Alice Larkin, Professor of Climate Science and Energy Policy at The University of Manchester, along with Dr John Broderick consider if the level of emissions from the Heathrow expansion is in alignment with the UK’s legal commitments on climate change. They argue that the proposed expansion jeopardises these legal commitments, given the absence of a policy framework for establishing long-term decarbonisation of the sector.

• Expansion of Heathrow airport is expected to increase CO₂ emissions from the aviation sector. Of the three schemes considered by Department for Transport, the proposed new runway leads to the largest absolute increase.
• Any growth in demand needs to be off-set by fuel-efficiency gains, the use of alternative carbon-neutral fuels or additional reductions in other sectors – there are not mechanisms in place to guarantee this within the UK’s climate policy framework.
• The expansion of Heathrow is premised on increased emissions in the short term and persistent high levels of emissions in the long term. Heathrow expansion jeopardises the UK’s commitment under the Paris Agreement (2015) as there is currently no robust mitigation policy framework for international aviation emissions.

What are UK’s relevant climate change commitments?

The UN’s Paris Agreement (2015) has the status of a treaty as defined by the Vienna Convention on the Law of Treaties. Article 2 establishes the treaty’s goal of avoiding a temperature increase of “well below 2°C above pre-industrial levels” and to pursue efforts to limit warming to 1.5°C. Rising temperatures relate closely to the total quantity of carbon dioxide emitted, much of which remains in the atmosphere for many centuries to come. Temperature targets can therefore be translated to carbon budgets and associated pathways, as for instance implemented by the UK’s Climate Change Act (2008).

How are emissions from aviation accounted for?

Article 4 of the Paris Agreement notes that “Developed country Parties should continue taking the lead by undertaking economy-wide absolute emission reduction targets”. However, the Climate Change Act (2008) and subsequent carbon budgets adopted by Government do not presently include emissions from international aviation, although they undoubtedly contribute to the warming of the climate. Emissions from intra-EEA flights are included within the EU Emissions Trading Scheme, but the cap on emissions and historic surplus within this scheme do not align with UK policy or Article 2 of the Paris Agreement. In the absence of limits on international aviation emissions, the Committee on Climate Change (CCC) advise that greater efforts will need to be made in other sectors, and establish a “planning assumption” that gross CO₂ emissions from aviation should total no more than 37.5 MtCO₂ by 2050. However, this assumes that other sectors adopt emissions reductions greater than 80% by 2050. To date there is limited evidence that this will be achieved, and there is currently a policy gap to deliver even an 80% reduction by 2050 by these other sectors. Recognising the Paris Agreement’s objective to meet a “well below 2°C” goal within our domestic climate policy would limit the carbon budget even further.

Do UK carbon budgets align with the Paris Agreement?

The government have adopted a series of carbon budgets proposed by the CCC as the minimum required to meet our international obligations. The Climate Change Act’s long-term target, proposed in 2008, allows greenhouse gas emissions of 159 MtCO₂e in 2050. This pathway is premised on a 63% chance of exceeding 2°C. The wording of the Paris Agreement, made later in 2015, implies a high probability of not exceeding this temperature threshold. Cumulative emissions pathways that align with this are therefore lower than the current level of UK carbon budgets and imply that a net-zero CO₂ target is required before 2050. If a proportion of this emissions budget is allocated to aviation beyond 2050 then almost all emissions must be eliminated from other sectors at an earlier date.

What emissions are forecast for the aviation sector?

BEIS records total emissions attributable to UK aviation as 35.5 MtCO₂e in 2016, returning from a plateau, following the financial crisis and recession, to growth in recent years. For most sectors, CO₂ cuts in line with the “well below 2°C” goal could feasibly be brought about through a combination of technological, operational and demand-side changes. However, within the aviation sector, technical change is slow and radical improvements in the short- to medium-term are not anticipated. Modelling by the Airports Commission and Department for Transport, forecasts emissions to continue to rise with and without the Heathrow Northwest Runway scheme, but assume that a strong carbon price, an increase in load factors and continuous improvements in fuel efficiency will allow emissions to stabilise towards 2050. The CCC have established a benchmark figure of 37.5 MtCO₂ in 2050, a doubling of emissions from the 1990 baseline year. This is a generous allocation which requires much less effort from aviation than other sectors to decarbonise. The Department for Transport anticipate this level will be exceeded if any of the London airport expansion proposals are realised. Future realignment of UK carbon budgets towards the Paris Agreement’s commitments would almost certainly include a need for a lower level of aviation emissions.

Could other actions increase emissions space for aviation?

The Airports National Policy Statement assumes that increased emissions from international aviation can be mitigated in some way but does not establish the specific means to achieve this. Three out-of-sector possibilities exist that would allow emissions from aviation to diverge from the decarbonisation path that the rest of the economy follows.

1. Carbon trading: emissions permits and credits could be bought from other sectors. This assumes that the trading schemes are procedurally and technically robust, i.e. that permits and credits issued are not “hot air”, and the quantity of permits and credits is aligned with the overall climate change objective – the Paris Agreement in this case. Existing schemes do not meet these criteria. It also assumes that other sectors are able to make reductions over and above their already challenging targets which becomes ever more difficult as we approach net-zero.
2. Biofuels and synthetic fuels: if the carbon within a fuel has come from the atmosphere, removed either by the growth of plants or by technical means, then its combustion can be regarded as carbon neutral. Such fuels might be licenced and produced at scale for aviation, however, substantial concerns about the wider effects of biofuel production must be addressed, including their carbon balance. Synthetic fuels are necessarily energetically costly to produce and requiring additional zero-carbon energy generation capacity.
3. Negative Emissions Technologies (NETs) remove CO₂ from the atmosphere but are currently unproven at scale, with scientific understanding on their development and deployment only recently starting to emerge. It is premature to assume they will be delivered at scale and in the timeframe required.

Aviation must fit within a UK decarbonisation pathway aligned with the Paris Agreement

Long lived infrastructure should be considered in light of our national and international obligations to economy-wide absolute emission reduction. The Heathrow Northwest Runway scheme is forecast to lead to an absolute increase in emissions. Any growth in demand needs to be off-set by fuel-efficiency gains, the use of alternative carbon-neutral fuels or additional reductions in other sectors. There are not mechanisms in place to guarantee this within the UK’s climate policy framework.

Because CO₂ is long lived in the atmosphere, stabilising the climate will require net-zero emissions. Decarbonisation pathways that meet the objectives of the Paris Agreement indicate that even with UK aviation entirely decarbonising by 2075, all other sectors must be close to zero before 2050. In the absence of a robust mitigation policy framework, expansion of Heathrow, increasing emissions in the short term and assuming persistence in the long term, jeopardises the international commitment made in Paris.