Bjorn’s Corner: Sustainable Air Transport. Part 52. What can be done before 2050?

By Bjorn Fehrm

January 6, 2023, ©. Leeham News: Since we started this series about our Air Transports and their pollution, we have covered different schemes of reduction such as improved Air Traffic Control (ATC), change to electric aircraft (battery/hybrids) or hydrogen as fuel, and lastly, eVTOLs.

Of these changes, only ATC can have a short-term effect, but it’s a slow mover for organizational reasons.

Changes to how our aircraft are propelled are, unfortunately, longer-term improvements, as we see in an example below.

But we need fast change. We’ve had the craziest of summer and now winter in Europe, where I live, and it’s not a one-time variation. And this is not confined to Europe; the weather change is faster than we thought, and it’s worldwide.

So what can we do?

Figure 1. CO2 emissions by region. Source: Our World in Data.

The need for speed

We have all seen climate change in the last five to ten years. That something is happening is evident; when you look at Figure 1, you understand why. Our CO2 emissions have been going up like crazy since 1950, and we see the effects.

Large populations like China have industrialized and claim their right to energy. The problem is our increase in energy consumption is predominately hydrocarbon-based (Coal, Oil, Natural gas), Figure 2.

Figure 2. Energy consumption by source. Source: Our World in Data.

Each kg of Jet fuel burned in our engines produces three kg of CO2 (3.16kg to be exact), and we consume about 300 to 350 million tonnes of Jet fuel per year, producing 950 to 1,100m tonnes of CO2. All forms of hydrocarbon energy use must change, including the 2.5% from air transport.

What to do?

The changes we have looked at are essential for long-term evolution, but they can contribute little to the goal of reducing CO2 emissions before 2050.

The one factor that can contribute short term is Sustainable Aviation Fuel or SAF. SAF is produced so that its net CO2 emission from production and consumption in the aircraft contributes zero CO2 emissions. We will discuss how this is done and what the problem areas are for a change from Jet fuel to SAF in subsequent articles.

SAF is a so-called “drop-in” fuel that can replace today’s Jet fuel. But it has a slightly different composition so that seals etc., in the aircraft fuel system and engines must be adapted before an aircraft can fly on 100% SAF.

Right now, aircraft can fly with a blend of Jet fuel and SAF, which is a real saver for our emissions. Here’s why:

Let’s do a thought experiment. We compare the effect until 2050 of changing the worldwide narrowbody production to 100% emission-free propulsion from 2025 (by 100% SAF or any other means), compared with using the SAF we can produce to achieve a 10% blend for all jet fuel consumption between 2025 to 2050.

Our assumptions are as follows:

  • The narrowbody total production by 2025 is 1,000 aircraft per year. It increases by 5% yearly, which means doubling narrowbody output every 15 years, a trend that has prevailed over the last decades.
  • By 2025 we will have converted all narrowbodies, so they don’t emit any CO2 by whatever technology (100% SAF, hydrogen, or battery electric with 100% green electrons. The fact that two of three are technically impossible until 2025, we ignore).
  • At the same time, 1,000 of the oldest, most polluting aircraft are retired each year as the new enter the market.
  • Against this, we assume that we will have enough SAF production worldwide by 2025 to blend 10% SAF in all jet fuel consumed (very few of the world’s jet-fueled aircraft cannot accept a 10% blend).

By definition, we will have a 10% reduction in the CO2 footprint between 2025 and 2050 compared with doing nothing for the blend alternative.

What’s the result of the other alternative? We achieve a 12.4% reduction for the year 2050, but on average, between 2025 and 2050, only a 7.5% reduction.

With this example, we understand that blending SAF into our Jet fuel is what can help us in the short term. The reason it’s so efficient is the worldwide flying every day of around 25,000 aircraft, where 20,000 are older than five years.

With an early output of 1,000 new zero CO2 emission aircraft, we only achieved a less than 4% reduction the first year, then slowly increased to 12% for the last year.

It assumes all 25,000 airliners have the same yearly emissions. They don’t; the older the aircraft, the higher the emissions. As the blend also encompasses older aircraft, it’s more effective than the example shows.

With the example, which is very theoretical for the 100% emission-free alternative and very realistic for the 10% blend one, we realize how important SAF is at any blend level. In reality, today’s aircraft allows higher blend levels than 10%. Even better!

So what are the roadblocks to getting there? This we discuss in the next Corners.

22 Comments on “Bjorn’s Corner: Sustainable Air Transport. Part 52. What can be done before 2050?

  1. The original premise of the emissions reduction movement was that, by reducing emissions by amount X before a certain date Y, the total accumulated CO2 at that date would be insufficient to cause a temperature increase of more than W.

