CCC Mitigation Monitoring Framework

8. Aviation

Key messages

• Technological developments. The Government’s pathway for aviation relies heavily on sustainable aviation fuels (SAF), a high rate of efficiency improvements, as well as a relatively small contribution from low-emission aircraft. The sector will require around 20% of total removals in the economy-wide pathway by 2050 (see Chapter 13 of the 2022 Progress Report). We monitor progress in reducing carbon intensity in the aviation sector through fuel consumption and uptake of lower-emission fuels and aircraft.
• Demand. The Government pathway contains little planned action to limit demand growth. However, given that the technological developments in the Government pathway are at the optimistic end of what might feasibly be deliverable, constraints on demand remain an important policy option. We monitor the demand-side of aviation through a range of metrics: passenger-km per capita, the share of travel attributable to business and leisure, flight prices relative to long-distance rail fares and public sentiment on aviation. We present a ranking of the UK against 30 OECD countries on its domestic and international aviation emissions.
• Aviation non-CO₂ We have introduced an indicator measuring the non-CO₂ effects of the UK aviation industry, as these have a significant climate impact. The relative size of these effects has the potential to diverge from aviation CO₂ emissions, as CO₂ reductions achieved through efficiency improvements and use of sustainable fuels are less effective in also reducing non-CO₂ effects, compared to reductions in demand.
• Offsets. We have introduced an indicator to track the use of offsets in the aviation industry given the need to have near-permanent, sustainable removals in place to offset residual emissions. This requires a transition to removals-based offsets.

The indicators presented here will be tracked against the pathway to Net Zero set out by the Department for Transport (DfT) in its March 2022 Jet Zero Consultation pathways where possible. Many indicators reflect the aviation market and, given demand mitigation is not included in the Department for Transport’s scenarios beyond the inclusion of a carbon price, cannot be directly attributed to emissions reduction in their pathways. However, the trends in the indicators will be useful to reflect whether demand and supply of low-carbon technologies are moving in the right direction for the sector’s decarbonisation.

How we monitor aviation

The Net Zero transition for aviation is dependent on three drivers of change, as shown in the three main branches of the monitoring map for aviation (Figure 8.1):

• The central branch represents the actions to reduce the carbon intensity of aviation, including progress on SAF, low-emission aircraft, and improvements in fuel efficiency.
• The right-hand side branch represents the demand-side, with lower demand for flights, including constraining net airport expansion, having the potential to limit both CO₂ emissions and non-CO₂ effects from aviation. Such measures will be required to a greater extent if reductions from technology under-deliver.
• The left-hand side branch represents offsetting/removals of residual emissions, which we currently measure through company commitments to purchase offsets.

The monitoring map shows how Government policies are necessary to create the conditions for success to deliver the required emissions reduction for the sector.

For reducing carbon intensity, the key enablers and policies are:

• Primarily, that the relevant technologies end up being scalable within the timescales set out in the Jet Zero Strategy.
• To increase SAF uptake, including the SAF mandate for 2030 on which Department for Transport have concluded a consultation. This will be assisted through provision of funding to the industry to develop new forms of SAF with the largest greenhouse gas emissions savings. The mandate will need to prioritise forms of SAF that result in a swift transition to low lifecycle emissions. It should rule out forms that are unlikely to provide substantial emissions savings and/or have considerable opportunity costs for other sectors (e.g. land use).
• Preparations to change infrastructure so it is ready for low- or zero-emission aircraft is necessary in order to realise emissions reduction once the technology is available. This has started to be implemented but will require significantly more funding. Further policies are required to encourage reductions in aircraft weight and airspace improvements to increase the efficiency of current air travel.
• Airlines will ultimately need to balance their remaining emissions with high-quality near-permanent removals, which will require a policy and governance framework to ensure that this is done appropriately.

On the demand side, the key enablers and policies are:

• Developing a strategy to avoid any net airport expansion, carbon pricing (including implementing a mechanism for the interaction between the UK ETS and the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)) and fiscal policy reform to encourage alternative lower-emission modes of transport.
• Public engagement will also be important, enabling consumers to find alternative lower-emission forms of travel. Another key enabler is that demand is sufficiently sensitive to price changes.

