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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Flying is worse for the climate than you think

Posted on 10 May 2022 by Guest Author

Flying is often at the top of the list of our climate change causing activities. But why are the emissions from flying so bad for the climate, and is there anything that we can actually do to fix it?

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Comments 1 to 8:

  1. "Ghost Flights" can be thought of as a bright point of distinction as to whether governmental climate  change mitigation policy is working at anything roughly approaching an effectively systemic level. 

    To Adam's thoughts on "fixing flying," I'd add: accept that flying costs more than we're paying. As with other of our activities, the cost of flying is artificially low because we're burning a messy fuel from the past that we didn't make and pushing the result onto people in the future, with no plan or intent to pay back. For our immediate benefit, we're stealing the future from other people. 

    Air travel at today's cost to us is theft.

    When the dust settles, it's highly unlikely that a fully accounted air fare from point A to point B will be as strangely "cheap" as it is now, once theft is removed from the equation. A reformed thief accepts that muggings are no longer part of everyday living. Our habits and expectations will likely need to change. 

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  2. I think that biofuel, properly sourced, is the obvious and most scalable short term solution to the carbon footprint of aviation. Both United and KLM have demonstrated transatlantic flights on pure biofuel. The airlines should be first in line for properly raised biofuel and should be given deadlines for conversion, or airports or countries could incentivize the conversion by giving better terminal slots, reductuions in landing fees, or higher scores in route bids for use of biofuel. New high speed land connections are of course feasible but as a rule they are anything but short term projects. Biofuels for long distance oceanic shipping ought to be second in line.

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  3. walschuler talks of biofuels. Does anyone know what the chemical composition of "biofuels" is and how they compare with standard jet fuel for CO2 emissions? Strictly speaking are not fossil fuels also biofuels?

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  4. Lawrie @3 , as far as jetfuels are concerned, their composition is described as predominantly  hydrocarbon chains of C9 - C16 length (kerosene-like).   "Biofuels" for jet engines have a similar composition ~ in part to allow usage in the already-existing modern jet engines (and in legacy jet engines too).  It would be problematic to re-design / re-manufacture jet engines to use short-chain hydrocarbon fuels such as alcohols.   And alcohols, although cheaper to produce, have lower energy density and would be proportionately heavier to carry : as well as requiring larger & therefore heavier tanks.

    What exactly are biofuels, you ask?   A loose definition would be :- any hydrocarbon molecule of one or more carbon atoms, derived from feedstock that has grown in recent years (say, less than 100 years)  . . . as opposed to fossil fuels ~ where the feedstock comes from organisms that grew  100+ million  years ago.   An easy difference !

    Why use the term "biofuels" ?   A convenient term, since it is brief and people intuitively know what is meant by it.

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  5. The video takes a rather drastic shortcut when it comes NOx emissions. The overall long term effect of NOx at altitude is likely to be a net negative radiative forcing because of the shortening of the methane residence time. The effect of contrail clouds is more difficult to ascertain and is likely a small net positive. Of course, the CO2 emissions remain the main concern, but presenting NOx emissions as making flying even worse is misleading. The whole picture is more complex.

    There is very large uncertainty as to the total net forcing and how it compares to the CO2 forcing alone. It is pretty much admitted, however, that the total net forcing is higher than the CO2 forcing alone.

    NOx is much more of a concern for low altitude operations and air quality around airports. Unfortunately, a similar trade-off exists to that of diesel engines for cars and reducing NOx involves higher CO2 emissions. 

    The truth remains that aviation is the most bang for the buck that burning hydrocarbons can deliver. That is where energy density really hits the spot. Unlike many other applications, there is currently no viable, or even prospective, alternative technology that comes close to the performance obtained with ICEs for propelling aircrafts. This holds true for both turbines and reciprocating, the latter being surprisingly more efficient in that role than is ususally believed. If we are to give attention to low hanging fruits, aviation certainly is not one of them (no pun intended).

    The only electric aircraft I know of that is currently well engaged in the certification process is ALICE. When ready, it will carry 8-10 passengers over 5 to 600 miles at speeds around 220 to 240 knots. That is the level of performance of a King-Air 200, without the ability to refuel and be ready for flight again in less than 30 min. 

    Biofuels produced with clean energy are the best bet for a future carbon neutral aviation. However, if all electricity production and terrestrial transportation could be carbon free, aviation would not be a much of a factor, as only these 2 dwarf aviation emissions. 

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  6. Thanks Eclectic @4. As a scientist I have always found the term biofuels to be problematic. Bio implies userfriendliness to the atmosphere. If jet fuels are constrained to hydrocarbons of similar energy density to currently used jet fuel then for climate change purposes CO2 emissions will be identical. We might feel better but the atmosphere won't notice any difference.

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  7. Lawrie @6. Traditional fossil fuels are not identical to effects on climate to biofuels. Traditional aviation jet fuel uses hydrocarbons that have been lying in the ground for millenia so they are essentially a new pulse of CO2 into the atmosphere. Biofuels are adding a pulse of CO2 that is the same as the CO2 their biomass removed shortly before, so they are effectively carbon neutral. (Ignoring carbon used in manufacturing the biofuels). 

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  8. There is also the possibility of future production of aviation fuel using CO2 captured from the air and renewable electricity (electrofuels).  This article describes the process and estimates that the cost of electrofuel would be about $4 per liter today. The projected cost would drop to below $1 per liter in 2050.  $1 per liter is comparable to current fossil jet fuel.  I note that fossil jet fuel is likely to increase in price in the future.

    To me the point is that it is possible to make jet fuel with no net release of CO2 into the atmosphere if you are willing to pay for it.  Today we simply avoid the payments by shifting the cost to future generations.

    The technologies exist to convert the economy to completely renewable energy once governments have the will to make those changes.  Then we will not have to worry about the Russians or OPEC damaging the economy by witholding oil from the market (and we will address climate change).

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