Listen carefully to Prime Minister Justin Trudeau's pipeline proclamations and a few words make repeat appearances: "consultation," "rigour" and "science."

That's more than just the language of public relations. The federal Liberal leader knows his rationalizations for killing or approving projects that affect millions of lives also have to stand up in court.

Courts get the last word

Beyond all the public forums, protests and political posturing, the death knell for Enbridge's Northern Gateway pipeline from Alberta to Kitimat, B.C., was ultimately rung last summer in the Federal Court of Appeal, whose judges ruled the Crown failed to properly consult the First Nations affected by the pipeline.

That's right, former prime minister Stephen Harper had thought his approval meant something as well.

If the Trans Mountain pipeline from Alberta to Burnaby, B.C., is to move ahead, the project will have to clear the same constitutional legal hurdles that felled Northern Gateway, in addition to challenges related to the environment.

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First Nations opponents took to the streets as well as the courts following the Harper government's approval of the Enbridge Northern Gateway pipeline in 2014. (Reuters)

That puts an already controversial project into the middle of one of the hottest and most tangled legal arenas in the country.

"We're seeing that while government may make a decision, government decisions are not the last word anymore, and the last word on some of these really big contentious projects is going to be the courts," says Ecojustice lawyer Karen Campbell.

"The courts have an incredibly important role. They've got to be there as a backstop for bad environmental decision-making or bad consultation."

'Meaningful' consultation essential

Well before the National Energy Board ruled on Northern Gateway, it was widely accepted that the project would live or die in the courts.

And sure enough, within days of the NEB giving its approval, legal challenges started piling up.

The Supreme Court of Canada found the Crown has a duty to consult and accommodate First Nations about projects affecting their rights in a 2004 case involving the B.C. Haida Nation.

The standard is "meaningful" consultation.

Keystone pipes

The Federal Court of Appeal found last summer that the Crown had failed to meaningfully consult with First Nations over the Enbridge project. (Alex Panetta/Canadian Press)

University of British Columbia Indigenous legal studies director Gordon Christie says that doesn't mean First Nations have to agree with the Crown's position. But talks have to meet some form of third-party standard for success.

Interestingly, the Appeal Court found no fault with efforts at consultation made by Enbridge itself. But the Crown can't download its duties to corporations.

The court said Ottawa's efforts "left entire subjects of central interest to the affected First Nations, sometimes subjects affecting their subsistence and well-being, entirely ignored."

You can argue the Appeal Court's decision gave Trudeau licence to pass on a project he didn't really want to approve anyway.

Christie says the decision has clear implications for the fate of the Trans Mountain expansion.

"You'd think [the government] would learn their lesson at some point," he says.

"I would think that at some point people within the government would sit down and say, 'What do we need to do? Let's do it,' instead of playing these games that end up not working in their interest in the long term."

Outside the 'ken of the courts'?

Like other environmentalists, Campbell celebrated the Appeal Court's overturning of Northern Gateway. But the same ruling may yet turn out to be a double-edged sword.

Even as the decision provided a victory for Indigenous groups, it marked a defeat for advocates who argued Harper had ignored environmental considerations and climate change in approving the project.

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Environmentalists claim the National Energy Board has failed to consider the Species At Risk Act in approving the Trans Mountain project at the expense of southern resident killer whales. (Dave Ellifrit/Centre for Whale Research)

The court dismissed them outright, saying cabinet was "entitled to assess the sufficiency of the information and recommendations it had received, balance all the considerations — economic, cultural, environmental and otherwise — and come to the conclusion it did."

"To rule otherwise would be to second-guess the Governor in Council's appreciation of the facts, its choice of policy, its access to scientific expertise and its evaluation and weighing of competing public interest considerations, matters very much outside of the ken of the courts," the ruling said.

Consider that conclusion for a moment in light of the challenges Campbell's clients have raised to the Trans Mountain pipeline.

They claim the NEB failed to consider Species At Risk Act in approving a project that would potentially doom the southern resident killer whale population to extinction.

They also say the project has failed to address the impact nearly tripling the flow of oil through the Trans Mountain pipeline would have on Canada's international climate change commitments.

But if all that is deemed to fall outside "the ken of the courts" then who is to say what's right and wrong?

'Ultimately political decisions'

An array of independent tribunals and laws are tasked with assessing the effects of projects like the Trans Mountain and Northern Gateway pipelines.

Campbell says her organization has made its name going to court to force government to consider the input of those outside bodies.

"These are ultimately political decisions, and it makes sense that those decisions are ultimately made by cabinet. Because that's who's accountable," she says.

"Our concern is that if and when cabinet makes those decisions, they do it transparently and they do it accountably."

Environmentalists have appealed to the Supreme Court of Canada in a bid to overturn the part of the Enbridge decision that defers to the wisdom of cabinet.

You can bet that Trudeau's lawyers have parsed every word of that ruling front, back and sideways.

Hence the language of his approval: "This is a decision based on rigorous debate on science and evidence. We have not been, and will not be, swayed by political arguments."

We trust politicians to uphold laws meant to protect all of us. But sometimes it takes a court to remind them just how that's done.