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I've been doing some web research on whether it is possible to offset carbon usage for non-critical long-distance air travel, or indeed whether carbon-offsetting should be rejected on the basis that flying emissions cannot be undone. I had imagined that this would be an easy question to answer with some authority (e.g. a scientific report of some kind, ideally peer-reviewed) but presently I am drawing a blank.

Here's some context to the question. I'm in the UK and have been invited to holiday in Bali, Indonesia, which is around 7,779 miles away (and of course I plan to come back two weeks later, so I can double that figure). I would very much like to go. I am not a frequent flyer (I think I've flown 4 or 5 times in total) and I've been car-free for four years (so I suppose I am somewhat in credit, environmentally speaking).

My starting consideration is that, to prevent global warming reaching a critical tipping point, climate journalists and meteorologists propose that the world needs to stop flying entirely until an environmentally sound fuel alternative can be found (yup, they're serious). Since only 5% of the world's populace will ever get on an aeroplane, I'm wondering if my ability to fly is a feature of my geographic, cultural and financial privilege, and thus I shouldn't mind.

Now, I could just offset my flight but I don't know whether that's a great idea, a clever scam, or a well-intended but self-defeating exercise. As to the latter, I wonder if environmentally-conscious organisations that encourage more flying aren't doing a very good job!

The question in a more succinct form: is carbon offsetting a scientifically acceptable approach to reducing flight emissions, or is it better to cut out non-essential flying entirely?

For the avoidance of doubt, a carbon offset is a scheme by which greenhouse emissions created in one place can be reduced in another, in order for there to be no net increase in emissions.

I accept that not everyone is persuaded of the merits of climate change, but my purpose here is not to start a political debate. I am looking for authoritative sources that take a view as to whether (long-haul) flights can be genuinely carbon-offset, given the current position of scientific knowledge.

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@halfer As far as I understand, the point is not mainly getting more oxygen in the atmosphere but rather less carbon (which plants assimilate through photosynthesis). What's left happens to be dioxygen, which has a lot of important consequences but that's not the main purpose of carbon offsetting. In that sense, carbon capture and storage is a related idea as the result is supposed to be less carbon dioxide in the atmosphere in both cases. – Relaxed Aug 8 '14 at 23:07
@Mark, question updated. – halfer Aug 12 '14 at 10:01
This questions belongs to the Skeptics StackExchange – JonathanReez Aug 12 '14 at 10:46
" is carbon offsetting a scientifically acceptable approach to reducing flight emissions" is a Skeptics question as it is a purely scientific issue. – JonathanReez Aug 12 '14 at 11:16
@JonathanReez: this question most certainly does not belong on Skeptics.SE. There is no claim to verify. It belongs on – vartec Aug 13 '14 at 14:37

In a first-order approximation, it definitely is technically possible to offset carbon emissions. There's very little debate about that. Both schemes to increase carbon capture (primarily tree planting) as well as schemes to decrease carbon emissions elsewhere (e.g. solar ovens for developing countries, eliminates wood ovens) work.

The two problems are however second-order effects and non-carbon pollution. If you have a forest planted, what use would have been made of the area otherwise? What about freshwater consumption? And even if you offset carbon, planes will still produce nitrous oxides high in the atmosphere.

The water vapor issue isn't that big a deal. Sure, the exhausts cause high-level clouds, but that's a short-term issue. Water in the atmosphere is in a quite stable balance, with rain removing excess water quite efficiently.

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Air travel burns fossil fuel, and therefore carbon that used to be buried deep under our planet's surface for millions of years ends up in the atmosphere as CO2. This is generally considered a bad thing because changing the long term global concentration of CO2 in the air changes the global climate.

You are basically asking "are commonly offered carbon offset schemes an effective way to reverse this effect of air travel", and I feel that is a question for the Skeptics stack exchange, as it needs thorough scientific consideration.

But you asked here, so that allows me to give my opinion that it's not, for two reasons:

One, the carbon was buried deep under the surface as part of our planet's long carbon cycle; a process that takes millions of years. Changes to it can't be fixed by planting extra trees, as the carbon that trees fix by growing and then release by dying and decomposing is part of the short carbon cycle. Even if the trees are replanted after dying, what's a realistic lifetime of a forest planted with your carbon offsetting money? A thousand years seems optimistic, and storing carbon for a thousand years does not offset releasing carbon that would have been stored for millions.

Second, if you hadn't flown, the oil would have been pumped up anyway. Oil is an incredibly useful substance and people are bidding on an open market for the right to burn it up (or make things with it that will eventually be burnt up). Unless countries with oil reserves get strong laws that forbid pumping up oil, all oil that can be pumped up using less total energy than it will generate by burning will be pumped up. Flying less just means that others get to burn it for a fractionally lower price.

TL,DR: Planting trees is a fine thing, but doesn't offset burning fossil fuel. If we want to stop global warming, we must make laws that forbid getting fossil fuel out of the ground.

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Thanks, interesting thoughts. Would I be right in characterising your view as (a) offsetting doesn't make any difference to the long carbon cycle, and (b) there's no point in reducing flights since the oil that would have been used will be burnt up for something else anyway? That approach might have a paradoxical effect: we know something has to be done, but since not flying is purely symbolic, we conclude that we may as well pollute with abandon. Hmmphh! :=) – halfer Aug 14 '14 at 19:43

I've found the following, from NASA climate scientist James Hansen. It's from a book he has authored (quoted here):

The public must be firm and unwavering in demanding ‘no offsets’, because this sort of monkey business is exactly the type of thing that politicians love and will try to keep. Offsets are like the indulgences that were sold by the church in the Middle Ages. People of means loved indulgences, because they could practice any hanky-panky or worse, then simply purchase an indulgence to avoid punishment for their sins.

Bishops loved them too, because they brought in lots of moola. Anybody who argues for offsets today is either a sinner who wants to pretend he or she has done adequate penance or a bishop collecting moola.

My interpretation is that he is of the view that offsetting does not work, since people will continue their (carbon-polluting) business as usual, and the problem of global warming is left inadequately addressed.

Edit: I am drawn to this post recently by a comment under the question, so I will update this answer to a resource I found last year. This booklet expands on the claim that all of us, including travellers, must reject carbon-offsetting if carbon output is seriously to be challenged.

For what it's worth, I decided last year not to take the flight from the UK to Indonesia. I went to Scotland instead, by train.

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Hansen's a known crook. He says it, it's propaganda, and factually incorrect. – jwenting Aug 22 '14 at 11:23
@jwenting: thanks. Can you cite references for any of that? Remember, I am approaching the question from the position of accepting the scientific consensus on climate change. My view presently is Hansen is speaking from a position of authority, and is working for a respected institution that ought to be taking a view on the topic. Do you think this specific scientific opinion - that carbon offsetting should be discouraged - is wrong? If so, why? – halfer Aug 22 '14 at 16:44

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