For offsetting/removals, the key enablers and policies are:

• The market should have near-permanent, sustainable removals in place to remove all residual emissions by 2050. They should not use land that is required for other priority uses (e.g. food production) and should only be used on emissions that cannot be eliminated through other means.
• CORSIA is a key international policy developed by the International Civil Aviation Organisation (ICAO) with the aim of having carbon-neutral aviation growth after 2020. Currently, the scheme is voluntary between 2020 and 2027 and the qualifications for offsets included in the scheme are insufficiently stringent.
• CORSIA will need to be strengthened and extended in order to deliver the necessary emissions reduction from aviation internationally. If this is not possible, the UK will need to implement a higher standard of carbon removals for aviation than exists through CORSIA.

Indicators

This section sets out the indicators we will use in our progress monitoring for the sector. For each indicator we assign an ID number and identify a current data source. We explain why each indicator is important and what we are looking to see in our monitoring. The historical data and, where available and relevant, the benchmark trajectories against which we compare them are presented in the supporting data alongside our Progress Reports. We follow the order laid out in the Monitoring Map (Figure 8.1), taking each main branch in turn to lay out required outcomes and enablers. We discuss policy needs (flagged as ‘Policy’) alongside the most relevant outcomes and enablers. Specific recommendations are made in our annual Progress Reports to Parliament.

We first cover carbon intensity of aviation – progress on measures that reduce the emissions of each flight – followed by indicators on demand and use of high-quality removals.

(a) Required outcome: Reduced emissions-intensity of aviation

Progress on use of SAF, on improving the fuel efficiency of new aircraft and on reducing non-CO₂ effects from aviation will all be important in reducing the climate change impact of aviation.

Indicator: Sustainable Aviation Fuels (SAF) share (%)

ID: AV3
Source: None
Unit: Percentage

• This indicator measures the proportion of fuel consumed in the aviation sector that comes from SAF, instead of fossil fuels. SAF can reduce the lifecycle CO₂ emissions relative to kerosene jet fuel and is one of the key policies in the Government’s strategy for reducing aviation emissions.
• SAF use should increase with implementation of the Government’s mandate policy and once the clearing house becomes operational. SAF is currently only produced at very low levels.
• Policy. There are several policies that will play a key role in incentivising SAF production and encouraging take-up by the aviation industry. These include the 10% SAF mandate by 2030, a SAF clearing house, innovation funding to both produce the fuel and research the most efficient forms.

Indicator: Fuel consumption per passenger-km

ID: AV2
Source: DfT Analysis of Civil Aviation Authority Data (unpublished); DESNZ Energy Trends: UK oil and oil products, ET 3.4 Supply and use of petroleum products: latest quarter
Unit: kWh of fuel used per passenger-km

• This is a measure of the efficiency of aircraft over time. Efficiency improvements are a significant proportion of the Department for Transport’s emissions reduction scenarios in the Jet Zero Strategy pathways.
• It also has implications for the price of air travel, with more efficient aircraft requiring less fuel, and therefore reducing prices. This has and will continue to have subsequent demand-side effects.
• Policy. Innovation funding and rules on tankering are the main policies to improve fuel efficiency in this sector.

Indicator: Non-CO₂ effects

ID: AV4
Source: Lee, D. et.al. The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018; ICAO The World of Air Transport
Unit: Net effective radiative forcing (non-CO₂ terms)

• This is a measure of the effective radiative forcing from non-CO₂ emissions from aviation.[1] A significant proportion of the warming from global aviation comes from non-CO₂ effects, e.g. creating contrails, emitting NOx or water vapour, amongst others, at altitude.
• Most SAF are likely to have non-CO₂ effects, even if they have zero lifecycle CO₂ Therefore, the UK should find a way to report a best estimate of the impact of non-CO₂ effects on global temperatures, as a significant part of aviation’s impact on the climate. These effects should particularly be considered when mandating certain fuel types.
• Policy. Demand-based mitigation policies are key to addressing non-CO₂ effects.

(b) Required outcome: Managed demand

This group of indicators reflects the demand side of the aviation sector. Demand management is key to reducing non-CO₂ effects from aviation and an important option for reducing CO₂ emissions, given uncertainty in technological developments.

Indicator: Passenger-km per capita

ID: AV1
Source: DfT Analysis of Civil Aviation Authority Data (unpublished); ONS Mid-year population estimates
Unit: Passenger-km per capita

• To assess whether policy is adequately managing demand, we track passenger-km per capita for flights departing the UK.
• Policy. Fiscal policies (e.g. taxes), quotas, public engagement, supporting lower-emission alternatives to flying such as trains and video conferencing, airport capacity management and carbon pricing are all ways of managing aviation demand.

