The leader of Canada’s biggest oil-producing province has declared she sees no long-term future in fossil fuels, predicting Alberta would wean itself off dirty energy within a century.

In an early reveal of her forthcoming new energy policy, Alberta’s Rachel Notley said she would fight climate change by cleaning up the tar sands, shutting down coal-fired power plants, and converting to wind and solar power.

Notley also forecast an eventual future beyond fossil fuels – a dramatic change for Alberta - and a track that has put her on a collision course with Canada’s conservative prime minister, Stephen Harper.

The Alberta leader is due to unveil the new policy ahead of the international UN climate conference in Paris this December.

The province sits atop the world’s third-biggest known carbon reserves in the tar sands, and has rapidly ramped up production to some 2 m barrels of crude a day. By 2020, the province will account for more than a third of Canada’s total carbon pollution, according to government figures.

Notley, whose election last May broke the Conservatives’ 44-year lock on power in the province, said she intends that to change. “I don’t think we are defined by energy. Certainly in the short to medium term that is an asset that we have, so we have to look at how we develop it carefully and responsibly because of the obligation we have to the people employed in the industry,” she told the Guardian.

She went on: “Do I see that as our reason for being 100 years from now? Well, I hope we will have learned a lesson of diversification by then.”

Notley visited Montreal, New York, and Toronto this week to try to persuade investors that Alberta under her leadership was committed to cleaning up tar sands production and tackling climate change.

The Alberta leader will try to make a similar case to the international community when she attends the Paris climate summit.

Canada is regularly held up as a climate super villain at the international climate negotiations. Harper pulled Canada out of the Kyoto climate protocol, and launched a quest to become an energy super power, blowing through emissions reductions targets.

Meanwhile, campaigners have targeted tar sands, together with coal, as particularly dirty forms of energy, because of its energy-intensive extraction and its widespread destruction of boreal forests.

Notley admitted Alberta would be squeezed to fight climate change while protecting jobs in the oil patch at a time of low energy prices. “It’s a bit of a conundrum,” she said.

“I want to change the direction, bend the curve and do it as effectively as we can while maintaining jobs that are important to Alberta. People deserve to see government both at the federal and provincial levels that are committed to very significantly changing the rate of greenhouse gas emissions coming out of both Alberta and Canada.”

Such pronouncements have put Notley at odds with Harper. The free market conservative, who is up for re-election on 19 October, has called Notley a “disaster”.

Over the last decade, Harper has championed his vision of Canada as an energy super power and lobbied aggressively in Washington and European capitals for more pipelines to get tar sands crude to market.

Harper’s opponents say the hardball tactics backfired. In an election debate this week, Harper was repeatedly accused of alienating Barack Obama and other US officials with hard arm promotion of the controversial Keystone XL pipeline project.

Notely has said in the past she is opposed to Keystone XL – but not other pipelines.

Her main focus now was getting the oil industry to clean up its act, Notley told the Guardian.

“We need to do much better with greenhouse gas emissions,” she said. “We need to take our environmental responsibilities seriously if we are going to have support for our products in other markets that have greater environmental concerns.”

The Alberta leader is expected to unveil new targets for reducing greenhouse gas emissions later this autumn, after hearing from an expert committee.

Notley also committed to phasing out Alberta’s coal-fired power plants, which provide more than 40% of the province’s electricity, converting to renewable energy, and putting a meaningful price on carbon.

The shift on energy and climate has won praise from environmental organisations – but Notley is facing a tough climb.

“She is starting from basically a blank slate,” said Simon Dyer, regional director of the Pembina Institute. A poll released on Wednesday from the environmental think tank found a majority of Albertans favoured strong policies to cut greenhouse gas emissions, even if it meant higher production costs for oil sands companies.

He noted that Alberta was one of the few regions in the US and Canada without programmes promoting wind and solar energy. “The premier is saying we are going to be a leader on this but obviously we are coming from very far behind in the pack,” he said.

Mike Hudema, a climate campaigner for Greenpeace, was reserving judgment. “I don’t think we are going to see anything reducing the rampant emissions coming from the tar sands,” he said. “The big reason they want a stronger climate policy is to increase market access. I don’t think the government has come to grips with the scientific reality that three-fourths of all fossil fuels will need to remain in the ground.”

The Alberta leader caused some unease this week when she said Alberta would not support the national cap-and-trade scheme put forward by Tom Mulcair, the federal New Democratic Party leader.

However, Notley said the reluctance was due to the idea of funds leaving the province, not capping emissions.

“Generally speaking cap and trade as one strategy is a bit problematic for us,” she said. “It would turn into a fairly major cash transfer from Alberta to other places … We are going to be more focused on a strategy that allows us to take investment that goes into reducing emissions and keeping it in Alberta.”