil), or a ‘synthetic’ fuel produced using clean electricity. These are all either experimental, or extremely limited in supply. The only real, effective solutions for aviation emissions right is simply running fewer flights – that is, replacing short ones with ground electric transport, reducing business travel and replacing it with zoom calls, and removing incentives for leisure travel across oceans. All of which come with deep and significant political and social problems.

It is a tight spot – a really tight spot. Considering the challenge, you’d think that no one would be actively trying to make the problem worse. But an emerging industry is trying to do exactly that: reviving hype around supersonic aircraft – just like the ill-fated Concorde of the late 20th century – a handful of American starts ups are promising ultra-fast, supersonic and – this one’s new – ‘clean’ travel across the planet, in a surprisingly short timeframe.

A new partnership was just announced between United Airlines and American startup Boom Supersonic. Their announcement is the stuff of dreams for time-poor technology writers like me. It’s shiny, sleek and cool. It’s far enough away in the future that it’s seemingly acceptable for important details to not exist, but close enough to be imagined as realistic – the partnership plans to launch by 2026 and carry passengers by 2029.

Their media release comes packed with 125 megabytes of images and videos (there are several gigabytes more on their site), and on the page you can spin around a detailed, high-res three dimensional model of the sleek pointy paper-plane looking thing. “Careful not to get too close, I might just go BOOM”, the soundtrack to the video angrily insists. “SUPERSONIC IS HERE”, the video’s bold text uses as a closer.

It is not here. The company’s only existing plane is the experimental XB-1, which will be flown either late 2021, or early 2022 (you can still watch a video of it being rolled out to a runaway, with a faceless pilot slow-motioning confidently towards it. Their press kit unfortunately used up all of their budget licenscing the BOOM song and the videos illustrating what the final product might look like ended up, sadly, looking like this:

It may be vaporware. But the broad and uncritical welcome it has received shows up a really deep and serious problem: we are not taking climate change and emissions seriously.

The emissions problem

The key problem here is that this technology adds an incredible new strain to one of the most strained areas of decarbonisation. There is a wealth of research to date suggesting that supersonic aircraft are very significantly worse for climate than standard subsonic aircraft, for a few reasons. Dan Rutherford, Shipping and Aviation director at the The International Council on Clean Transportation, has been tracking the development of supersonic craft for years, and is vocal on Twitter about the risks. “Imagine an oil major announcing that it’s going green by investing in tar sands. That’s what United did today with supersonic aircraft”, he said, after the United Airlines announcement.

It’s justified: a 2019 study by ICCT found that supersonic planes could emit around seven times more per passenger than existing planes. The modelling looked at a potential fleet of 5,000 flights per day at 160 airports, and found that it “would consume about one-fifth of the entire carbon budget afforded international aviation under a 1.5°C climate trajectory, assuming that aviation maintains its current share of emissions”.

The press release came packaged with a promise for all flights to use “sustainable aviation fuel” (SAF), and for those flights to be “net zero carbon”.

Both are mysterious and ambiguous claims. The airline industry’s International Air Transport Association (IATA) set a goal of using 6% alternative jet fuels by 2020, but reached the year at around 0.25%.

Maybe it’ll be different this time? Digging through Boom’s website to find details of the SAF that will be used yields literally no results; beyond a huge image of the supersonic jet with a calming image of a forest projected onto its top side.

The most I can find is a few sentences about a partnership with a company called ‘Prometheus Fuels’ – another buzzy startup company with 3D models and a snazzy website and absolutely no technical details or design specifications.

This company will purportedly capture CO2 from the air, use renewable electricity to convert it into a ‘synthetic fuel’ – that is, something identical to jet fuel, or petroleum for cars,  but manufactured using electrical power and captured carbon rather than from crude oil. Prometheus advertised weirdly low costs for this carbon capture, as they were factoring in the future sales of synthetic fuels. But the near-certain dominance of electric vehicles – which do not require liquid fuels to run, obviously – is studiously avoided in all marketing materials and the website.

It is a wild oversight, considering the market for liquid fuels could shrink to nothing, thanks to electrification. Dig deeper into some older document and releases, and you get an important fact: BMW is a major investor. The manufacturer is surely compelled to find alternatives to building and releasing electric vehicle models.

I asked Dan Rutherford about the chances that Boom could figure out SAFs in time for the launch of their plane. “Highly unlikely without using offsets, which United’s CEO has ruled out. The economics of a plane that could burn 5 to 10x more fuel per passenger than subsonics using fuel that costs 3 to 4x fossil jet fuel will be extremely challenging”, he told me.

The other tell here is that it isn’t only carbon emitted by a plane. The clue is in Boom and United’s marketing materials, which only ever mention “net zero carbon”, rather than “net zero emissions” or greenhouse gases. Other gases can still warm the planet by trapping heat in and below the atmosphere, and because planes deposit these substances very high up, they can linger – “residence time” – for much longer durations, resulting in a greater heating effect.

There are other tells. Boom only says that the plane will “be optimised to fly on 100% SAFs” – not that it will fly solely using these fuels. United’s language doesn’t specify why they’re including a “net” in their net carbon – presumably, they’ll ‘offset’ their emissions instead of reducing them.

There is also the important problem of the incredibly limited supply of SAFs. “Should the industry be happy dedicating the entirety of SAF production at the end of the decade to supersonic rather than more broadly supporting a reduction in emissions for air travel?”, wrote aviation journalist Seth Miller on Twitter. In his piece for Pax, he writes that “If Overture does manage to fly by the end of the decade and wants to operate on 100% SAFs there’s a very real possibility that it would consume (nearly) all of the SAF supply in the markets where it operates”.

Boom is a signatory to ‘The Climate Pledge’, an initiative led by Amazon and Global Optimism aimed at corporate climate action. That entails aligning with the Paris agreement “through real business changes and innovations, including efficiency improvements, renewable energy, materials reductions, and other carbon-emission elimination strategies; Neutralize any remaining emissions with additional, quantifiable, real, permanent, and socially beneficial offsets to achieve net-zero annual carbon emissions by 2040”. It also entails measuring and reporting greenhouse gas emissions, which are nowhere to be found on the site.

“Aerion [another supersonic startup] and Boom are angling for new, supersonic-specific environmental standards that are more permissive than subsonic standards, acknowledging the supersonic sector’s emissions potency”, wrote Aerospace America, in 2019. That doesn’t exactly inspire confidence. And United has had plenty of time to invest in Sustainable Aviation Fuels – this is what their current mix looks like, according to their latest report:

The use of SAFs by United has risen from 0.00% in 2015 to Climate-Pledging 0.028% in 2019. Their emissions have risen 10% in that same timeframe. That’s a pretty awful track record, and all after the signing of the Paris Climate agreement.

There’s no guarantee this plane will leave the tarmac, let alone be built. But it represents something incredibly important: the muddling of ambition and wastefulness. San Francisco to Tokyo in six hours, instead of ten hours! The only cost? Hoarding climate solutions from uses like, say, decarbonising existing aviation and putting it towards hurling those rich enough to afford these flights towards their destination slightly quicker. Worth it? No, it is not.

It is very reminiscent of the problem with Bitcoin mining, where an incredible, eye-watering energy consumption – mostly from fossil fuel sources – gets directed towards an activity that mostly enriches a few concentrated adherents, rather than benefits that are spread more fairly. It certainly smacks of the same anxious greenwashing designed purely to ward off regulators and appease investors.


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