The Climate Change Committee (CCC) said the government could allow the airport to add a third runway and new terminal capacity only if the aviation industry adopted tougher measures to bring its emissions into line with the UK’s legally binding climate commitments.
Under current policies, the committee said, Heathrow expansion would make it harder for Britain to meet its carbon budgets and its target of reaching net zero emissions by 2050. Heathrow currently accounts for around half of UK aviation emissions, while the committee estimates that the full impact of expansion could represent 6.9% of the UK’s remaining carbon emissions in 2050.
The CCC said the aviation industry would need to combine greater fuel and operational efficiency with increasing use of sustainable aviation fuel (SAF) and, critically, the permanent removal and storage of carbon dioxide that cannot otherwise be eliminated.
Nigel Topping, chair of the CCC, said the government could not expand the airport without making the industry responsible for cleaning up its emissions.
“The government cannot expand Heathrow airport without requiring the aviation industry to clean up its emissions.”
He added:
“Therefore, the government should legislate policies that require the aviation industry to fully address all of their emissions by 2050, either directly or by purchasing engineered removals. The polluter-pays principle must apply.”
The committee published its advice to the government on Wednesday as ministers consider changes to the policy framework governing Heathrow expansion.
Passengers could face higher fares
The cost of meeting the additional climate requirements would ultimately be likely to reach passengers through higher airfares.
According to the CCC's assessment, the combined costs of sustainable aviation fuel and engineered carbon removal could add about £150 to a return flight between Britain and Alicante by 2050. A return journey to New York could cost about £400 more.
The committee envisages those costs being introduced gradually over the next 25 years rather than imposed immediately.
The approach reflects the CCC's broader view that aviation can no longer rely on emissions reductions elsewhere in the economy to compensate for continued growth in flying.
Aviation emissions have more than doubled since 1990, while emissions across the wider UK economy have roughly halved. The CCC has warned that aviation is falling behind other sectors in decarbonisation and that, without additional measures, emissions from the sector would not fall sufficiently by 2050.
James Richardson, the CCC's director of analysis, said the scale and growth of aviation meant it could no longer be treated as a relatively small contributor whose emissions could be balanced by cuts elsewhere.
The sector has grown substantially over the past three decades. Passenger numbers increased from about 100 million in 1990 to around 300 million in 2025, while aviation now accounts for about 9% of UK emissions.
The CCC expects aviation, alongside agriculture, to remain among the UK's two largest-emitting sectors by 2050 unless significant changes are made.
Campaigners challenge reliance on emerging technology
Environmental campaigners have criticised the CCC's approach, arguing that the proposed expansion would create additional emissions now while relying on technologies that have yet to reach the scale required.
Tony Bosworth, a campaigner at Friends of the Earth, accused the committee of “pulling its punches” and pointed to research from the Tyndall Centre suggesting that sustainable aviation fuel and carbon-removal technologies remain insufficiently proven and may not expand rapidly enough to offset the emissions associated with a larger Heathrow.
“The CCC should have made it crystal clear: there is no plausible way to expand Heathrow without wrecking the UK’s climate targets,”
Bosworth said.
The CCC, however, maintains that engineered carbon removals will form an important part of Britain's pathway to net zero because some sectors, including aviation, are expected to retain residual emissions that cannot be eliminated completely. Its wider climate strategy envisages permanent engineered removals being used to balance those remaining aviation emissions by 2050.
Flying remains concentrated among wealthier travellers
The debate over Heathrow's future is also bringing renewed attention to who benefits from the growth of aviation and who ultimately pays for its environmental costs.
Air travel in England is heavily concentrated among frequent and higher-income travellers. National Travel Survey figures for 2024 showed that only around half of people in England took an overseas flight during the year.
Yet people who took two or more international flights accounted for about 80% of all overseas flights. Those taking five or more return international flights represented roughly 5% of the population but accounted for about a third of all flights.
The highest-income group accounted for 38% of overseas flights — around four times the number taken by people in the lowest-income group.
The CCC said policies requiring airlines to pay for emissions reductions should take those inequalities into account, although it stopped short of recommending a specific frequent-flyer levy.
Airlines warn against making flying unaffordable
The aviation industry has pushed back against the proposed approach, arguing that forcing airlines and passengers to absorb the full cost of decarbonisation could make air travel unaffordable for millions of people.
Tim Alderslade, chief executive of Airlines UK, said the CCC's proposals risked turning flying back into an activity available mainly to wealthier travellers.
“You can’t solve the climate crisis by pricing Britain out of the skies.”
He argued that the focus should instead be on expanding the availability of sustainable aviation fuel, improving airspace efficiency and increasing carbon-removal capacity.
“The answer is affordable SAF – already cutting emissions since the mandate began – airspace reform by 2035 for more direct routes and scaled-up carbon removals.”
The CCC's position does not rule out aviation growth. Rather, its advice sets conditions under which additional airport capacity could be reconciled with the UK's climate budgets.
Heathrow says growth and net zero can coexist
Heathrow has defended its expansion plans, arguing that economic growth and climate action do not have to be mutually exclusive.
A spokesperson for the airport said:
“Heathrow expansion cannot be a choice between economic growth and net zero – it must deliver both.”
The airport said the CCC's assessment recognised that key technologies were already available and that it would continue working with the government and the wider aviation sector to expand their use.
“We will continue working with government and partners across the aviation sector to ramp up today’s proven technologies, while examining options for how the billions of pounds passengers already pay in carbon taxes can be used to support this.”
The CCC's advice says Heathrow expansion would make meeting the UK's climate targets more difficult, but it also sets out a route under which expansion could potentially be accommodated if aviation takes full responsibility for its emissions.
Government faces decision
The government is not legally required to accept the CCC's recommendation. The committee was established under the 2008 Climate Change Act to advise ministers on carbon budgets and progress towards the UK's climate objectives.
Topping warned that if Heathrow expansion were approved without legislation requiring the aviation sector to address its additional emissions, the issue would remain a major concern in the committee's reporting to Parliament.
The Department for Transport said any Heathrow expansion would have to comply with the UK's net zero objectives.
A government spokesperson said:
“Any expansion proposal [for Heathrow] would need to align with our net zero targets.”
The department also pointed to £219m of government investment in sustainable aviation fuel production and a further £43m for cleaner aviation technologies.
Ministers have said Heathrow expansion could generate around £40bn for the economy and support up to 60,000 local jobs.
The decision therefore leaves the government balancing competing economic and environmental objectives: whether to increase aviation capacity at one of Europe's busiest airports while ensuring that the resulting emissions do not undermine Britain's legally binding climate targets.
The CCC's message is clear: if Heathrow grows, the aviation industry must bear the cost of cleaning up the emissions associated with that growth rather than relying on other sectors to compensate for them.