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Can a new Heathrow runway meet both the government’s growth and climate goals?

Transparency is vital if the government is to make the case for a new Heathrow runway.

Higher aviation emissions could theoretically be offset elsewhere.
Assessing the government's runway plans is hard without detailed government net zero plans or a formal proposal from Heathrow.

The chancellor’s support of a third runway at Heathrow is part of her drive for growth, but Thomas Pope and Rosa Hodgkin argue that the government must first show how a new runway meets its climate obligations and reassure the private sector that it really will go ahead

The aim and content of Rachel Reeves’ speech on how she would ‘kickstart economic growth’ were laudable. Having previously failed to convince markets and business that she had a plan for growth, Reeves both set out an overall approach and sent a signal that this government will take a more permissive approach to infrastructure than its predecessors. She did this by announcing nine new reservoirs (the last new reservoir in the UK was built in 1992) and, most notably, announcing the government’s support for a third runway at Heathrow.

This is a clear sign that the government is serious about growth and it signals that growth is the priority, even when it might conflict with the government’s other goals. However, if the government wants to press ahead with both its growth and environmental agenda, while also steering clear of a political backlash, it will need to explain more clearly how this, and other decisions in the future, align with its strategy for net zero.

Aligning another runway at Heathrow with carbon budgets could be challenging

Reeves told the BBC  25 https://www.bbc.co.uk/programmes/m0027d6r  that plans for a third runway would need ‘to meet strict rules about environmental and carbon emissions’, which she believed they could. And before Reeves’ speech, Ed Miliband, the Secretary of State for Energy Security and Net Zero, told an Environmental Audit Committee (EAC) hearing  26 https://committees.parliament.uk/oralevidence/15287/pdf/  that a third runway at Heathrow would only go ahead if it was ‘consistent’ with carbon budgets. The Climate Change Committee (CCC), the government’s official advisory body on climate, advises on five-yearly ‘carbon budgets’ which set emissions reduction targets. The next carbon budget, which will cover 2038-2042, is due in February. 

The ‘balanced pathway’ from the last carbon budget advice  27 https://www.theccc.org.uk/wp-content/uploads/2020/12/The-Sixth-Carbon-Budget-The-UKs-path-to-Net-Zero.pdf , CB6 (published in 2020) allowed for a 25% increase in aviation demand from 2018 by 2050 but did not allow for any net airport expansion. In 2023 the CCC  28 https://www.theccc.org.uk/wp-content/uploads/2023/06/Progress-in-reducing-UK-emissions-2023-Report-to-Parliament-1.pdf  said that if the Heathrow and Gatwick expansions were approved along with other applications under consideration this would increase total capacity to 467 million, just below the previous government’s plans for an increase to 482 million, a roughly 70% increase in terminal passengers compared to 2018 levels. 

Last year’s CCC progress report  29 https://www.theccc.org.uk/wp-content/uploads/2024/07/Progress-in-reducing-emissions-2024-Report-to-Parliament-Web.pdf  said that there should be no airport expansion unless aviation was outperforming its emission baselines - effectively becoming less carbon-intensive more quickly than current projections. 

Higher aviation emissions could theoretically be offset elsewhere

Miliband laid out a clear position at the EAC earlier this week, stating that government’s goal was ‘neither on the one hand to stop people going on holiday or stop the economy getting what it needs, nor is it business as usual as if climate change is not a problem’. The solution, he said, was to manage that balancing act through carbon budgets.  30 Emissions from international aviation were not originally included in carbon budgets. The previous government committed to including them from 2037 but did not bring the secondary legislation required to do so. The current government has stated its intention to bring that legislation and include emissions from international aviation.

That is a reasonable position if there are credible plans in place to offset emissions from increased aviation demand elsewhere. The government inherited a situation where, according to the CCC, only a third of required emissions reductions to get to net zero by 2050 were backed by credible plans, and it is likely to wait until later this year to release its own updated carbon budget delivery plan. Without that information, demonstrating that credible plans are in place more broadly that allow Heathrow expansion to align with carbon budgets is challenging.

Relying on uncertain technological advancements is risky

When questioned on the Today programme about Heathrow expansion, Rachel Reeves suggested that the position on aviation had meaningfully changed due to increased fuel efficiency and the development of sustainable aviation fuels (SAF), alongside the fact that less time spent circling by planes would mean less wasted fuel.

Reeves also announced new funding for SAF production. But production and usage has been limited so far and the SAF mandate  31 https://www.gov.uk/government/news/greener-flights-ahead-for-uk-aviation , planned under the previous government, which came into force at the start of January, only requires at least 2% of all jet fuel in flights taking off from theUK from 2025 to be sustainable, rising to 10% by 2030 and 22% by 2040. It is also expensive. Many green technologies have developed faster than expected, with rapidly dropping prices, but the CCC described relying on this (as the previous government’s Jet Zero strategy also did) as ‘high risk’.  32 https://www.theccc.org.uk/wp-content/uploads/2023/06/Progress-in-reducing-UK-emissions-2023-Report-to-Parliament-1.pdf

Determining whether a third runway at Heathrow is compatible with the government’s net zero plans relies on estimating how much a new runway would increase the number of flights taken, to what extent that would translate into increased emissions given potential technological advances, increased fuel efficiency, and the emissions from circling planes, and, looking at the global picture, how far (in the absence of Heathrow expansion) emissions would otherwise be displaced to other airports. And then that would have to be set against how far those increased emissions could be offset and how much that might cost. 

More transparency would help the government make its case on Heathrow

This won’t be easy. And it is even harder without detailed government net zero plans or a formal proposal from Heathrow. But the government should clearly outline its reasoning and the evidence behind it to allow for an informed debate about its plans. This transparency is key to avoiding a backlash and convincing both the public and industry that it is committed to both its growth and net zero goals. 

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