Written evidence submitted by Dr Lois Pennington, Professor Alice Larkin, Dr Chris Jones and Dr Diarmaid Clery (The University of Manchester) (HEN0072)

The Tyndall Centre for Climate Change Research is an internationally recognised climate-change research group, bringing together natural scientists, economists, engineers and social scientists to develop sustainable responses to climate change.

This submission is by researchers from Tyndall Manchester based at The University of Manchester. Our work focuses on climate mitigation, with expertise in aviation emissions, sustainable fuels, carbon removals and carbon budgets. All the views in this submission are those of the named authors and do not necessarily reflect those of the wider Tyndall Centre or The University of Manchester. This submission has been supported by Policy@Manchester. The authors would be willing to provide oral evidence, if requested.

We have developed a model of the UK aviation sector’s carbon emissions, both with and without an expanded Heathrow under a range of scenarios. We use the results from this model to support this submission. A published report will be available in September 2026 and we would be pleased to share this with the Committee as soon as it is available.

Executive Summary

We find that UK aviation is projected to exceed its share of the Seventh Carbon Budget (CB7) in every scenario the Government has published, before a third runway is even considered. On the Department for Transport's own central forecast, the excess is around 50 MtCO2, roughly a third of the sector's share (~146 MtCO2e). The technologies relied on to reduce aviation emissions are not being delivered: the SAF mandate missed its first target, and worldwide durable carbon removals are tracking far behind what the CB7 pathway assumes for the UK alone. Every tonne aviation emits above its share must be accounted for by further reductions in other sectors or even more carbon removals.

Against that backdrop, the case for a climate-friendly third runway is incoherent and based largely on a single assumption that undermines any economic argument. The DfT assumes three quarters of the runway's traffic is displaced from other UK airports, so the runway's climate impact appears small on the Department's own assumption only because that same assumption means it delivers almost no new flights, jobs or growth. The risk is great: if the runway instead generates new flying, its addition approaches 29 MtCO2 in CB7 alone. The growth case and the carbon case cannot both be true. Importantly, on the DfT’s own assessment, over 98% of the scheme’s 185 MtCO2 of additional emissions arrives after 2042, outside any budget yet legislated, in periods that will be legally binding when set, and against a remaining global 1.5°C carbon budget of around 130 GtCO2, barely three years of current global emissions. It is essential that any expansion is assessed against these future budgets, which must be lower than CB7.

Our core recommendation is that the draft HENPS should not proceed to designation. Aviation emissions should instead be capped in line with the sector’s share of the statutory carbon budgets, with demand managed through measures such as a frequent flyer levy, which holds majority public support. Our recommendations are presented below, before our full submission.

Summary of Recommendations

1.              No third runway should be built at Heathrow: the draft HENPS should not proceed to designation, and aviation emissions should instead be capped in line with aviation’s share of the UK’s statutory carbon budgets (Question I).

2.              The designation of Heathrow expansion as Critical National Growth Infrastructure should be removed, as it is not supported by the Government’s own appraisal (Question C).

3.              The climate change mitigation test should be reframed so compliance is assessed against aviation’s share of the carbon budget as a minimum (Question D).

4.              Decisions should account for the emissions already committed by existing capacity and consented expansions, and the impact of any expansion on the UK's ability to meet future carbon budgets should be estimated (Question D).

5.              The HENPS should state how non-CO2 effects will be quantified, and the quantified appraisal should present a sensitivity on that approach (Question D).

6.              The Department should publish annual with- and without-expansion emissions series for each scenario (Question F).

7.              A carbon-capped scenario, consistent with aviation’s share of the legislated carbon budgets, should be reinstated as a core case and as the absolute minimum (Question F).

8.              A framework should be established for assessing total UK airport capacity against the UK’s carbon budgets and Paris Agreement commitments (Question J).

Submission

We address the Committee’s questions in the following order (I, B, C, D, F, J) to focus our submission based on our climate expertise.

