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> For all the talk about fighting global warming, I almost never hear about this. It seems like the most inconvenient truth of all: if we want to fight global warming, we have to fly less.

I don't know what circles you hang out in, but I've heard this many times. The focus is on road vehicles and land power consumption because that's where the low hanging fruit is. And airlines do already have a profit motivation to decrease fuel consumption, which equates to reduced emissions. I'd like to see a CO2 tax to help align incentives.

Cleaner burning fuels might be an option at some point.

> But there is no electric airplane.

(I assume you're talking about commercial airplanes. Electric airplanes do exist, but have limited range and/or speed, and thus limited commercial application, due to reduced energy density.)

That could change, if batteries get a lot cheaper and lighter. Or you know, kerosene gets more expensive (government-enforced pricing of the externality of CO2 emission). Some of both.

It's obviously more viable for short-haul flights than long-haul, but even that would help.

>That could change, if batteries get a lot cheaper and lighter.

The batteries could be free. Until they literally burn up so the plane can get lighter and therefore can land, it's pretty much a non-starter for anything over a few hundred miles. The max takeoff weight of a Boeing 787 is 50 tons more than it's maximum landing weight, which will probably damage the gear in some capacity.

> The max takeoff weight of a Boeing 787 is 50 tons more than it's maximum landing weight

I honestly don't know, but could this be part of the design simply because the engineers know the plane will weigh less on landing? Seems like that design would change if so much mass from fuel was no longer lost/burnt.

The stronger the gear needs to be, the heavier it becomes. Planes are optimized for safety first and foremost, but weight is a very close second. Heavier plane = more batteries = more weight = more batteries etc.

This, but the reason it's engineered that way is because landing gear face far higher loads on landing. During takeoff, landing gear essentially only have to support the weight of the aircraft. During landing, the gear have to arrest the aircraft's descent (which may be momentarily 3 or 4 g's of acceleration if the aircraft encounters turbulence while landing); and then they need to brake the entire weight of the plane within the remaining length of the runway, which is a high loading in a different direction (along the aircraft's longitudinal axis). So maximum landing weight is set by the landing gear, while maximum takeoff weight is usually set by the wings and engines.

I didn't realize that most of the braking on landing was handled by the landing gear. I'd always assumed that the obvious sound of the engines reversing when we landed did most of the work, but some casual googling suggests that it's only supplementary, to reduce the load on the landing gear.

https://www.pprune.org/archive/index.php/t-379610.html is interesting :-).

Also, https://aviation.stackexchange.com/questions/1219/for-large-... .

yes and no, because now it's a pain in the butt when there is a takeoff issue. If there is a tail strike, an engine issue on take off, or a passenger emergency early in the flight, now they have to loop around in circles for hours with a damaged airplane before landing. Or they have to dump fuel, but they do it extremely rarely, because most planes can't even do it, and it's a pain in the butt and actually quite slow for the planes that can do it.

here is an example: https://www.youtube.com/watch?v=VSq9r05lVTo

and because fuel dump is only allowed above 4000ft/1300m.

It is way more complicated than just altitude, with zones and procedures, incredibly long checklists and a bit of maths. But a plane that can't reach 4000ft is probably in a mayday situation, and there is absolutely no time to try to dump fuel, it's a slow procedure.

All aircraft landing gear are certified for landing at MTOW, they just need inspected afterwards before the plane can re-enter service. The fact that frequently the captain's judgement is to prefer to land at a lower weight is a separate issue.

Just to put illustrative numbers on it and not to dispute the parent comment in any way, the big 787's (787-10) have 251 Mg max take-off weight and 202 Mg max landing weight.

In comparison the A380 has a max landing weight of 386 Mg. Clearly the 787 is not up against a hard practical limit in terms of landing weight. Yes, stronger gear weighs more.

We agree that weight of batteries impacts their usefulness for aircraft. That's why I mentioned it in the quoted sentence :-).

You're arguing facts not in evidence.

The 787 can operate out of many airports the A380 cannot.

> You're arguing facts not in evidence.

I don't understand what that sentence means.

> The 787 can operate out of many airports the A380 cannot.

Yes? I said batteries would have to be a lot lighter and kerosene a lot more expensive before they are a practical replacement. I think we agree, but I think you think we disagree?

Managing a few hundred miles on electricity would in itself have a huge positive impact. Most of the busiest air routes in the world call under that heading.

be careful with airline motivation, they are looking into their profit margins, and one way to reduce fuel price is to increase the economy of scale, that means more passengers, more pollution, more fuel, but less fuel per passenger. That was the whole point of the A380, a giant gas guzzler, but per passenger it was more efficient, it only works if you destroy smaller planes or increase passenger traffic.

The second aspect of it is that economies of scale are on the last leg, most airline companies use smaller planes, with a hub and spoke model, and a highly energy inefficient system, because it's better in their overall profit making system.

They are there to make money first, carrying passengers is the hoops they have to go through to get people's money (but by cleverly worded passenger carrying contracts, they are more and more getting around the issue), and fuel price is a variable in the system.

Economies of scale is a perfectly viable strategy for legs that already have plenty of passengers. Busses are gas guzzlers compared to mopeds...

Boeing had a choice between a more fuel efficient, durable and quieter airplane design, or a trans-sonic airframe design. The trans-sonic design lost, we got the 787.

Since then Boeing refreshed all their other planes (some might call it "stapled new wings and engines on") and called them -8 and -9 models.

But the problem is that the more efficient the tech is, the more of it people use. An extra 500 miles of range opens up decentralization of routes, which means more planes flying.

> But there is no electric airplane.

Not for consumer use, but they exist.

https://en.wikipedia.org/wiki/Electric_aircraft

I didn't know that! I'll update my comment.