Indicator: Air transport movements (ATM)

ID: AV13
Source: Civil Aviation Authority
Unit: Number

• To assess demand, we monitor Air Transport Movements (ATMs) as an indicator of the overall number of flights taking off from airports in the UK. 
• Demand management is a key policy required to address the uncertainties of technology solutions
• Policy. Fiscal policies (e.g. frequent flier levy, taxes, quotas), public engagement, subsidising lower-emission alternatives to flying such as trains and video conferencing, airport capacity management and carbon pricing are all ways of managing aviation demand and the number of flights taking off.

Indicator: Terminal passengers

ID: AV14
Source: Civil Aviation Authority
Unit: Number

• To assess and track demand and airport capacity changes, we track the number of terminal passengers moving through UK airports in a year.
• Demand management is a key policy required to address the uncertainties of technology solutions.
• Policy. Fiscal policies (e.g., frequent flier levy, taxes, quotas), public engagement, subsidising lower-emission alternatives to flying such as trains and video conferencing, airport capacity management and carbon pricing are all ways of managing aviation demand. The number of flights may also fall due to system efficiency improvements which can be pursued through the modernisation of airports and airspace.

Indicator: Business travel

ID: AV5
Source: ONS Travelpac: travel to and from the UK
Unit: %

• This indicator tracks the proportion of travel that is attributable to business travel.
• Different types of consumers can play a role in managing the demand for aviation. Businesses can continue their behaviour in the recovery from the COVID-19 pandemic by continuing to hold international meetings virtually using video conferencing software. All travellers can look to replace their demand for aviation with alternative, lower-emission forms of transport.
• Policy. Large businesses can also be required to include plans to mitigate their aviation demand in their plans to achieve Net Zero. This will soon become a requirement for large companies and certain financial sector firms.
• Policy. Fiscal policies can be used to alter the behaviour of all travellers (see examples for indicator AV1).

Indicators: Cost per km of short-haul flights and cost per km of long-haul flights compared to long-distance rail

ID: AV6, AV7
Source: ONS International Passenger Survey; HMT GDP Deflator; ORR Office of Rail and Road Rail Fares Index
Unit: Pence per passenger-km

• We track the cost of a passenger-km of air travel using a ‘basket’ of 10 frequently flown short-haul destinations and 10 common long-haul routes. The prices include all relevant taxes. We use HM Treasury’s GDP deflator to convert to real prices and compare to indexed long-distance rail prices.
• Policy. Price is a key driver of demand, and a reflection of the efficiency of aircraft (as well as the price of fuel). Policies to change the price of air travel can be used to influence demand, so tracking prices paid by consumers for flights can give an indication of potential trends in demand. As aircraft technology improves and becomes more efficient, this could lead to a fall in the price of air travel (as has been seen over the last decade). Falls in price, as indicated by the Department for Transport’s elasticity assumptions and the evidence underpinning these, will likely see an increase in demand which could prevent the sector sufficiently reducing its emissions by 2050.
• Policy. It will be important for Government to help consumers choose lower-carbon options such as alternative forms of transport (not alternative flight routes) and to adjust fiscal policy as necessary to encourage this modal shift.

Indicator: Seat occupation

ID: AV12
Source: Civil Aviation Authority UK Airlines data
Unit: Percentage

• This  tracks the percentage of seats occupied on flights, which impacts the intensity of fuel consumption per passenger-km.
• Policy. The DfT should monitor seat occupancy in the next few years (3-4) during recovery from the COVID-19 pandemic to ensure that the sector either returns to prior occupancy levels or routes are adjusted to account for lower occupancy rates.

Indicator: Public sentiment (proportion who think about the environmental impact when deciding to travel by air)

ID: AV8
Source: Civil Aviation Authority UK Aviation Consumer Survey
Unit: Percentage

• Despite a current absence of policies to reduce demand, tracking public sentiment can give an indication of whether consumers will change their behaviour on their own, without Government intervention.
• We are therefore now tracking whether individuals consider the cost to the environment when they choose to travel by air, and whether individuals are willing to pay extra for tickets if it reduces the environmental implications of their behaviour. Both show a steady increase in individuals thinking about the environmental impact of their air travel choices.
• Policy. The Government should take opportunities to build on this willingness to change behaviour by presenting consumers with the emissions cost of flights taken relative to lower-emission alternatives (e.g. rail travel) and should not limit the comparisons to alternative air routes. However, compulsory flight foot printing could be effective at influencing consumers to choose lower emission routes and incentivising airlines to make their operations more efficient.

