One protester made it on board a British Airways flight and forced it to return to the terminal Thursday, while dozens more blocked an entrance to the airport.
A British Airways statement said people from that flight have been booked on alternative flights to Amsterdam, and the airport confirmed in an update at 2pm local time that a booked passenger had climbed on top of a plane and said other operations were unaffected.
Protesters also crowded the walkway from the nearby light-rail station and sat on the road outside the airport, while two managed to access the roof.
Mr Brown, who was later arrested for endangering an aircraft, was even able to live stream his actions on social media, telling his followers: "This is all about the climate and ecological crisis".
The airport said it was investigating the incident concerning the BA plane to "ensure the safe and secure continuation of service". A statement from Aer Lingus said he was scheduled to travel on the flight and was removed "due to disruptive behaviour on board".
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"And the final irony of the climate protest on our flight".
Airport and Aer Lingus airline officials said that a morning flight to Dublin had to be delayed by almost two hours after a ticketed passenger got up to make a speech about the climate as the plane prepared to take off.
"I'm extremely sorry to disturb everybody here".
"We have two generations of human civilisation left if we carry on doing what we're doing", the unidentified man said, holding up a smartphone.
Extinction Rebellion's colourful protests have managed to attract a mass following since its creation previous year by United Kingdom academics studying the effects of harmful carbon emissions on Earth.
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Extinction Rebellion led protests around the world as thousands of people took to the streets in NYC, London, Paris, Berlin, Sydney, and 55 other cities.
LBC reporter Rachael Venables was at London City Airport as police put up security outside the airport, meaning no one could get into the airport without a boarding pass.
Witnesses reported "an extraordinary number of police officers" at the terminal as demonstrators try to emulate protesters who cancelled more than 1,000 flights as they condemned police brutality in Hong Kong.
The airport said it is "committed to building a more sustainable future for the airport and the aviation industry" and has said it will achieve net zero carbon emissions by 2050.
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