Bjorn’s Corner: Sustainable Air Transport. Part 2. The problem to solve?

By Bjorn Fehrm

January 14, 2021, ©. Leeham News: Before we dig into the different alternatives we have for more Sustainable Air Transport, let’s look at the problem and its sources.

Figure 1 shows the emissions of CO2 per person since 1900 and the rise of the world temperature. The increase in world temperature changes the weather, with increased weather-related emergencies in recent years.

Figure 1. The increase in CO2 emission per capita and the rise of the world temperature from 1900 to 2018. Source: Wikipedia.

The sources of global warming

As shown in Figure 2, the dominant part of the Greenhouse emissions comes from CO2 (75%), with Methane in second place (17%).

Figure 2. Greenhouse emissions by gas. Source: Wikipedia.

The question is: What’s the source of the CO2? When burning hydrocarbons like our different fuel types (Gasoline, Diesel, Kerosene…), about 3kg CO2 gas is created for each kg of fuel we burn.

Figure 3 shows the parts of society that use hydrocarbon fuels to generate different forms of energy and their emission of CO2 in these processes. It also includes the emissions of Methane, mainly from Agriculture and other Greenhouse gases.

Figure 3. Greenhouse gases by sector 2016. Source: Wikipedia.

We can see that aviation was somewhere around 2% in 2016. The important part is not if it’s 2% or 3% and when this occurs. It’s that transport overall represents 17%, Industry 24%, Agriculture 12%, Residental heating 11% and so on.

Like the discussion in the comments from last week, one can ask why a 2%-3% part of the problem, where alternatives to the used high energy density fuel are hard to find, should be in the lead in fixing the problem? Isn’t the investments better used in other sectors, where these would achieve more?

It’s a discussion that is not possible to have because the whole theme is infected with different agendas and easy-to-understand messages. I’m not advocating that air transport back-pedal on its responsibility, but the discussion is not done in a fundamental and holistic manner.

A very similar situation was where nuclear power was banned in a very one-eyed debate, without realizing that it forced the increased use of carbon-based energy, and speeded up our climate crisis.

I will not spend the series on this base debate. But the reflection is valid. The targets are the visible ones, easy for the public to identify, rather than those that can change our path most efficiently. It’s about if you are in the public eye or not, not what’s the sensible thing to do.

The transport problem

We see that the transport sector in total is close to a fifth of the problem. The shipping and railways are non-weight-sensitive, and their change to more sustainable means of power from stored energy would cost less than for aviation. Yet it’s not actively debated.

Railways use electrical power to a large degree, but from where does this come? From hydrocarbons? Then it’s straightforward to change; power stations can employ more sustainable energy conversion processes without complex technical problems to solve, and the cost of change is moderate. The same goes for ships.

Road transport is a bit more weight sensitive but is on a path for change. Battery cars or hybrids function well for personal transport (where the battery charging time is less of a problem).

For trucks, the world’s largest manufacturer Daimler (Mercedes trucks) says battery-based trucks for local distribution and hydrogen fuel cell trucks for the long haul (range limitations and charging times disqualify battery stored energy for these trucks).

Why do cars function with batteries and hybrids and aircraft don’t?

Let’s reiterate why batteries and hybrids work for cars and not aircraft. The fundamental reason is that cars are energy hogs like no other parts of society, whereas aircraft, especially our airliners, are wonders of efficiency.

The modern airliner uses over 40% of the energy in the fuel to propel the aircraft on its route. It includes the propulsive (fan/propeller) losses.

Compare this with our cars, and we are below 10%. With a typical efficiency of around 7% in our daily commute (as we waste the kinetic energy we’ve built up at every stoplight) a battery or hybrid car has an easy task to improve. Part of it is while combustion engine that should reach a 30% efficiency operates very far off their efficiency point as they are way too large.

Get car efficiency over 15% (by regenerating energy to the battery during braking), and you are hailed as a wonder of efficiency. The truth is, you are a mitigated disaster! The latest car technology is miserably inefficient and can’t be used for aircraft. We are about 200% to 300% short of what we need.

The non-realization of the above is what leads so many naive enthusiasts down the wrong path. They extrapolate the false facts and stick their heads out with lofty promises before doing a proper analysis. They don’t even know that the base efficiency difference in the technologies is some 200% to 300% before the lofty ideas are communicated.

Then they pedal inventions like the possibility to have more propellers, as these are now driven by easy-to-replicate electric motors. It will fix the problem together with “improvements in battery technology.” Had they done their homework, they would have observed we’ve had about a 5% yearly improvement in battery energy density over the last decade and the gap to cover is 50 times that. And the real bummer is more propellers lower the efficiency, but we come to that.

We have a lot to cover

With the above, we have set the scene. Our quest for Sustainable Air Transport is essential, but it won’t fix our Greenhouse gas problem. It will affect it marginally and cost comparatively more than if we took this effort to other parts of the problem. But this is not on the cards, so we dig in and look at what we can do with the resources and means we have.

93 Comments on “Bjorn’s Corner: Sustainable Air Transport. Part 2. The problem to solve?

  1. Round up the usual suspects?

    I will keep it short: “Airbus sucks.”

    Germany does not spend enough on defense.

    And climate change is a Trilateral Commission sponsored myth.

    • Well remove me from Airbus sucks (guilty on 2 though dropping the nukes is the environmental issue) .

      Also remove me from the Anti Climate Change.

      We know what the players are.

