When Justin Trudeau swept into power in 2015, he pledged to make fighting climate change a top priority for his government.

Three years later, Canada’s prime minister is on the defensive, scrambling to both revive his party’s unravelling climate strategy as a growing number of provinces refuse to participate in national carbon tax – and to temper frustrations over his government’s continued investment in the fossil fuel industry.

“From the beginning, [the government] decided they were going to try to thread the needle on the need for climate policy and fossil fuel resource development. They even made the two interdependent,” said Matthew Hoffman, a political science professor at Toronto’s Munk School of Global Affairs.

But on the surface, the strategy appears to be quickly falling apart.

Trudeau’s political foes have already seized on the carbon tax in anticipation of the upcoming federal election – still a full year away – but the prime minister has shown no signs of backing down.

“Pollution should not be free anywhere across this country,” he said last week.

The political infighting comes as the UN’s intergovernmental panel on climate change warned that drastic changes are needed to offset the impacts of global climate change.

As part of a strategy to reduce Canada’s emissions, provinces are required to introduce a tax of at least $20 per tonne on emissions from January 2019, with increments of $10 each year until 2022.

In provinces which fail to produce an adequate carbon pricing plan, the federal government would implement its own tax, or “backstop”.

Last week, Manitoba became the fifth province to publicly opt out of carbon pricing, arguing that its own plans to combat climate change were sufficient.

Saskatchewan, which still relies heavily on coal for its power, has called the carbon tax a “ransom note”.

In Ontario, Canada’s most populous province, the rightwing premier, Doug Ford, has vowed to rally opposition to the measure, which he described as “the worst tax ever”.

Alberta, home to the country’s oil sands, announced it would leave the plan after the federal government failed to push through construction of the Trans Mountain expansion pipeline – a project Alberta argued was critical to its economy.

“Until the federal government gets its act together, Alberta is pulling out of the federal climate plan,” said Premier Rachel Notley in August. “And let’s be clear, without Alberta, that plan isn’t worth the paper it’s written on.”

Only two provinces, British Columbia and Quebec, have signalled a willingness to remain in some form of carbon pricing agreement.

When the original agreement was laid out, many of the provinces had Liberal politicians in power. Now, a conservative wave across the country has changed the party in power – and the political calculus.

Construction on the Kinder Morgan pipeline was halted over the summer. Photograph: Ben Nelms/Reuters

“This is a political move by the provinces. It’s conservatives wanting to give the Liberals a black eye,” said Nelson Wiseman, a professor of Canadian studies at the University of Toronto. “If you ask people, ‘Should the government do something about climate change?’ they’ll say yes. If you ask them, ‘Are you prepared to pay higher taxes?’ they’ll say no.”

The recent stumbles, however, could end up being a benefit for Trudeau, argued Mark Cameron, director Clean Prosperity, an environmental thinktank.

“If anything, this may end up making the carbon price backstop more effective,” he said. “Instead of one or two provinces that are going to be falling under it, there will be four or five. You’ll be getting a more coherent national carbon pricing system.”

Carbon taxes are supposed to be revenue neutral, meaning any increase a person pays are offset elsewhere. With its own carbon tax, the federal government could circumvent antagonistic provincial governments and deliver cheques – as high as $600 per year– to individual households. “The [upcoming federal] election is going to be in October,” said Wiseman. “Imagine, in July, people start getting cheques in the mail!”

Experts agree that any plan to fight the tax is probably a losing battle: courts have repeatedly affirmed the right of the government to impose a tax on provinces. “Whether that court victory leads to political victory is another question altogether, said Hoffman. “[Trudeau’s] got to build popular support for this.”

As he grapples with carbon pricing, Trudeau is also engaged in a delicate task of placating his environmental supporters over frustrations that oil development is detrimental to emissions reductions.

Construction on the Trans Mountain pipeline expansion, which the government purchased from Texas-based Kinder Morgan, was halted over the summer by a federal court order, largely the result of inadequate consultations with indigenous communities.

The government remains committed to pushing the pipeline through – and recently hired a retired supreme court justice to buttress its consultations with First Nations.

“The idea that the environment and the economy are not opposing goals, is a great framing,” said Hoffman. “But it’s tough to do when you’re framing the economy not as a transformed economy in a low-carbon world, but as further exploitation of fossil fuel resources.”