A protest at the White House against a pipeline from the Alberta tar sands is emerging as the biggest green civil disobedience campaign in a generation, organizers said.
The campaign is seen as a last chance to persuade Barack Obama to stop a planned 1,600-mile pipeline that will carry oil from the tar sands of Alberta across rich American farmland to the Gulf of Mexico.
The State Department is expect to produce its final environmental analysis of the pipeline by the end of the month. Obama will then have 90 days to decide whether going ahead with the project would be in the national interest.
The Keystone XL project has been a major focus of environmental protests. Greenhouse gas emissions of tar sands crude are 40% higher than conventional oil, and the open-pit mining has devastated Alberta's boreal forest.
Recent pipeline accidents in Michigan and Montana have also deepened fears about potential dangers along the pipeline's route through prime American farmland.
The veteran environmentalist Bill McKibben, who is leading the protest, describes it as the biggest civil disobedience action in environmental circles for years.
It also puts Obama on the spot to make good on his promises as a presidential candidate in 2008 to act on climate change.
Congress failed to act on the main plank of Obama's green agenda – climate change legislation – and pressure from Tea Party activists has forced the Environmental Protection Agency to delay or weaken regulations on dealing with climate change.
This time though, Obama has freedom of action – or at least that is McKibben's hope.
Obama must personally sign off on the pipeline, if it is to go ahead. "We think we may have a chance because for once Obama gets to make the call himself. He has to sign – or not sign – the permit," McKibben said.
"As environmentalists this is the one clean test we are ever going to get of Obama's real commitment to climate issues."
The protest will begin at about 11am on Saturday morning when a first group of 100 activists will gather at the gates of the White House, an area that is supposed to be kept clear, and wait to be arrested.
Unlike other campaigns, the next fortnight's actions have geographical reach – with protesters descending on Washington from areas along the pipeline's route.
One group from eastern Texas, has hired an RV to make the journey.
The campaign against the pipeline has steadily been gaining in momentum amid concerns about pipeline safety.
The pipeline route crosses rich farmland and important aquifers.
Campaigners argue the thick heavy tar sands crude could do far more damage than conventional oil, and that the State Department has rushed through its environmental review.
The oil industry, meanwhile, pushed back with a study this week claiming the pipeline would create 20,000 new construction jobs.