The Liberal government formally ratified the Paris climate accord Wednesday, after easily beating back an effort from the Conservative opposition to give provinces the sole authority to deal with carbon pricing.

Members of Parliament comfortably approved a motion late Wednesday supporting both the United Nations agreement and the federal-provincial declaration issued last March in Vancouver that committed Canada to undertake the joint action needed to "meet or exceed" its Paris commitment to reduce greenhouse-gas emissions by 30 per cent from 2005 levels by 2030.

The ratification vote came as the UN reached a crucial threshold on Wednesday for bringing into force the Paris agreement, in which 194 countries pledged to limit the rise in average global temperatures to less than 2 degrees C above preindustrial levels, with an aim of less than 1.5 degrees.

Story continues below advertisement

On Monday, Prime Minister Justin Trudeau introduced the motion on the Paris accord with the announcement that Ottawa would require provinces to have a carbon-pricing plan – either a tax or cap and trade – in effect by 2018. Where premiers refuse to do so, Ottawa will impose a tax of $10 per tonne, rising to $50 per tonne in 2022, the equivalent of 11 cents per litre at the pump.

MPs continued to spar Wednesday over Ottawa's carbon-price plan, with Conservatives attacking it as an onerous tax and Liberals defending it as both necessary and flexible enough to allow provinces to use the resulting revenue to provide offsetting tax breaks.

Saskatchewan Premier Brad Wall kept up his social-media campaign against Ottawa's plan, saying it would hurt farmers and the mining and energy industries.

The federal Conservatives sought to introduce an amendment to the motion, saying carbon pricing should be left to the provinces and opposing a tax, but the Liberals and New Democrats voted together to defeat that attempt. Though he and his caucus voted in favour of the motion, NDP Leader Thomas Mulcair complained the government has embraced the former Conservative government's 30-per-cent target for 2030, which he characterized as too weak.

Debating the motion on Wednesday, Natural Resources Minister Jim Carr called climate change "the great challenge of our time."

"The Paris agreement highlights the urgency of our environmental responsibility while pointing us toward new economic opportunities," Mr. Carr said.

"It speaks to the necessity of co-operation toward a common goal. The agreement also reflects a compelling reality that while the transition to a lower-carbon future might be long, the trajectory is clear. We simply cannot continue along the present course."

Story continues below advertisement

In order to come into force, the agreement needed formal support from at least 55 countries representing 55 per cent of global emissions. The European Union formally submitted its ratification on Wednesday taking the accord over that threshold and meaning it will go into force in 30 days – just before the U.S. presidential election.

Republican nominee Donald Trump has promised to scrap the deal, but it could take four years for the United States to withdraw. If he wins in November, Mr. Trump could undermine the agreement by withholding promised financing to developing nations and gutting environmental laws aimed at meeting U.S. emission-reduction commitments.

Democratic nominee Hillary Clinton supports the Paris accord.

UN officials and national governments can now begin the mammoth task of implementing the accord, including putting in place monitoring and verification mechanisms to ensure countries are doing what they claim to be doing.

Environmental groups welcome the UN milestone, but said governments need to increase their ambition and their actions if the world is to meet the 2-degree target, let alone the 1.5-degree one.

In a statement on the White House lawn, President Barack Obama applauded the coming-into-force of the agreement. Mr. Obama has said climate change is likely to cause severe environmental strains that will be "enormously destructive" and "terrifying."

Story continues below advertisement

"The Paris agreement alone will not solve the climate crisis," he said. "Even we meet every target embodied in the agreement, we'll only get to part of where we need to go. But make no mistake: This agreement will help delay or avoid some of the worst consequences of climate change. … This gives us the best possible shot to save the one planet we've got."