A five-billion-U.S.-dollar proposal by U.S. energy giant Kinder Morgan, which will nearly triple the capacity of its pipeline bringing oil from Alberta to the British Columbia coastline, dominated talks at Earth Day celebration in Vancouver on Sunday.

The company currently operates the Trans Mountain pipeline that brings about 300,000 barrels of oil per day from Alberta's tar sands to a marine terminal in the Vancouver suburb city of Burnaby. What has many local residents upset about the proposed expansion is the increased volume of tanker traffic it would create in the city's pristine harbor.

If approved, the pipeline capacity would be increased to about 700,000 barrels daily with the oil exported to energy-hungry markets in the U.S. and Asia. Vancouver Mayor Gregor Robertson, who has set a goal of making the city the greenest in the world by 2020, said the plan presents too much risk for potential ecological disaster.

"There cannot be risk and cost piled on to our local community to serve industry in another province, particularly. So we have to make sure that those liabilities and those costs are addressed and I don't think it fits what Vancouver is today and what our compelling future is," he told those gathered at a local park for the Earth Day.

Kinder Morgan's proposal also calls for the expansion of its Westridge Marine Terminal. For tankers to get the Burnaby facility requires sailing through Vancouver's picturesque harbor while passing under three bridges, including a particularly tight rail bridge where oceanographer Peter Baker claims the clearance between the ocean floor and the biggest tankers with a capacity of 700,000 barrels is less than 1.5 meters.

The pipeline giant also wants to dredge areas of the Second Narrows, the site of both vehicle and rail bridges, as part of its plan that if approved would be operational by 2017.

Kinder Morgan said earlier it would file its application to initiate a regulatory review with Canada's National Energy Board by 2014. It would also have up to two years of community engagement with aboriginal groups, environmental groups and other interested parties along the 1,150-km pipeline.

While control of Canada's harbors is under federal jurisdiction, and the ruling conservative government keen to export the country's abundant oil resources, Robertson said he was sure that the majority of Vancouverites don't share Ottawa's enthusiasm and will oppose the expansion.

"I think we are going to see this community rise up in opposition to it. We have a very strong healthy economy here in Vancouver, it will be threatened by potential oil spills and a completely different vision of an economy that is on its way out on this planet right now," said the mayor.

"We have to exercise our voice in every way that we can, whatever legal tools and creative work we can do. We have to make sure that the federal government and the provincial governments understand it's not okay here in Vancouver."