Former U.S. vice-president and climate change crusader Al Gore is praising Ontario's cap-and-trade system, calling it better than a carbon tax.

Gore, who sat down with Premier Kathleen Wynne in a one-on-one interview in front of hundreds of students at Ryerson University on Thursday, says the way Ontario currently fights climate change is the "superior" system.

He says cap and trade lets government work directly with emitters to cut carbon emissions over time.

Carbon pricing is shaping up to be a key issue in the province's spring election, with all four candidates vying to lead the opposition Progressive Conservatives vowing to scrap cap-and-trade and fight the imposition of a federal carbon tax, if they're elected June 7.

Al Gore and Ontario Premier Kathleen Wynne sat down for a conversation at Ryerson University in Toronto on Thursday. (Martin Trainor/CBC)

Gore praised Wynne for her Liberal government's efforts to fight climate change and took a shot at the Tory leadership hopefuls, saying their proposals would set the province back.

Ontario's cap-and-trade system, launched last year, is aimed at lowering greenhouse gas emissions by putting caps on the amount of pollution companies in certain industries can emit. If they exceed those limits they must buy allowances at quarterly auctions or from other companies that come in under their limits.

'Optimism and hope'

Among the university students were around 200 students from various high schools who were invited to the talk in downtown Toronto. They each hailed from one of Ontario's nearly 2,000 certified EcoSchools — a program which "focuses on environmental action and learning," according to Lindsay Bunce, the executive director of Ontario EcoSchools.

"Access to leadership like this, and access to innovation and ... the reinforcement of the positivity and optimism around climate change is so critical for these students to hear," she told CBC Toronto.

"It was critical that an event like this is focused on optimism and hope."

Juliana Melino, left, and Darren Joseph are students at Francis Libermann Catholic High School, one of nearly 2,000 EcoSchools in the province. (Martin Trainor/CBC)

Juliana Melina and Darren Joseph, students at Francis Libermann Catholic High School, both attended the talk on Thursday.

"[Gore] really told us that we had to take action, that we can and that we will or should," said Melina.

Joseph explained that his school is holding an environmental conference this year, and that they regularly host cleanups around the property.

"We've done so much, and we want to follow in Al Gore's footsteps to be a better school and to make a better world," he said.