      The Hydrogen player vs the Clean Fuel party really is Aviation in a nutshell.

      Its not a technical issue, those can be overcome.

      Its an economic issue and as Hydrogen has been put forth by the EU as the answer, the question is, how does it get implemented?

      A huge side bar is Where?

      Sub Set: If the EU goes Hydrogen and the rest of the world does not (say clean fuel) where does that leave the EU?)

      Specifically does Airbus have to have a two aircart product line (we are talking single aisle so far).

      Tax is one way (how about of of EU aircraft and entry?)

      Mandate is another way. But then Airbus has to have a funding mechanism for the Hydrogen Aircraft that is government.

      How do you make it (grin and bear it) Fly?

  2. Thanks Bjorn for an excellent, balanced and strategic summary of the many challenges of chemistry, physics, mathematics, product development, history and politics in the sustainable aviation debate. Really look forward to the next chapter!

    • Agreed:

      I am more interested in the politics side as to how to make it a go. And does the EU shift to a clean fuel solution when the cost of HydrogenT is so high.

      • Always a very good thing to have dissention in a scientific debate.
        However, have you also got a link to the tens of thousands of papers that show that CO2 *does* have something to do with temperature?
        Based on numbers alone, which do you think is the consensus opinion?

        • “Consensus” implies general agreement. The media and politicians have an consensus. But scientists do not.

          The dam is breaking. The entire edifice has broken links, top to bottom. Example (just published):,_Its_14C_Specific_Activity,.2.aspx

          ” Our results show that the percentage of the total CO2 due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming.”

          • Interesting.
            Strnge place to publish.
            Is this actually peer reviewed?

            Athmospheric N-Bomb tests really ruined the C14 numbers for good and for quite some time.
            I have to grog that article for further discussion.

          • Hmm. convoluted.
            IMU they miss out on fossil carbon being returned to the C-14 activation environment.
            i.e. the time frame they estimate for the bomb test pollution to turn invisible applies to the depletion caused by fresh fossil carbon too.
            ( we watch changes in a stationary process not a static environment )

  3. What has actually been promised?
    What does “net zero” target actually mean?
    Aviation is quite efficient per passenger mile, its the number of passenger miles that is the problem.
    Does this target include travelling to the airport? It ought to really, because its part of the journey and is no more efficient.

    • “its the number of passenger miles that is the problem.”

      This needs to be measured in an appropriate timeframe.
      Sure, a plane traverses more kilometers in a *day* than a car does. But let’s look instead at the number of kilometers traversed by a car passenger in a *year*, and compared that with what a typical plane passenger flies in a year. There is a very small number of people that are constantly jetting around the globe, but does a “normal” plane passengers make any more than 1-3 round-trip journeys per year?

      Remember that someone who uses a car for a 75km home-work commute each day will travel 36,000 km in a year (assuming a 48-week working year). That equates to a round-trip journey from Europe to Australia. Since a modern plane has a per-passenger fuel consumption that is about 5 times lower than a single-occupancy typical car (2L per 100 km versus 10L per 100km — see link), our plane passenger can actually make 4-5 return trips to Australia for the same fuel used by the car commuter.,fuel%20per%20year%2C%20or%200.4%20litres%20per%20day.

      • “…our plane passenger can actually make 4-5 return trips to Australia for the same fuel used by the car commuter…” Perhaps Bjorn can remind us how much lower overall fuel consumption would be if folk didn’t insist on the fewest possible stops. Remember: the fuel burned during the last mile flown into Sydney has to have been tankered all the way from the original point of origin: put in a few refuelling stops and see the fuel requirement fall… This will be true for every trip, whether every day or once a decade.

      • Aircraft are vastly more efficient than automobiles. A Wizz Air A321neo will achieve under 2L/100km per passenger at the typical 85% capacity factors in the airline operates at. (Wizz fleet achieve 57 grams CO2 emission per km per passenger). If I drive a Golf or Corolla hatchback the same distance at speed on a German autobahn or an Australian freeway say Sydney to Melbourne I wouldn’t be able to match even with 4 passengers in a hybrid Corolla at those speeds. Chances are there will be only 1/2 at most 3 passengers in that car.

        Catching a hybrid taxi or train (typical for LCC) to the airport add little.

        The application of the VFT has its place but is vastly over rated and it’s limits and true costs hidden. The vast subsides VFT often require would best be spent elsewhere.

        An BEV over the same distance changes matters but is still no better.

        The distance between Sydney to Melbourne by air is 600km but by car is 800km due to hills and unavoidable meanderings.

    • @Grubbie
      Maybe you meant to say the number of trips. That is, do you really need to fly somewhere? Reducing air travel in general would be a social solution to carbon emissions rather than a technical one. High speed rail might split the difference – don’t fly, but still travel, particularly for short- or medium-length trips.

      • Well, I typically drive about 16000 miles a year and before the pandemic I did an urgent repair job by air that involved more than that in 3 days. Many people I talk to (including passionate environments) are more than happy to travel huge distances to sit in a beach resort “compound”, when they could easily get a similar holiday via a 2 hour Ryanair flight or something more interesting locally. With cars there are technical solutions that could easily save 30 of the energy, mainly by just using smaller cars. Planes are already fairly efficient owing to the tyranny of wieght, so the social restrictions are the only realistic option.

      • Grubbie:

        Bjorn talked about rail (passenger only?) as electric, but the electricity comes from someplace.

        I think EU is the only area heavy into Electrical Rail, US is all diesel (and some natural gas) electric.