    However, we seem to have already passed this juncture, in view of the ongoing positive feedback loop associated with permafrost thawing and associated methane release. Perhaps it’s time to admit that climate models employed to date made (grossly) insufficient allowances for knock-on effects, and that their predictions were thus too conservative? It’s not just permafrost thawing: thermal outgassing from metastable methane hydrate on the ocean floor is another big elephant in the room.

    Is the continuing discussion of emissions reduction an example of “fiddling while Rome burns” ? The goal certainly is noble, but how effective will it be? Even if emissions were brought to zero in the morning, that wouldn’t stop the abovementioned positive feedback loops: they’re powered by what’s already in the atmosphere (zero-order effect), not by new emissions (first-order effect).

    Of course, this is a very inconvenient narrative for the old “consensus” — but shouldn’t it still be openly discussed? In view of the fact that real-world climate change effects are obviously and dramatically much greater than predicted by old models, it would be foolhardy to try to pretend that original goals are still achievable.

    • ” In view of the fact that real-world climate change effects are obviously and dramatically much greater than predicted by old models,”


      Which ones? The ones proposed by science that where derided
      or the ones pushed by the likes of Brothers Koch ?

      Science was ignored, the US is still squandering energy like mad while lambasting China for the emissions that displaced to China production causes there. ( fair: attach carbon footprint to the final consumer ).
      But don’t fear USA is racing towards Armageddon.
      No future, no climate issue. ( bit like the solution to mouth and hoof disease. no bovine, no … )

      • Take a look at the giant-size, *absurd* trucks and SUVs virtually everyone now drives here in the USA, then try to tell
        me that those who rule us are in any way serious about
        climate change™.

        • You see the downside of living in a demoted reality fully overlayed with oversized projections.

          This has fully engulfed US society. Not just politics associated Power Projection.
          Reality is what you can (successfully) push onto others.
          ( Boeing being a prime example.)

    • “but shouldn’t it still be openly discussed” the ability to discuss these things died 30 years ago when a particularly influential Amercian decided to ‘cancel’ skeptics and treat them the same way as racists. Now we have the result of this: nothing but emotionalism and sensation, ad hominem: the stock of the main stream media and entertainment used in manipulation. Along with this was rational discussion thrown out. Much of the population is desensitized and the much is prone to virtue signaling and hypocrisy. Are things worse climate wise? Honestly I don’t think so. There is falsifying evidence as well. My own belief is in prudent, rational action. We are now in a situation that polarized ideology not rational runs the debate and political agendas are linked meaning scientific dissenters are treaty as political dissidents. There are now trillions in promoting green energy: manufacturing, finance, engineering, market analysis. I have been to those conferences and have met the people involved, people that were once rational (when they were friends from uni or work elsewhere) until their job depended on it.
      -The result is that many of the ‘solutions’ offered don’t even work.

      • “The result is that many of the ‘solutions’ offered don’t even work.”

        Yes, indeed.
        There’s a lot of tunnel vision in the climate discussion.
        And, as you point out, too many people with vested interests.

        Little to no discussion of carbon capture — which might be far more effective than emissions reduction on a “per dollar” basis.
        And almost impossible to get a discussion going regarding mass deployment of (thorium and SMR) nuclear fission.

        Meanwhile, Rome burns.

  2. Fascinating reading about this. I hope people in high places are also learning about this and are concerned enough to tackle this challenge to mankind.

  3. Drop-in SAFs should be redesignated as Surrealy Absurd Farce. There is no way – repeat, no way – humans can sustainably mimic (cost, scale) what Mother Nature has managed to produce, over millions of years, and in colossal quantities. Drop-in SAFs are a smart drop-out move by the aviation and airline industries to keep change away from their worlds. Smart and macabre.

    • > Drop-in SAFs are a smart drop-out move by the aviation and airline industries to keep change away from their worlds. <

      Yes- they're Delusionol™.

    • -I have studied the matter, with data, numbers and a spread sheet. Without facts and numbers, you only have onions. SAF can be made to work depending on the energy source.
      -The conversion efficiency of electricity to SAF using water electrolysis and Direct Air Capture of CO2 is at present 45%. That’s the lower end. Processes that demonstrate 55% have been achieved in the lab using the electrolysis route and 60% is achievable. Thermochemical water splitting could get to 65%
      -45% efficiency would mean that 1L of jet fuel containing 0.8kg in mass and 9kW in energy would require 20kW to make.
      -65% efficiency 13.5kW.
      -The production of cryogenic hydrogen is at the moment less than 70% but may achieved 80%.
      -Using SAF means we are going to lose 50% to 35% of the energy. Using LH means we are going to lose 30% to 20%.
      -Aviation produces 2.4% of emissions or 8-10% of transport emissions. It’s fairly obvious that land transport can be converted to battery power with almost 100% efficiency meaning that the energy required for SAF production is quite small.
      -The key will be not the process itself but the source of carbon neutral energy. I am skeptical of wind turbines achieving a reasonable energy payback even with electricity production only when networks and recycling is considered. They wind turbines will need a life of 20-25 years not the 5-8 we’ve been seeing.
      -But there is always nuclear fission and that is what we will likely need anyway.

