Bjorn’s Corner: Electric aircraft, the first fall on the Hype curve

Bjorn’s Corner

May 31, 2019, ©. Leeham News: Last week the new Airbus CTO, Grazia Vittadini, said we should not expect electric aircraft anytime soon when presenting at Airbus Innovation days. What is realistic is hybrid developments, not battery-based designs.

After having made the basic checks about Electric aircraft in my Corner series 18 months ago, this was music to my ears. Finally, someone was curbing expectations.

Figure 1. The Gartner technology hype curve. We are somewhere in the first peak.  Source: Gartner.

Battery-based aircraft is a near impossibility, hybrids are difficult

Vittadini’s team had made the sums. Battery driven aircraft is a near impossibility. Since doing my check on the efficiency of different electric aircraft, all I have learned in the 18 months since the series is making the equation worse.

I wrote batteries are 40 times heavier per energy unit (kWh/kg) than Jet fuel. A more correct figure would be 100 times. Battery systems designed for the first electric aircraft have a systems level energy specific weight of 0.12 kWh/kg and jet fuel is at 12kWh/kg. The battery systems might improve to 0.30kWh/kg over the next decade but not more. Not for certifiable battery systems. This is what Vittadini’s team told me.

The 100 times increase in weight for the energy is devastating but the full story is worse. If we start a flight of a jet fuel aircraft at say MTOW (Maximum TakeOff Weight), we would land the aircraft with around 20% lower weight as jet fuel gets consumed during the trip. For a battery-driven aircraft we takeoff at MTOW, fly the route at MTOW and land at MTOW. This worsens the efficiency of the electric aircraft further.

An electric aircraft has larger freedom of positioning its propulsors on the aircraft, Figure 2. But it can’t make up for the energy density problem, it brings at most a 20-30% improved efficiency.

Figure 2. Airbus concept for Boundary layer ingestion propulsors. Source: Airbus.

It means we have now a drag improvement of 30% compared with a 10,000% efficiency loss on the fuel side. Over the next decade, it improves to a loss of 4,000%. We don’t even have to calculate the aircraft weight and by it, the induced drag of a battery based electric airliner, to understand it’s a non-starter. Today, tomorrow and after tomorrow.

Hybrids are difficult

Vittadini also talked about electrical hybrids, with the BAe146 based E-FanX project with Siemens and Rolls-Royce as an example. She said it was a project to learn from. To learn about transferring 2MW (MegaWatts) at altitude over a 3,000V conduction chain. To learn how a 2MW battery can be designed and work safely in an aircraft.

The sizing of the battery is one of the problems. If the battery shall give 2MW during one hour it will weigh 20 tonnes, which is not possible. The Bae146 has a maximum payload of 11 tonnes.

With crew, test equipment and other items on board, there might be 5 tonnes left for the battery. It would then last 15 minutes when feeding a 2MW propulsor.

By the above, we realize an airliner hybrid is a gasturbine based system with a minimal battery for starting the gasturbine and as a backup in case of an engine or generator problem.

But we still have the challenge to explain why a Gasturbine-Generator-Conductor-Converter-Motor-Fan is more efficient than a Gasturbine-Fan combination. At each step in the hybrid chain, we lose a minimum 2%, most times 5% in efficiency.

The Gasturbine-Fan skips the complexity, efficiency losses and weight/volume of the Generator-Conductor-Converter-Motor complex. No-one could explain to me the elegance of the more complex and heavier system, at least not over the last 18 months.

Hype curve dynamics

After the euphoria of the first peak of the Hype curve, Figure 1, comes the ride down to the Through of Disillusionment. To me, we are now starting this downward ride.

Many projects are still born with inflated expectations, seeking to be the Tesla of the skies. The Corner series about Electric aircraft explains why we don’t have a Tesla situation for airliners. The Sky lacks stop lights.

But the first signs of a more realistic approach are there. Airbus’ innovation team tempers the expectations for the first time. We will see more of this going forward.

54 Comments on “Bjorn’s Corner: Electric aircraft, the first fall on the Hype curve

  1. “No-one could explain to me the elegance of the more complex and heavier system”

    The principle is that you can run the gas turbine at maximum efficiency *the entire time* which, in some applications like terrestrial load-following power generation, can make a noticeable improvement to overall efficiency of your primary energy source.

