The study which ranks all major international airports found that in 2019 only Dubai’s airport racked up more carbon emissions.
Overall, London had the highest CO2 emissions ranking of any city in the world across its six airports with almost two thirds of that being accounted for by Heathrow.
Campaigners are calling on the government to scrap expansion of the airport under the Airports National Policy Statement which could allow up to 260,000 more flights there per year.