Below is the foreword I wrote for my Tyndall colleagues’ detailed and rigorous report examining whether further expansion of Heathrow can be reconciled with the UK’s domestic, legally binding carbon budgets.
The report, Heathrow Airport Expansion: Risks for the Climate Change Act, was published last week (3rd Sept. 2026). Its lead author, Dr Lois Pennington, subsequently gave evidence to the Parliamentary Transport Select Committee as part of its scrutiny of the Government’s draft Heathrow Expansion National Policy Statement.
The full report is available at: Heathrow Airport Expansion: Risks for the Climate Change Act, with a short accompanying video here.
Dr Pennington’s evidence to the Parliamentary Select Committee is available here (between 16.00 and 16.59).
When asked for the headline conclusion of the analysis she had led, Dr Pennington was unequivocal:
“Every aviation scenario the UK Government has published overshoots the carbon budget Parliament has legislated, before a third runway at Heathrow is even taken into account. Aviation cannot continue to grow if the sector is to make a proportionate contribution to meeting the UK’s carbon budgets” … consequently … “the Government must reassess the case for expansion.”
Her conclusion goes to the heart of a much wider problem with the way climate policy is too often developed and assessed:
“Climate policy must be grounded in what we can demonstrate and evidence, rather than what we hope may become possible.”
I would add one further and important point to the report’s findings. The UK’s domestic carbon budgets, the framework against which the proposed expansion is assessed, are themselves based on the advice of the Climate Change Committee (CCC). Yet those budgets far exceed any reasoned interpretation of the UK’s international climate obligations consistent with limiting warming to 1.5°C, and even with the considerably weaker objective of remaining below 2°C.
Note: for an earlier commentary on the expansion of Gatwick airport, see: Gatwick Expansion: A Direct Assault On Our Climate Commitments
Foreword to the report
The climate context – beyond comfortable narratives
The climate we experience today is, on average, the least extreme climate that our children will ever know. Unless we exchange comforting narratives for meaningful action, we are on course to leave them, and future generations, a world of escalating climate disruption, deepening food and water insecurity, increasing displacement and growing conflict.
Despite frequent references to a “new normal”, there is nothing normal or stable about our trajectory. Every tonne of carbon dioxide emitted from burning fossil fuels adds to global warming. Cutting emissions only slows the rate of warming; it does not stop it. Temperatures stabilise only when fossil fuel emissions reach zero. Until then, climate impacts will continue to intensify.
This is not a new challenge. In 1992, governments committed under the UN Framework Convention on Climate Change to prevent “dangerous” interference with the climate system. In Paris, in 2015, they clarified what that meant: holding warming to well below 2°C while pursuing efforts to limit it to 1.5°C. Yet, more than three decades after that original commitment, global emissions continue to rise and the world is now moving beyond 1.5°C. Most tellingly, away from the climate rhetoric of our leaders, humanity has emitted more CO₂ since 1992 than it emitted throughout all of human history up to 1992.
The remaining carbon budget is now extraordinarily small. Once we set aside the increasingly implausible assumption that future generations will somehow remove hundreds of billions of tonnes of carbon dioxide from the atmosphere, the implications of the science become stark. Even retaining a reasonable chance of limiting warming to well below 2°C demands global emissions reductions approaching 8% every year, starting immediately and continuing until fossil fuel emissions cease. For wealthy nations such as the UK, which have repeatedly committed to reducing emissions earlier and faster than poorer countries, the required annual reductions are higher still.
Against this backdrop, claims of UK climate leadership deserve much closer inspection. Once emissions from international aviation and shipping are included, alongside those embodied in the goods we import and export, UK emissions have fallen by around 20% since 1990 – equivalent to less than 1% per year. This record of incrementalism is far removed from the scale or urgency of the challenge.
It is within this context – not the reassuring language of political rhetoric, but the unforgiving reality of the climate system – that proposals for airport expansion must be judged.