    While I understand that battery-driven *large-size* aircraft may indeed still be a ways away, I think the author shouldn’t be as dismissive because other applications/mission types still have a real opportunity. Short-distance cargo and passenger ferries are a prime example. Yes, the trough of disillusionment is real in innovation theory but I would say that in terms of lightweight, drone-like passenger travel, we may already be past the initial technological hurdle.

    • Hi Martin,

      the argument about running the gas turbine at maximum efficiency because of the hybrid layout is often put forward. It’s moot, however, airliner gas turbines are already running at peak efficiency at cruise, which is 85% of the time. Commercial turbofans/turboprops are designed with the “TSFC bucket”, i.e. the point of maximum efficiency at cruise power. Takeoff and climb power are in a region where the pressure ratio and fan/compressor/turbine efficiencies are below peak efficiency which is OK as this only constitutes about 7% of mission time.

      Extreme short distance transport (below 100km) works, as I wrote about in last week’s column. There the challenges are the rules for certification.

      • It depends a bit on how you define efficiency. If you only look at TSFC the numbers are quite different at T-O and at cuise.
        Normaly at T-O it is around 0,32 lb/lb/hr and increase to 0,54 lb/lb/hr at Cruise. Stationary aeroderivative gas turbines you want to run at max continious thrust for max available efficiency (& Power)

      • Hi Bjorn,
        I wouldn’t have thought a time based comparison would be enough to make that moot, as fuel use rate is much higher in that 7%. But more importantly, it could increase how efficient peak efficiency is.

        I see it as an extension of the geared turbofan concept: with electric transmission there would no longer have to be any direct relationship between the speed of the main fan and that of the high pressure part of the engine. Also, rather than selecting ever bigger engines to increase efficiency, electric transmission would give the option of adding extra engines without the expensive heavy HP part.

  2. Is there a battery type that would even theoretically match or exceed 12 kWh/kg? The highest I can think of is Li Air at just under half that.

    There is however also the potential for batteries to be structural components, which could possibly be a significant factor (and which was demonstrated for a small hand held RC 7 – ? – years ago already and where research for vehicles is ongoing – eg and obviate at least part of the end of flight dead weight disadvantage. Perhaps part of the battery requirement becomes this structural battery and to reach total requirement part is a higher density non-structural battery. Of course, even if technologically feasible, certification would be a whole other issue and structural battery lifespan would need to match required airframe lifespan etc..

    • Who says you need a full sized battery? Think outside the box using a space based Laser energy transfer system. Then you would only need a 1/4 of the batteries to use as a buffer and for landing & take off.

      • “Say Jake, did you do the calibration for the satellite aiming system this month? No? That may explain why Peoria just burned down”.

  3. Read your origonal articles and now this.Sadly have to agree with everything stated.Energy density/ weight is paramount for aircraft.So electric propulsion is just not economic.Let alone the question as to how ‘clean’ the ‘ground’ electricity was in the first place.If it came from a coal powered station the whole think is a double joke.
    Far better imho to concentrate on the development of composite laminar flow wings and second generation geared fans ( or OR).

    • Energy density / weight is also of some importance in cars too. Teslas weigh 2+ tons, way heavier than the equivalent petrol / diesel fuelled cars. It has been reported that Tesla’s chassis is way too stiff for what’s actually required, so perhaps they’ve put too much metal into it, but I suspect that a lot of that 2+ tons is battery. It takes a lot more energy to move 2 tons vs 1.5. Colin Chapman (he of Lotus F1 “add lightness” fame of yesteryear) must be spinning in his grave. Now, if only we could tap that as an energy source…

      BMW’s i3 is carbon fibre, so that’s probably quite light. Well, it’s injection molded plastic with carbon fibre shreddings, so it’s sort of a half way house.

      What we all need is McLaren’s hollow section carbon fibre tech; best possible lightness for the material, and only 4 man hours per chassis.

      • Tesla’s batteries are structural components of the car. If you can engineer an aviation battery as a structural component of an airplane, you can cut into the potential energy per pound deficit electric has.

