I object to any expansion of Heathrow Airport, including construction of a third runway, because the proposed ANPS / HENPS climate assessment and mitigation amendments underpinning expansion proposals remain fundamentally incomplete, and any expansion would lead to enormous and therefore unacceptable increases in the non-CO2 climate impact, not to mention the CO2 climate impact, of UK-attributable aviation, and therefore constitute an unjustifiable setback in the achievement of the UK’s climate goals and commitments.

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Firstly, as others (including the Government’s own Environmental Audit Committee less than 12 months ago) have noted, the economic reasoning for expanding Heathrow is unconvincing at best and unfounded at worst: “Whilst the Government support for airport expansion has been largely based on its expectation of economic growth, the Government has been unable to direct the Committee to any evidence that supports its assertion.” Therefore, the so-called “need” which is supposedly resolved by the expansion of Heathrow is a moot point.

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More importantly, due to the ongoing climate emergency, growth in the aviation sector must not be encouraged. It is currently estimated that aviation contributes approximately 4% of global warming annually, with half of that impact over a 20-year period arising from non-CO₂ effects, particularly persistent contrails and contrail-induced cirrus cloud formation. The UK Government’s own Jet Zero Taskforce, through the Contrail Impact Mitigation Task and Finish Group’s March 2026 report, has confirmed that there is a “consensus” that “annual global average radiative forcing from contrails is net positive” and “significant”.

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The draft HENPS asserts that due to the uncertainty surrounding the exact magnitude of contrails’ warming effects, no quantitative attempt would need to be made to measure the increased non-CO2 climate impact of an expanded Heathrow. This is dangerously reckless and does not reflect the latest science. Recent research from the University of Cambridge and Imperial College, London comprehensively demonstrates that immediate action on contrails is more climate friendly than inaction regardless of which metric is selected to quantify their warming effects (Borella et al., 2024, Smith et al., 2026). Moreover, the precautionary principle, enshrined into international law by the Rio Declaration, dictates that action should be taken to prevent environmental harm even in cases of scientific uncertainty. As research on the climate impact of contrails dates back to at least 1999, when the first IPCC report on this issue was published, the HENPS position is clearly outdated and problematic from both a legal and a scientific standpoint.

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Furthermore, the UK's independent Climate Change Committee (CCC) reported in its Seventh Carbon Budget (February 2026) that aviation’s non-CO₂ warming impact has tripled since 1990, showing that action on this issue is urgent. Due to the effects of contrails and the lack of progress on Sustainable Aviation Fuels, it also predicts that aviation will become the UK’s highest-emitting sector by 2040. Therefore, from both a CO2 and non-CO2 standpoint, aviation growth through airport expansion is the antithesis to positive and necessary climate action.

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Heathrow is also uniquely problematic in this regard. It is already Europe’s biggest airport and the UK's principal hub for long-haul and transatlantic flights. Scientific evidence increasingly shows that these are precisely the flights most associated with contrail warming. The latest research finds that flights lasting more than five hours accounted for 40% of contrail warming while representing only 10% of European departures. Likewise, studies have shown that the North Atlantic accounted for only 5% of global flight distance in 2019 but 10–11% of annual contrail warming effects.

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Recent analysis by Estuaire.com further highlights Heathrow's significance with regards to contrail-induced climate change. The American Airlines Newark – Heathrow flight was ranked as the third most climate-damaging flight route of any flown globally in 2025 with regards to non-CO2, producing 150,299,443.68 kg of CO2 equivalent overall. Moreover, the British Airways and Virgin Atlantic Heathrow – New York JFK routes were ranked, respectively, as the 5th and 12th most climate-damaging flight routes globally with regards to non-CO2. Finally, the Air China Beijing – Heathrow flight was ranked 10th on this list. If the UK is to show leadership on climate action, it clearly cannot allow Heathrow to be expanded.

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Heathrow expansion should not proceed because the full climate impacts of aviation, including contrails and other non-CO₂ effects, are not currently incorporated in the proposed amendments to the ANPS/HENPS sustainability appraisal or mitigation process. From either a non-CO2 or CO2 standpoint, any expansion of Heathrow would not be compatible with the UK’s climate goals, commitments and pathways.