        India I believe is the same DE as is China, etc.

        And while its going down, plug in cars in US get 20% or so of the power from coal.

        And of course Germany is going back to coal.

        • TransWorld, you are either badly informed again, pedal some weird agenda or try to get some Germans back to posting… Well, here you have me, a member of the Green party, entrepreneur (carbon fibre products) and ex privat pilot.

          But to the point: No Germany is not going back to coal but to completely exit coal until the end of this decade. For all of you US centrist not really interested in anything outside your “world” – we have a new government coalition in Germany in which the Green party is the second largest faction and the new minister for economy is one of ours. What you will see is heavily increases in wind and solar energy. Hydrogen and synthetic fuels will play a big role it it.

          Besides, we are now also working hard on changing steel production from coal to hydrogen. Same for heating our homes, all goes to heat pumps, completely electric.

          For all climate denialists – we need to get 100% off of carbon fuels, the sooner the better. And that of course includes planes. The only question really is how fast we can get there, and it needs no explaining that the faster the better.

          Oh, and here’s one for the nuclear fanatics: Before you enter any weird ideas: Nuclear energy is the most expensive form or electrical energy, and the only reason nuclear power plants have ever been built is to produce fissile material (plutonium) from (abundant but not fissile) uranium 238. Oh, and til this day there is not a single final deposit for highly radioactive waste and probably never will. Any volunteers here who’d care to stand watch for the next 20.000 years?

          • Your post was going so well…until the science fiction in the final paragraph.
            Three comments:
            – (1) Price isn’t everything: reliability/controllability of supply is also extremely important. That makes nuclear very attractive. Issues of available space also make nuclear important.
            – (2) Please go and do some reading on Thorium nuclear power. It produces about 1% of the volume of waste of regular fission, and that waste itself has a half-life of the order of just decades — much shorter than the waste products produced by regular fission. Mining tailings are a much worse problem.
            – (3) Are you suggesting that past governments in countries like Germany, Belgium and The Netherlands (which don’t have nukes) were secretly passing fissile material to the French, British or US? Any evidence for that weird conspiracy theory?

          • @Gundolf

            Thanks. Anti-American is bad? Anti-rest-of-the-world and poorly informed is a deadly combination!!! What happened in the last couple of decades??

          • My post will relevant because it explains the pitfalls of renewables at present and the impact this will have on the cost of the reliable renewable energy aviation would need.

            While Transworld was mildly imperfect in explaining the situation in Germany yet he was informing. I found your post was mixed with information & false information. Lets stay away from attacking each others credibility.

            The situation in Germany is that 22% of the electrical energy in 2020 was renewable and 78% fossil (including large nuclear imports from France and coal from Poland).

            In recent months the weather has iced up all of the photovoltaics and completely becalmed the wind turbines. They are generating essentially 0% energy. Germany is relying on Coal, electrical imports of French Nuclear and Polish Coal to make up the shortfall plus natural gas.


            This is exactly the thing Green Ideologues denied could happen. In fact they heap scorn, shame, derision and personal attacks on sceptics issuing warnings and arguments. That’s what the Green-Left ideologues do: attack and label. Ideology taints and destroys science.

            Given this situation how can the renewable energy for aviation be supplied. How can any an economy be wealthy enough to subsidise renewables.

            Germany’s “Green Economy” relies on exporting emissions and reimporting energy intensive goods and materials at a cheap price from elsewhere creating the illusion of virtuous progress at the cost of jobs. Polish coal now keeps Germans warm.

            The problem will be this: generating true green hydrogen will be extremely expensive.

            “During the twenty-year period, the Germans also paid a hefty price for the program. For example, the average cost of electricity for German households has doubled since 2000. By 2019, households had to pay 34 U.S. cents per kilowatt-hour, compared to 22 cents per kilowatt-hour in France and 13 cents in the United States, according to data from IEEE Spectrum”

            A consumer cost of 34c/ gives an indication of hydrogen production costs of about $3.40 per equivalent litre of oil (assuming 80% efficiency and 8kWhr Litre for gasoline). (Current oil cost is $0.25/Litre at $50/barrel.)

            The situation in Germany where there is a TOTAL BECALMING of the solar and wind energy shows how huge an investment in batteries(short term storage over at least 12 hours), fuel cells and hydrogen for long term storage will be needed. These will likely double prices again. There will need to be a quadrupling of renewable energy to get beyond the current 22% to 100% for electricity supply then a 30% to 50% again to cover the inefficiencies of long terms storage followed by something like a doubling to cover direct use of oil, gas and coal such as aviation fuel, earth moving machinery, electric cars and manufacturing.

            I would expect an economy to break down under these costs.

            So Germany needs 8-10 times more wind mills and solar to power its electricity, iron and steel, ammonia, cement. plastics and transport.

            You think this is possible?

            As to your claim about Nuclear Power being the most expensive.

            The US EIA (Energy Information Agency) costs the load levelized production cost of nuclear electricity at $0.01/ That’s 1 cent.

            These are meticulous calculations of what power costs at the output of the plant.

            This includes mandatory allocations for reactor decommissioning costs and waste treatment and disposal.

            The load levelized cost of wind renewable is seven times that at $

            However if the costs of providing backup for wind, running fossil plants inefficiently to provide backup, transmission lines, accelerated depreciation and network costs the load levelized cost is aroudn$0.12 to $0.14. It’s not better in Germany.

