TORONTO — Canada's highest court is set to decide whether it will hear arguments in a trailblazing climate change lawsuit that could clarify whether governments are constitutionally required to tackle planet-warming emissions.
Thursday’s decision could set the stage before the Supreme Court of Canada in a case where seven young people have challenged Ontario’s weakened climate target.
The group has argued the revised target commits the province to dangerously high greenhouse gas levels, in a way that jeopardizes their right to life and forces them to bear the brunt of future climate impacts.
The case is the first in Canada where a court, in a full hearing, considered whether a government climate plan could violate the Charter of Rights and Freedoms.
Ontario asked the Supreme Court of Canada to weigh in on the case, saying it raises questions of national importance about whether governments are constitutionally required to fight climate change.
Even if the Supreme Court decides not to hear the case, the climate activists are set to see their challenge revived with a new hearing in the lower courts.
What’s at stake?
Legal experts say the case could fundamentally alter how governments are held to account on climate change.
Before this case, courts had dismissed citizen-led Charter challenges of climate targets on preliminary grounds, often because they found them to be too broad or too political. Despite Ontario's attempts to have this case tossed out on similar grounds, the seven young people made history.
It was the first case in Canada to consider – in a full hearing, with piles of expert evidence on the risks of global warming – whether a government's climate plan could actually violate the Charter.
Here's one way to think about it, says climate law expert Stepan Wood: it's a case about whether governments can choose whatever target they believe to be politically expedient, or whether choosing one out of line with accepted science amounts to threatening life and discriminating against young people.
"This case is really important for basically the trajectory that Canada is headed in terms of combating climate change and whether or not, as a country, we will be able to avoid the worst, most catastrophic impacts of climate change on a timescale that is meaningful, especially for young people," said Wood, Canada Research Chair in law, society and sustainability at the University of British Columbia's Allard School of Law.
What are the details of the case?
In 2019, at the height of the youth-led wave of climate activism, 12-year-old Sophia Mathur and six other young people joined together to challenge Ontario's watered-down emissions target.
The group alleges the target commits the province to dangerously high levels of planet-warming greenhouse gases, in a way that jeopardizes their right to life and discriminates against them as young people who will bear the brunt of future climate impacts.
Ontario brought in a new emissions target in 2018 after scrapping the law underpinning its cap-and-trade system. It replaced the target in that law – 37 per cent below 1990 levels by 2030 – with a new aim of 30 per cent below 2005 levels.
The young people brought evidence to show the revised target could allow for 30 additional megatonnes of annual emissions, the equivalent emissions from about seven million cars every year from 2018 to 2030.
They asked the court to direct Ontario to set a science-based target consistent with what would be necessary to meet Canada's international climate commitments.
The Ontario Superior Court agreed the target fell "severely short of the scientific consensus" on what would be sufficient. By not taking steps to further reduce greenhouse gases, Ontario was contributing to an increase in the risk of death faced by the young people, the judge said in a 2023 ruling.
The court also dismissed the province's argument that its share of global emissions was so small as to have a negligible impact. That argument could be applied to all individual sources of emissions in a way that would "impede collective action and hinder the solving of global problems," Justice Marie-Andrée Vermette wrote.
What have the courts decided?
The initial judgment ended up turning on a question at the heart of constitutional legal theory and one that courts continue to grapple with to this day: could the Charter ever require a government to act to preserve our rights, or does it just restrain it from violating them?
Here's that question again, but applied to this case: did the government's emissions target potentially endanger life, or did it just not go far enough to protect it?
Lawyers for the climate activists recognized this as a fraught distinction and tried to argue it was the former, in line with more traditional Charter claims.
But Vermette, the trial judge, sided with Ontario instead. The ruling suggested the young people were trying to impose a “freestanding” obligation on the province to fight climate change. The target didn’t increase emissions, it just allegedly didn’t do enough to reduce them, the ruling said.
The young people appealed to Ontario’s highest court and won.
The Court of Appeal for Ontario agreed with the young people's framing of the case: the government had voluntarily chosen to fight climate change, and it needed to do it in a way that did not violate the Charter.
With that new framing in mind, the court sent the case back to Vermette for a new hearing. But Ontario instead decided to ask Canada's top court to weigh in.
In court filings, Ontario says the case raises three pressing questions: does the government have a constitutional obligation to fight climate change; does the Charter require a government target be set to a minimum standard; and does it require the government to follow a particular process to establish that standard?
Wood, the UBC legal expert, says the Supreme Court deciding not to hear the case could be seen as positive for the activists' chances. It would go back to a hearing before the trial judge with the favourable Appeal Court decision standing as precedent.
Then again, punting the case back to the lower courts only for it to potentially wind up back in front of the Supreme Court down the road, may mean more time spent without clear court direction, said Nathalie Chalifour, a University of Ottawa law professor.
"Every year that goes by, the climate emergency worsens and we shut out options, we risk passing tipping points that are irreversible on a human time scale," said Chalifour, who was also a lawyer for an intervener, environmental group Friends of the Earth, when the case went before the Ontario Appeal Court.
"The sooner we hear these matters the better," she said.
Are there other cases similar to this one?
Climate litigation around the world has "exploded" in recent years, said Chalifour.
"And what we're seeing is that Canada is becoming increasingly an outlier," she said.
Courts in other countries have been quicker to accommodate climate cases, Chalifour said.
The Netherlands' top court ruled in 2019 that the government had a duty to protect citizens from the potentially devastating effects of climate change. Last year, a group of older Swiss women won their case before the European Court of Human Rights, which found the government had failed to uphold its duty to fight climate change and meet emissions targets.
In Canada, there's another major case that's been working its way through courts alongside the Ontario challenge. That case, known as La Rose, challenges the federal government's climate actions.
Catherine Boies Parker, a lawyer on that case, said she will be watching closely to see whether the Supreme Court weighs in on the Ontario case.
"I think that those international cases are interesting and helpful, even though they may be based on a different framework. I think some of the principles are still going to be transferable to a Canadian context," said Boies Parker.
"The point is whether or not the government is acting in a manner that's consistent with protecting people in the most basic freedom of all, which is to live in an atmosphere that can sustain them."
This report by The Canadian Press was first published April 30, 2025.
Jordan Omstead, The Canadian Press