Question I: How well the draft HENPS reflects Government policy on airports and aviation, and on other elements of broader a) transport, b) planning and c) climate and environment policy

1.              The draft HENPS is inconsistent with the UK’s climate policy and obligations. The UK’s climate commitments are reflected in its legislated carbon budgets such as Carbon Budget 6 (CB6) and 7 (CB7), representing 5-year periods over which the Climate Change Committee (CCC) recommend greenhouse gas emission reduction targets, in carbon dioxide equivalent (CO2e). These targets include a national-level total carbon budget, and also sector-level pathways including for aviation which, since CB6, includes both domestic and international traffic.

2.              Since the 2018 Airport National Policy Statement (ANPS), the predecessor to HENPS, CB6 and CB7[i] have both been legislated, meaning the UK Government has a legal requirement to meet these national targets. While the sector-level pathway is a recommendation and not legally binding, any excess on the part of one sector requires more stringent cuts in others. As the third runway is proposed to start operation in 2035 and ramp up, the most relevant carbon budgets for this test are CB7, which covers the period of 2038-2042, and CB8 (2043-2047) which has been estimated but not formally recommended by the CCC. As such, we refer to aviation’s share of CB7 as a starting point to test the alignment of the HENPS with UK climate policy.

3.              Our independent analysis, corroborated by the Department for Transport’s (DfT) own published emissions forecasts, finds that none of the scenarios presented in the HENPS or its supporting documentation achieve an outcome that maintains aviation’s CO2 emissions below its share of CB7 - ~146 megatonnes (Mt) CO2e. The DfT presents eight aviation forecasts, with and without expansion at Heathrow, to support the analysis done for the HENPS. Using the DfT’s Current Trends scenario, which is the central scenario used in the Heathrow Expansion Appraisal Report (HEAR), we calculate that UK aviation will exceed its share by around 50 MtCO2, or roughly a third, even before a third runway is considered at Heathrow. Moreover, in the DfT’s Technology Development scenario, the most optimistic scenario presented, our analysis indicates that overall aviation emissions are forecast to exceed the sector’s share by around 16 Mt CO2, before the third runway is considered at Heathrow. That scenario requires SAF production for the UK alone of around 4.5 Mt a year by 2050. This is nearly two and a half times current global SAF production, and 50% higher than the SAF mandate; a huge, and arguably, unlikely leap, based on current delivery and development trends. The Technology Development scenario also expects fleet-fuel efficiency of roughly double the historical rate, among other technological advances – despite aviation’s technological maturity. Meanwhile, we also test a scenario in which SAF delivers only 50% of the mandated volumes, noting that in the first year of the mandate only 1.6% of total UK jet fuel was delivered as SAF against a mandate of 2%, and that 50% of the mandate in 2040 equals around 90% of today’s global SAF production. In this case, the UK risks exceeding its CB7 budget by around 62 MtCO2, or 43%.

4.              Neither the HENPS nor its supporting appraisal presents information in a way that makes this likely budget breach evident. Emissions totals are published for two of the eight scenarios, but they does not clearly state that firstly, these are both optimistic scenarios, and secondly, that UK aviation already significantly exceeds the share of the carbon budget set by its climate strategy, even before a third runway is considered. Given that UK aviation is already projected to exceed its share of the carbon budget in every published scenario, we argue that there should not be a consultation about a project that will take the UK even further over this budget. Nonetheless, the proposed runway’s own contribution deserves scrutiny.

5.              The impact of the third runway on the UK’s short-term climate commitments rests almost entirely on a single assumption: how much of the new runway’s traffic is displaced traffic moving from other UK airports to Heathrow, and how much is truly new traffic and passengers to the UK. The DfT’s Current Trends scenario assumes that 74% of the nearly 20 million passenger per annum (mppa) increase at Heathrow in 2040 is displaced from other airports. These passengers, who are assumed to have been travelling anyway, are taken principally from Gatwick (~ 6.4 mppa), Luton (~ 4.3 mppa) and London City (~ 2.6 mppa) - noting that each of these has recently been expanded or had expansion approved.

