LONDON (Reuters) - Four environmental campaigners breached security at London's Heathrow airport on Monday, climbing aboard a parked aircraft and unfurling a banner protesting against runway expansion plans.
Police later arrested the four from Greenpeace who walked through security at one of the world's most policed airports.
"Climate emergency. No 3rd runway" read the banner they hung on the tailfin of a passenger plane that had just landed after a domestic flight from the northern city of Manchester.
The protest, with others to follow outside parliament later in the day, came just two days before the end of the government's public consultation on the planned expansion which has pitted business against environmentalists.
Plans to build a third runway for what is already the world's busiest international airport have sparked protests and a virulent blogging campaign stressing a contradiction between major aviation expansion and attempts to fight global warming.
"The arguments in favor simply don't stack up," said Nic Ferriday of the Aviation Environment Federation.
"You can't have the massive expansion of aviation in this country -- led by Heathrow -- when the government is at the same time promising to cut carbon emissions to fight climate change."
Heathrow already handles 67.3 million passengers and 471,000 aircraft movements a year, figures which are forecast to double over the next 30 years if expansion goes ahead.
Businesses say Heathrow provides vital links to the United States, Europe and booming Asian economies like India and China.
More than a third of businessmen polled by London's Institute of Directors took a business flight 10 times or more last year and say work would suffer if flights were curbed.
With about two million people under Heathrow's flight path if expansion goes ahead and hundreds of homes due to be bulldozed, many local residents want expansion stopped.
Scientists say global average temperatures will rise by between 1.8 and 4.0 degrees Celsius this century due to carbon emissions from burning fossil fuels for transport and power, with emissions at altitude twice as harmful as at ground level.
"Aviation accounts for about 13 percent of Britain's climate impact. That percentage will rise very sharply as the number of flights doubles and efforts are made to cut emissions elsewhere," said WWF transport campaigner Pete Lockley.
The government argues that aviation expansion is vital for the economy, an argument Lockley said did not hold water if a true climate cost was factored into the equation.
Campaigners say only about one quarter of flights are for business reasons.
"At the predicted rate of expansion, aviation will account for all of Britain's emissions target by the middle of the century," said Patrick Gillett of Plane Stupid.
Aircraft manufacturers have improved planes' fuel efficiency in recent years, and trials are under way to power them with biofuels, but most airlines are counting on emissions trading and carbon offsetting to balance most of their impact.
Such schemes come at a cost, but nearly two thirds of those polled by the IoD said they were willing to pay 5-10 percent more for a business flight on environmental grounds.
A bill going through parliament and expected to become law within three months commits the government to cut emissions of carbon dioxide, the main climate change culprit, by at least 60 percent from 1990 by 2050 and by 26-32 percent by 2020.
Environment Secretary Hilary Benn has promised to look at raising the end target to 80 percent.
Editing by Peter Millership