        The first electric airplane will be a bush plane with unique VSTOL/VTOL attributes like NASA’s Greased Lightening. Flying in gas to remote locations is a very expensive way to operate. Solar cells refueling will eliminate an extra trip devoted to hauling gas. VSTOL/VTOL and redundant power-plants will also make it safer to operate in remote locations.

        A natural market will help propel steady advancements in increasing electricity storage while reducing weight so that electric power will be used in other niche applications (freight comes to mind). Slowly electric power will become part of the aviation transportation network.

        • I don’t think Tesla batteries are structural – they’re fitted in a discrete battery box and can be removed (with a lot of effort) from the structure.

          True structural batteries might help the case for electric aircraft but there’s no chance of battery swap in that situation so you’re going to end up with a lot of sitting around while the battery recharges. I doubt the airlines are going to be overly keen on that.

  4. As with the Diesel scandal in the automobile sector, the attraction of hybrid aircraft power trains may lie in emissions (that is other than CO2, which is merely another way of referring to fuel consumption after all).

    Diesel cars don’t so much have a fuel consumption issue (their overall efficiency continues to be very competitive, for many of the same reasons you’ve outlined for aircraft), it’s the – local – pollution challenges which come with combustion engines. Recently, it has been demonstrated that production cars with modern exhaust aftertreatment systems CAN meet the latest regulation even in real driving, but the cost of said elaborate aftertreatment is steep. So even if the scandal has certainly not killed the Diesel in general, the times of deploying these engines even in cheap compact cars like a Smart or Polo may well be coming to a close as a result.

    The Gas turbine combustion process is very lean, so it has a NOx problem – much like a Diesel. I didn’t get the rationale for a hybrid gas turbine power plant either until I came across this article:

    It could indeed be prudent to hedge against future tightening of regulation on things like NOx and UHC around airports. Given the mass flows involved and weight sensitivity, exhaust aftertreatment is simply not an option in aviation 😉

  5. @Björn
    Instead of trying to make battery based aircraft, is there any future in making jetfuel out of hydrogen?
    Electrifying the fuel (production of the fuel to be more exact) vs electrifying the aircraft’s engines.

    • Skylon will be hydrogen powered, but that’s not a mass-transit application of Reaction Engine’s promising looking tech.

      The traditional problem with hydrogen is storing it; it’s not compact, it’s very awkward to handle, etc. There has been some work to make use of hydrogen to reduce iron oxide back to iron, and using the iron as a fuel in an internal combustion engine. Amazingly this does work, up to a point. Burning iron nano particles, collecting the iron oxide ash from the exhaust, and converting it back to iron in some factory saves having to carry the hydrogen around.

  6. about 10 years ago, I was looking at new cars and considering a Prius. at the time, the cost of the Prius was about $5-7k more than the cost of the equivalent non-hybrid Corolla. using the published EPA all around fuel efficiency numbers and a spec gas price of $3.50 (which seemed to be the likely long term price at the time in the US) the break-even point was somewhere around 350,000 miles assuming equivalent gas engine system reliability and zero hybrid related maintenance costs (i.e. no battery degradation or replacement or extra maintenance costs due to the MGU)

    needless to say, that was a non-starter for me. at that same time, my sister bought a lexus 450h because she liked the idea of hybrid. yes it was a nice car, but in 160k miles she had to replace the battery 3 times (although I think the first was covered under warranty).

    today, the cost premium for hybrids has dropped considerably, making the cost crossover fall within the economic lifetime of the car.

    I expect that over time, we will see the same thing happen in the aviation realm, probably first in the GA area, and eventually (if we don’t nuke/human induced environmental catastrophe ourselves to the stone age) the technology will develop and bubble up to long haul.

    but I expect it to be a solid 30+ years before we see anything beyond a mild hybrid on a transport category aircraft.

    an interesting possibility would be an extension of the T1000/GEnx 1B high capacity generator into an MGU system with some additional electrical storage on board a 787 class aircraft where the MGU would help drive the fan during takeoff climb (allowing the gas turbine to run at cruise efficiency) and charge through windmilling during descent. this would provide a reasonable marginal improvement in fuel consumption with minimal extra battery/MGU weight. but the appropriate battery tech for that is probably 10 years out.

