Dr Doğuşhan Kılıç and Dr Paul Williams (The University of Manchester)              AECN0028

Written Evidence Submitted by Dr Doğuşhan Kılıç and Dr Paul Williams

(The University of Manchester)

Airport expansion and climate and nature targets Inquiry

Dr Doğuşhan Kılıç is an atmospheric chemist at The University of Manchester, where he has worked since 2020. His research focuses on aviation emissions, with a particular emphasis on field measurements to assess their environmental impact across several European countries. He has published widely on the chemistry and climate implications of aviation emissions.

Dr Paul Williams is a Senior Research Fellow in Earth and Environmental Sciences at The University of Manchester. His research interests include aircraft engine emissions (measurement and modelling), including impacts of conventional vs sustainable aviation fuels. He also works extensively with aviation emissions standards and regulation.

This submission was supported by Policy@Manchester

Question 1

Statutorily, the Climate Change Act 2008, as amended in 2019[1], commits the UK to achieve net zero greenhouse gas emissions by 2050. The Government is further bound by the Carbon Budgets legislated under this Act, including the Sixth Carbon Budget (2033–2037)[2], which includes the UK’s share of international aviation and shipping (IAS) emissions.

International obligations include the UN Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, under which the UK has committed to limit global temperature rise to well below 2°C, ideally 1.5°C by reducing all greenhouse gas emissions by at least 81% by 2035, compared to 1990 levels (excluding IAS emissions)[3]. Though international aviation is not fully regulated under these frameworks, the inclusion of IAS in the UK’s domestic carbon budgets represents an effort to align with these targets.

The Environment Act 2021 introduces new legally binding targets for air quality, water, biodiversity, and waste, which must be considered in the development of any major infrastructure, including airports[4]. Non-statutory obligations include the Jet Zero Strategy (2022), which sets an ambition for net-zero domestic aviation emissions by 2040 and net-zero UK aviation by 2050.

For specific developments such as Heathrow or other South East airports, decisions are also guided by the Airports National Policy Statement (ANPS), which has planning weight but may require revision given updated climate science and legal obligations. These developments are also subject to environmental assessments under the Town and Country Planning (Environmental Impact Assessment) Regulations 2017 and Strategic Environmental Assessment Regulations 2004.

Question 2

The inclusion of international aviation emissions in the Sixth Carbon Budget (SCB)[5] represents a significant policy shift. Historically, aviation emissions have been considered outside the scope of national climate targets, partly due to the complexity of assigning responsibility for international flights. Their inclusion now makes clear that the UK intends to take full responsibility for the climate impact of flights departing from its airports.

This development substantially tightens the carbon envelope for aviation, which is a hard-to-abate sector due to the lack of commercially viable zero-emissions aircraft in the near term. The inclusion of IAS increases pressure to either reduce absolute emissions from the aviation sector or secure credible, scalable carbon removals.

Meeting the SCB while expanding airport capacity presents a fundamental policy contradiction unless aviation emissions are offset by equally ambitious reductions elsewhere or mitigated through high-impact strategies within the sector. This likely necessitates a combination of demand-side measures, such as emissions-based pricing mechanisms, and supply-side technological innovation. One example of a pricing approach is the reform of the UK’s existing Air Passenger Duty (APD) into a progressive levy tied to carbon intensity and flight distance. Internationally, France has introduced an eco-tax on airfares (ranging from €1.50 to €18 depending on flight class and destination) and is restricting short-haul flights where rail alternatives exist. Germany, as part of its 2020 climate package, increased its aviation tax and reinvested revenues into rail infrastructure to encourage modal shift. These examples illustrate how fiscal instruments can play a role in managing aviation demand in alignment with climate objectives.

Alongside pricing reforms, the Government must also stimulate technological change by investing in the R&D, and deployment of low-carbon aviation technologies. This includes Sustainable Aviation Fuels (SAF), hydrogen and electric propulsion systems, and improvements in aircraft efficiency and air traffic operations. Public policy levers such as mandates or quotas for SAF adoption, capital subsidies, and investment in supporting infrastructure (e.g., SAF production facilities), can help de-risk early innovation and scale-up. Coordinated support across policy, funding, and regulation will be essential to reconcile the UK’s ambitions for aviation growth with its legally binding climate targets.

