Turbulence Ahead? The Latest Aviation Emissions Science and What It Means for Climate Campaigners

Note: the diagrams in this post have been shamelessly swiped from an excellent presentation by Dr Chris Jardine of the Environmental Change Institute at Oxford University (you can see more of his work here). The words and opinions, however, are all my own fault.

Update - 8.30pm 26/08/08. I've corrected the figure for the percentage of the UK's domestic emissions that the Government estimates come from aviation, and added a reference - thanks to Joss for that one!

Update - 6.15pm 27/08/08. Stupid analogy added at the bottom of the post in case it helps.

Aeroplanes, eh? How can a technology be so utterly awe-inspiring and yet so hideously polluting at the same time? It really isn’t fair.

The roaring, jet-fuelled argument over the building of new runways at major airports has – quite rightly – dominated the aviation debate over the last year. However, a related issue that’s been quietly simmering away in the background is now coming to the boil, and pro-aviation lobbyists may be tempted to use a piece of new research to try to shift the debate in their direction.

The issue at stake may seem rather obscure at first. Aircraft don't just produce CO₂, they also produce other gases that warm the planet. In order to calculate this extra impact, should the amount of CO₂ produced by a flight be multiplied by 2.7, or 1.9, or something else entirely, in order to capture the total warming effect of burning aviation fuel in the upper atmosphere?

Although this sounds like something of interest to only the most hardcore eco-geeks and carbon obsessives, it is actually quite important for this simple reason: the lower the number used, the less polluting aviation seems to be. For an industry that’s been dragged over the coals (or the vat of burning jet fuel) for its disastrous environmental impact, anything that can make it appear less polluting is likely to be seized upon by industry apologists and milked for all its worth.

New and credible research suggests that the CO₂ from aviation should in fact be multiplied by the relatively low figure of 1.3 in order to gauge its full climate impact. So far the big flight operators haven’t made too much of a public song and dance about this, but rest assured that they are very interested. The topic is being discussed intensely at industry conferences and in environmental consultancy circles, and it’s only a matter of time before it creeps out into the public sphere. When it does, climate campaigners need to be ready for it.

The rest of this blog post is therefore split into two sections:

A) The sciencey bit: Why the correct number to use for calculating aviation’s full climate impact is probably about 1.3, and why this is less to do with science than with (woo-hoo!) accounting.

B) The policy-y bit: Why using this number doesn’t actually change things that much in a practical sense, why mass aviation is still completely unsustainable, and how climate campaigners should respond to this latest potential distraction.

A) The Science Bit – Why 1.3?

Anyone who cares about climate change (which, honestly, should include anyone who likes living on a reasonably habitable planet) will know by now that mass aviation is a major barrier between us and a saner, safer future. Back in 2007, the Government admitted that flights from UK airports accounted for about 6.3% of the country’s domestic CO₂ emissions. However, climate campaigners were quick to point out that the aviation figure was still an under-estimate, as it didn’t include the extra warming – or “radiative forcing” – caused by gases other than CO₂ being released from planes into the upper atmosphere.

The best estimate at the moment is that aviation emissions cause about 1.3 times as much warming as the CO₂ from aviation would alone. This differs noticeably from earlier estimates of 2.7 times and 1.9 times. Let me try to explain why…

The diagram below shows the chemical reaction that takes place when an aeroplane engine burns fuel in the upper atmosphere. The fuel, which is made up of carbon, hydrogen, and sulphur atoms, reacts with nitrogen and oxygen in the air to produce a shedload of motor energy and an exciting cocktail of exhaust gases (click on the picture for a bigger version):

The gases in red rectangles produce a warming effect when released at high altitude. The ones in blue rectangles have a cooling effect. NO_x is rather special because although it has no direct global warming effect, it reacts with other gases in the upper atmosphere to create ozone (O₃) which has a warming effect, and to destroy the greenhouse gas methane (CH₄), creating a cooling effect.

As if this wasn’t complex enough already, all of these gases vary both in terms of the amount produced per kg of fuel burnt, and in the amount of warming (or cooling) they cause per kg released. In addition, the contrails produced by planes have a short-lived but powerful heat-trapping effect, and aircraft also have a not-yet-fully-understood impact on cirrus clouds. The IPCC (Intergovernmental Panel on Climate Change) did an initial assessment of the comparative effect of all of these factors based on total aviation up to 1992 (the blue bars in the chart below); this was later scaled up to include data up to the year 2000 (the white bars below); the IPCC concluded that, up to this date, the warming impact of aviation had been 2.7 times the warming effect of its CO₂ alone (not including the effect on cirrus clouds, which has still not been fully quantified). A more up-to-date study with improved methods (called TRADE-OFF, and summarised in the red bars below) in 2003 updated this figure to 1.9.

In the chart above, RF stands for “Radiative Forcing”, and is measured in milliWatts of warming per square metre of atmosphere - click on the picture for a bigger version

So historically speaking, aviation has been responsible for almost twice (1.9 times) the global warming that would have been caused if the planes had only been emitting CO₂.