6.              The DfT assumes this effect continues out to 2050. With a third runway, the national-level passenger number increase is assumed to be just 17 mppa in 2050, reaching 45 mppa only by 2055 once terminal capacity is fully phased in. The appraisal itself states that expansion “primarily results in displacement within the London system” with passenger volumes at non-London airports in fact 1% lower by 2055, directly in conflict with claims of “economic growth across the country”, one of the four Government tests for expansion.

7.              We have concerns about the assumption that expansion will only lead to a net increase in national-level passengers of just 17 mppa while overall capacity growth is substantially greater. While under this assumption near-term CO2 emissions would be only slightly (~2 MtCO2 within CB7) higher with the third runway than without it, this requires significant under-utilisation of UK airports and almost no accrued economic benefit due to the small number of new flights and zero net job creation (presented by the DfT itself). If instead, it is assumed that Heathrow expansion delivers the new activity one might expect a runway to be built for, then we calculate that the runway’s contribution can approach 29 Mt CO2 in CB7 alone, rising to nearly double that for CB8, when the runway is used for genuinely additional flying capacity.

8.              The statutory test is compatibility with the carbon budgets, not with CB7 specifically, though CB7 is the only currently legislated budget likely to be impacted by the third runway, as CB8 is yet to be formally recommended. Given around two-thirds of the runway’s eventual traffic, and from the DfT’s own assessment, over 98% of its lifetime additional CO2 emissions, arrives after 2042, it is future carbon budgets that are likely to be most affected by new construction now. A runway built in 2035 is a commitment to decades of operation. While the CCC’s pathway shrinks aviation’s allocated budget from around 146 Mt CO2e in CB7 to around 130 Mt CO2e in CB8, the runway will be scaling up during this time. Consenting to build the third runway now will lock in emissions for future budgets, that will be legally binding when set, and that must, by law and maths, be smaller than the budget aviation is currently already exceeding. The question for the committee is not whether the runway can fit within CB7, but whether it can fit into any future budget. The answer is that it cannot. Instead, the UK Government needs to take urgent action to reduce its aviation emissions through reducing the number of flights, in addition to investing in aerospace and fuels research, rather than consenting to new activity.

9.              Our first and core recommendation is that the Committee work to ensure that no third runway is built at Heathrow, concluding that the draft HENPS should not proceed to designation. No evidence has been presented in which a third runway is compatible with the UK’s climate commitments. Aviation emissions should instead, as a minimum, be capped in line with the UK’s statutory targets. To do this, it should more fully explore policy levers to limit demand. One such policy is the frequent flyer levy, which would affect the roughly 15% of the population who take 70% of flights, commands majority public support and ranked among the most popular climate policies in the UK Climate Assembly.

Question B: The robustness of the Government's evidence and rationale for the need for a third runway at Heathrow Airport

10.              The Government’s own appraisal through the Heathrow Expansion Appraisal Report (HEAR) provides limited evidence that a third runway at Heathrow is needed.

11.              As presented in Question I, under the DfT’s 2026 central forecasts used in the appraisal[ii], the assumption is that 74% of Heathrow’s nearly 20 million passenger per annum (mppa) increase represents passengers lost from other airports in 2040.

12.              The forecasts also assume that in 2040, the number of direct international passengers to or from the UK falls with Heathrow’s expansion (by about 0.5 mppa compared to the equivalent case without expansion) and the increase in total travellers is dominated by transfer passengers; people who change planes at Heathrow, many of whom are travelling between two other countries and never leave the airport. By 2050, transfer traffic accounts for around two-thirds of the proposed increase. Therefore, any benefits of hub connectivity mostly support passengers who are neither UK residents nor UK visitors and are merely passing through the airport terminal.

13.              These assumptions are reflected in the economic appraisal. The HEAR model applies a “zero net employment assumption”, meaning the scheme creates no new jobs overall, merely moves them, and any measured effects reflect redistribution, rather than creation of activity. While a headline figure of up to 61,000 jobs is presented, this is a local-area figure, and the appraisal describes workers as relocating to “higher productivity areas, particularly London and the South East”. The benefit it claims is therefore a productivity gain from concentrating activity in the South East, not new employment across the country, contrasting with the named test for economic growth across the country. In addition, once environmental costs are included, the Department finds that the scheme’s costs exceed its benefits by between £23 billion and £63 billion depending on the carbon accounting approach used, and whether costs are passed to passengers.

