No catastrophic financial hit required to fight climate change, scientists say in landmark court case

Canada does not need to shut down its industries or take a catastrophic financial hit to effectively fight climate change, one of the country's leading climate scientists testified during a landmark trial in a Vancouver courtroom this week.

Canada needs to transform its energy system and prepare for a new, low-emissions future, said Simon Donner, a professor at the University of British Columbia who has been a major voice on climate science and policy for years.

"It's going to cost money to change technologies, to transform the way we do some things. But there's also benefits, because that means the new technologies are things that can also make you money," Donner told the court Tuesday.

Donner was testifying as witness for the 15 youth plaintiffs who are suing the federal government, arguing that Ottawa is violating their constitutional rights by not doing enough to reduce carbon emissions and ensure a livable future.

Simon Donner is a leading climate science and public policy researcher at the University of British Columbia. (Don Erhardt)

The government, whose witnesses will testify next week, is expected to argue that Canada's action cannot be sufficiently linked to the climate harms facing the plaintiffs as climate change is a global problem. In their cross-examination of Donner, the government's lawyer asked him if specific carbon molecules in the atmosphere, and therefore specific climate impacts, could be linked back to Canada.

"No one ever thinks about a pollution problem this way," Donner said in response.

"If you have a whole bunch of factories that have pipes dumping mercury into a lake, no one is looking at, 'Did my specific molecule of mercury, is that the one that led to the death of this fish?'"

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Donner's message is familiar — he has been speaking about the need for decarbonization and contributing to international and Canadian climate policy for over a decade — but his courtroom platform is new, reflecting the recent trajectory of climate action under Prime Minister Mark Carney's government.

Feds, climate advisory body at odds

Donner was the co-chair of the Net-Zero Advisory Body, an independent panel of experts established by Justin Trudeau's government in 2022.

The body was supposed to guide the government's climate plan, but in 2025, Donner and Catherine Abreu, another member, publicly quit and said their advice was not being sought or considered by the government as it tried to fast-track approvals for LNG and other fossil fuel and mining projects.

The NZAB is now down to three members, from a potential size of 15, and its work is in "remission" according to Damon Matthews, one of the remaining members and a climate scientist at Concordia University.

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Matthews told CBC on Tuesday that the NZAB does not have the resources to fulfill its mandate, and that there has been minimal communication from the government since the last election. Though, he said NZAB is currently in talks with the federal environment minister on a path to revive its work.

Matthews has contributed a report on behalf of a group of youth applicants in another climate lawsuit targeting the Ontario government.

"Maybe the legal system is a way that we can put some brakes on the headwinds that are trying very hard to stall, delay, and prevent climate action in this country," he said.

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Scientists outline path to lower emissions

Donner has been joined by several prominent Canadian scientists testifying in the Vancouver courtroom on behalf of the youth plaintiffs. The trial is currently in its second week, with witnesses for the plaintiffs testifying.

The government's witnesses, which include experts in climate science, law and economics, will testify from Nov. 9 to Nov. 20. After that, the court will take a pause and return in February, when lawyers for both sides will make their closing statements.

Last week, Kirsten Zickfeld, a professor of climate science at Simon Fraser University, took the witness box to speak about the carbon budget, which is the amount of carbon emissions that can be emitted before global warming reaches unsafe levels.

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Canada, as one of the 10 largest carbon emitters in the world both currently and historically, has already surpassed its fair share of the carbon budget, she testified.

"To stabilize global average temperature, global carbon dioxide emissions need to be reduced to at least net zero and the emission of other greenhouse gases such as methane and nitrous oxide need to be strongly reduced," she said.

In the coming week, University of Ottawa professor Nicholas Rivers, a prominent expert in climate policy and economic modelling, will testify on pathways to achieve lower emissions.

Youth should be 'planning their futures, not fighting in court'

Many of the youth plaintiffs also testified about how climate disasters have affected their lives. Most of them were in their tweens or teens when the case was first filed in 2019; since then they have lived through disasters like the 2023 Yellowknife wildfires, the 2021 B.C. heat dome, major floods, drought and poor air quality from fire smoke.

Donner's testimony focused on research from government reports and climate attribution studies that says such disasters will become more severe and frequent if emissions don't come down.

"These are stories that so many Canadians have either lived firsthand or know people who have been through those types of impacts," said Andrew Gage, staff lawyer at West Coast Environmental Law, which is supporting the case.

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Tzeporah Berman, a Canadian climate campaigner, says the timing of the trial is remarkable both because climate disasters have become so obvious and frequent — at the same time that the federal government is scaling back action on reducing emissions.

"I've heard a lot of people this week saying they admire [the youth plaintiffs]. We owe our youth more than admiration, we owe them action," said Berman, who chairs the Fossil Fuel Non-Proliferation Treaty Initiative, which seeks to build global agreement on ending the use of oil, gas and coal.

"These young Canadians should be planning their futures, not fighting in court to protect the possibility of having one."