  7. The advantages of electric hybrid aviation (disregarding the disadvantages) are to my mind:

    1. Propulsive efficiency
    2. Aeronautical efficiency
    3. Optimisation of the thrust requirements over the duration of the flight
    4. Redundancy / safety
    5. Noise/pollution control at airports.

    The first two don’t need a battery – just electric propulsion. The third will happen with any size of battery – the bigger the battery the bigger the win.

    Safety is a key issue for general aviation/ commuter planes, which is where I think the initial push for electrification will come from. With relatively few passengers they can be designed to carry a larger battery relative to the aircraft weight than a commercial airliner.

    I am somewhat hopeful for electrification for smaller aircraft

    • Smaller aircraft also have a much lower useful load and can rarely even take full tanks of fuel with the seats full. I think the viability of that is even less than the big jets.

      • Which means overbuilding the plane relative to the number of passengers carried I think. There needs to be a compelling reason to do so. The compelling reason for general aviation might be that it is not as safe as it needs to be. Electrification would be part of a push to greater redundancy, autonomy of control and reliability.

        Those factors don’t apply to commercial aviation.

  8. Bjorn, what do you think of the Harbour Air plan to electrify their Seaplanes fleet. This would seem to be a perfect proving ground for the tech. I looked at the Harbour Air flight map ( Of the 15 major routes 11 are between 30 and 45 minute long.

    • While I think it’s technically more feasible, the utility isn’t much. It’s likely (in the beginning) only for short sight seeing flights of the harbour. Add to that Harbour air is a very specific niche model of air transport.

  9. Finally a realistic article on electric and hybrid aircrafts, other than the pie in the sky stories that are published in other notable publications that this is happening almost tomorrow.

    Thank you.

    • Full agreement, AlanA. Even in this blog thread, we see “true believers” ever hopeful that unobtainium will be discovered and commercialized “soon.”

  10. Why focus exclusively on batteries? With the exponential progress in Hydrogen Fuel Cells lately there’s now several players who go down the Fuel Cell Electric route. Please note those do not use combustion, they are electric aircraft that get their electricity from a Fuel Cell. Here’s a couple of examples:

    And from a site that’s known to be VERY skeptical of hydrogen, just to get that perspective:

    And recently:

    Interview with CEO:

    (Skai has one mockup in California, one prototype in Massachusetts. The one behind the CEO is the mockup.)

    And a note about energy costs in the time frame when such airplanes might fly. Here’s what former energy secretary Steven Chu thinks about that:

    Hope that helps inform the debate a bit.

    • There are two major drawbacks to is transporting it the other making it.
      Major commercial aircraft fly from a limited number of large international airports.So the transporting issue ( as in automobiles) is pretty much eliminated -as it is with point to point hydrogen fuel cell busses.
      That leaves the manufacturing of hydrogen.It is energy intensive so this has to be achieved using clean energy if it is to be of any use.
      Of course the huge advantage ( over batteries) is hydrogen’s much higher energy density

      • Air travel is the fastest-growing source of carbon emissions. Aviation is responsible for 5 percent of anthropogenic climate change and its rapid growth puts it on track to consume a quarter of the world’s carbon budget by 2050. Hence, the aviation industry is on the brink of an enormous change. If the industry is not going to be far more proactive with respect to carbon emissions, I’m afraid that societies might start putting a stranglehold on the current aviation business model.

        LH2 powered aircraft have been studied in detail, are very doable, and are the best option for non-carbon aviation.

        LH2 has only around 30 percent as much energy per volume, but Jet-B has only some 30 percent as much energy per mass. LH2 has to be stored in large rounded tanks in a fatter fuselage. The increased tank and fuselage weight, decreased fuel weight, and increased fuselage drag roughly balance out, so range and energy cost are similar to today’s.

        The max flying altitude should be reduced to about 30,000 ft in order to avoid leaving water vapour (and some NOx) in the stratosphere — i.e. leading to only a slight reduction in efficiency.

        LH2 should be produced and liquefied at the airport itself.

        It’s important to note that an airport environment is ideal to house massive photovoltaic facilities, because airports tend to have a lot of land available (including building roofs). Furthermore, the energy produced is directly consumed at the infrastructure itself and, therefore, there is no need to ship the LH2 over large distances. If the generation of LH2 cannot be fully met by the massive airport solar photovoltaic facilities, electricity from the grid would maintain hydrogen production via electrolysis using off-peak electricity.

