Prime Minister Stephen Harper says it is unlikely that Canada will join the United States in a pledge to meet tough new targets for greenhouse-gas emissions over the coming decade.

Canada has historically matched its targets with those set south of the border, a bar that was raised late last month when the U.S. said it would cut emissions by 26 per cent to 28 per cent by 2025, relative to 2005 levels, and is on track for an 80-per-cent cut by 2050.

However, at a media event in Winnipeg on Thursday, Mr. Harper suggested the lock-step approach with the U.S. is about to end.

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"It's unlikely our targets will be exactly the same as the United States'. But they will be targets of similar levels of ambition to other major industrialized countries," the Prime Minister said. "And I will just say, broadly speaking, that there will have to be additional regulatory measures going forward to achieve these targets."

It was unclear what types of regulations the government is contemplating. As recently as December, Mr. Harper said regulating carbon emissions in the oil industry would be "crazy" at a time of depressed crude prices.

Canada's environmental record is likely to be raised often by the opposition in advance of a fall election.

A report last week prepared by Environment Canada suggested this country had little hope of meeting its international commitment to reduce greenhouse-gas emissions by 17 per cent from 2005 levels by 2020. That pledge was made by Mr. Harper at a climate summit in Copenhagen six years ago.

Canada's post-2020 targets will be released in May, the Prime Minister said. That means they will be known in advance of a meeting of G7 leaders scheduled for Germany in June at which climate change is expected to be high on the agenda. Countries around the world are also in the process of drafting an international agreement on climate change that is to be adopted in Paris later this year.

Louise Comeau, the executive director of the Climate Action Network Canada, said she fears Canada will now try to meet the emissions targets of nations that have adopted a far more lax approach to greenhouse-gas reduction than that of the U.S.

Japan has already indicated its goals will be weak, Ms. Comeau said. After the Fukushima nuclear disaster of 2011, Japan started phasing out nuclear energy and phasing in coal, she said. Coal plants are a major international source of carbon dioxide emissions. According to a recent analysis, Japan is considering reducing emissions of greenhouse gases by around 20 per cent by 2030, Ms. Comeau said. "That's just so not acceptable."

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Mr. Harper said the federal government decided to hold off setting emissions-reductions targets for the country until after premiers met earlier this month in Quebec City to discuss climate change. "As you know, the provinces didn't actually announce any targets, so we will obviously move ahead," the Prime Minister said.

In fact, the premiers did not intend to set targets at the Quebec meeting. Rather, it was a forum for provinces to share information about what they are doing on climate change. It took place a day after Ontario Premier Kathleen Wynne and Quebec Premier Phillipe Couillard struck a deal for Ontario to join Quebec's cap-and-trade system.

Mr. Harper said that whatever steps his government takes to reduce emissions, they will not involve carbon taxes. "The reason governments do carbon taxes is not so they can reduce emissions, it's so they can get more tax revenue in the government's pocket," he said.