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Comment by superqwert | Hacker News Reader

It is not exactly clear whether passenger flights are less environmentally friendly than various other options. Driving for long distances can be worse for the environment than flying commercially[0]. The article claims that Greta saved energy by travelling by train, but it is unclear how the method of calculation (ecopassenger.org) works, whether it considers that rail and road infrastructure requires far more energy and fuel for maintenance than the air and runway does and even the data entry is flawed, since you cannot change the load of plane and train separately, even though it is clear that flight operators often overbook planes, while trains often run with pretty low loads.

[0] http://www.umtri.umich.edu/our-results/publications/making-d...

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It is not unclear how their method, they explain it quite clearly and in detail [0]. In general, you are correct that road and (especially) rail require substantially more infrastructure than air travel. For combustion vehicles, however, such infrastructure is less than 10% of the total impact of such travel [1]. As energy source get cleaner, the relative impact of road construction and maintenance will increase. However, we run into difficult questions of allocation of burden, as essentially all damage to roads is done by heavy transport (damage goes by something like axle load to the fourth power), and by weather (irrespective of how much the road is used).

It is rather difficult to determine the actual impact of any one person's decision to fly or not fly. The state of the art considers the aircraft, the average load factor of the operator (or even load factor over a specific route), and the demand for urgent freight on that route (i.e. an empty seat might be compensated by more freight). Moreover, the marginal impact of one person is not the same as the marginal impact of e.g. a new travel policy for a large institution. Do to low data availability, we often take the average impact instead of the marginal.

For those actually interested in helping making open source and open data tools to help others make informed decisions, please check out BONSAI [2,3] (I am affiliated with the BONSAI NGO).

[0] http://ecopassenger.hafas.de/bin/help.exe/en?L=vs_uic&tpl=me... [1] https://pubs.acs.org/doi/abs/10.1021/acs.est.8b00261 [2] https://github.com/BONSAMURAIS/bonsai [3] https://bonsai.uno/

It seems that [1] is referring to roads though? Rail maintenance is far more expensive.

Thanks a lot, this has been a most helpful reply!

A one-person switch doesn't cancel a flight, or change the world, just as a one-person boycott doesn't get Nestle to change a recipe.

Yet trains are far less emitting than aircraft, so the more people that join the sooner flights will be cancelled or routes dropped as unprofitable. Increasing carbon taxes are inevitable, so that will further speed any changes.

Every kg less that's carried means less fuel burnt. Sure each one person reduces the fuel usage by only a small amount.

But, you can't have less air travel without people stopping flying. It's going to happen incrementally.

What evidence are you citing here?

Is anybody denying that? I found a study by Mikhail Chester and Arpad Horvath suggesting that total life-cycle energy inputs and greenhouse gas emissions contribute an additional 63% for onroad, 155% for rail, and 31% for air systems over vehicle tailpipe operation. However, even than rail generally appears to be less damaging than air by far. What are your sources?

when less people pay for things it becomes less profitable.

Yes, but the evidence is required for this claim:

"Yet trains are far less emitting than aircraft"

https://www.eea.europa.eu/data-and-maps/daviz/specific-co2-e...

Rail: 28 kg/passenger km Air: 144 kg/passenger km

2014 figures.

> whether it considers that rail and road infrastructure requires far more energy and fuel for maintenance than the air and runway does

This lack of maintenance is showing its signs. There are surprisingly many potholes at 10km altitude, and no one spends any money trying to fix them!

> It is not exactly clear whether passenger flights are less environmentally friendly than various other options. Driving for long distances can be worse for the environment than flying commercially[0].

There might be some question whether cars less efficient than planes, but I am not aware of any such doubt w.r.t. trains, which is what we are discussing here. Also note that few people would drive the long distances that a plane or train enable them to cover.

> but it is unclear how the method of calculation (ecopassenger.org) works, whether it considers that rail and road infrastructure requires far more energy

The methodology is available [0]. It considers direct emissions, so no maintenance or manufacture. Can you make an argument why these should be more than a low percentage of the direct emission? I mean sure, it might require 1000x more energy to maintain, but its not like that is a large part of the final emission per kilometer.

> since you cannot change the load of plane and train separately

Why would you need to? Of course people who take the train instead of the plane reduce demand for planes and increase demand for trains. So there are fewer plane trips and more rail trips. Assuming that rail trips are environmentally advantages, why would that be a bad idea?