            Costs of nuclear at $0.25/KW.Hr used in modelling invariably use estimates of 4th generation reactors (such as SMR) whose R&D costs have not be amortised. It is misleading when current PWR reactors are producing at 1 cent.

            So where is the energy for the hydrogen and electricity coming from? 10X more wind turbines? Expensive Fuel cells and electrolysers that only run 25% of the time?

            Greens claimed Renewables were reliable and didn’t need expensive backup systems and now renewables are producing no power in Germany for months. Why should greens be trusted again? Because they can shout down the voice of reason again? Call us “nuclear fanatics” to dismiss us.

            It’s a matter of having affordable fuel for aircraft as well as an realistic energy source not built on subsidies that can keep a population happy and healthy.

      • The best place to discuss “Social Solutions” is probably with the judgy chattering folks at media like the Guardian although they seem to have shut down “comments are free”.

        We’re here for technical solutions that will in effect allow us to fly with limited restrictions.

        There are so many technical solutions.

        Social solutions of that kind involve an apparatus of totalitarian compulsion. They always involve the manifestation of the Paretto Principle (80:20 rule)where a privldige elite escape the burdens. Other social solutions include compulsory sterilisation, single child policies, euthanasia of the sick and elderly. Good seldom comes out of them.

        Lets stick to technical solutions and don’t even think of these ugly things called social solutions.

  4. just looking at percentages comes up short imho.
    You have to look at transport efficiency.
    i..e fuel per mass and distance.
    air transport is abysmal in that respect aggravated by long distances covered.
    container shipping is about as efficient as it can get.
    very high efficiency engines 55%+ and an intrinsic low energy transport method.

      • The numbers for rail almost certainly do not include the fact the rail journeys are 25% longer than as the crow flies flights. Furthermore the significant cost of building and maintaining the rail infrastructure. Track repair, the materials and cost for track, catenary and signal maintenance need to be accounted for. That’s a great many workers whose energy is needed.

        Rail also despoils the landscape cutting wildlife and communities from each other. I don’t want rail through the Amazon destroying river banks and lake sides.

        VFT simply don’t work except in the case of two large wealthy cities about 400km apart.

        Trains are mind numbingly slow and time wasting. Imagine waiting 24 hours longer to get a field services engineer to repair a CAT scanner. A B727 is a very bad reference when a A321neo has 35% of the per passenger fuel burn. As SAF blends in to 15%, 30% then ultimately 63% in 2050 this will reduce.

        • Indeed.
          The number one climate advantage of aircraft is that they don’t require any roads/rails to get from A to B. All that linear ground infrastructure has a gargantuan environmental footprint. It’s not a “one off” investment, because it requires continuous overhaul/upgrading/maintenance.

          • Bryce — “…All that linear ground infrastructure [is] not a ‘one-off’ investment, because it requires continuous overhaul/upgrading/maintenance…” Whereas, of course, international airports do not. The first ground for what became London’s Heathrow Airport was broken on June 6, 1944; it’s not finished yet…

          • @ Pundit
            Which do you think has a larger area of concrete/steel: all the airports in the UK (or any other country) added together, or all the roads/railways in that country added together?

          • We will see if a version of the hyperloop can replace most railroad tracks with 5-6m dia tunnels semisubmerged and easy and safe to cross for traffic, humans and wildlife. Their size are just a bit bigger than the 737/A320 fuselage and is targeted to fly at 1″ altitude in an atmosphere of 100 000′ powered by sustainable electricity generated along the track. If aircraft manufacturers target this market with modified fuselages and Linear induction motors in the belly we will see after the regulations for tracks, stations, swiches and pods are issued.

          • “Which do you think has a larger area of concrete/steel: …”

            A rather worthless comparison.
            Look at traffic volumes managed. vastly different.
            and note: airplanes are rather more expensive per seat than any other form of transport vehicle.
            Finally you are not finished with “just an airport” investment. How do you get passengers freight to/from airports ( which tend to be much further out of town than Bus or Rail stations )?

          • @ Uwe
            – Feel free to divide those concrete/steel amounts by the “traffic volumes managed”: aviation will still be a clear winner, because it needs virtually no ground infrastructure as a function of the distances traversed.
            – “airplanes are rather more expensive per seat than any other form of transport vehicle”. Not if you include the price of associated ground infrastructure — particularly for high-speed rail. Just look at what the channel tunnel (including its associated feeder lines) cost. A high-speed rail line typically costs €25M per kilometer! What about the costs of a hyperloop line?
            – Just as you need to get passengers to/from airports, you also need to get passengers to/from train stations — after all, not everyone lives in city centers. Ever gone through London traffic to get to King’s Cross?

  5. Aerospace is a technology leader. Not the concrete, farming, construction and steel/weapon industries well politically connected since centuries. They also move forward when there is easy money to fetch. What really matters are net emissions and lots can be done with reforest projects for both CO2, water and erosion benefits. With a seawater rise of 2-3m many airports has to be rised a similar amount at enormous costs.

  6. It’s complicated. “By 2020, aviation emissions were 70% higher than in 2005 and they could grow by 300% by 2050.”

    I think the height aircraft have emissions is far more damaging than transport/ construction ~sea level. -> We can not ignore by only mentioning absolute percentages.

    “In the tropopause, emissions of NO x favor ozone (O3) formation in the upper troposphere. At altitudes from 8 to 13 km (26,000 to 43,000 ft), NOx emissions result in greater concentrations of O3 than surface NOx emissions and these in turn have a greater global warming effect.”

