Four Greenpeace activists climbed on top of a commercial airplane which had arrived from Manchester in Heathrow Airport Monday to protest against plans of building a new runway.

The protesters managed to walk out of Terminal 1, cross a patch of tarmac and then climb on the Boeing 777, without being seen by the airport’s security. Then they unveiled a banner reading "Climate emergency -- no third runway," protesting against the intention of London’s Heathrow airport to build a third runway.

"We may have exposed a hole in security at Heathrow, but it's not as big as the hole in (Prime Minister) Gordon Brown's climate change policy," said Sarah Shoraka, one of the protesters, according to CNN.

Asked about the cause of their action, the protesters said that airports contribute greatly to the climate change. They consider that another runway would damage the environment, increasing pollution, noise and destruction of local property.

"I'm standing on this plane because our planet and the people who live on it are in danger," Anna Jones, another protester, told CNN. "Climate change can be beaten, but not by almost doubling the size of the world's biggest airport."

Sarah also wondered why flights between Manchester and London are necessary, when traveling by train is also a good alternative.

"The push for a third runway is being fueled by totally unnecessary flights like this one," Shoraka said.

But the government and the airlines consider that Heathrow is a large airport and needs a third runway built.

A Heathrow spokesman declared, according to The Guardian:

"There is an important debate to be had regarding airport expansion and the government is currently consulting on the future of Heathrow airport. All interested parties have the opportunity through the proper democratic process to make their views known."

All four Greenpeace protesters were removed and arrested by police.