        Here’s an interesting design for a LH2 turbo-electric single aisle aircraft::

        • Interesting links. Yes, LH2 as energy carrier has been studied a lot. However, it’s only very recently that the parts have started to come together. Quote from the NASA funded study I linked to above:

          “Since the hydrogen would be stored at cryogenic temperatures, we also had the idea of doubling the use of this cryogen as a heat sink to enable superconducting electrical transmission and motor systems. These improvements in the drivetrain result in dramatic increases in the overall efficiency, specific power, and rated power capabilities for electric aircraft propulsion.”

          Some numbers from same interview:
          Energy Density of Fuel Cells at stack level:
          15 years ago: 0.3KW/kg
          Now: 2KW/kg
          Mid-term projection: 8-10KW/kg

  11. Pure batteri flight Will first comeback to verk stort range flights. Some Will figure out how to have a high power high voltage light power cord to Make the T-O on pure grund power.

    • Takeoff power is needed for some minutes , not seconds. So how long do you want your ‘power cord’ to be.
      Unless its a scenic jaunt at low level, higher power is still required till ‘top of climb’ to reach cruising altitude quickly.

      • A high strength, low weight, low electrical resistance wire for high voltage and current will be needed, I would start with carbon fiber with electrical conductor then move to carbon nano tube composites when its very high cost comes down. I would say 400m to 1/4mile long wire will give an electrical quadcopter with decent CL/CD a good start and some fwd speed before the wire is unhooked and wound up on it spool at the helipad.
        The average trip distance from the Airport to a down town skyport is perhaps 20-35km, as you gain fwd speed with a Lilium type of jet that has a meaningful CL/CD you burn most electrial Power during T/O and climb, but you need battery Power for advese conditions at cruise including de-ice and heating/AC.

  12. My cycle of choice (Ural) recently cam out with an electric concept bike.

    This truly has potential as you can add batteries and the short range can be workable around densely populated areas for personal use or even delivery.

    A good days run on a cycle is 400-600 miles and you would need an on board generator to try to keep up.

    You can add more batteries (more weight) or you can increase their capacity (or both) but you are fighting it all the time.

    Engines on the highway are like jet engine, they are pretty much as efficient as they get. A Prius can work quite well around town but not exceed a gas or diesel engine on the highway. And compromises to do that with special tires that are not what you want in bad weather, snow ice etc (yes you can get the right tires and that takes form the efficiency end of the package)

    Charge up times and places? None in the air, on the ground you can build some of that.

    So, to paraphrase Nevil Shute, There Are NO Charging Stations in the Skies”

    So like open rotor, Harbor Air in Seattle aside, its not going to work for anything other than niche tethered or short range applications much like fork lifts and electric delivery vehicles do.

    Being an technician, I never got on that curve, its alwyas been obvious the limitations and the hype does not overcome reality.

  13. Good article Bjorn, low feasibility for electrical flight but a lot of interesting technology being developped that will be used in other ways.

    On the energy, I think it is good everybody understand we have an environment problem, a big, global problem. Everything is getting more electric. On cars it is growing strongly in Europe, but nobody wants to know how we produce that electricity and avoids real (painfull) action.

  14. A simple reality check. Bye Aerospace has got $165 million in orders in only a few months for its two and four seat pure electric (yes battery alone) aircraft. They exist. They fly for three hours or more, climb faster than a Cessna and have a fraction of the total cost of ownership. It is almost impossible to hear them at 500 feet overhead so all hours flying is in prospect. 40 have been ordered for a Norway flying school and 100 for a US air taxi service. Now read about Pipistrel and others. Or are you too busy calculating that Tesla cannot exist? Read IDTechEx report “Manned Electric Aircraft 2020-2030”.

    • You are entirely correct. For small planes with the typical usage pattern of a flight school, battery electric is working well and it’s here now. For commercial high utilization aviation it’s a different story. The biggest issue being that Battery Electric doesn’t scale well for aviation, and improvements in battery energy density is progressing slowly. But there’s hydrogen fuel cell for longer range and bigger planes. Skai (not really long range, but still…) is aiming for certification late 2020. Before anybody writes that off as ridiculous they should watch the interview with the CEO I posted a link to above.

