Environmental impacts of Heathrow expansion

The London Assembly Environment Committee is holding a one-off meeting to investigate the environmental impacts of a third runway at Heathrow airport. 

In January 2025, the government announced that it supported a third runway at Heathrow, and in June invited proposals by 31 July 2025, with the aim of “delivery of an operational third runway by 2035, with applications for planning consent coming forward in time to enable decisions to be made this Parliament”. Proposals were submitted by seven organisations, with those from Heathrow Airport and the Arora Group being shared in public.The government has stated that any scheme must be delivered in line with the UK’s legal, climate, and environmental obligations.

In this meeting, the Committee will investigate the environmental impacts of expansion proposals at Heathrow Airport, in the context of proposed changes to airspace and expansion proposals at several other London airports - including the approval in September 2025 of a second runway at Gatwick Airport. It will particularly focus on noise, air quality and climate impacts.

• The aviation sector is a major cause of UK emissions (although only take-off and landing are counted in London’s emissions register). The Climate Change Committee (CCC) has previously advised against expansion of airport capacity unless the sector can show that its emissions reductions are on track to exceed what is necessary to reach net zero.
• Aircraft noise already causes significant disturbance over London.  Heathrow’s proposals would potentially increase the number of flights from 480,000 to 756,000 flights per year.  The government announced in June 2025 a new Airspace Design Service (UKADS) to enable the redesign of UK airspace. It aims to be operational by the end of 2025 and will be run by NATS.   The government has announced that DFT and CAA intend to start consulting by September 2025 on possible airspace changes. 
• As well as expansion at Heathrow, there are proposals for increased capacity at several other airports that serve London, including Luton, City Airport, Stansted and Gatwick. 
• The Mayor has stated that he is against Heathrow expansion.  However, in the past he has supported Gatwick expansion.  In July 2025, he said: “I remain opposed to a third runway because of the severe impact it will have on noise, air pollution and meeting our climate change targets. Moreover, changes to airspace must not prioritise Heathrow at the expense of other airports. My London Plan policy T8E is clear that any changes to London’s airspace must treat London’s airports equitably.” 

• How does the expansion of Heathrow align with London’s climate targets and can the expansion of Heathrow be kept within overall environmental limits (such as carbon budget, and safe noise and air quality health levels)?
• How will aircraft noise over London be impacted by the changes to airspace modernisation and an expanded Heathrow? What are the timescales for this?
• What impact will an increase in flights to almost 760,000 a year at Heathrow have on London’s air quality?
• How does expansion at Heathrow relate to proposals for expansion at other airports in London?
• How should the views of Londoners impacted by proposed changes be heard and considered?
• How are the Mayor and GLA seeking to influence any decisions on airport expansion and airspace modernisation?