TORONTO – Climate change is an international emergency and political leaders across the globe -- including Canada -- aren’t doing enough to confront the crisis, Swedish teen activist Greta Thunberg told a Montreal crowd on Friday.

“If the people in power won’t take their responsibility, then we will,” Thunberg told a crowd of hundreds of thousands, including many children who skipped school to attend the rally.

Liberal Leader Justin Trudeau marched alongside protesters in Montreal and met privately with Thunberg, who he thanked for “pushing us all to do more.” NDP Leader Jagmeet Singh and Green Party Leader Elizabeth May also attended climate demonstrations.

Conservative Leader Andrew Scheer was the only leader of a major federal party to skip the event.

Thunberg encouraged climate strikers to put pressure on their leaders to take decisive action on climate change before it’s too late.

Last fall, the Intergovernmental Panel on Climate Change called for governments to act rapidly to limit global warming to 1.5C. Scientists say greenhouse gas emissions need to significantly drop by 2030 and reach near net zero globally by 2050.

“If the people in power won’t take their responsibility, then we will,” she said. “We are the change, and change is coming.”

Thunberg has been mocked by some of the world's most powerful people, including U.S. President Donald Trump, who dismiss her calls to climate action as the musings of silly school girl.

Following Thunberg's remarks, CTV News' Lisa LaFlamme asked the teen activist how she feels about being attacked by grown men in powerful positions.

"I don't understand why grown-ups would choose to mock children and teenagers for just communicating and acting on the science when they could do something good instead," Thunberg said.

"I guess they must feel like their views or interests are threatened by us. That is, we should take as a compliment that we are having so much impact and that the people want to silence us, we've become too loud for people to handle so they try to silence us."

Thunberg said she told Trudeau the same thing she tells all world leaders.

"Just listen to the science," she said.

Asked why he didn’t attend the event, Scheer instead touted his party’s plan to invest in public transit projects, a promise he described as a “real, concrete” way to lower emissions by making sure “people will be stuck in traffic less.”

Scheer also used the opportunity to attack Trudeau.

“He’ll be marching with so many people today who realize that his plan is not as advertised, it will lead to higher costs of living, while not achieving our targets,” he said.

In conjunction with the march, Trudeau promised that a Liberal government would plant 2 billion trees over the next 10 years – a plan the Liberals say would help take carbon out of the air and “hold ecosystems together.”

On Twitter, the Green Party dismissed the Liberal’s promise “cute.” May, who is running on a platform to ban gas-powered cars by 2030 and eventually shut down the oil industry, said her party’s platform is the only one capable of meeting the IPCC’s bold climate targets.

May, who is running on a platform to ban gas-powered cars by 2030 and eventually shut down the oil industry, lauded the countless children across the world who skipped school to demand action from leaders.

“We are at the point where years, decades of procrastination have brought us to a place where we’re running out of time,” May said.

“This is a very significant moment and assuming we succeed, the future generations can look back at this and say, ‘This is when our kids saved us.’”

Speaking in B.C., Singh reiterated his party’s promise to fight the Trans Mountain pipeline extension, a plan he says would protect the province’s coastline from the possibility of an oil spill.

“One spill would devastate the entire environment,” he said.

MARCHING ACROSS CANADA

Climate marches began early in St. John's, N.L. as crowds marched to Memorial University's clock tower. The march is set to make its way to the provincial legislature on Confederation Hill.

More than 80 cities across the country are capping off a week of international protests and a call for action for governments to do more to slow climate change.

In Halifax, hundreds of people, including large groups of students from Dartmouth High School, gathered in Victoria Park for the protest. The Halifax march's route is expected to wind through the centre of the city to the headquarters of Nova Scotia Power, where some of those participating planned to participate in a so-called "die-in."

In New Brunswick, students staged a mass walkout at Samuel de Champlain School in Saint John.

Sept. 20 was the kick-off for a week of climate activities, with two global climate strikes planned on Sept. 20 and Sept. 27. The UN emergency climate summit was held on Sept. 23, in between the two climate strike dates. The global strikes were inspired by #FridaysForFuture, a movement following Thunberg’s call for students to strike.

Demonstrators in Toronto arrived at the Ontario legislature ahead of the 11 a.m. protest. Mayor John Tory said on social media the city's iconic Toronto sign will not be lit today in solidarity with all those taking part in #ClimateStrikeCanada.

More than 600 students at the University of Calgary were expected to walk out of morning classes and parade down to city hall for a rally scheduled for noon. With just weeks until the federal election, the group is calling for a Green New Deal and demanding climate policies from all candidates.

In Vancouver, the city said it's expecting about 10,000 people to join the mass climate strike. Protestors are meeting at 1 p.m. local time at Vancouver City Hall before marching over the Cambie Street Bridge to the Vancouver Public Library at Georgia and Hamilton streets, CTV News Vancouver reported.

School districts in Vancouver and Surrey allowed students to attend the strike as long as they had parental permission.

Emily Carr University of Art and Design cancelled all classes Friday afternoon to allow students to participate.

The University of British Columbia and Simon Fraser University said students who planned on taking part should discuss their plans with instructors.

Three Canadian retailers will also take part and shutter operations for the climate strike.

The 22 MEC stores in Canada will be closed on Friday until 5 p.m. local time to allow staff the opportunity to participate in protests.

Another Vancouver-based company, Lush Cosmetics , made a similar decision. The toiletry maker said it will shut down its 50 shops, manufacturing facilities and online shopping in Canada on Friday in an effort to encourage its 2,216 staff and customers to participate in local actions.

An Indigo Books & Music Inc. spokesperson says the retailer's home office teams in Toronto and Montreal will have the opportunity to participate.

At the UN’s global summit last Monday, Thunberg said the current plans to tackle the climate crisis do not take it seriously enough, saying that the strictest emission cuts being talked about would only give the world a 50 per cent chance of limiting future warming to another 0.4 C, which is a global goal.

“We are in the beginning of a mass extinction,” Thunberg warned world leaders. “And all you can talk about is money and fairytales of eternal economic growth. How dare you!”

A climate report put out this week says that oceans are becoming more acidic and warmer, glaciers are shrinking, new illnesses are breaking out due to warming waters, and by 2060 it is estimated that coastal floods off British Columbia and the Maritimes that used to occur once a century will be annual events.

With files from CTV News.ca’s Alexandra Mae Jones and The Canadian Press