14.              We refer back to our recommendation to question I, that the Committee conclude the HENPS does not proceed to designation due to a lack of evidence of any economic benefit to the wider country combined with strong evidence of the risk of severe climate harm linked to a third runway at Heathrow.

Question C: Whether it is appropriate for Heathrow expansion to be designated as Critical National Growth Infrastructure

15.              In our view, the designation is not supported by the Government’s own evidence. Any such designation adds weight to the unreasoned assumption that it is necessary to expand, yet as presented above, the appraisal shows the activity is largely redistributed between airports and regions rather than created.

16.              It is important to assess the designation carefully, as our analysis and the DfT’s Appraisal of Sustainability both find that there will be significant adverse effects on climate change (and most environmental aspects) even after mitigation. Anything used to elevate a weakly evidenced growth narrative above well-evidenced environmental harm would not be a sound basis for decision making.

17.              Fundamentally, the growth case and the carbon case currently rest on contradictory assumptions. If the third runway is “critical” because it enables substantial new activity, then the carbon analysis understates the resulting emissions. If the carbon analysis is correct that activity is largely displaced, then the scheme cannot be critical to growth.

18.              We recommend the Committee conclude that the designation of Heathrow expansion as Critical National Growth Infrastructure is not supported by the Government’s own appraisal.

Question D: The assumptions and requirements of the climate change mitigation test

19.              The climate change mitigation test as drafted is too general and effectively infallible. The HENPS states that any increase in emissions “must not be so significant that it would have a material impact on the ability of the government to meet its carbon reduction targets”. “Material” is undefined and given that the aviation pathway is not mentioned in the test, it runs the risk of being compared with the whole-economy carbon budget. CB7 is equal to 535 MtCO2e, against which most schemes can be argued to be immaterial, or have a sufficiently low share of these emissions. Within the constraints of the UK’s own carbon budgeting framework, a more reasonable comparison is with the share of the budget the CCC has set aside for all domestic and international aviation (around 146 MtCO2e). Furthermore, the state of play before any expansion must be accounted for. If the UK is already over its budget for aviation as highlighted above, then there should be no test for expansion: it should not be considered.

20.              As presented above, most impacts are expected to arise in the period following the currently legislated carbon budgets. This is a gap that must be addressed. Because global warming is driven by cumulative CO₂ emissions, any CO₂ emitted outside the specified budget periods will matter as much as the CO₂ within them: the atmosphere does not distinguish a tonne emitted in CB7 from a tonne emitted in 2050. Presenting 96% of the scheme's emissions in an unallocated "remainder" line after 2047 does not reduce their impact; it only places them beyond scrutiny against the framework Parliament has legislated. For context, the DfT’s calculation of the scheme's additional 185 MtCO₂ under Current Trends is equivalent to more than a third of the UK's entire five-year CB7 budget of 535 MtCO₂e and arrives against a remaining global 1.5°C budget of around 130 GtCO₂ from the start of 2026 (Forster et al., 2026).

21.              While the pathway for aviation emissions in the UK’s carbon budgets are not legally binding, unlike the national-level targets, every tonne of CO2 above the budget allocated to aviation must be covered elsewhere for the Government to meet its statutory carbon targets. This may be through additional engineered removals (noting that ~60% of UK engineered removals are earmarked for aviation by 2050) to those already assumed in the CB7 pathway (21.3 MtCO2/yr by 2040, 35.8 MtCO2/yr by 2050) or by deeper cuts to emissions in other sectors. This has important risks associated with it. The other sectors expected to have emissions available to cut – e.g. agriculture and heavy industry – are themselves typically considered ‘hard to abate’. Globally delivered, durable engineered carbon removals currently stand at around 0.3 Mt CO2 per year. No UK engineered removals plant is currently operating; the UK is therefore heavily relying on the infrastructure being developed for CCS that is in need of significant funding from the Government.

