What Does Third Heathrow Runway Mean for UK Sustainability?

During a landmark speech, delivered at Siemens Healthineers' Oxfordshire manufacturing and development hub, the UK's Chancellor of the Exchequer Rachel Reeves revealed plans to build a third runway at London Heathrow , the UK's largest airport.
A third runway at Heathrow has been under consideration for many years now, with several successful governments debating its construction. Never before, though, has a government officially formalised plans to go ahead with construction, simply because of the levels of controversy the project brings in tow.
On the one hand, it is a relatively simple financial lever to withdraw: the more flights that come to the capital, the more money is spent on British soil.
On the other, a third runway will see an immediate 50% increase in Heathrow's aviation-based emissions.
Right now, this is a compromise this government is willing to make, with Prime Minister Sir Keir Starmer driving a growth-centric approach from the top.
“Growth is the defining mission of this government,” he says.
The context
Rachel Reeves' speech touched on a huge variety of topics, but the announcement that sent the most shockwaves around the country was left to the very end of the press conference.
“Finally, I came to the decision that, perhaps more than any other, [this project] has been delayed, has been avoided, has been slowed,” she said, regarding the UK government's plans for Heathrow.
“The question of whether to give Heathrow - our only hub airport - a third runway has run on for decades.”
But why has this issue always been such a sticking point for politicians and the public alike?
Firstly the expansion would lead to a significant increase in carbon emissions, making it far harder for the UK to meet its climate commitments. Air pollution in the surrounding areas would also significantly worsen, as more flights and road traffic contribute to already poor air quality.
Noise pollution is another major concern, with more aircraft movements affecting hundreds of thousands of residents under the flight paths.
These concerns, amongst several others, have prevented plans for a third runway from proceeding since May 2003, when the airport first called for an expansion.
The UK government's position
Rachel Reeves dedicated a great deal of time to outlining the positive impacts that the expansion of Heathrow could have for the UK.
“Heathrow is at the heart of the UK’s openness as a country,” she explained.
"It connects us to emerging markets all over the world, opening up new opportunities for growth. Around three quarters of all long haul flights go from Heathrow. Over 60% of UK air freight comes through Heathrow. And about 15 million business travellers use Heathrow in 2023.”
“I can confirm today that this government supports a third runway at Heathrow and is inviting proposals to be brought forward by the summer,” she said.
"We will then take forward a full assessment through the airport national policy statement.
“This will ensure that the project is value for money and our clear expectation is that any associated service transport costs will be financed through private funding.”
Undoubtedly, Reeves understands the historical context of this subject, as well as the controversy that this announcement will stir, especially for a government with an explicit focus on climate action.
As such, she was at pains to relate the government's plans for the airport back to its big picture environmental aims.
“[The assessment] will ensure that a third runway is delivered in line with our legal, environmental and climate objectives,” she explained.
The backlash to the third runway
Plans to expand Heathrow's capacity have been the source of controversy for more than two decades now, eliciting the ire of environmentalists and local residents alike.
Estimates vary from source to source, but it is generally predicted that an extra runway at Heathrow will add more than six million tons of carbon emissions to the atmosphere each year.
Following Reeves' announcement, global environmental NGO WWF published a statement, saying the Chancellor is “making a serious mistake by prioritising costly projects like airport expansions that take decades to build, send carbon emissions skywards and leave real growth stuck on the runway.”
Dissention has also come from within Labour ranks, with Mayor of London Sadiq Khan opposing the plans “because of the severe impact it will have on noise, air pollution and meeting our climate change targets”.
Likewise, former Shadow Chancellor and current Labour MP, John McDonnell, was quick to respond critically to the government's announcement.
“This is such a huge political, economic and especially environmental mistake that sadly I fear it will inflict an irreparable scale of damage on the government,” he wrote in a post on X.
Alethea Warrington, Head of Aviation at climate charity Possible, believes that the project could be a real mistake for this government.
"Approving airport expansions would be a catastrophic misstep for a government which claims to be a climate leader," she says.
"This huge increase in emissions won't help our economy, and would just encourage the small group of frequent flyers who take most of the flights, further worsening the UK's huge tourism deficit."
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