Perhaps I should clarify more seriously.

A study of US resources as a first step is to be welcomed, of course, but it is not the relevant scale for working out whether biological SAF is practical, which needs worldwide estimates, with the US being perhaps almost uniquely favourable.

Nor does the estimate seem to indicate vast surpluses, so that it could both to some degree be exported, and would tend to show that even if many regions were less favourable, they might have adequate resources also.

Important facts about Air Travel.
The United States has significantly more Airline passengers than any other country (over 50% more than number 2 China which has four times the population).
https://en.wikipedia.org/wiki/List_of_countries_by_airline_passengers

Over 80% of the CO2 produced by Airlines is for flights greater than 2000 miles or 3000 km. This requires a room temperature, liquid fuel with very high VOLUMETRIC energy density, i.e. Wh/liter and Jet fuel has four times the energy density of liquid hydrogen. Read this: “ four litres of liquid hydrogen would be the equivalent of one litre of standard jet fuel. ”
https://www.airbus.com/en/newsroom/news/2021-12-how-to-store-liquid-hydrogen-for-zero-emission-flight

It will take $trillions to develop a “Green Hydrogen” infrastructure and a complete redesign of Commercial Airliners (also a multi billion Euro/$ effort plus over 20 years to develop).

I have known about Hydrogen technology since 1970. I had a close up view of the RS-25 LH2 engine also known as the Space Shuttle Main Engine (SSME) at the Marshall Space Flight Center in Huntsville, Alabama USA. The Soviet Tupolev TU-155 was the first Liquid Hydrogen Airliner and flew in 1988, so the technology works.
It is simply not practical or makes any economic sense.

I have several concerns about this report:

1. Until we have well established economical methods of liquid hydrocarbon fuel production from waste biomass with known yields how do you estimate fuel production?

2. What if it turns how that certain biomass feedstocks are cheaper to process and produce higher yields than others? How do you prevent a purpose grown energy crop industry from emerging?

3. In a business as usual global economic growth scenario (It is a pretty safe bet that the people who assume that it is essential to maintain a "healthy" jet airplane industry are also counting on such a scenario) the potential upside demand for jet airplane travel is quite large. If frequent jet airplane travel is part of the life style of the most highly developed economies of the world there is no reason that the developing world should not demand equity in the long term.

4. If truly economical liquid hydrocarbon fuel production from biomass is developed then other hard to decarbonize economic sectors may wish to jump on this "green" band wagon.

5. In my view bio-refineries should be striving to recycle nutrients as well as to produce fuel. Our food production systems cannot depend on mined rock phosphates forever. A bio-refinery system that balances these priorities may not produce as much fuel as one that is focused primarily on maintaining a vigorous jet airplane industry.

My view is very simply that we should not be expanding the fleet until GHG emissions are under reasonable control, or have realistic prospects of becoming so.

The free pass without even equivalent taxes to road transport has to end.

What is being traded off is biomass converted to aviation fuel versus potentially using it to sequester carbon.

You can only take so much out without depleting the soil so your budget has limits.

Here is salted biomass sequestration, which comes in at around $60/ton:
https://www.greencarcongress.com/2023/05/20230507-saltedbiomass.html

The comparison is not like for like, as more or less anything will do for salted biomass sequestration, whilst biofuel production is much more picky.
For reference total CO2 releases are of the order of 35 billion tons/year:

https://ourworldindata.org/co2-emissions

By salting biomass:

https://news.berkeley.edu/2023/04/11/to-more-effectively-sequester-biomass-and-carbon-just-add-salt/

'According to the paper, for every metric ton (tonne) of dry biomass, it would be possible to sequester approximately 2 tonnes of carbon dioxide.'

So the choice would be whether to utilise the resource to decrease the CO2 impact, or to fly more and more and spend it.

The figures make clear that at present the impact is relatively small compared to the size of the problem, but turning it into jet fuel is going in the wrong direction.

And the aircraft industry hopes to vastly increase, not decrease, its use of fuel.

Why it should be imagined to be imperative to increase long distance air travel when destinations closer to home could be chosen for vacations and videos work fine for business is mysterious, but that is the the framework the aircraft industry seeks to impose.

