Heathrow expansion will cause enormous environmental impacts
6th July, 2026
After months of speculation, the Department for Transport recently published its draft Heathrow Expansion National Policy Statement (HENPS), the framework against which any application to expand the airport will be measured.
The government has long said that the expansion must meet its four tests – these are:
• that it contributes to economic growth across the country
• that it meets our air quality obligations
• that it is consistent with our noise commitments
• and crucially, that it aligns with our legal obligations on climate change, including net zero
The NGO community argued in this briefing that those tests were vague and could not guarantee that expansion could take place without significant harm to the local community and the environment.
Does the plan for Heathrow expansion meet the “four tests”?
The simple answer is no – the DfT’s own Appraisal of Sustainability shows that the expansion would result in major adverse impacts on every indicator measured, except economic benefits, where the picture was merely mixed and in some cases “uncertain”.
Will Heathrow Airport expansion lead to economic growth and a better environment?
Here are the headlines from AEF’s latest analysis on the likely impacts of Heathrow expansion on the four areas of the HENPS tests:
Economics: The expansion will provide an average of just 0.02% to the GDP of the UK’s regions, not to be fully realised until 2056, but 0.17% growth in the GDP of London. The national picture is 0.05% GDP impact by 2056 – ten times less than the Chancellor claimed when the project was resurrected.
The government’s own welfare assessment generated a Net Present Value of MINUS £62bn when environmental costs are fully included.
Air quality: Although the Appraisal of Sustainability assessed that the UK’s legal limits on NO2 and PM2.5 would not be breached, these limits are double what is currently allowed in the EU and do not capture the full health impact of air pollution.
Using an updated methodology, NOx emissions from aircraft will now be 55% higher in an expansion scenario than previously thought. NOx emissions from planes are increasing because engine technology prioritises reducing CO2.
Noise: The government published its long awaited noise attitude surveys just before the HENPS, which revealed that annoyance from planes occurs at much lower levels of exposure than previously thought.
Using those new metrics, the 3rd runway results in 900,000 more people still being exposed to these harmful noise levels in 2055 than would otherwise be the case.
Climate: In the government’s central assessment scenario, the 3rd runway will result in emissions from aviation being 41Mt in 2050. This is more than twice the Climate Change Committee’s balanced pathway of 21Mt.
The 3rd runway is expected to be opened in 2035 during Carbon Budget 6 (2033-37). In that year, the Climate Change Committee’s pathway for aviation suggests emissions should average just 31Mt per year throughout that period.
However, the Department for Transport’s new aviation forecasts show that emissions will average 37.8Mt per year during that period, 6Mt per year coming from Heathrow alone, clearly impacting the government’s ability to meet its legally binding emissions reduction targets.
Want to know more? Read the full analysis:
Image credit: Photo by Troy Mortier on Unsplash