  4. Well I had to do some research to find out if Bjorn was slipping his clutch on 3X more CO2 produced than a Kg of fuel.

    Yep, as per normal, he is write (pun intended).

    Weird stuff.

    • Why is it weird?
      Oxygen has an atomic weight of 16 — and there two oxygens present in each CO2 molecule, whereas the C in the molecule only has an atomic weight of 12.

      The fuel is predominantly made up of C and H (atomic weight 1). Oxygen from the atmosphere is the main source of weight in CO2 resulting from combustion.

  5. There are ways of using atmospheric CO2 and massive amounts of electricity to produce SAF mainly at sea running windmills at full stream (the power the grid cannot swallow). Still in short term, phasing out old polluting aircrafts and increase new production of new ones. Using desert salt water ponds to grow oil algea on a massive scale would help with rain in dry areas and SAF raw materials. Planting forests on a massive scale where it is poorly managed has a similar effect and gives other positive effects on erosion, building materials besides residues for SAF production. Using more wood and less concrete in construction has an impact on CO2. All of this require government regualtions/support/permits and that can take time.

    • -Certainly, more efficient aircraft are likely to be far more effective than SAF or hydrogen. The loses in the production of SAF or cryogenic hydrogen and the subsequent conversion to mechanical energy by gas turbine at a fan shaft compounds to around 66%-75% energy lose. Any improvement in flight efficiency is thus well worth it.
      -The ability to exploit renewables in remote areas is what may make carbon neutral Electrofuel’s such as SAF attractive. The sunniest locations on earth (eg Ethiopia, one of the sunniest most cloud free places on earth) or those with consistent winds (say Northwest Coast of Australia) become areas that can be harvested. The chemical fuels can be transported with greater ease than transmitted electrically. Even a nuclear reactor can be located remotely. Extraction of CO2 from sea and fresh water is very viable so production offshore or on a floating wind turbine.
      -The number of wind turbines needed to keep something like an A320 flying is stupendous. A 2.5MW wind turbine with a diameter of 92m and a hub height of 92m weight of 1000T and producing 24MW.Hr/day would produce 2000L/day so 6 would be needed to give one A321LR a full fuel load.
      -The order of ‘decarbonization’ should be electricity supply, hydrogen for decarbonization of iron smelting and cement production, road transport.
      -Decarbonization of aviation is not low hanging fruit and according to the Pareto principle it is actually wrong to put money into it at this point because there is an opportunity cost. A million dollars spent on SAF is a waste not because it doesn’t work but because it is best spent on a million dollars in backup batteries for the electricity grid instead.

  6. Without being too flippant about it, bjorn neglects that production of aircraft has a huge ‘carbon footprint’ beyond the burning of fuels while they are flying. Aluminum, carbon, mfg facilities, pneumatics, electronics, and heaven forbid lithium batteries etc. all have huge energy/environmental impacts.

    Second, consider the history of epic failures toward carbon goals by ‘green’ policies. And I don’t just mean in aviation/with Ukraine-Russia in 2022.

    It’s all a piss-ant drop in the bucket.

    Finally, is there really an ‘emergency’ of any kind, as presumed?

    Wrecking the aerospace industry in Europe in the interest of ‘climate’ emergencies is utterly insane, and will not be matched by China, reciprocally. Perhaps something to consider. Oh, and China is at a rapacious pace producing more and more refined lithium/cobalt etc. to take on the auto industry globally as well. Hmmm…is there a common trend here? Who is falling for what propaganda?

    • Without being flippant:

      That is quite a load of BS you wrote there.
      ( you could try and do the math on your own
      before you lambast Bjorn for lack of competence 🙂

    • Germany: 2023->
      NO VAT on householdsize renewables,
      latetr selling to the grid : no VAT and income tax,

    • “CO2 is plant food.”

      And if someone dumps a ton of food every day on your doorstep, will you be able to consistently eat all of that, or will it be more than you can eat?

      And the portion that you don’t eat — do you think that might cause any adverse effects while it piles up on your doorstep?

      By the way: methane is also a greenhouse gas — and plants don’t eat methane.

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