If we want to reduce CO2 emissions into the atmosphere quickly and massively we sequester fossil fuel power plants, put it in empty oil and natural gas wells, simple as that slam dunk.

By the way we can make materials like carbon fiber and synthetic feels like jet fuel using that stored carbon we can also take the storage of nitrogen oxides and make nitrogen fertilizer, without using natural gas which spews the CO2 into the atmosphere making the ammonia, these are not difficult solutions.

Indirect burning of biomass is a criminal waste. Why not go for alternative air fuels and avoid fights where electric trains are feasible and more green.

At my age my memory horizon stretches back to what I had for breakfast, if I am lucky, not discussions from 10 years ago!

Roger, I had thought you over-optimistic about hydrogen for long distance flight in practice, but recent advances are confirming your arguments, in particular this advance in Dewar tanks, which they reckon can hit a 70% hydrogen fraction by mass with rapid chill down so enabling swift flight turnarounds:

https://www.businesswire.com/news/home/20240313965264/en/GTL-Announces-Pioneering-Validation-of-LH2-Composite-Dewar-Tanks-for-Aviation-Applications

Of course transatlantic aircraft will not be the first ones, as it is way more practical to start smaller.

But the misconception is that those critical of the notion that SAF has much prospect of effectively enabling decarbonisation have an obligation to come up with stuff permitting the aircraft industry to expand right now as it wants to.

There is no such obligation, as flying extensively is not a necessity.

It seems to me to currently be about as sensible as redisigning Venice to enable ever larger cruise ships, thereby destroying what people want to go there for in the first place.

At minimum flight fuel should be charged and taxed equivalently to other means of transport, and preferably for other nuisances to others such as noise etc.

That would pretty much take care of the projected increases in CO2 from flying, as it would not happen,

This is starting to charge for the true costs, instead of allowing them to be offloaded, not some derigiste level of control.

The airlines are having a freebie, and blathering on about SAF is in the hope of being allowed to continue to do so.

@SJC
? They seem to reckon they can hold it down to only 1% per day:

' During this test, the subscale dewar-tank experienced only 2.8 watts of heat load. Based on this, GTL expects that the flight tanks will see only 1% LH2 boiloff per day.'

Although 5% would do, as you say.
They very low boil off rates presumably reduce management issues for boil off as well as wasting less fuel.

@SJC

As Tonto apocryphally said when he and the Lone Ranger were trapped by Indians and the Lone Ranger said they were going to be killed
:
'Who's we, white man?'

Are you referring to the US, or the world?

And would the agricultural residues be better employed sequestering carbon, instead of producing jet fuel?

@SJC

International airflight, which is where the vast bulk of the GHG emissons happen, is just that.

So the relevant resource base is world production, and whether producing SAF is practical at any resonable cost, which has not yet been established, let alone in the vastly increased quantities needed compared to simply replacing present jet fuel, which is what the report seems to focus on.

The aircraft industry, in receipt of all sorts of tax waives, projects massively increased production and travel.

So can SAF worldwide be produced to cope, without impacting food supplies etc?

I have seen no figures to date to indicate that the problem is even being seriously considered, let alone evaluated.

The aircraft industry is looking to massive tax break funded expansion, and by their own figures massively increased GHG emissions, on the grounds that:

'Something will turn up'

It is unclear if they are hoping for SAF from lignin, or a fairy Godmother in a sustainably powered pumpkin.

In any event, they remain content to project increased GHG emissions out to the foreseeable future, with just a pious hope not a plan to contain or reduce them.

Roger said:

' It seems to me that long-distance tourism is a significant driver of world-wide economy and employment... and should not be discouraged.'

Yep, if it can be done without broiling the planet. It is hardly seminal like cement and steel production arguably are though.

Mindlessly expanding air travel so that people can go to Malaga instead of Weston-Super-Mare and contributing to making it too hot to go to is absurd however.

Nor is it a case of laying down laws from above, just making tax and charges equitable between air transport, which is currently exempt, and alternative ways of getting about.

The free ride for the air transport industry has to stop.