22.              We recommend the climate change mitigation test should be reframed so that compliance is at the very least assessed against aviation’s share of its carbon budget. Moreover, decisions should take account of the emissions already committed due to existing airport capacity and consented expansions, rather than assessing each project in isolation. We also recommend that the UK’s ability to meet future carbon budgets is considered, through estimations, before formal recommendations are made by the CCC.

23.              It is welcome that non-CO2 effects are included in the assessment, but the draft should be clearer about the benchmark. We recommend the HENPS states which approach to calculate non-CO2 impacts will be used, and that the quantified appraisal (which currently excludes non-CO2) includes a sensitivity on it.

Question F: The robustness of the methodology, data and scenarios underlying the analysis

24.              There are significant gaps in the scenarios underlying the analysis. Of the eight scenarios included in the supporting documentation, only two are published as part of the carbon appraisal: Current Trends and Technology Development. The highest risk scenario, High Growth, in which built capacity is used, is not included in the published carbon appraisal. If these scenarios have been built for the DfT, their associated emissions should be published.

25.              The 2018 ANPS included a “carbon capped” scenario which limited UK aviation emissions to the CCC’s then-planning assumption of 37.5 Mt CO2 per year. That scenario has now been dropped. None of the eight scenarios in the 2026 modelling suite limits aviation emissions to a level consistent with legislated UK carbon budgets. Our modelling shows that only demand-side limits bring aviation close to its share of the budget (~146 MtCO2e in CB7). Even if the SAF mandate delivers in full, growth in aviation must be curtailed to zero so that demand remains flat. If the SAF mandate delivers only 50% of the mandate, demand must shrink by ~0.5% per year, reaching around 283 mppa in 2040, roughly 23 mppa (8%) below today's level. Even in the most optimistic scenario, Technology Development, no combination of the technology assumptions meet the carbon targets without demand management beyond that induced by increasing prices due to the expensive decarbonisation technologies.

26.              Aviation warrants more precautionary treatment than most sectors, not less. It has among the fewest and least developed technological alternatives for decarbonisation and limited remaining efficiency gains given the maturity of airframe and engine technology (a useful contrast is shipping, where more options exist (Bullock et al., 2025)). In a sector in which mitigation depends on technologies that have not yet scaled, emissions growth carries a very high risk of becoming locked in. Given the precautionary principle that should be applied to climate change mitigation in general, this calls for greater scrutiny and more robust scenarios and data than lower risk sectors. It appears that the opposite has happened in this case – with the carbon-capped constraint being dropped even as the relative importance of aviation for meeting the UK’s national budgets and targets grows.

27.              We recommend that a carbon-capped scenario, as in the 2018 ANPS, consistent with aviation's share of the legislated carbon budgets, be reinstated as a core case in the appraisal, as a minimum position. If Heathrow expands, staying within the carbon budgets will mean correspondingly fewer flights elsewhere. The Department's own Current Trends scenario already assumes this displacement, with 74% of the runway's 2040 traffic moved from Gatwick, Luton and London City. But the displacement is not like-for-like: because of the prevalence of long-haul, the average Heathrow departure currently produces around two and a half times the CO₂ of the average departure from any other UK airport (roughly 0.44 versus 0.17 tonnes CO₂ per passenger). A carbon-capped scenario would make this national-level impact explicit.

28.              We also recommend that carbon emissions pathways are published for all scenarios included in the analysis and yearly numbers. We will publish our own analysis in September 2026.