  15. Here’s another reality check.
    It’s all smoke and mirrors, as the real aim is to do an IPO off mugs.
    Ask yourself why Cessna isn’t doing it?

    • A Hybrid that make sense: VTOL (up front helicopter ) craft.

    • Isn’t Cessna ossified comparable to the US car/small trucks industry?
      Selling 1930tech into a captured market?

  16. Ironically diesel electric submarine technology may point the way forward since submarines have long grappled with electric propulsion.

    Hydrogen peroxide proved the way to store energy for underwater propulsion, but the technology is fraught with danger. Hydrogen Peroxide combustion produces steam and this can power a steam turbine.

    The fact that naked flame cannot survive above 9,000ft or below -23deg Centigrade may offer a way to develop a hybrid aircraft only using Hydrogen Peroxide at altitude.

    Another possibility is using ionised Deuterium to heat steam. The Nazis experimented with this as far back as 1944

    • Hydrogen peroxide is no longer used on submarines today. There were just a few experimental once. It was just used for torpedoes but it is extremely dangerous – Kursk.

      Current submarines use fuel cell systems with compressed oxygen and hydrogen is stored in metal hydride tanks. Next generation of submarines will run on methanol – CH4O. Methanol is liquid and easy to handle.

      Heating value for methanol is about one third less compared to diesel or kerosene jet fuels. So a normal APU could still be used.

      There are several attempts to store solar power energy as methanol because of the ease of storage an transportation.

  17. for a GA/trainer aircraft it is pretty hard to beat a Cessna. they are cheap, plentiful, durable, simple, owner maintainable, easy & cheap to repair have good enough load and range capacities with very benign handling qualities.

    could we do better in all those areas with modern materials and aerodynamic knowledge? for sure we can make a plane that is as durable with better load, range and handling qualities, but it would cost more, be harder to maintain & repair.

    the Cessnas are “good enough” enough that the drive for something better runs into the wall of cost/benefit.

    • Limits move slow.

      The reality is that you could densify a battery 10x and still not be able to do what fossil fuels do.

      Why are the improvements in aircraft efficiency almost all in the engines?

      Because aerodynamic have inherent limits.

      They have been working on batteries since the 1850s? Slow arduous progress.

      It still has to be commercially viable at a cost that compete with fossil and other than niche applications, its not there.

      We have had elecric forklift forever because weight is a good thing to anchor a forklift to the ground and you can charge them up at the end of a shift.

      And prey tell what does it cost to extract the materials and make them?

      Yea, that is fossil fuel driven and more environmental aspects (and are they toxic and can you dispose of them or recycle them?)

      And god help you if you use fracted gas to make the electricity. Much better to buy it from the Middle East or Russian.

  18. People see their computers, phones, memory capacity improving 100% + every year. And easily believe battery capacity must go the same route.

    But battery power is more growing like the speed, efficiency of cars, aircraft, magnetrons. Not doubling every year during the previous 50 years. Despite billions being invested & promises by interest groups.

    If we like an idea, we easily ignore physics & put blind faith in technology we don’t understand.

    • Spot on, no two techs are the same.

      Aerodynamics and batteries are slow movers.

      • Aerodynamics wasnt that slow to develop.
        the Concorde cruise at mach 2, the Blackbird and B70 Valkyrie could cruise at mach 3, this was all 50 yrs ago. And that was done with mainframes and numbers coming from boxes of printouts that took a day turnaround to run.

        Nothing like the computer models now of the aerodynamics can do much more detail and quicker and more accurately as well as use discontinuities in the airflow to your advantage. Then there is FBW to unload the structure or limit the loads.
        Likely more computer power now used everyday for stock market picks or flash trading in nanoseconds

        However extreme energy conservation in long range aviation will take us back to the Electra and Britannia speeds

  19. Björn your numbers for battery energy density are way off: packs for the Harbour Air Beaver & Otter conversions are 300 wh/kg at the pack level (not cell), today (not in ~10 years). Tesla Model 3 pack is 248 wh/kg at the pack level, today. Innolith has pilot grid storage cells deployed in the US with 1,000 wh/kg, today. Electric motors are also ~2.5x more efficient than the best gas turbine engines (~95% for electric vs. ~40% for jet engines), so divide jet fuel’s energy density by 2.5 as a starting point.