Aviation already accounts for around one in every ten tonnes of the UK’s carbon dioxide emissions, while UK citizens fly around six times more per year than the global average. But these stark figures obscure the profound inequality in who flies. In any given year, around half of the UK population does not fly at all, while around 70% of flights are taken by just 15% of the population. Aviation’s climate challenge is not about the occasional holiday or a visit to family overseas. It is the high and frequent levels of flying concentrated among a relatively small, affluent section of the population – much of it for tourism.
The economic case for ever more aviation capacity is also less straightforward than its proponents suggest. In 2023, inbound tourism brought around £31 billion into the UK economy, undoubtedly a significant contribution to the tourism industry and the Exchequer. Yet UK residents spent around £74 billion on tourism overseas that same year. The result was a net tourism outflow of £43 billion. Expanding airport capacity in the hope of further stimulating aviation risks increasing rather than reversing this structural imbalance.
But the fundamental problem is climate change. The aviation industry points to continuing efficiency improvements, so-called “sustainable aviation fuels” and, increasingly, the prospect of removing carbon dioxide from the atmosphere. These technologies may each have a role to play at the margins. None, however, provides a credible basis for continued expansion in airport capacity. Efficiency improvements are repeatedly outpaced by growth in demand; sustainable aviation fuels remain limited in scale and face significant constraints; and large-scale carbon dioxide removal remains speculative, expensive and deeply uncertain. The danger is not that researchers and engineers working on these technologies lack expertise or good intentions. It is that their potential is being used to postpone the much more difficult question of how rapidly aviation emissions actually need to fall.
That question cannot be avoided by passing responsibility to future generations. The remaining carbon budget is finite and rapidly shrinking. Every tonne of CO₂ emitted by aviation is a tonne that cannot be emitted elsewhere if the UK is to remain within its climate commitments. Continued growth in aviation therefore places additional pressure on hospitals, schools, industry, households and other sectors to decarbonise still faster, so that a highly carbon-intensive form of consumption that disproportionately benefits an affluent minority can continue to expand.
It is in this context that the role of the Climate Change Committee (CCC) must be scrutinised. The CCC was established to provide independent advice on how the UK can meet its climate commitments. Its role should therefore be to test government policy against climate science, carbon budgets and the UK’s international obligations.
Yet its approach to aviation has inverted that relationship. Rather than asking what level of aviation is compatible with those commitments, the CCC has sought to accommodate aviation growth by building its pathway around a suite of risky assumptions about future efficiency, sustainable aviation fuels and carbon removals.
This is not a minor technical disagreement. The CCC’s continued adherence to a “net zero 2050” framework cannot itself be reconciled with the UK’s UNFCCC and Paris commitments. On aviation alone, its pathway envisages this single sector emitting more than 20 million tonnes of CO₂ in 2050, and, by implication, continuing to emit substantial quantities year after year well into the second half of the century.
That is unequivocally the wrong direction of travel.
A credible climate advisory body must be willing to say when a politically attractive policy is incompatible with the UK’s climate commitments. It should guide policy in accordance with those commitments and the science, rather than massage its assumptions to accommodate policy.
This brings us directly to Heathrow and the central focus of this report.
Heathrow expansion is not an isolated infrastructure decision. It is a decision to create additional, long-lived capacity for aviation at precisely the point when UK emissions need to be falling rapidly. The same fundamental contradiction applies to proposals for expansion at Gatwick, Luton, Stansted, Bristol, Manchester, Newcastle and elsewhere.
No amount of glossy presentation, carefully calibrated modelling or reassuring technological promise changes that underlying reality. The physics does not negotiate. A rapidly shrinking carbon budget cannot simultaneously accommodate sustained growth in aviation and deliver the deep emissions reductions required to meet the UK’s climate commitments.
As this report demonstrates in detail, the conclusion is therefore clear.
Heathrow expansion is incompatible with any reasoned and credible interpretation of the UK’s international climate commitments. As such, it should not proceed.