Indicators: Rank of international and domestic aviation emissions

ID: AV10, AV11
Source: OECD Air Transport CO₂ Emissions; United Nations World Population Prospects
Unit: Rank amongst OECD countries

• The rank of the United Kingdom amongst OECD countries gives an indication of the emissions from domestic and international aviation travel per capita relative to other countries. This will be useful to track comparative countries as they implement policies to reduce demand for air travel (or in response to public pressure campaigns).

(c) Required outcome: Removal of residual emissions

Indicator: Use of offsets by the aviation industry

ID: AV9
Source: Civil Aviation Authority UK Airlines data; Berger, S et al. Willingness-to-pay for carbon dioxide offsets: Field evidence on revealed preferences in the aviation industry. Company reports: Acropolis Aviation Carbon offsetting; Aer Lingus Sustainability; Gama Aviation carbon reduction plan; EasyJet Sustainability plan; IAG Sustainability report 2021; BlueIslands LTD Caring for Our Plant; Jet2 PLC Sustainability Plan; LoganAir Environmental Engagement; LuxAviationUK The Environment; RyanAir Sustainability Report 2021; TAG Aviation Green Commitment and Virgin Atlantic Our Line in the Sand; Wizz Air Sustainability
Unit: %

• We track the percentage of seat-kms flown by airlines that are offset by the aviation industry and consumers using Civil Aviation Authority data, company reporting and an assumption on consumer voluntary scheme uptake. The indicator does not make a judgement on the quality, additionality or location of these offsets accurately.
• A transition to removals-based offsets in the UK will be required by the aviation industry as emissions will not be fully eliminated by 2050. The quality of the offsets used and which emissions are offset are important to track. CORSIA will need to be expanded to cover all emissions, not just additional emissions, to account for the residual emissions in the Government’s pathway.
• Policy. The Government should ensure that offsets are only used where other mitigation options are not possible given current available technology. We should be able to track this once CORSIA is fully operational and reporting data is available.

[1] Radiative forcing is the heat trapping potential from emissions and provides a quantitative basis for estimating potential surface temperature changes.

Future improvements

Planned updates to the indicator framework

• We will look to use data from ICAO to further track offset use through CORSIA once it is fully operational and data is released.
• We will look to update our tracking of the non-CO₂ and CO₂ effects from aviation with a more tailored approach for the UK, building on the assumptions we have made for this Progress Report.

Data gaps

There are some areas where lack of data is preventing our ability to measure progress accurately in the aviation sector. This is particularly an issue for offsetting/removals within the industry and measuring consumer response to greater awareness of the harmful impacts of flying on the climate. We aim to add the following indicators once more reliable data is available:

• The carbon intensity of, and demand for, different ticket types (e.g. business, first class, economy class), and demand for private flying is not currently tracked, making it difficult to understand how different demand management approaches could reduce the carbon intensity of flying. The UK Government should begin to track and monitor this data.
• Tracking offset use for a specific industry is difficult given data availability in the market. For this indicator, we rely on company reporting and there is no indication of the quality of offsets being used and whether they are the near-permanent, sustainable GGRs required to offset residual emissions in the sector. Efforts should be made by the Department for Transport and DESNZ to ensure offset purchases are in the public domain, including evidence of location (i.e. whether the removals are UK-based and can therefore count towards the UK’s carbon budgets), quality, additionality and avoidance of leakage.
• The non-CO₂ effects of aviation should be estimated annually and published alongside CO₂ emissions from aviation.
• Modal shift is hard to measure, particularly when trying to compare the cost between routes by air and surface transport. The Department for Transport should track the cost of passenger-kms for long-distance rail and air travel for comparable routes to measure the impact of carbon pricing and policies to motivate modal shifts.
• The Department for Transport should use Civil Aviation Authority data to track the occupancy of aircraft, especially as the industry recovers from the pandemic. They should use this data to consider whether a minimum occupancy standard should be enforced and ‘ghost flights’ banned.
• Consistent annual surveys should be collected of individual behaviour to measure shifts in demand from air travel to alternative lower-emission transport options and to determine the key factors behind any behaviour changes.