However – and this is the new bit – this doesn’t take into account the fact that CO₂ remains in the atmosphere for 200 years (on average), whilst contrails and nitrous oxide have much shorter-lived effects. Therefore, much of the CO₂ released by planes in the past is still warming the planet today, whilst most of the contrails and other gases from historical aviation have had their impact already and have now dissipated. This means that the 1.9 figure underestimates the long-term warming impact of CO₂, and makes the other warming effects seem more severe in comparison.

A well-argued research paper by Forster, Shine and Stuber takes all of this into account and suggests that, when we consider what impact a flight taken today will have over the next 100 years (which is the standard method for measuring climate effects), a typical flight will have a warming effect of about 1.3 times the effect of its CO₂ emissions alone.

This doesn’t mean that the earlier 1.9 figure was wrong. It’s just that the two numbers are measuring different things – one refers to the total warming caused by aviation up to the year 2000, while the other represents the impact that flights taken today will have over the next 100 years. We should use this latter figure in our climate calculations because that’s how all other carbon footprints are measured.

If you’re still not sure what I’m on about (and fair enough if so), there are a couple more graphs at the bottom of this post that may (or may not) help. Do also feel free to drop a question into the comments box and I’ll do my best to answer it (or to point you to someone who might be able to explain it better than I can).

Of course, this all still leaves one crucial question: who cares?

B) What All This Means For Campaigners

First and foremost, it should be seen as a victory for campaigners that this stuff is being discussed by the aviation industry at all. The “new” research I’ve been referring to was in fact carried out back in 2006, and has only now come to the fore because of the increased pressure on flight operators to properly account for their greenhouse gas emissions. Because Kyoto doesn’t include aviation, there has been no statutory requirement up until now for the emissions from flights to be properly measured. The only real pressure on the aviation industry to own up to its full impact has come from climate campaigners, and (ironically) from the recent inclusion of aviation emissions in ineffective and corporate-friendly carbon trading schemes as an attempted response to those campaigns.

The discovery that the 1.3 multiplier is a more appropriate measure than the IPCC’s original 2.7 might seem like a boost to the aviation industry – but it isn’t really. There are two reasons for this. Firstly, the 2.7 multiplier (and the 1.9 multiplier after it) came with all sorts of caveats and uncertainties (which were freely admitted by the researchers involved) and were recognised as being a rather crude measure of aviation’s extra greenhouse gas emissions; as a result neither figure was universally applied. The 1.3 figure is based on more solid methods, and stands a far better chance of being widely adopted. This would bulldoze though the aviation industry’s claims that “the science is unclear so we should only count the CO₂ and not the extra stuff”, and is probably a reason why they’re not endorsing this new research too loudly just yet.

The second reason is that, even if you don’t count the extra emissions and only look at CO₂, aviation growth is still hopelessly unsustainable. The graph below takes the amount of CO₂ that would be produced by a range of global aviation growth scenarios (from high growth to low growth), and superimposes it on top of the IPCC’s graph of the global CO₂ emissions cuts we need to make to have any chance of preserving a habitable climate (in gigatonnes of carbon, click on the picture for a bigger version):

The five thinner lines at the bottom represent the CO₂ from five different aviation growth scenarios, and show that – if the number of flights taken continues to grow – then aviation will take up between 20 and 75% of our global CO₂ emissions budget by 2050! This would clearly not only be ridiculous (do we really believe that flying is several times more important than heating, lighting, food production etc.?) but also utterly unjust (flying is and always will be the preserve of a wealthy minority). Note that these figures include generous assumptions about improved aircraft technology and flight efficiency, thus laying the huge concrete runway of physical reality over the aviation industry’s happy little village of technofix fantasies.

The above graph shows that aviation growth is unsustainable based on its CO₂ emissions alone, even without taking other greenhouse gases into account.

It’s probably time to wrap up this stupidly long post. Below, in one of those numbered lists that I love so well, is my advice to climate campaigners on how to respond to all of this:

1) Start using the 1.3 figure. It’ll probably be refined by further research over the next few years, but for the moment it’s the best we’ve got and is definitely more defensible than the 1.9 and 2.7 figures. It has another important attribute: if the aviation companies do suddenly start trumpeting the 1.3 multiplier around, with cries of “Look! We’re only half as polluting as the IPCC made out!” we’ll be ready to say, nonchalantly, “Yeah we know, we’ve been using the lower figure for ages now. Oh, by the way, you’re still utterly unsustainable and we still need to massively reduce the number of flights we take, not increase them, to have a decent shot at avoiding catastrophe”.

2) Stand firm on those extra emissions. There’s a real possibility that the industry are going to say “Look, it’s 1.3 – but we shouldn’t really include that extra 30% at all, because those gases aren’t included in the Kyoto Protocol. In order to be consistent with international carbon accounting methods, we should only count CO₂. So nerr.” This is a beautifully circular argument. The extra warming effects of aviation are specific to aviation – no other human activity creates contrails, fiddles with cirrus clouds or releases gases like NO_x or SO_x straight into the upper atmosphere (at least, not yet). Kyoto didn’t include aviation, and so it didn’t need to include these extra warming effects. In other words, the only reason that the extra impacts of aviation aren’t currently included in international climate agreements is because aviation itself isn’t yet included in these agreements – and as soon as aviation is taken into account, those extra impacts should logically be brought in as well. They may not exist under Kyoto, but they certainly exist up in the atmosphere, and are cooking us as surely as the “official” greenhouse gases.