Incidentally Uber (who are developing electric air taxis with Embraer, et al) are live streaming their annual summit on the topic starting tomorrow. https://www.uber.com/info/elevate/summit/

The most viable long term solution for long-haul air transport will probably be carbon-neutral liquid fuels. For example, in principle it could eventually become possible to genetically engineer algae which pulls CO2 out of the air and produces kerosene.

Eventually? In principle? Ethanol is a thing, just not one that was able to compete without taxing its competitors' externalities. Not sure how the math works out for jet engines, but I suspect it works out better than batteries.

Ethanol could fuel a jet engine, but kerosene has a higher energy density.

Ethanol production doesn't tend to be carbon neutral either, though maybe it's closer than petroleum pumped out of the ground.

Maybe it's better than petroleum? The hell? It's not only better, EtOH becomes entirely neutral in the limit where it takes over. The carbon released from burning all comes from the plant, which in turn all comes from the air. All other carbon costs are incidental (e.g. it doesn't make sense to immediately convert transportation, farming, and production equipment) or one-off and amortizable (ploughing fields).

For long haul air transport we would have to redesign engines, fuel systems, and airport infrastructure to use ethanol safely. And even then it would make flying less efficient because ethanol contains less energy. Synthetic kerosene or something similar would be an easier transition and give better results.

Aviation is a sideshow. It accounts for around 2-4% of carbon, depending on how you count its impact. And be careful extrapolating today's trends into a straight line, it rarely works out that way.

You could stop the world from flying tomorrow and it wouldn’t make a dent in your PPM growth.

If aviation busts the carbon budget, so will most everything else, and by vastly larger margins.

Better to direct your limited resources at lower hanging fruit, unless you'd prefer the perfect to kill the good.

might be an unpopular prediction on this board but i believe climate change will be solved by technology and not reduced consumption. electricity generation also has significant environmental impact and is not a solution in itself

I very much want to believe this. But how?

It cannot be achieved through reduced consumption. Humans won't allow it. It's technology or bust.

I think the idea is that humanity itself dies off in large numbers due to lack of food, potable water, wars, etc. There's how you get your reduced consumption. The earth itself is just fine with this natural cycle.

Here's your technological solution: Use more efficient, less polluting (and slower) turbofan engines instead of less efficient, more polluting (and faster) turbojects.

And here's the attendant public policy: Tax the turbojects' users enough to offset the negative ecological externalities incurred by their use. That will likely make commercial SST unprofitable.

As far as I know, and according to Wikipedia, most commercial airliners already use turbofans [1], which are high-bypass turbojets [2]. Unless you were referring to turboprops?

[1]: https://en.wikipedia.org/wiki/Turbofan

Almost nobody uses turbojets anymore. Certainly not airliners. Even fighter jets use turbofans.

Exactly my point.

> electricity generation also has significant environmental impact

Hydropower? The primary materials used are concrete and steel, and dams last for centuries with minimal upkeep. As long as appropriate measures (such as fish ladders) are taken, the local and global environmental impact is negligible.

Maybe, but we at least need to buy time until we otherwise solve the problems using technology.

How much energy does it take to turn CO2 back into oil? Is there a viable synthesis pathway? Carbon neutral oil would be fabulous. I'm guessing you have to spend a significant amount of energy to turn it back into oil, but is it 1.01x? 1.5x? 10x? 200x? The lower range would be viable to work with other kinds of renewables.

Can't store solar at night? Turn atmospheric carbon into oil. It doesn't have to be cheaper than oil (it almost certainly can't be unless it gets too hard to drill), but we can subsidize it within some kind of range.

EDIT: Oh cool, some people are trying this.

https://www.technologyreview.com/s/407748/making-gasoline-fr...

https://www.sciencemag.org/news/2015/09/feature-there-s-too-...

Aircraft fuel can be carbon neutral, if the fuel is made by CO2 reduction (CO2 to methanol/methane and Fischer-Tropsch). It's just not economical today. CO2 reduction will never compete with electric cars, because it's just too inefficient, but for aircraft, even throwing away 2/3 of your input energy might make economic sense if that energy is clean.

Do I understand you correctly that if we would stop flying right now, we could reverse some effects of global warming (the water vapor part of it would be gone instantly)?

>the water vapor part of it would be gone instantly

Not to mention the parts of the economy that rely on air travel ;)

Not to mention the remaining parts of the economy which would grind to a halt even if not directly related to air travel

You don't have to to stop flying, only stop flying so high. Low level cloud cover has a massive net cooling effect.

Problem is planes don't fly high for fun, they fly high because the air is thinner up high which improves fuel economy.

Jet engines are massively more efficient at high altitude. Turbulence is much worse at lower altitude. Safety margins are reduced at lower altitude. Winds are far less predictable at lower altitude.

> if we want to fight global warming, we have to fly less

Most people prefer to say they want to fight global warming as opposed to actually doing anything. If the average person really wanted to fight climate change, they'd:

• Stop eating meat

• Buy as few new items as possible

• Never get on an airplane again

• Not have kids

And even then one person's actions really can't do a damn thing so who can blame them for just enjoying their life and doing whatever they want?

.... also get more politically active as it’s government policy which will probably have the most impact (such as a carbon tax).

This isn't even remotely true: "Unlike the electric car, there is no emerging technology that can save air travel from this environmental impact."

Something as simple as flying low enough to create low level cloud cover would more than reverse the net effect of NOx and CO2 produced by planes. It's just more expensive because it takes longer and consumes more fuel.

Do you have any references for this? I couldn't find any mention of this in my research. For example it's not mentioned here: https://en.wikipedia.org/wiki/Environmental_impact_of_aviati...

I'm yet to find someone who doesn't ever fly at least once because of the environment.

I don't, I stopped about twenty years ago once I became aware of the damage it was causing.