    I heard people say that for the huge costs of making aviation significantly cleaner, much more could be achieved in other sectors. Making earth the winner.. But we should give aviation freecards, they’ll (w’ll) abuse for growth.

    Than there the reality aviation is >75% for fun, holidays.. and only 20% for business, necessary family visits etc.

    • “Than there the reality aviation is >75% for fun, holidays.. and only 20% for business, necessary family visits etc”

      One could make a similar statement with regard to car transport.

    • They’re not going to grow 300% or the 240% predicted by air traffic growth.
      Apart from natural efficiency improvements the ICAO CORISA regulations will keep them at 2019 level.

    • The record of ‘atmospheric science is terrible. This is because they are based on conjecture and modelling rather than experiments (which would involve isotopes)

      Here is a list of errors.
      1 Acid Rain causing forest die back in USA and Europe.
      -Blamed on Coal Burning.
      -Actual Cause “adjacent land use’ (read farming with fertiliser)

      (In fact coal burning stations remove particles with precipitators and use SCR to remove nitrous oxide and disulphurise their exhaust)

      2 Nitrous Oxides causing Photochemical Smog and shortening life spans
      -Blamed on internal combustion engines, particularly diesels.
      -Actual Cause Fertiliser over use. Actually using more than needed.
      Radioisotope studies in the Antarctic finally proved it was fertiliser not diesel.

      Ozone Depletion
      -Blamed on Jets, Concore, Fluorocarbons, Hydrofluorocarbons and Hydrochlorofluorocarbons.
      -Actual Cause: Halocarbons (fire high end fire extinguishers)

      I’m pretty sure the models on emissions for gas turbines at altitude will be grossly in error.

  7. I want aviation to be a shining light, much like our industy is the widely recognized standard of excellence in regards to safety. Whether we are the worst villain or not – we should the example!

    • Aviation is simply are area of interest, its gets people and product from A to B.

      A lot of people is no work related.

      I think aircraft are extraordinaire interesting but I don’t see it as a shining light.

      Its highly visible target as the PANAMAX Container carrier using Bunker C at mid ocean .

    • John B — If aviation is the “worst villain,” we certainly don’t want it to be the “shining-light” example, do we?

      • Aviation is highly visibility to the public

        Huge Cargo ships are not. They are as bad as coal plants when they burn Bunker C.

        Out of sight (of land) and out of mind.

  8. Bjorn, great start to what I think will be a stimulating and informative set of articles, thank-you. Your efforts to set the broader context by placing aviation within the wider transport sector is valid and well made; the rationale for aviation’s emission reduction journey is not where we are now as a % of sector emissions but where we are likely to be in the future as other easier to abate forms of transport clean up their act.

  9. For those who aren’t convinced that CO2 increases are having any effect on the climate, one should at least realize that increased atmospheric CO2 is causing increased acidification of oceans — which isn’t a good thing, seeing as many oceanic lifeforms have alkaline body parts (like shells).

    • Fake news! Just like COVID or my kitchen needs to be cleaned. If you don’t like or understand the message call it “fake news”.

      @Bjorn: “Why e in ePlane […]” is an excellent series!

      • Not sure why you’re labeling this as “fake news”: it’s easy to find the data (apart altogether from the fact that it’s a logical consequence that can easily be deduced).

        Here’s a detailed link on ocean acidification from the NOAA.

        “Ocean acidification is already impacting many ocean species, especially organisms like oysters and corals that make hard shells and skeletons by combining calcium and carbonate from seawater. However, as ocean acidification increases, available carbonate ions (CO32-) bond with excess hydrogen, resulting in fewer carbonate ions available for calcifying organisms to build and maintain their shells, skeletons, and other calcium carbonate structures. If the pH gets too low, shells and skeletons can even begin to dissolve.”

  10. How about starting with good data? You offer emissions per capita – much harder to measure than actual CO2 levels in the atmosphere (especially considering what an enormous carbon sink the oceans and plants are)

    We can measure CO2 numbers total – by actual data in the atmosphere.


    It is highly significant that CO2 growth does NOT track at all with your “per capita” emissions.

    Temperature: look at

    So the temperature has gone up 1 degree C compared to the 1961-1990 average. With huge error bars. I get that much variation all the time in my back yard.

    Given the importance to the global climate of methane, water vapor, clouds, and carbon absorption by plants, it is clear that the premise of this post is specious.

      • A single observatory measuring CO2 in a consistent manner is going to be far more accurate that projections about how much CO2 is formed by every lawnmower or container ship. We can actually measure outcomes accurately – we cannot measure the production accurately at all. Unless you tell me that Chinese and Indian reporting is accurate?!

        • your are barking up the wrong tree.

          I commented on your (wrongly) disqualifying statement made over temperature rise or not.

          I never said a word in relation to numbers on CO2 sources or measurements.
          The Hawaii numbers actually are rather consistent and jibe with measurements done elsewhere.

  11. Of some note, Ford in the US has released its all Electric Pickup.

    Demand is high on pre-orders and they are shifting production from 80k to 150k.

    Interesting test as the Pickup in the US is more popular than cars.

  12. People, this post is not about electric cars, electric trains or the oceans. Stay on topic.


    • Scott:

      My apologies. I thought the uptake of surprisingly large numbers of the Iconic pickup in the US had some bearing on what is possible in the area as to US attitude towards the subject in general.

      I had not expected it, let alone for a Pickup.

