OTTAWA (Reuters) - Greenpeace activists scaled a bridge in the Canadian capital on Wednesday and unfurled two large banners urging U.S. President Barack Obama to take a tough stand on Canada's huge oil sands when he visits on Thursday.
"Climate Leaders Don't Buy Tar Sands" read one of the banners, which faced toward Parliament. The oil sands represent the largest reserves outside the Middle East, but extracting the heavy crude from the sands releases enormous amounts of greenhouse gases, blamed for global warming.
Obama -- who has vowed to spend billions developing cleaner sources of energy -- is due to spend a few hours in the houses of Parliament while in Ottawa on his first foreign visit since taking power last month.
"President Obama and the American public need to know that tar sands produce the dirtiest oil on earth ... the tar sands are an international global warming disaster," said Mike Hudema of Greenpeace.
The problem for Obama is that Canada is the largest single supplier of energy to the United States. Canadian oil production last year was 2.75 million barrels a day, of which the oil sands accounted for just under half.
Speaking to the Canadian Broadcasting Corp on Wednesday, Obama declined to characterize crude from the sands as "dirty oil" which should somehow be curtailed.
He acknowledged the sands create "a big carbon footprint" and said the United States and Canada should collaborate on ways to capture carbon and then store it to prevent greenhouse gases from being emitted into the atmosphere.
Separately, a group of 50 prominent Canadians sent Obama an open letter on Wednesday saying it would be wrong to have much faith in such untried methods.
"Costly and unproven technological fixes such as carbon capture and storage do not provide 'silver bullet' solutions to addressing emissions from tar sands," the letter said.
Reporting by David Ljunggren; editing by Rob Wilson