Canada has imposed a landmark carbon tax on four provinces which had defied Ottawa's push to combat climate change, prompting unhappy premiers to say they would challenge the measure.
Prime Minister Justin Trudeau, citing international commitments to fight global warming, had made clear for two years he would slap the tax on any of the 10 provinces that did not come up with their own plans by April 1.
The measure is opposed by Ontario, the most populous province, where Trudeau's Liberals need to do well to retain power in October's federal election.
Carbon pollution will initially cost $C20 ($US15) a tonne, rising by $C10 a year until it reaches C$50 in 2022.
"As of today, it's no longer free to pollute anywhere in Canada," Environment Minister Catherine McKenna said.
Official data shows Canada has little chance of meeting its climate change goals of reducing emissions by 30 per cent from 2005 levels by 2030.
Canada will heat up twice as fast as the rest the world, with northern regions warming at an even greater pace, a Canadian environment ministry report said.
Smaller snow packs and a loss of glacier ice could mean water supply shortages in the summer, it added.
Although Ottawa said the money collected from the next tax will be returned to Canadians in the form of rebates, right-leaning parties portray it as a cash grab.
The Conservatives, who polls show could win the October election as a political scandal dogs Trudeau, promise to scrap the measure.
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