  13. The best way to reduce emissions is of course debatable and some may argue that aviation is a poor place to work on the problem. However, it should be recognized that:
    1. as other sectors reduce their emissions aviation’s portion will become a bigger part of the problem,
    2. changes in aviation happen slower than in other sectors so change should start ahead of need,
    3. even if a particular entity doesn’t value climate, their customers or perhaps customers-of-customers may, and that value can lead to decreased usage/sales, taxes/policy changes or outright bans.
    4. smaller and shorter range airplanes are easier to electrify so this is where change will happen first,
    5. there are compelling hybrid arrangements for larger airplanes,
    6. the electric EPU is really quite good (fast response, reliability advantages, failure mode advantages, operating cost advantages), if it was not for the deficiencies in energy storage (which will be solved in time) making the change would be the obvious choice,
    7. as transportation electrifies the quantity available and distribution of the petroleum products will at some point become an issue,
    8. there are potential cost savings from electrifying (electricity is cheaper than petroleum and maintenance is argued to be less).

    There are both pushes and pulls which drive change.

    • 1. Aviation is also reducing its emissions via increasing adoption of SAF.
      2. The article makes it clear that the opposite is true: changes in aviation technology in the past 50 years have left the automotive industry far behind.
      7. Crude oil is used to make a whole scala of products other than fuel, including solvents, lubricants, tar and asphalt. There’ll be a demand for it for a long time to come.
      8. Price differences are very much a function of how the electricity is generated. The electricity distribution grid has HUGE annual maintenance costs.

      As regards electric aircraft: Bjorn has written a whole series on that subject, essentially dismissing the concept on the grounds of energy density. To the extent that they materialize at all, eVTOLs are mere noise in the margins.

      • SAF is somewhat similar to selling filtered cigarettes. Sure, its healthier than the unfiltered one, but there is still plenty to be concerned about.

  14. Looking forward to the series but this post and letters combained are a mixed bag – some useful scale references and other confusing ones (e.g., efficiency as % of the energy in the fuel used vs. transport efficiency.. as fuel per mass and distance, or per passenger-distance, etc). I don’t have an answer, but other angles to consider for context, aside from projected growth in cargo & passengers, and emissions. Another take, from:
    “Aviation is a unique sector in terms of its environmental challenges because in addition to its significant fossil fuel consumption, it is the only human-made source of pollution emitted at altitude. These emissions give rise to phenomena that are currently thought to double (or more) their climate impact relative to the same emissions at ground level.”

  15. There are two important facts to consider when there is a discussion about aviation and global warming. In this post, Bjorn understates the contribution of aviation towards global warming. When one considers contrails and the effect of where within the atmosphere the pollution occurs, the contribution from aviation is closer to 3.5% of total global warming than the 1.9% stated here.

    The second item to consider is the effect of compounding. Aviation travel has consistently grown at 4-5% per year. Using the simple rule of 72, a 5% growth rate year-over-year results in a doubling of CO2 emissions in a 15-year time frame, e.g. 72/5 = 14.4 years. By the 2040 timeframe, all things being equal, aviation will have doubled its percentage contribution. So the issue is not so much as what the percentage contribution is today, it is actually what is the future percentage contribution of aviation within the total global warming budget. Should the rest of the economy de-carbonize and aviation continue on its current trajectory the result would be aviation to be using a greater and greater percentage of the world’s carbon budget.

    The issue then becomes one of fairness. Why should the wealthy first-world continue using a large percentage of the CO2 budget on aviation, which is for the most part a discretionary expense, while the remainder of developing and emergent world have to invest under the constraints of minimizing carbon-pollution while at the same time having to address the significant costs of extreme weather events.

    • “Why should the wealthy first-world continue using a large percentage of the CO2 budget on aviation”

      You don’t think that there’s significant aviation outside the “first world”?

      In the first link, look at the top-10 list of aviation growth markets and count the entries that don’t belong to the “first world”.
      The second link discusses how aviation is being primarily driven by LCC growth in emerging economies.

      • Not surprising, it simply follows globlal experience. As incomes rise more people can afford to travel abroad an more people want to visit and see those other lands they may hear, see and read so much about (same as those who can today do). It’s an inevitably growing sector in the near and foreseable future. Hence the topic’s growing importance going forward.

        • Everything is “an inevitably growing sector”. Just look at the explosive growth of motorized land vehicle traffic in China and India. The growth of container traffic at sea. The increased output of the concrete and steel industries.
          In that regard, there’s nothing particular about aviation growth.

    • The ICAO CORISA regulations, which will become compulsory in member nations, recognise the growth of aviation and are designed to keep emissions at the 2019 level in absolute terms. There is a slight reduction since the regulations started in 2021 and the target back dates to 2019. It’s a very good system they’ve come up with.

      At the recent CP26 summit the proportion of SAF to be blended was set to 63%.

      There are tremendous possibilities for SAF production. There are of course the waste oils but also that fermented from crop and municipal waste and the electro fuels (potentially 65% efficient). Certainly scores of methods.

      In the end I feel aviation may decarbonise more than automotive which for decades has used every advance in technology (with rare exception such as the Prius) to upsize thus negating much of the improvments.

      • The increase of the SAF blend target from 50% to 63% by 2050 should lead to a 26% reduction in CO2 emissions if I’m not mistaken. SAF itself can be made to produce less contrails due to the reduction of nucleation points caused by lower soot levels from the more complete burning of linear hydrocarbons so the warming effect can be reduced there as well. The CORISA regulations are well developed and are at the point that airlines can be ‘audited’. This is a key to implementation.

