Image caption Sea level rise was once mainly due to thermal expansion of the oceans, but the melting of Greenland and Antarctica has now taken over as the principal driver

For the first time in more than a decade, climate change is at the forefront of a federal election campaign in Canada. Can Justin Trudeau again win the heart of environmentally minded voters?

Swedish climate activist Greta Thunberg had words for Liberal leader Justin Trudeau: - the Canadian Prime Minister is "obviously not doing enough" on climate change.

The 16-year-old schoolgirl has earned a reputation for speaking truth to power - but Mr Trudeau nonetheless chose to meet her on Friday before she led the climate strike march in Montreal.

"I agree with her entirely," said Mr Trudeau later. " We need to do more."

The Liberal leader has been laying out increasingly ambitious climate policies this week on the federal campaign trail - though they lacked key details on how they would be achieved - from a commitment to reach net-zero emissions by 2050 to a vow to plant two billion trees over the next decade.

It's not the first time Ms Thunberg expressed frustration at Canada's climate policies.

In June, parliamentarians passed a motion put forward by the Liberal environment minister declaring a national climate emergency.

The next day, the Liberal government approved the controversial Trans Mountain pipeline expansion project.

On Twitter, Ms Thunberg called it "shameful".

On the campaign trail, his political opponents also weighed in on Mr Trudeau's environmental record.

"Justin Trudeau is protesting his own government's record of failure," retorted Conservative leader Andrew Scheer, referring to the Liberal leader's participation in the Montreal climate march.

The Green Party dismissed the new Liberal goals as "greenwashing".

Mr Trudeau says if re-elected on 21 October, his government "will not only meet our 2030 targets, but exceed them".

This federal election is the first in over a decade in Canada where climate has been at the forefront - and it's taking place amid renewed international pressure on world leaders to act.

What are the parties promising on climate?

Liberals: Net-zero emissions by 2050; exceed Canada's 2030 emissions goal.

Conservatives: Repeal price on carbon. Fund and export green technology innovation, meet current Paris targets.

NDP: Bring in emissions targets in line with keeping global warming to 1.5C; end oil and gas subsidies.

Green Party: Reduce by 60% greenhouse gas emissions to below 2005 levels by 2030; net-zero emissions by 2050.

Canadians are anxious about climate change - an effect seen across regions, ages and genders.

Sébastien Jodoin is a professor at Montreal's McGill University, whose research focuses on looking at social and legal solutions to complex problems like climate change.

He says he thinks Canadians have "changed their minds" on climate over the last few years due to a growing awareness of the severe weather predicted to accompany rising temperatures.

In Quebec, large scale flooding in recent years has hammered the message home. The province is currently working on new rules for construction in areas prone to inundation.

Image copyright Reuters Image caption The Liberals faced criticism from environmentalists for supporting the Trans Mountain oil pipeline project

Other Canadian provinces are seeing costs related to extreme weather events balloon.

Alberta had two of the most costly disasters in Canada's history in recent years - the 2016 Fort McMurray wildfires and major floods in 2013.

But climate and energy issues have been driving a wedge between provinces in recent years.

Quebecers are among the most environmentally-minded Canadians. The province also has lower per capita emissions than other provinces, mainly due to its vast hydro power reserves.

British Columbia - especially the coastal regions of the province - also has a strong green bent.

Both provinces strongly oppose oil pipeline project within their own jurisdiction, putting them at odds with land-locked, oil-producing Alberta.

University student and climate marcher Nina Blancas, 20, told the BBC in Montreal that she wanted political leaders who would move Canada away from its dependence on energy intensive natural resources.

"Invest in innovation, invest in change," she said.

Canada is the fourth largest producer and exporter of oil in the world.

Image copyright Getty Images Image caption The effects of a changing climate are being seen more acutely in Canada's Arctic

Most of those reserves are in Alberta's oil sands, which account for 11% of Canada's total greenhouse gas emissions and 0.1% of global emissions - as well as hundreds of thousands of jobs and billions in government revenue.

Oil producers and analysts say increased pipeline capacity is necessary to boost the industry, allowing it to export its product to globally and to command higher prices.

Albertan Miles Matulinios told the BBC in Calgary that both the environment and the economy need to be considered by policy makers.

"Canada's strength is natural resources, so the most important thing is we can't just ignore that," he said. "People still need to eat and live, so I think it has to be a balance."

François Geoffroy, a Quebec college professor and one of the activists behind the Montreal strike, says one of their top demands is for climate laws to be put in place that would force governments to reach their emissions targets.

"Once we have that, we can have a discussion together about how we want to achieve these goals," he said. "But these goals should not be optional, they should be mandatory. That's what the science says that we need to achieve."

Canada's emissions are currently higher than they were in 1990, though down slightly from levels seen in the early 2000s.

"We don't have time for empty promises anymore," says Mr Geoffroy. "The time for speeches is over."

Canada - a country of 37 million people - is among the world's top 10 emitters of greenhouse gases as well as one of the world's largest per capita emitters.

Mr Jodoin said Liberal governments in Canada from the 1990s to the early 21st century made grand commitments on climate action but with few real results.

And under former Prime Minister Stephen Harper, who governed from 2006 to 2015, Canada formally abandoned the Kyoto protocol, a legally binding international agreement setting targets for industrialised countries to cut their greenhouse gas emissions.

Mr Harper was critical the deal failed to include the US and China, the world's largest emitters.

Despite the withdrawal Canada continued to participate in global climate talks, though it was frequently criticised as being an uncooperative participant.

Canada is currently not on track to meet its Paris Agreement targets to reduce its greenhouse gas emissions by 30% below 2005 levels by 2030.

According to the Climate Action Tracker, Canada's efforts are "insufficient" and "not consistent with holding warming to below 2°C, let alone limiting it to 1.5°C as required under the Paris Agreement".

Analysts have said Mr Trudeau's main climate policy - a national carbon tax imposed on provinces without an equivalent plan already in place - is capped too low, at C$50 ($38; £30) by 2020, to ensure Canada meets its targets.

Image copyright NurPhoto via Getty Images Image caption Canada has high per capita emissions

"If we just go with their current policies, they're inadequate," said Mr Jodoin.

Mr Trudeau's federal Liberals also took the rare step last year of buying the Alberta-to-BC Trans Mountain oil pipeline for C$4.5bn ($3.4bn; £2.6bn) to help ensure a project to expand its capacity goes ahead.

While there has been daylight between Mr Trudeau's promises and his policy, Mr Jodoin did say "the measures [the Liberals have] taken - they're the most ambitious we've seen in Canada".

He calls the Conservative plan, which would cancel Mr Trudeau's carbon tax and focus on the innovation and export of green tech innovation as "more a shield than a sword - they just don't want to be seen that they're doing nothing".

Mr Jodoin says he is cheered by the fact that climate has become a high-profile political issue, but is still skeptical that it will truly be a deciding factor for many voters.

"I'm not sure how many people are really voting on this specific issue and assessing the climate science," he said.

With contributions from the Canadian Press