Question 3

The Climate Change Committee (CCC) has advised that UK aviation emissions should be reduced to 23 MtCO2e by 2050, a significant decrease from current levels (around 38 MtCO2e in 2019). This target assumes modest growth in passenger demand (25% above 2018 levels by 2050), improvements in aircraft fuel efficiency, sustainable aviation fuel (SAF) adoption, and a reliance on limited engineered carbon removals5.

The Government’s support for airport expansion, such as at Heathrow and other regional hubs, poses a direct challenge to meeting this reduction pathway[6]. Expansion implies an increase in flight frequency and passenger numbers, which, without corresponding and verifiable decarbonisation measures, will result in elevated emissions. This tension is further underscored by the Government’s Jet Zero Strategy, which, even under its most optimistic scenario, anticipates a residual carbon burden from aviation to be addressed through engineered removals such as Direct Air Capture (DAC) and bioenergy with carbon capture and storage (BECCS). Yet, these technologies remain commercially immature, with uncertain scalability, permanence, and cost-effectiveness.

Crucially, the Jet Zero Strategy does not impose a hard emissions cap or binding limits on aviation demand growth or airport capacity. Without such safeguards, there is a significant risk that infrastructure expansion will outpace mitigation progress, leading to overshoot in sectoral emissions and undermining the UK's legally binding commitments under the Climate Change Act 2008 and the Paris Agreement.

A precautionary, conditional approach is therefore essential linking any increase in airport capacity to demonstrable emissions reductions, binding decarbonisation milestones, and credible pathways for residual carbon removals. For example, capacity increases could be made contingent upon verified SAF uptake targets, enforceable emissions caps, modal shift improvements in airport access, and independent emissions monitoring. In the absence of such safeguards, unconstrained expansion risks locking in high-carbon infrastructure and making the CCC’s carbon budget target for aviation infeasible.

Question 4

Forecasts by the Department for Transport (DfT) suggest that, under a “baseline” scenario with no additional policy constraints, UK air passenger demand could rise from approximately 297 million passengers in 2019 to 445 million by 2050, with air freight demand expected to grow by around 2.1% per year[7]. However, the CCC in its Sixth Carbon Budget report calls for demand growth to be constrained to 25% above 2018 levels by 2050 to stay within carbon budgets. Moreover, airports are significant sources of both primary and secondary air pollutants, which can adversely affect local air quality[8],[9].

Current airport expansion proposals—including the third runway at Heathrow, the reactivation of Gatwick’s second runway, and capacity expansions at Bristol, Stansted, and Luton—tend to rely on the DfT’s higher-growth assumptions. When considered collectively, these proposals risk overshooting the CCC’s recommended demand limit, especially when regional airport growth ambitions are taken into account. While such proposals may technically meet demand under high-growth scenarios, they appear misaligned with the UK’s net-zero trajectory.

To address this misalignment, the UK should adopt a coordinated national aviation strategy that explicitly aligns capacity planning with climate objectives. This strategy could include:

• Demand management tools, such as carbon-based passenger caps or emissions allowances per airport;
• Sustainable Aviation Fuel (SAF) blending mandates;
• Conditional expansion approvals tied to demonstrable emissions reductions and compliance with net-zero pathways.
• Support for zero-emission aircraft innovation.

Additionally, the government should shift infrastructure investment toward strengthening the national rail network, especially for domestic and short-haul travel, where rail offers a viable low-carbon alternative to planes. Reducing short-haul flights by improving rail connectivity, rail freight electrification, rail route upgrades can significantly alleviate pressure on airport capacity while supporting regional economic integration.

Several European countries offer instructive examples. France has legislated a ban on short-haul flights where rail alternatives under 2.5 hours exist. Germany has implemented an aviation ecotax while concurrently investing in rail–air modal shifts. The Netherlands, responding to environmental concerns, plans to cap flights at Schiphol Airport. While no single country has yet implemented a fully integrated aviation climate strategy (to our knowledge), these cases highlight practical components the UK could incorporate.

