The act of approving a pipeline is relatively simple: the federal cabinet makes a decision, an official memorandum is sent over to Rideau Hall and the governor general signs it.

It’s merely everything else about the extraction and transportation of oil in the 21st century that’s complicated and burdened by emotional arguments about economic welfare, national unity, climate change and the future condition of the planet. The stuff of sit-ins and marches and shouting.

Late Tuesday afternoon, Justin Trudeau strode onto the stage at the National Press Theatre to announce the official niceties of deciding were done, whatever might ensue.

“Prime Minister Trudeau is showing some extraordinary leadership today,” declared Alberta Premier Rachel Notley, who was in Ottawa to respond to Trudeau’s decision to reject the Northern Gateway pipeline, and approve the Line 3 pipeline and, most controversially, the Trans Mountain project.

“I am profoundly disappointed with today’s decision,” countered Gregor Robertson, the mayor of Vancouver, near where the Trans Mountain pipeline would come to an end.

Interim Conservative Leader Rona Ambrose said approving Trans Mountain was just the beginning for Trudeau.

“Now he needs to use his political capital to see this project built,” she said. “And I don’t think he has enough of it. I think that the protests will ensue. The fight is on.”

Trudeau didn’t hide his plans

If nothing else, it can’t be said the prime minister didn’t warn us he might do something like this.

A day after declaring his candidacy for leadership of the Liberal Party in 2012, Trudeau went to Calgary and said, “There is not a country in the world that would find 170 billion barrels of oil and leave it in the ground.”

A year later, he went back to Calgary and said he believed it was “a fundamental role of the Government of Canada … to open up markets abroad for Canadian resources, and to help create responsible and sustainable ways to get those resources to those markets.”

At some point that responsibility was personalized.

“It is a fundamental economic responsibility for the prime minister of Canada to help get our resources to global markets,” he told the Liberal convention in Montreal in 2014.

That principle was then put down in the natural resources minister’s mandate letter.

So unless the prime minister was ready to fail to meet his own standard, he was going to have to approve a pipeline that reached an ocean.

Yes to pipelines, yes to a price on carbon

But what Trudeau presented Tuesday was an environmental argument: his moral and economic case for acting to combat climate change.

His government would establish a national price on carbon and accelerate a phase-out of coal-fired electricity. This has always been the Trudeaupian bargain: yes to a price on carbon and yes to pipelines; doing the former so you can do the latter responsibly.

But more than that, Trudeau argued that developing Canada’s oil resources will help fund the transition to a cleaner economy.

The bargain is also political.

Trudeau stressed that Alberta’s climate policies, with its cap on emissions from the oil and gas sector, made it possible to approve Trans Mountain. And with a pipeline — through which Alberta will be able to access international prices for oil — Notley will be able to support Trudeau’s plan for a higher price on carbon.

That still leaves B.C. Premier Christy Clark and her five conditions for pipeline approval, though Trudeau addressed one of her concerns directly when he said he never would have approved Trans Mountain if he wasn’t assured the B.C. coast would be sufficiently protected.

Potentially just as pivotal was a commitment that new pipeline projects will fit into a plan that sees Canada meet its international commitments to reduce greenhouse gas emissions.

But there’s still the matter of the shouting.

Trans Mountain protests

“If Prime Minister Trudeau wanted to bring Standing Rock-like protests to Canada, he succeeded,” said Greenpeace’s Mike Hudema, referring to the pipeline fight in North Dakota that has become an international cause and recently featured police using water cannons against protesters.

Green Party Leader Elizabeth May told reporters she’s willing to be arrested for blocking construction.

“I think we are under no illusions,” Trudeau said, “that the decision we made today will be bitterly disputed by a number of people across the country who would rather we had made another decision today.”

So what happens if, a year or two from now, there are indeed people lying down in front of bulldozers?

It will be argued the process for reviewing Trans Mountain was insufficient.

Indigenous concerns — though several Indigenous groups support the proposed pipeline — will be set against Trudeau’s promise of reconciliation.

And Trudeau’s previous insistence that it is communities that “grant permission” for pipelines could be used to claim a veto for any community in the pipeline’s path. Two B.C. Liberal MPs — Terry Beech and Ron McKinnon — have already said their constituents oppose Trans Mountain.

In theory, sound climate policies are supposed to provide “social licence” — or at least minimize the outrage. But this might be the first time anyone’s ever tried to make that calculation work in practice.

Trudeau insists Trans Mountain is in the national interest, a notion that could be said to trump any single objection. But it will be Trudeau who is held responsible for getting a sufficient number of the nation’s voters to agree.

“Obviously one of the great things about Canada is people are more than free to express their opinions, to express their disappointment with governments in peaceful ways and we expect them and encourage them to,” Trudeau said.

“That is our right as Canadians, but at the same time, we know that this decision is the right one for Canadians.”

That will be debated at some length and at some volume.

“I have a feeling,” Trudeau said in parting, “we’re going to be talking about this for a while to come.”