      • NB the blending in of 63% SAF by 2050 (COP26 target) instead of 50% should lead to a 26% reduction of emissions assuming 240% growth and efficiency improvements and provides a buffer if growth is 300%. Obviously a technology that can produce 63% SAF can also produce 100% SAF.

  16. The ICAO CORISA regulations seem entirely sensible.
    1 Set an emissions target for both passenger traffic and freight that reduces every year.
    2 Implement various technologies to achieve the goal. If an airline fails it must compensate with additional SAF or by purchasing offsets. There are no subsidies or taxes involved. Presumably fines if there is non compliance.

    The technologies at present are:
    1 Increase fuel efficiency of the aircraft. We can likely get 15%-30% in the next 15-30 years though fleet renewal and new engine and airframe technology.
    2 Better air traffic routing eg open skies policies.
    3 The progressive blending in of SAF. The proportion of SAF was meant to be 50% by 2050 but seems to have been raised to 63% at COP26. The amount of SAF that can be produced is probably the riskiest aspect of this scheme but it seems certain we can get more than half the way there.

    The above ‘plan’ does not exclude the use of electric flight, hydrogen fuel flight or cryogenic hydrogen flight through fuel cells or turbines. In fact the solution may be solid oxide fuel cells burning hydrocarbons or something else.

    It’s fairly obvious that with current aviation certified batteries at 135WHr/Kg and a mass fraction of under 30% that an electric aircraft can fly 100nmi with a useful load. There are batteries now capable of 400WHr/kg in lab quantities which suggests a range of 300nmi should be possible. If they can be made to have a life of 15000 cycles they would work.

    Hydrogen Fuel cells with electrical propellers also can operate over the same distance using gaseous compressed hydrogen (and obviously with the more difficult cryogenic hydrogen over twice the distance)

    So we might be able to get away Jets for flights below 300nmi.

    The big problem is that the renewable economy doesn’t seem to work.
    -Wind turbines don’t last long enough by a factor of 3 or so and their are land use issues.
    -Photovoltaics have a similar life/performance/cost issue.
    -Battery Energy storage is far to expensive.

    So its a leap of faith.

    The only way forward is blue hydrogen where natural gas is converted to hydrogen and the by-product CO2 sequestered by pumping it under ground. This technology seems to work very well.

    In as few years we might see NuScale’s SMR small modular reactor start up. A the moment there are on skeleton engineering staff keeping know how alive.

    So whatever is don’t is a ‘leap of faith’. There is no economically viable solution yet.

    • Scott:

      Please punish the offender not the rest of us who are trying to discuss the subject (yes I was guilty but I did think it had some direct relevance)

      Some people think they are the Aviations Town Criers.

      • If Scott followed that advice, the rest of us would be hearing very little from you 😏

        • Offenders include you.

          I sometime follow off topic but stick to top in main posts.

          I don’t jump in and plead fake forgiveness.

          The pickup production was off topic per Scott and I accept that, for the US its pretty phenomenal for the Rugged Pickup Image (if silly) that there is that much interest in electric, phonemically so acualy by our standards.

          As the EU types are grossly ignorant of US, culture and the government and how it works its good to educate them.

          Just following NPR that its better to discuss than fling dirt.

          None of it is anti EU. While I disagree with EU, its beyond better than the alternatives. Reminds me of the original 13 US colonies. We had to grow up and we still aren’t there.

          • You continue your off-topic rants while my post is at least aviation related and can be of significance as FedEx doesn’t have any Airbus A321 in its fleet nor placed any order.

          • Another unnecessarily long jumble of topics, none of which has anything to do with eco-aviation…and, of course, including the usual digs at the EU and “EU types”.
            Some people just can’t control themselves.

    • About 20 years ago, on the subject of graphs can prove anything, now long-retired Airbus svp marketing Adam Brown used to project a chart showing a clear relationship in the 1930s between the number of BBC Radio reception licence-holders and the population of mental asylums in (I think) England & Wales…

  17. Here’s a very informative and balanced overview article of the developments/challenges in reducing aviation emissions. It mentions BA, AB and ZeroAvia; discusses SAF and hydrogen (both liquid and gaseous); talks about shorthaul vs. longhaul; discusses different types of fuel cells; and alludes to production, storage, distribution and safety issues.
    Many of the topics have been covered in previous Bjorn series, but this gives a handy snapshot summary.,are%20key%20to%20making%20hydrogen%20competitive%20in%20aviation.

  18. The only thing missing from your treatise is the tag line “You Will Own Nothing an Be Happy”.

  19. The company Elysis (Alcoa Rio Tinto with apple) has deveḻoped inert carbon neutral anodes for electrolytic refining of aluminium. Apart from making possible carbon neutral aluminium refining for aircraft alloys it makes feasible carbon neutral aluminium air batteries in which the electrodes are replaced as cartridges at the end of a flight or number of flights. These batteries should achieve densities of 2KWHr per kg. It’s the battery Wright Electric Aircraft are evaluating along with Hydrogen fuel cells.

  20. Just for the fun of it:
    5.1e15t : mass Earth atmosphere
    1.39e12t : 278ppm( CO2 levels pre 1800 )
    2.08e12t : 416ppm( CO2 levels today )
    ( difference .96e12t )

    2.5:1 : average Co2 equivalent output from burning oilequivalent fossil mass
    0 to 12,000Mtoe use of fossils over the last 100 years
    1.5e12t CO2 released from fossil fuels.