By aligning capacity planning with climate commitments and investing in low-carbon alternatives like rail, the UK can ensure its long-term aviation policy remains both environmentally responsible and socially equitable. The DfT should seek to harmonise its Net Zero Aviation Strategy with Network Rail’s Decarbonisation Strategy to promote modal shift and reduce the demand for short-haul flights.

Question 5

The DfT’s Jet Zero Strategy (2022) presents a “high ambition” scenario in which UK aviation emissions fall to net zero by 2050 through the deployment of Sustainable Aviation Fuels (SAF), improved aircraft efficiency, airspace modernisation, and greenhouse gas removals[10]. However, even under this scenario, residual emissions remain in 2050 and must be removed via carbon dioxide removals (CDRs) such as Direct Air Capture (DAC) or nature-based solutions[11].

Environmental impacts beyond carbon—such as non-CO2 effects (e.g. contrail formation and NOₓ emissions)—are largely unaddressed in current Government modelling, despite evidence that these may double or triple aviation's climate impact[12]. Similarly, airport development contributes to noise pollution, air quality degradation, and biodiversity loss, particularly in the South East where environmental constraints are already acute[13].

The CCC has repeatedly highlighted that Government projections appear overly optimistic regarding the pace and scalability of aviation decarbonisation, and that failure to account for non-CO2 effects underestimates the full environmental cost[14].

Question 6

(a) Technological innovations such as improved aircraft fuel efficiency, hybrid-electric propulsion, and SAF are central to Jet Zero, yet they face substantial barriers, including the high cost and limited availability of Sustainable Aviation Fuel (SAF), the slow pace of fleet renewal, and significant technological and infrastructural challenges related to battery- or hydrogen-powered aircraft. SAF is expected to contribute up to 39% of emission reductions by 2050, but current production is less than 0.1% of total UK jet fuel use[15]. SAF production is also constrained by feedstock availability, scalability, and cost competitiveness with fossil jet fuel. Battery- and hydrogen-powered aircraft are not anticipated to serve long-haul routes before 2050. Further there is little evidence to suggest that hydrogen-powered aircraft would be capable of long-haul flights after 2050 and there are currently no sustainable alternatives for such flights.

The government can help address these barriers by offering long-term policy certainty, increasing R&D funding, supporting SAF production through subsidies or contracts-for-difference schemes, and investing in infrastructure to support emerging technologies (e.g. electric charging systems) and regulatory streamlining to accelerate deployment.

(b) Emissions trading schemes (ETS), including the UK ETS and CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation), play a complementary role. However, they have limited stringency: CORSIA only applies to growth beyond 2019 emissions and lacks robust enforcement mechanisms[16].

To strengthen ETS enforcement, regulators could tighten the emissions cap over time, introduce floor prices for carbon credits to avoid market volatility, and enforce stricter penalties for non-compliance. Moreover, aligning the UK ETS with broader international schemes (like the EU ETS) and removing exemptions could improve transparency, accountability, and environmental integrity.

(c) Operational changes such as single-engine taxiing, continuous descent approaches, and airspace redesign can offer modest efficiency gains (around 10%) but are insufficient alone to offset demand-led emissions growth[17].

To meet net zero by 2050, the Jet Zero Strategy assumes residual aviation emissions will be entirely offset by carbon removals. However, the feasibility of this strategy depends on unproven scale-up of engineered removals (e.g. DACCS), which face challenges in cost, energy requirements, and land use[18]. The CCC reiterated its warning in the Seventh Carbon Budget report against over-reliance on carbon removals, instead recommending a stronger focus on demand management and the implementation of strict emissions caps[19], which are essential components of a credible decarbonisation strategy. While technological innovation and carbon removals are crucial, their delivery is uncertain and long-term. In contrast, managing demand, through measures like frequent flyer levies, improved rail alternatives, and caps on airport capacity, offers immediate emissions reductions and helps avoid locking in unsustainable growth trajectories.

Question 7

The Airports National Policy Statement (ANPS) provides the policy framework for expanding airport capacity in the South East of England. Its underlying assumptions regarding aviation growth and environmental impacts, however, are increasingly outdated.

