He joined representatives of the Canadian Arctic Resources Committee, Alternatives North, Sierra Club and Pembina Institute in a conference call with reporters.
Ewins compared the situation to the late 1970s, when a judge, Thomas Berger, banned pipeline development in the vast, sparsely populated region for years so native groups and the government could solve numerous land claims.
Now, regulators should demand that a network of protected areas and a comprehensive land-use plan is in place before a pipeline that would open up the region to major oil and gas operations goes ahead, Ewins said.
"As most Northerners have been saying, 'We sort of do want a pipeline now, but not at any cost,"' he said.
The Mackenzie proposal would ship up to 1.9 billion cubic feet of gas a day 1,200 km (750 miles) to southern markets from the Mackenzie Delta on the Beaufort Sea Coast.
It has been hit with a number of setbacks, leading at least one of the proponents to question its viability publicly. Earlier this year, Imperial and its partners, Royal Dutch Shell, ConocoPhillips, Exxon Mobil, and the Aboriginal Pipeline Group, more than doubled the cost estimate, blaming runaway inflation in labor and materials costs as well as regulatory delays.
They are in talks with Ottawa aimed at winning some financial breaks to improve the project's economics.
The hearings, conducted by the Joint Review Panel and National Energy Board, were originally slated to wrap up at the end of 2006.
Imperial's application should deal with impacts of exploration beyond the three fields that will feed the pipeline initially as well as the carbon dioxide emitted when the gas is burned in its end use, said Sierra Club lawyer Keith Ferguson.
Matt McCulloch, co-director of the Pembina Institute's corporate consulting division, said carbon dioxide from the Mackenzie gas project and the fuel's end use would push Canada's greenhouse gas emissions 10 percent further away from its Kyoto Protocol commitment.
Canadian emissions are already 30 percent above the target of 6 percent below 1990 levels, McCulloch said.