# The Naked Scientists Forum

### Author Topic: How do you calculate the carbon footprint of jet travel?  (Read 7675 times)

#### Karsten

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##### How do you calculate the carbon footprint of jet travel?
« on: 06/12/2009 15:38:07 »
How is this done?

I assume you need to know the distance, number of passengers, fuel consumption of the jet per mile, and how it mixes with air to create a certain amount of exhaust. You also need to know how much of the exhaust is CO2 (or whatever would be considered part of the carbon footprint).

So, let's say it is a Boeing or Airbus typically involved in overseas travel (you pick the model), and let's fly from Montreal to Munich, Germany. I don't know any of the other numbers or data. Let's assume no lengthy waiting on the ground or air.

What is the amount of carbon in kilograms per passenger as a result of that trip?

Anyone wanna step forward and give this a whirl?

#### Bored chemist

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##### How do you calculate the carbon footprint of jet travel?
« Reply #1 on: 06/12/2009 21:42:54 »
You can simplify that by assuming that all the carbon in the fuel is converted to carbon dioxide.
Most of the data you need is here.
http://en.wikipedia.org/wiki/Boeing_747
You also need to know the density of the fuel which is about 0.81 kg/litre.

#### Karsten

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##### How do you calculate the carbon footprint of jet travel?
« Reply #2 on: 07/12/2009 01:05:07 »
You can simplify that by assuming that all the carbon in the fuel is converted to carbon dioxide.
Most of the data you need is here.
http://en.wikipedia.org/wiki/Boeing_747
You also need to know the density of the fuel which is about 0.81 kg/litre.

I am getting a fuel consumption of around 0.046 liter per km per passenger. (183380 liters per 9800 km per 400 passengers). That is 4.6 liters per 100 km. Or around 50 miles per gallon.

That is pretty good! Why are people so upset? Did I make a mistake?

Now I need to know the distance between Montreal and Munich (or any other typical flown distance between North America and Europe).

Sure, it is 460 liters of fuel for 9800 km per person, but where do numbers like 4000 kg of carbon per Europe trip come from? ( I heard that mentioned recently - no source).

#### chris

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##### How do you calculate the carbon footprint of jet travel?
« Reply #3 on: 09/12/2009 17:13:24 »
Your numbers sound pretty good - the guys at the Cambridge silent aircraft initiative quoted me economies on-par with a Toyota Prius when I asked them this a few years back.

#### Don_1

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##### How do you calculate the carbon footprint of jet travel?
« Reply #4 on: 10/12/2009 08:51:30 »
There is just one factor missing when these 'carbon footprints' are calculated, well actually, a whole range of factors missing.

Carbon footprint of the manufacture of the aircraft (divided by the number of air miles it covers in its operational lifetime).

Carbon footprint of the spares, repairs, replacement parts and general maintenance and of its breaking and recycling at the end of its working life.

I believe all of these and other ancillary bits and bobs (like food & drink, cleaning etc.) should be factored in to give a more accurate figure. The problem is, how many air miles will that particular plane cover in its life time, how many replacement tyres, and other parts? You will not know until its ready for the scrap heap.
« Last Edit: 10/12/2009 08:54:20 by Don_1 »

#### teragram

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##### How do you calculate the carbon footprint of jet travel?
« Reply #5 on: 10/12/2009 18:18:52 »
Don’t forget that 1 Kg of oil based fuel produces about 2.5 Kg of carbon dioxide. Also that carbon dioxide produced at high altitude has 2 to 3 times the global warming effect of that at ground level.

The claim that an aircraft can achieve similar consumption to a Toyota Prius seems a bit optimistic. No doubt the calculations assume that the aircraft had a full complement of passengers. Nothing wrong with that assumption, but did the Prius also have a full complement of passengers? That may make a difference.