    Just 3/5 have found a place beyond “atmospheric storage”.

  21. I think there may be a place for eVTOL (or Hydrogen eVTOL as H2Fly is working on) as well as I suspect eSTOL.

    Consider the problem of transporting people from Dublin to London. This can not be done with electric aircraft except with extremely high battery mass fraction aircraft that are essentially sail planes. Eviation Alice will likely do it but it will be a heavier aircraft than a chemically fuelled aircraft.

    However, using the 6 seater LiliumJet as an example, we can fly from Dublin to either Liverpool, Manchester or Birmingham. From there we can fly to London. A person may not care which hub so long as the schedule matches.
    With the high flight frequency possible the time spent at the hub does not become long. The mass fraction of battery is not excessive since the range is short

    Moreover instead of only 1 Airport in Dublin and 3 or 4 in London it should be possible to build multiple eVTOL Lilipads in Dublin and in London. Maybe 14 landing points instead of 4.

    eVTOL aircraft will be quiet, their developers know they have to be. eVTOL will relay on breaking dependence on huge runways and airports that consume 6 sq km of land.

    Noise will determine how many many eVTOL ports can be built and where.

    There is no law of physics that prevents a 6 seater eVTOL to scaling to say 39.

    I also believe the traffic and noise concerns can be eliminated. Is an already quiet eVTOL landing on a 25 story high rise with anechoic liners going to be an issue?

    We also now have interesting technologies developing such as Aluminium Air batteries that will have a energy density of 2kW.Hr/Kg These will require electrodes to be removed as cartridges but as there are some 260 aluminium smelters, many even in Europe where they can be refined back to aluminium.

    There are also Hydrogen Fuel Cells, with 60% efficiency that will have power densities of 4kW/Kg, likely in 3-4 years.

    These could make electric flight feasilbe and may impact eVTOL aw well.

  22. How much Ethanol is produced annually for car fuels? Would that not make up a significant amount for SAF in the future when the car combustion engines are phased out and replaced by batteries or fuel cells?

    • In the US about 18 billion tons of bioethanol is produced annually. Jet Fuel consumption is about the same (15 billion gallons). Conversion of ethanol to jet fuel is about 90% efficient. Note however jet fuel has a higher energy density so you only get about 55% by volume Jet fuel but the US could already meet its 50% SAF mandate today. I suspect Brazil could do over 100% right now and Australia about 50%.

      Obviously with BEV displacing ICE within 15 years the bioethanol won’t be needed.

      Lots of ways of doing this but Lanza / Lanzatech are basically dehydrating the ethanol to ethylene and then polymerising the ethylene to jet fuel.

      The ethanol cam be made from fermentation of municipal as well as agricultural waste using the correct bacteria. A little less optimal than biomethane but much easier to convert to diesel or jet fuel.

      Most of the US production of bioethanol is from maize. Each 4 units of energy output in the form of bioethanol needs 1 unit of energy input in the form of tillage, harvesting, transport, fermentation and distillation. This is an improvement on the 2.5:1 ratio of 10 years ago mainly through rationalisation of transport. Most of the energy input is for the distillation and there is hope membranes will halve this.

      Surgar Cane is far more efficient (bagasse can be burned for fuel).

      Australia uses Wheat Grain. Slightly political since Wheat not Maize is the main crop in Aus. However I remember reading a meticulous German study on tritical and wheat found that wheat, which looked like a modest crop for energy production was quite good when the value of the silage was accounted for. Silar are the green leaves and stalks of of wheat, maize etc that can be used as animal fodder as well as fermented into biomethane or bioethanol.

      So your Wheat farm could be making bread, biomethane, jet fuel, beef from both the grain and silage.

  23. Interesting article hydrogen busses. Operationally too expensive.

    Often we do research, make a plan do some ambitious assumptions on breakthrough technology around the corner (ok than, 5yrs) and present he highly desirable end results, using awesome media technology.

    Concerned / elected decision makers jump on the train, for their grand children & a better world. Naysayers are sidelined. Then the assumptions start falling apart.. but the caravan is moving already.

    • At the moment Toyota are the go to guys on Hydrogen Fuel Cell traction with the best performing equipment. These pioneering Daimler Benz Citaro buses are a bit old.

      Having said that Toyota are also running a Hybrid Yarris with an IC Engine and it works well.

      RCCI/HCCI engines are running at 58% efficiency in the lab and even if they run at 50%-52% in an automobile or aircraft will compete with fuel cells in consideration of the fact that fuel cells will have some losses in energy conversion of the motor and inverter.

      Daimler Benz was running HCCI engines and starting them at 40,000ft in 1940. The piston engine in aviation should not be dismissed.

      Given that there are now automatic pickups for the catenary for trolley buses and that batteries within the buses give off wire capability of 15-25km I suspect the hydrogen municipal bus will disappear.

  24. Australia has started commercial exports of cryogenic hydrogen to Japan.

    The hydrogen is manufactured from brown coal with the CO2 piped and stored in depleted offshore oil fields. This is so called ‘blue hydrogen’.

    The plan is to export the equal of 1 million tons/year of coal as blue hydrogen.

    I can see coal transported by rail to Texas/Gulf of Mexico for conversion to liquid hydrogen. It may be easier to make the hydrogen at the coal field and pipe the CO2 rather than rail.,load%20super-cooled%20liquid%20hydrogen%20for%20transit%20to%20Japan.

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