3) Don’t get distracted. This is definitely one of those “acknowledge it and then move on, don’t waste time dwelling on it” issues. My main purpose in writing such a detailed post about this topic was to minimise the time and effort other campaigners might spend fretting about the issue. Don’t! Be aware of it if it comes up, check back here if you need the references, but remember that climate change is far more than a numbers game. We need to get our figures right, but we also need to remember what’s really at stake here, and keep focused on the bigger picture. Aviation growth is incompatible with any effective and fair solution to climate change. It’s a luxury activity that benefits a tiny minority whilst spewing out a disproportionate amount of climate-trashing pollution, devastating the lives of millions of the world’s poorest people. It’s one of the starkest examples of climate injustice in existence. A few figures may have changed, but the basic facts haven’t. So get involved!

www.climatecamp.org.uk
www.planestupid.com
www.airportwatch.org.uk
www.stopairportexpansion.org

Putting It Another Way: Further Explanation of the Science Bit (With Extra Graphs and a Daft Analogy)

If you add up all of the global warming caused by aviation so far in history, then about half of it is from CO₂ and half of it is from other gases (i.e. the total impact is about 1.9 times the CO₂ alone). This is shown in the graph below - click on the picture to enlarge it (note that this shows the amount of warming caused over time by the three different effects, not the amount of greenhouse gas produced in that time):

However, if you take the emissions from a single flight today, and look at the warming effect it will have over the next 100 years, you'll find that most of the warming will come from CO₂ and only a minority from other gases, because of the short-lived nature of the contrails and the NOx effects, as shown in the (not to scale) graph below (again, click to enlarge):

This may seem counter-intuitive, but think about it this way: much of the CO₂ released since aviation began is still in the atmosphere, and still warming the planet. This present and future warming effect from past CO₂ emissions (right up to emissions released in the year 2000) isn't counted in the historical warming graph, and so the 1.9 figure underestimates the full effect of the CO₂ over its lifetime. The 1.3 figure, by comparing the effects of all the different aviation gases over 100 years, captures more of the CO₂'s warming effect.

Remember, these two numbers are measuring different things – one refers to the historical impact of aviation, while the other represents the impact that flights taken today will have over the next 100 years. We should use this latter figure in our climate calculations because that’s the standard method of doing it, and allows us to compare the climate impacts of flying with the impacts of everything else.

Of course, if all else fails, there's always the "bad analogy" option:

Imagine a huge, pristine, white wall, somewhere near you, probably built and maintained using Our Bloody Council Tax. Unfortunately, the local Youth, probably wearing Hoodies and listening to Rap Music, have realised that it’s an ideal spot to ruin with their filthy, filthy, graffiti.

One day, ten youths arrive at the wall. Each youth carries a blue spray can, a small pot of red paint with a large brush, and a large pot of black paint with a small brush.

You can see where this is going.

Each young ruffian starts painting, using the can and both brushes at once (they’re surprisingly talented, these kids), and keeps painting until all of their paint runs out. The blue spray can produces large amounts of paint, but runs out after an hour. The red paint gets slapped on quickly and covers a decent area, but runs out after a day. The black paint with the small brush lasts 20 days – it goes on slowly, but there’s a lot of it.

The next day, twelve more kids arrive and start painting.

The following day, fifteen more join in.

The day after that, twenty more young rapscallions start painting. The next day, twenty-five turn up.

Now, we obviously want to control this disgraceful vandalism. One thing we want to know is – what colour of paint is the biggest problem, blue, red or black? And how do they compare to each other?

The first youths arrived at the wall five days ago. Looking at the wall, what do we see?

Firstly, we see that all eighty-two of the kids are still there, but that fifty-seven of them are now only applying black paint with a small brush. Twenty-five are using both red and black, but their red has nearly run out.

By the end of day five, the wall will have been daubed with the contents of eighty-two blue spray cans, eighty-two small pots of red paint, and about 13% of the contents of eighty-two large pots of black paint (yes, I worked it out, I am that sad). The wall is half black, a quarter red, and
a quarter blue.

“Aha!” we cry. “The black paint is only half of the problem. The red and blue paints make up the other half!” And in terms of all the painting that’s happened so far, we’d be right.

However, what we need to know today is: how much of a graffiti menace is one of these youths compared to, say, a professional street artist or an activist with a pack of marker pens? To work this out, we need to compare these different vandals fairly, so let’s say: how much graffiti would each of them produce in ten days?

In ten days, one youth would produce graffiti equal to one blue spray can, one small red paint pot, and half a large black paint pot. This ratio turns out to be about 77% black and 23% other colours – or to put it another way, multiply the amount of black by 1.3 to get the total amount
of paint used.

How's that?

(To be totally clear: each youth is one flight, the paint pots and cans are the different gases, and the paint on the wall is the amount of warming caused. Also, I have very little shame.)