#### Karsten

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##### How do you calculate the carbon footprint of jet travel?
« Reply #6 on: 12/12/2009 00:44:48 »
Very true, the carbon footprint of an airplane is more than just the kerosene it burns. Same for a car. Since I cannot know how much energy either either requires for manufacture and maintenance I will assume that it is more for a modern jet. I would not be surprised if they replace items way before they are broken. Understandably, the safety standards for a jet are higher than for a car. So much easier to pull over with a car.

And yes, the fuel consumption of a jet as calculated above is per passenger while the fuel consumption of a car is calculated per car. And I also ignored issues like waiting time in the air and on the ground.

Good to know that a kg of fuel results in 2.5 kg of CO2.

Why is CO2 emitted high up more potent than a lower altitudes?

#### teragram

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##### How do you calculate the carbon footprint of jet travel?
« Reply #7 on: 12/12/2009 17:37:02 »
Why is CO2 emitted high up more potent than a lower altitudes?
I don't know, but have heard it many times. Any climate experts out there with the answer?

Also, for interest's sake, here is part of an article in "New Scientist" in August 2008:-“A Virgin 747 flew from London to Amsterdam, consuming 22tonnes of fuel, 5% of which was biofuel…”
This article covered a flight that was made to demonstrate that biofuel is a viable alternative to conventional aviation fuel. I cannot vouch for the authenticity of the article, and maybe the reporter meant that 22 tonnes of fuel were CARRIED, not consumed.
The distance from London to Amsterdam is I think less than 400 Kilometres.
« Last Edit: 12/12/2009 17:40:40 by teragram »

#### yor_on

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##### How do you calculate the carbon footprint of jet travel?
« Reply #8 on: 12/12/2009 18:19:04 »
Here’s how I understand how Earth’s ‘radiation’ works discussing H2O and CO2. (And I’m not discussing ‘convection cycles’ now.)

Each ‘layer’ of air in our atmosphere will reach ever new equilibrium’s of warmth as the heat and molecules radiates / get freed from Earth, that as molecules in each layer also warm each other as they radiate (In reality it is their 'bouncing into each other' that produces most of the new heat as they radiate out at different wavelengths than they receive.)

As this is happening Earth will slowly become a place where the radiation from those molecules, reflected in all directions, will cause the Earth to start conserving this energy by building up ‘heat’ in the air layers as the heat gets more and more ‘trapped’ by our new molecules. - And - - This ‘imbalance’ creating evermore warmer layers will keep on, until the highest level of our atmosphere is so ‘warmed up’ that it reflects as much heat in space as the planet is receiving from the sun and ..Us. - That as it is only in that highest layer Earth can regulate its temperature through radiating out in space -. Did you know that before we started our industrial era we were actually in a slowly cooling period on Earth?

As for water-vapor it is well known that the higher up you come the ‘dryer’ the air will be, that means that most of the water-vapor falls out as rain further down. As the Co2 and H2O molecules drifts upward their mode of absorption changes. At a sea level the absorption is concentrated into discrete spikes with narrow gaps between the spikes and ‘shallow’ valleys. The ‘spikes’ we’re talking about is light (heat) absorbed in very specific wavelengths shown as dark lines in a spectrum. When the molecules are at the higher layers this absorption will change as the air-pressure goes down. Then their ‘spikes’ becomes much more defined and closer together (more heat absorbed per molecule) And CO2 won’t fall out as water vapor does (H2O-humidity-rain) at those lower altitudes, instead it will stay mixed no matter the height even though it will ‘thin out’ the higher we come just as our atmosphere. That’s why climate scientists talk about amount of heat conserved in different molecules and of global warming potential (GWP).

http://www.thenakedscientists.com/forum/index.php?topic=25747.msg276937#msg276937
« Last Edit: 12/12/2009 18:23:51 by yor_on »

#### Karsten

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##### How do you calculate the carbon footprint of jet travel?
« Reply #9 on: 12/12/2009 21:18:22 »
The higher in the atmosphere you come the less density there will be, that means fewer molecules to take up that radiation.
Why are there fewer molecules higher up? Gravity? If that is so, will the extra particles that are brought up there as jet fuel (= the kerosene components that are burned with the air that is already there) not "fall" back towards Earth?