> even though it is clear that flight operators often overbook planes, while trains often run with pretty low loads.

The model considers rail load factors based on real world data where available, substituting 35% as an approximation where no data is available. Do you have any reason to object to that?

0: http://ecopassenger.hafas.de/hafas-res/download/Ecopassenger...

Nice find, I didn't see this before! I think the conversation should be left up so this can all be found, though.

Additionally, her environmental impact would only really be true if her flight was cancelled as a result of her taking the train. Is there evidence that this happened?

That's wrong.

If a plane has 200 seats, and 400 people are willing to fly a given route, the airline sends 2 planes. Make it 401 people, they'll send three a day. That means each person who flies or doesn't brings the count closer to the next threshold, where the number of planes flying changes.

Of course, this is oversimplified, not as instant as I described it, there are price politics and what not, but you can still very much say the climate footprint of each passenger is (total plane print/passengers). The idea is not to make super accurate global calculations but to quantify individual behaviour without employing a super computer.

> If a plane has 200 seats, and 400 people are willing to fly a given route, the airline sends 2 planes. Make it 401 people, they'll send three a day.

No. They will send one with 400 seats in the first scenario, and possibly two with 300 seats or one with 400 and one with 100 seats in the second scenario.

It's a very common scenario

Making the scenario more complicated doesn't change the fact that there are thresholds which everybody (not) flying influences!

It's not a more complicated scenario. IIRC a company loses money if the plane is not at least half full. So there's no chance a company will send two planes if the second one will only haul 1 or two passengers.

If the demand increases and they are always booked to capacity, they will send a bigger plane first.

If the demand decreases, and they are never booked to full capacity, they will send a smaller plane or will cancel the flight.

> there are thresholds which everybody (not) flying influences

There are. But, unfortunately, flying still beats everything else on convenience for anything but the shortest trips. And even on shortest trips the distinction between a train trip and a flight might not be that obvious (if we take into consideration convenience alone).

You're claiming the argument is wrong, then supporting it again.

The person(s) who go over or under the threshold are the ones that make a difference. If thresholds aren't breached by the amount of people changing route, then there is not a very significant difference.

As you indeed state:

"but you can still very much say the climate footprint of each passenger is (total plane print/passengers)"

You can indeed say as much, but "this is oversimplified".

Just to be clear - I am not arguing that we should not pick routes responsibly, with the environment in mind. I am merely trying to ensure we are clearer about what impacts we are actually making and that we are considering all the impacts and not just doing a simple calculation that actually misses out the many complexities of transport.

So, you're arguing that the straw that broke the camels back is the only straw that matters at all?

In transport, we have learnt over the past century to not use aggregate models, as they do not provide the same detail and results as disaggregate models[p.18 Modelling Transport 4th Edition Ortuzar & Willumsen]. We should not lower our standards when discussing emissions and pollution.

This article above is a very worrying case - where the reader is encouraged to shame people for flying, without showing necessary statistics as to whether flying is indeed much worse than other transportation methods.

No, I'm arguing that the calculations for emission per person are simplistic.

This is some seriously ridiculous mental gymnastics (continuum fallacy). Someone who never flies is now responsible for the environmental impact of those who fly, because specifically their lack of flying is not canceling any flights (or preventing any flights from happening)?

Certainly not. Responsibility is a very complex issue, especially if you devolve it to the users, rather than keeping it in the hands of the managers/operators.

But even if we assume a large part of responsibility rests in the users, then the responsibility would clearly be only held by those planning to make the trip and deciding which form of transport to use (potential users).

Surely you must be aware that the point of an action like this is not the single action itself, in isolation, but the setting of a trend?

If it becomes a trend, that will be good if indeed the efficiencies are true. As stated earlier, it is unclear how the calculations are made and whether the actual total emissions cost was lowered.

Do you have any idea how astronomically inefficient jet aircraft are? How ridiculously large amounts of energy they burn?

The whole flight does not need to be cancelled. Underselling flights are often replaced with smaller aircraft. One person might not make a difference, but if 10 or 20 cancel, an A321 may get replaced by A320 or A319, which are lighter and burn less fuel.

Switching to a smaller aircraft isn't necessarily good for the environment.

