Hundreds of climate change protesters marched near London's Heathrow airport oday and pledged civil disobedience to draw attention to the impact of aviation on global warming.
Protest organizers say they plan to form a human chain at the site of a proposed third runway at the world's busiest international airport and to picket the headquarters of Heathrow's operator BAA through the night.
The protesters want Heathrow's expansion plans dropped and the growth of air travel halted. Their action comes at the height of the holiday season at an airport that handles nearly 70 million passengers a year.
Marchers with carnival-style floats and speakers adorned with flowers blaring music left a tented camp chanting "No third runway" and carrying a banner saying: "We are armed ... only with peer-reviewed science."
A smaller group of protesters scuffled briefly with police blocking their path as they marched down a road near the camp.
Scientists say air transport contributes to global warming, and the carbon dioxide gas and water vapor emitted by aircraft are four times more potent at high altitude than at sea level.
The British government says it is committed to tackling climate change and plans to set legally binding targets for cutting CO2 emissions -- but it also backs an expansion of air travel, which is set to double in the next 25 years.
The climate change activists have been camped out for a week at Heathrow, west of London, and more protesters trickled onto the site on Sunday. Organisers estimated there were 1,000-1,200 protesters to take part in 24 hours of "direct action."
"We believe in unlawful protest when it is peaceful and justified," one of the organisers, Leila Harris, told reporters.
Activist Peter McDonell said that besides the human chain and picket there would be a variety of "autonomous acts," or civil disobedience, but said he did not know the details.
At least 40 activists have been arrested over the past week after protests ranging from attacking an Israeli-owned food import warehouse near Heathrow to super-gluing their hands to doors at the Department for Transport in London.
Heathrow's operator, Spanish-owned BAA, expressed concern that chaos could ensue, but police said they planned to use up to 1,800 officers and were confident they could keep control.
"There's been so much media hysteria about baby-eating anarchists. What we're saying is that this is a peaceful protest. The only thing we are armed with is the consensus of the scientific community," said McDonell.
The campaigners insisted that their quarrel was with the aviation industry, not with passengers. They said they would not do anything to endanger passengers, such as blocking runways.
Police have expressed concern that hardline elements may break away from the main group and take violent action.