  20. Thankyou Bjorn.

    It was pandering to politicians who believe the scam that humans can ruin earth’s climate.

    Fundamentally, the physics of greenhouse gas molecules limits the amount of temperature rise that CO2 can cause, to a small amount most of which has already been realized. That’s the ‘saturation’ effect of energy flow from overlap of absorption/emission spectra of carbon dioxide and the most common greenhouse gas named dihydrogen monoxide. Even the IPCC agrees with the basic physics I point to, but they botched the calculation and theorize positive feedbacks while ignoring the evidence of negative feedbacks such as water vapour.

    Beware that the claimed 2 degree threshold of disaster was an arbitrary choice by an alarmist, then regurgitated by True Believers without checking – even the climate alarmist ‘scientist’ Phil Jones of the CRU of East Anglia University stated that. (Yes, the Phil Jones who conspired to muzzle questioners. If the science is as certain as alarmists claim why do they have to force people to believe it?)

    • Reality is that the climate is not warming at an alarming rate, and sea level is not rising at a rate significantly faster than it has been since the end of the long cool period around 1750AD. (See for government data bases.) Records of surface temperatures are incomplete and contain unexplained ‘adjustments’, I’ll instead go with traditional weather balloon thermometers and satellite sensors.

      Me, I want the Medieval Warm Period, when Vikings farmed southwest Greenland, warmer yet climate was stable. Warm is good for living things, and carbon dioxide is good for our food source (plants, whether directly or indirectly).

    • @Keith Sketchley

      Disclaimer: Off-topic comment.

      People tend to hold overly favorable views of their abilities and knowledge in many social and intellectual pursuits — AKA, the Dunning-Kruger effect.

      David Dunning and Justin Kruger suggested that this overestimation occurs mostly because people who are unskilled in certain pursuits suffer a double problem: Not only do these people reach wrong conclusions and make inappropriate choices and decisions, but their incompetence prevents them from realising it.

      Now, the mistaken idea that the Greenhouse Effect is “saturated” — that adding more CO2 will have virtually no effect — is based on a simple misunderstanding of how the Greenhouse Effect works. What matters is the change in what happens at the top of the atmosphere, not what happens down near the surface. As we climb higher in the atmosphere the air gets thinner. There is less of all gases, including greenhouse gases. Eventually the air becomes thin enough that any heat radiated by the air can escape all the way to Space. How much heat escapes to space from this altitude then depends on how cold the air is at that height. The colder the air, the less heat it radiates. So if we add more greenhouse gases the air needs to be thinner before heat radiation is able to escape to space. So this can only happen higher in the atmosphere. Where it is colder. So the amount of heat escaping is reduced. By adding greenhouse gases, we force the radiation to space to come from higher, colder air, reducing the flow of radiation to space. And there is still a lot of scope for more greenhouse gases to push this higher and higher, into colder and colder air, restricting the rate of radiation to space even further.

      A Saturated Gassy Argument


      The simple physics explanations for the greenhouse effect that you find on the internet are often quite wrong. These well-meaning errors can promote confusion about whether humanity is truly causing global warming by adding carbon dioxide to the atmosphere. Some people have been arguing that simple physics shows there is already so much CO2 in the air that its effect on infrared radiation is “saturated”— meaning that adding more gas can make scarcely any difference in how much radiation gets through the atmosphere, since all the radiation is already blocked. And besides, isn’t water vapor already blocking all the infrared rays that CO2 ever would?

      The arguments do sound good, so good that in fact they helped to suppress research on the greenhouse effect for half a century. In 1900, shortly after Svante Arrhenius published his path-breaking argument that our use of fossil fuels will eventually warm the planet, another scientist, Knut Ångström, asked an assistant, Herr J. Koch, to do a simple experiment. He sent infrared radiation through a tube filled with carbon dioxide, containing somewhat less gas in total then would be found in a column of air reaching to the top of the atmosphere. That’s not much, since the concentration in air is only a few hundred parts per million. Herr Koch did his experiments in a 30 cm long tube, though 250 cm would have been closer to the right length to use to represent the amount of CO2 in the atmosphere. Herr Koch reported that when he cut the amount of gas in the tube by one-third, the amount of radiation that got through scarcely changed. The American meteorological community was alerted to Ångström’s result in a commentary appearing in the June, 1901 issue of Monthly Weather Review, which used the result to caution “geologists” against adhering to Arrhenius’ wild ideas.