The ANPS is based on forecasts and environmental assessments made prior to key policy developments such as:

• the UK’s legal commitment to net zero emissions by 2050,
• inclusion of international aviation in the UK’s Carbon Budget, and
• emerging understanding of non-CO2 climate effects and biodiversity concerns[20].

Projections at the time assumed unconstrained growth of passenger demand and minimal consideration of the implications of climate targets. For example, the ANPS references a central forecast of 480 million passengers per annum (mppa) by 2050, which is significantly higher than the CCC advised upper limit of 365 mppa to remain within decarbonisation pathways[21].

Environmental impact assessments within the ANPS also underestimate the scale and complexity of emissions reductions required, particularly in light of revised technological timelines for Sustainable Aviation Fuel (SAF) deployment and the scalability of carbon removals.

Given these discrepancies, the government urgently needs to review and amend the ANPS to account for the updated demand projections, our legal commitments, and environmental constraints.

Question 11

To ensure that climate and environment obligations continue to be met, a robust, dynamic oversight mechanism is required, which should comprise of:

• A periodic review mechanism which mandates a statutory review of aviation policy every five years and is aligned with the Carbon Budget cycle. This should consider updated assessments of aviation emissions, technological progress, and demand trends.
• An independent monitoring authority within or alongside the CCC or Office for Environmental Protection (OEP) with powers to assess the compliance of airport expansion plans against climate targets and recommend corrective actions.
• A requirement for all airport development plans to include Integrated Environmental Impact Assessments covering carbon and non-carbon effects, biodiversity loss, and local environmental pressures. EIAs should be aligned with net zero tests that assess the cumulative climate impact of expansions and should be regularly updated with the science.
• A formal requirement for Public and Parliamentary scrutiny for all major airport developments. This should include an opportunity for consultation with devolved administrations, members of the public, and scientific experts to ensure health and environmental implications are well understood and mitigated.

Such arrangements would provide transparency, scientific rigour, and accountability, which are essential given the high environmental stakes and long planning horizons involved.

Question 12

Policy safeguards should reflect the precautionary principle, climate science, and equity considerations. Recommended safeguards include:

• Legally binding emissions cap: Introduce a sectoral emissions cap for aviation consistent with the CCC’s most recent Carbon Budget pathway (currently seventh). This cap should cover both domestic and international aviation and account for non-CO2 effects through radiative forcing multipliers or similar tools[22].
• Sustainability conditions for expansion: Make any airport expansion contingent upon demonstrable compliance with emissions caps, environmental performance thresholds, and proven availability of low-emission technologies. This includes:

       Quantitative emissions impact assessments showing that the expansion will not breach the aviation sector’s carbon limits.

       Clear evidence that mitigation measures such as SAF usage, operational efficiency improvements, or carbon removals will fully neutralise any increase in emissions.

       Consideration of non-CO2 climate impacts and local environmental effects, including noise and air quality[23],[24].

       Regular compliance reviews tied to project milestones, with capacity growth conditional on real, measurable progress.

• Independent verification: These conditions must be verified by an independent body prior to approval. Oversight responsibilities could fall to an arm’s-length regulator such as the Environment Agency or a dedicated Sustainable Aviation Regulator, in coordination with the CCC. Verification should involve independent environmental auditors, transparent methodology, and opportunities for public and scientific scrutiny.
• Technology-readiness benchmarks: Link policy support for airport growth to quantitative progress in SAF deployment, zero-emission aircraft development, and carbon removal availability. Failure to meet technological readiness thresholds should trigger a moratorium on further capacity expansion.
• Carbon pricing and demand management: Expand and strengthen carbon pricing mechanisms, including reform of the UK ETS, to reflect the true environmental cost of flying. Explore measures such as frequent flyer levies, which more equitably distribute emissions burdens and manage demand[25].
• Integrated National Strategy: Ensure aviation policy is integrated into a cross-sectoral net zero strategy, particularly in coordination with surface transport, tourism, and industrial decarbonisation plans.

These safeguards should be embedded in legislation and planning policy to ensure that climate and environmental commitments are not subordinated to economic growth imperatives.

April 2025