For example the A319 burns 5%/less fuel than the A320 but has 15% fewer seats, in common configuration. So the per-seat emissions are worse than if they had sold the remaining A320 seats at cost

Good point, but once again - the crossing of thresholds is the major change, rather than the individual changes between thresholds.

A flight with 50% empty seats consumes less fuel than a full cabin. The difference is not huge, but it's there.

Yes, this all sounds like a complicated way to say "obviously we've got to reduce air travel, but I'm not going to fly less, because what can one person do".

This should be a named fallacy.

Works in all sorts of situations: "obviously I have to eat less, but not this mealtime".

There is a difference between decision making and calculations of change.

I am certainly not arguing that decisions shouldn't be made responsibly. I am merely trying to point out that the calculations that have been made are simplistic.

That is certainly true, but from the scale of the calculations, I am assuming that ecopassenger.com is not just calculating that difference, but the overall emmission cost as a ratio of flight.

That is a strange argument. Are you too responsible for all the flights you don't take?

That is not what I am arguing at all. I am merely pointing out that it is unclear as to what the ecopassenger.com website is calculating and what we can gather from this information.

That's just ridiculous and no-one thinks that.

That is certainly the implication :-

"Environmental website ecopassenger.org calculates that Greta’s train journey to Davos, Switzerland, emitted just 44 kilograms of CO2, compared to an expected 262 kilograms had gone by plane."

They are trying to suggest that she chose this trip, because it is environmentally better, but actually irrespective of her choice, there was most likely a total of emmission of 306kg of CO2.

There could certainly a benefit, if the aim is to just fund transport that is more efficient and less pollutant. However, as mentioned earlier, it is unclear how the calculation is made and whether it is actually true when considering the wider requirements for the services - e.g. maintenance.

That's interesting. My assumption was that they were using individual examples to show the aggregate effect of large numbers of people making such choices, at a scale great enough to influence flight planning, but in a way that seems relevant to us as individuals. After all, there are hundreds of millions of people in Europe. If 1% of them make a small but material change in their travel habits that's millions of people taking fewer flights, which clearly could have a material effect on flight schedules. It would never have occurred to me that, in fact, they literally meant us to think that one person making that choice would individually have that effect.

> compared to an expected 262 kilograms had gone by plane.

I still very much doubt that 262kg is per person. There's no way a plane emits tens of thousands of kilos of CO2 on a trip.

I think you're going to be surprised.

A Boeing 747F has a fuel capacity of c.200,000kg, 200 metric tons (http://www.airliners.net/forum/viewtopic.php?t=738927).

It's mostly heptane (C7H16) and octane (C8H18). Rough calculation, that's 15x12 : 34x1 ratio of C to H (180:34).

So let's say 86% by mass, of 90% is Carbon.

But CO2 is mostly Oxygen from the air, about 12:32 ratio. So the Carbon is a quarter of the total mass.

This gives us (0.86 x 0.90 x 200tons) x4 as a ball park figure.

That's 600,000kg of CO2 produced by 200,000kg of fuel.

With 400 passengers that's 1500kg of CO2 per passenger if they burnt the full fuel capacity; ie that's a top bound estimate.

So ...

Meanwhile you might be surprised to find trees are made of CO2 with the oxygen removed. A large oak tree weighs c.5000kg and half of that is Carbon.

So very, very roughly you'll want to plant and grow to full size a large tree for every couple of long haul flights (to account for fuel only).

262 might be a high estimate. At 750 gallons/hour[0] and 9.57 kg CO2/gallon[1] that's about 18000kg for a 2.5 hour flight.

[0] https://eu.usatoday.com/story/travel/columnist/cox/2014/10/1...

[1] https://www.eia.gov/environment/emissions/co2_vol_mass.php

The 262 number was for total trip there and back. So about 5 hours of flight time in total.

A passenger jet burns 10-15 liters of fuel pr km. Stockholm-Geneva is about 1600 km, so 3200 km round trip. So the numbers seem at least to be in the right ball park.

Here's a bunch of physics if you're into that sort of thing: https://therocketscienceblog.wordpress.com/2016/08/01/how-mu...

There is a way :) Don't forget that each atom of carbon combines with two oxygens from the air.

> Greta’s train journey to Davos

a journey that took around 25 hours

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