Expanding either Heathrow or Gatwick airports would damage air quality and biodiversity as well as increase carbon emissions and noise pollution, according to the body advising the government on the issue.
The findings were outlined in a consultation published by the Airports Commission, an independent body created by the government in 2012 to consider the location and timescale of airport expansion in the south east.
The document asks for views on the commission’s assessment of proposals to build new runways at Heathrow or Gatwick airports.
Two separate proposals have been put forward at Heathrow. Heathrow Airport Ltd wants a new runway to the north west of the existing northern runway. Heathrow Hub Ltd, meanwhile, suggests operating the existing northern runway as two separate strips.
In West Sussex, Gatwick Airport Ltd is promoting a new runway built to the south of the existing takeoff and landing area.
The commission found that all three options would have a negative impact on a range of environmental factors, including noise, carbon emissions, air quality, landscape, biodiversity and water.
The consultation states: “In general, while good detailed design and operational delivery by the airport operator could significantly reduce the impact of the scheme, the impacts in some cases will never be entirely mitigated.
“However, the mitigated impacts are not predicted to exceed domestic or international regulations, except in the case of air quality, where further work is required to fully quantify the limited risks.”
The commission has published detailed analysis of all three options alongside the consultation, including the likely risks to the environment.
On noise, expansion at Gatwick would double or treble the number of people exposed to noise pollution, the commission found. This is true under both high and low-growth traffic scenarios for the airport, it said.
However, even under a high-growth scenario, the number of people affected by expanding Gatwick would be considerably lower than if Heathrow was to increase in size, the commission found. The extended northern runway scheme at Heathrow could impact an extra 100,000 people compared to today, it found.
Mitigation measures proposed, such as incentivising quieter fleets would have to be “extremely significant” to reduce the commission’s assessment of noise impacts from “significantly adverse” to “adverse”, it said.
The north-west runway scheme would also lead to “significantly adverse” noise impacts for “tens of thousands of people”, the commission found. However, mitigation could reduce this to “adverse”, while night-time noise would fall, it found.
The consultation is available here and closes on 3 February 2015.