You’re with me so far?

Not sure.

#### Karsten

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##### How do you calculate the carbon footprint of jet travel?
« Reply #10 on: 12/12/2009 21:29:02 »
Also, for interest's sake, here is part of an article in "New Scientist" in August 2008:-“A Virgin 747 flew from London to Amsterdam, consuming 22tonnes of fuel, 5% of which was biofuel…”
This article covered a flight that was made to demonstrate that biofuel is a viable alternative to conventional aviation fuel. I cannot vouch for the authenticity of the article, and maybe the reporter meant that 22 tonnes of fuel were CARRIED, not consumed.
The distance from London to Amsterdam is I think less than 400 Kilometres.

A Boeing 747-8I can carry 243,120 L of fuel (~22 tons?) for a maximum distance of 14,815 km. Like you said, it probably did not use all this fuel for the trip between Amsterdam and London. Biofuel or fossil fuel, if it is more damaging to leave CO2 up high, it does not matter where it comes from.

#### yor_on

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##### How do you calculate the carbon footprint of jet travel?
« Reply #11 on: 12/12/2009 22:51:28 »
Well, you got the answer to why molecules is more heat trapping on higher altitudes. As for why there are fewer molecules higher up? Gravity seems the most reasonable answer here, just as you assumed.

#### teragram

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##### How do you calculate the carbon footprint of jet travel?
« Reply #12 on: 13/12/2009 19:18:31 »
I think 243,120 litres, at density 0.8 Kg/litre, is 243,120 x 0.8/1000kg = 194 Tonnes approx.

#### Karsten

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##### How do you calculate the carbon footprint of jet travel?
« Reply #13 on: 13/12/2009 19:42:36 »
Well, you got the answer to why molecules is more heat trapping on higher altitudes. As for why there are fewer molecules higher up? Gravity seems the most reasonable answer here, just as you assumed.

Of course, maybe a hotter planet results in more molecules higher up since they would be more agitated.

But, if it is mostly gravity that results in a certain amount of molecules being at a certain altitude, could I also assume that those that get put there by humans drift back down and end the heat trapping at higher altitude?

#### yor_on

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##### How do you calculate the carbon footprint of jet travel?
« Reply #14 on: 17/12/2009 19:55:50 »
It seems like our air acts a little like 'layers', sort of like an onion, and the heat from the molecules will expand those layers before growing upward, and therefore also expand the outermost atmospheric layer around our earth. But i suspect it to be a simplification, and that the reality to be more like when you pour ink into water, 'seamlessly' blending it. Never the less I agree, a hotter planet will give the molecules more kinetic energy, making them take a 'greater place' expanding the atmosphere.

Add to that the fact that we by burning our 'hidden resources' add totally new molecules, not suitable for breathing in, at least, :) And you will have an expanding atmosphere with less oxygen versus the rest of the mix we breath.
« Last Edit: 17/12/2009 20:21:58 by yor_on »

#### rosy

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##### How do you calculate the carbon footprint of jet travel?
« Reply #15 on: 17/12/2009 21:17:59 »
In answer to the question about why people get worked up,.. although (assuming the aircraft is full, which they often aren't) it's only about equivalent to driving on your own in a medium sized  car the same distance, most people just wouldn't take a car across the atlantic (well, obviously, since there's an ocean in the way, but even if there weren't it would be a very loing drive...)
So one reason air travel is a problem in terms of fossil fuels burned is just that iot makes it possible for more people to do more miles more often, thereby greatly increasing emmissions.

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##### How do you calculate the carbon footprint of jet travel?
« Reply #15 on: 17/12/2009 21:17:59 »