      In sum, the way radiation is absorbed only matters if you want to calculate the exact degree of warming — adding carbon dioxide will make the greenhouse effect stronger regardless of saturation in the lower atmosphere. But in fact, the Earth’s atmosphere is not even close to being in a state of saturation. With the primitive techniques of his day, Ångström got a bad result, as explained in the Part II . Actually, it’s not clear that he would have appreciated the significance of his result even if he had gotten the correct answer for the way absorption varies with CO2 amount. From his writing, it’s a pretty good guess that he’d think a change of absorption of a percent or so upon doubling CO2 would be insignificant. In reality, that mere percent increase, when combined properly with the “thinning and cooling” argument, adds 4 Watts per square meter to the planets radiation balance for doubled CO2. That’s only about a percent of the solar energy absorbed by the Earth, but it’s a highly important percent to us! After all, a mere one percent change in the 280 Kelvin surface temperature of the Earth is 2.8 Kelvin (which is also 2.8 Celsius). And that’s without even taking into account the radiative forcing from all those amplifying feedbacks, like those due to water vapor and ice-albedo.

      In any event, modern measurements show that there is not nearly enough CO2 in the atmosphere to block most of the infrared radiation in the bands of the spectrum where the gas absorbs. That’s even the case for water vapor in places where the air is very dry. (When night falls in a desert, the temperature can quickly drop from warm to freezing. Radiation from the surface escapes directly into space unless there are clouds to block it.)

      So, if a skeptical friend hits you with the “saturation argument” against global warming, here’s all you need to say: (a) You’d still get an increase in greenhouse warming even if the atmosphere were saturated, because it’s the absorption in the thin upper atmosphere (which is unsaturated) that counts (b) It’s not even true that the atmosphere is actually saturated with respect to absorption by CO2, (c) Water vapor doesn’t overwhelm the effects of CO2 because there’s little water vapor in the high, cold regions from which infrared escapes, and at the low pressures there water vapor absorption is like a leaky sieve, which would let a lot more radiation through were it not for CO2, and (d) These issues were satisfactorily addressed by physicists 50 years ago, and the necessary physics is included in all climate models.

      Then you can heave a sigh, and wonder how much different the world would be today if these arguments were understood in the 1920’s, as they could well have been if anybody had thought it important enough to think through.

      Question: Any idea what levels of CO2 required would cause saturation ? Looking at the graph on the Part II article it looks like there is still extra areas to absorb at 100,000 times pre-industrial CO2 levels, up at the 21-22 micron wavelengths, and some down at 11.5 microns or so that would take 10,000 times as much to be absorbed at the other end of the peak. It seems unlikely there is enough carbon around for us to burn to get it that high, so in practise we aren’t going to reach saturation at any point.

      Response: Quite true. In fact, you need to look in the spectrum beyond the graph in Part II to see when CO2 really gets saturated, because the portions of the spectrum outside the wavelength range shown can be considered transparent to thermal infrared for the purposes of discussing Earth, but start to absorb significantly at extremely high CO2 values like those on Venus. Of particular interest in this regard is the CO2 continuum, which starts just to the shortwave side of the graph in Part II. When you take the CO2 continuum into account you find that for gravity like Earth or Venus, CO2 starts to become saturated for a surface pressure of about 10 bars (10 Earth atmospheres). Venus has a surface pressure of about 90 bars, and has an almost pure CO2 atmosphere. Even for Venus, to infer that CO2 absorption is saturated one needs to go to absorption data beyond what’s in the HITRAN database, since the high surface temperature causes the surface of the planet to radiate into shorter wave parts of the infrared than does Earth. On Earth, both the lack of saturation and the “thinning and cooling” argument come into play in determining the climate. Venus is an example of a planet that can be considered saturated in the sense imagined by Angstrom for Earth, but which nevertheless gets warmer as you add additional CO2 because of the “thinning and cooling” argument.

      Part II: What Ångström didn’t know

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