Question J: To what extent the draft HENPS adequately takes into account changes in the context of airport expansion since 2018, such as, for example, current and future capacity at other airports, new legislative requirements, and developments in technology

29.              On capacity: in its Sixth Carbon Budget advice the CCC said there should be no net expansion of UK airport capacity unless the sector is outperforming its emissions trajectory, a condition not being met. That recommendation was dropped for CB7, but the pathway still requires demand management to deliver over half of aviation’s emissions reductions to 2040, assuming passenger growth of 2% total to 2035. Capacity decisions are running far ahead of this: consented expansions at Luton (19 to 32 mppa), Stansted (43 to 51 mppa) and Gatwick (to around 80 mppa) already add tens of millions of passengers of annual capacity, before any decision on Heathrow. It would be a reasonable assumption that capacity build is capacity intended for use. This incoherence is present in the appraisal's own forecasts: the third runway fills largely by drawing traffic mainly from Gatwick, Luton and London City, the very airports whose expansions have just been consented. The current approach thus builds capacity across the London system while simultaneously planning to empty it to feed Heathrow. The draft HENPS does not address this because each scheme is assessed in isolation. There is no framework for assessing what total UK airport capacity is compatible with the UK’s carbon budgets; precisely the question a national policy statement exists to answer.

30.              On equity: aviation is already privileged within the carbon budgets. It is required to deliver a 17% emissions reduction by 2040 while other sectors decarbonise at far greater pace. It is allocated ~60% of the UK’s engineered removals. Around half of UK citizens do not fly in any given year, and 15% of the population account for around 70% of flights: a framework that further accommodates aviation growth raises significant equity concerns (Larkin, 2024). Internationally the picture is even more stark as the UK occupies a privileged position in the aviation world, where 90% of the world’s population does not fly in any given year (Gössling and Humpe, 2020). A decision to expand Heathrow, to use more of the UK’s already tight carbon budget on aviation, asks the non-flying majority to underwrite the behaviour of those who fly the most.

31.              On technology: engineered carbon removals capacity, that climate policy compliance leans on, is tracking behind forecasted expectations. Worldwide durable removals delivered are roughly 0.3 MtCO2 per year against the 21.3 Mt per year the CB7 pathway assumes for the UK alone by 2040; no UK carbon removal plant is in operation, power BECCS at Drax has been deferred beyond 2031, and the first UK carbon capture and storage (CCS) projects are still in very early stages of construction. The HENPS also does not adequately account for developments in SAF, which has likewise under-delivered on 2018 expectations. The first UK mandate year supplied about 1.6% against the 2% obligation, entirely from imported used cooking oil, and global production (1.9 Mt in 2025, 0.6% of jet fuel) is two orders of magnitude short of mid-century requirements; the Royal Society found no scalable UK feedstock route without claiming over half of agricultural land or several times current renewable electricity capacity. Since Heathrow expansion’s compatibility with the carbon budgets rests on these technologies scaling as assumed, their track record since 2018 is a material change in circumstances that the draft HENPS does not confront.

32.              On climate impacts: since 2018 the impacts of climate change have escalated more rapidly than previously understood. The decade 2015–2024 was the hottest on record, and the World Meteorological Organization now expects global average temperatures to breach 1.5°C by 2029 — a threshold that was not expected to be crossed until around 2045 when the Paris Agreement was signed in 2015 (or 2035 as understood in 2018). Reflecting this, the 2025 advisory opinion of the International Court of Justice confirmed 1.5°C, rather than 2°C, as the primary temperature goal of the Paris Agreement, and that mitigation measures must be based on the “best available science”. Those escalating impacts fall first and hardest on the countries least responsible for the emissions driving them. A developed economy expanding its highest-emitting transport sector is an injustice. The imperative is to strengthen mitigation across sectors, not weaken it.

33.              Global emissions are higher than in 2018: around 40 GtCO2 then (fossil fuels and land use), rising to 42 GtCO2 by 2025. Forster et al. (2026) estimate the remaining 1.5°C budget from 2026 at 130 GtCO2, barely three years of current emissions. While it is now all but impossible to limit warming to 1.5°C, damage limitation is essential, and it reinforces the same point: this is a moment for strengthening mitigation effort, not for schemes that weaken it.

34.              We recommend that the Government establish a framework for assessing total UK airport capacity against the UK’s carbon budgets and its Paris Agreement commitments, and that no further expansion is consented in the absence of such a framework.

July 2026

Endnotes