Measurement issues with bringing international aviation into the UK’s national carbon budget
The UK government recently announced that it will bring international aviation and shipping into its greenhouse gas emissions budget. Up until now, only domestic aviation emissions were included. That was in line with international norms for the reporting of national emissions, reflecting the difficulties of attributing to countries emissions which are by definition international in nature.
At the same time, the government brought forward the target date for achieving a 78% cut in emissions from 2050 to 2035. Both moves substantially increase the challenge of meeting the UK’s climate change targets.
The emissions reduction target is stated relative to a baseline of 1990. Using the old definition of “territorial emissions”, which excluded international aviation and shipping, the UK reduced annual emissions by 354 million tonnes between 1990 and 2019, a 44% reduction. But over the same period, international shipping emissions only fell by 8% and international aviation emissions more than doubled, together adding 20 million tonnes a year to the baseline. These international emissions still represent less than 10% of the total, but back in 1990 they were less than 3%.
On the new broader measure, the UK has reduced its emissions by 40% in 29 years. To get to a 78% reduction compared to 1990 levels requires emissions to be reduced by a further 316 million tonnes, or 63% compared to 2019. And that change needs to happen much more quickly, meaning annual reductions of 20 million tonnes. In the last nine years, the UK managed an annual reduction of 17 million tonnes, but much of the “low hanging fruit” has already been picked.
Source: UK Greenhouse Gas Emissions, Final Figures 2019, ONS
How do you define the UK’s share of international aviation emissions anyway?
Whilst I can understand why the UK has decided to bring aviation emissions within the scope of its national carbon “budget”, one of the reasons why it was left out in the first place was the difficulty of assigning these emissions to an individual country. International flights by definition operate between two countries, and if every country included the emissions of all the flights operating to and from their territory, aviation emissions would get double-counted.
Up to now, the standard approach to tracking these emissions has been for every country to record only the emissions for departing flights. That’s a pragmatic approach to ensure that the international community has a solid base of data to work from when considering global aviation policy. But it was never envisaged as a basis for passing legally binding national reduction targets.
We don’t know for sure that they intend to use the same basis, but I suspect it is very likely. I’m not at all sure that is the right solution. Let me explain why.
Attribution based on where fuel is uplifted
The UK figures for international aviation are based on data for the total volume of fuel uplifted in the UK for outbound flights.
This “departure only” basis means that when it becomes possible again to head off on holiday to Spain, only the fuel that is used to get you there will count towards the UK’s emissions. Your flight back is Spain’s problem. Likewise, a US tourist visiting London only counts towards the UK’s emissions when they fly home. Maybe that makes sense - the economic benefit of a tourist trip accrues to the citizens of both countries - UK residents get to enjoy some sunshine and also provide benefits to the Spanish economy through the money they spend there. The current approach effectively divides the emissions burden 50/50 between the two.
But consider the case of a German business person who flies from Dusseldorf to Heathrow on Lufthansa and then catches a connecting flight from Heathrow to Chicago on United Airlines. Most of the emissions for that journey will be recorded as “UK emissions”. You could argue that the only involvement the UK has had is to provide a refuelling point along the way.
Or think about a British person who flies from Manchester to Kuala Lumpur with KLM. They will add very little to the UK greenhouse gas total, as only the short flight from Manchester to Schiphol will count. Whereas if they had travelled with British Airways via Heathrow, the whole journey would contribute to the UK emissions totals.
With UK emissions being calculated like this, the easiest way for the UK to bring down its aviation emissions would be to ban all long-haul flights and make everyone who wants to travel longer distances does so via a hub in Ireland or Continental Europe. Whilst that would indeed deter travel, the main impact would only be to shift the emissions elsewhere in Europe. Plus of course destroying rather a lot of UK jobs and making doing business with the UK or visiting it as a tourist rather unappealing. I’m not saying that any government would actually do such a thing, but the tyranny of the target may push them into pursuing taxation or other policies which have a similar effect over time.
Perhaps there is a better way to measure things?
Attribution by nationality of the traveller
Another way to allocate international aviation emissions would be to attribute them to countries according to the residency of the traveller. So the emissions of UK travellers would count towards the UK total and those of foreign visitors or transiting passengers would not.
This has some intuitive appeal. For a UK resident holidaying in Spain, both the trip out and the trip back would count. All the emissions of a Manchester - Kuala Lumpur trip would get counted, regardless of whether the traveller made their connection in Heathrow or Schipol.
Whilst this way of calculating things would require some more data crunching, the world of emissions accounting is complicated anyway and governments and airlines already collect the kind of data that would be needed to do the sums.
What would it do to the UK greenhouse gas figures? We need to start by looking at the mix of air travel split by the residence of the traveller. That’s something we can get from the UK’s international passenger survey.
In 2019, UK residents accounted for 75% of air trips between the UK and Europe, mainly because most of these trips are leisure and UK residents holidaying in the rest of Europe outnumber those going the other way by more than 5 to 1. Could it be something to do with the weather?
It is more balanced for long-haul trips, but it is still weighted towards outbound travel with 62% of travellers being UK resident. The most emissions-intensive segment is long-haul premium travel, due to the extra space occupied by flat bed seating in business and first. Whilst not everyone travelling in those cabins is a business traveller, that is the main customer type and long-haul business travel is the segment that is closest to a 50/50 mix of UK and overseas residents.
Source: International passenger survey, GridPoint analysis
Based on these splits, together with ONS figures for emissions by haul and cabin, I’ve made some estimates for the breakdown of emissions from UK flights by cabin and residency of the traveller, shown in the chart below.
This approach suggests that 65% of the passenger related emissions from international flights to/from the UK in 2019 were attributable to UK residents. That’s a 30% increase compared to the default approach of just counting departure emissions.
What about cargo?
A significant amount of the UK’s International aviation emissions relate to cargo. About 20% of British Airways’ global emissions in 2019 for example were attributed to cargo. The standard approach of measuring international aviation emissions on fuel uplifted in the UK means that only fuel for cargo exports will be counted in the national totals.
That is the opposite of what most voters in the UK would recognise as the UK’s contribution to climate change in this area. What environmental campaigners focus on with consumers is “air miles”. How far has the food on your table had to travel? What emissions were involved in bringing that iPhone you just bought from where it was assembled in China? The emissions for both of these relate to inbound cargo, for which the fuel will have been uplifted outside the UK. Unless the UK changes the way it measures international aviation emissions, changes in behaviour by UK citizens will have no impact on the UK’s reported greenhouse gas numbers.
Which approach is better?
There is no single ideal approach, of course.
I’ve already pointed out some of the issues with a departure only approach. An allocation based on traveller residency solves many of these, but has some other issues. For example, inbound tourism would not contribute at all to the UK’s emissions figures. We could see such nonsense as a UK government trying to suppress outbound travel by its citizens in the name of the environment, whilst spending lots of money promoting the UK as a tourist destination to overseas travellers.
The only approach that would be worse than both would be to define UK aviation emissions to be equal to the emissions of UK-registered airlines. That would imply that you can travel as much as you like, as long as you travel on a foreign airline. That makes absolutely no sense as a UK government policy. You might think that nobody in their right mind would ever consider this definition, but sometimes campaigners or lazy policy-makers do focus on such figures and explicitly or implicitly base their arguments on them.
My main point is that where international travel is concerned, no single measure is going to give you the whole story. Both policy-makers and the media need to be very careful not to use headline figures without properly thinking through the consequences, intended or not.
I can only hope that as the UK government brings international aviation into its legally binding framework, the imperfections and potential distortions caused by whatever measure they choose are properly considered and “chasing the target” doesn’t overwhelm common sense in deciding policy.
