Publication

Green Targets on Trial: Ontario v. Mathur

Published:

June 26, 2025

Author(s):

• Abigail Herrington
• Melanie Gillis

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On May 1, 2025, the Supreme Court of Canada denied leave to appeal in Ontario v. Mathur, a significant climate litigation case that brings youth applicants one step closer to challenging Ontario’s greenhouse gas emissions targets under the Canadian Charter of Rights and Freedoms. The Court’s decision means Ontario v. Mathur will proceed to a new hearing on the merits – the first Charter-based climate litigation in Canada to be litigated to its conclusion. And that means that, as the first decision of its kind, new ground will be forged whatever the outcome. 

Ontario v. Mathur has significant legal implications for future climate change litigation:

Constitutional Scrutiny of Emissions Targets. If successful, the applicants could secure a ruling requiring Ontario to implement a more ambitious emissions reduction target, potentially influencing other provinces to reassess their own targets.

Positive Rights & Government Obligations. The Ontario Court of Appeal’s handling of “positive rights” versus “negative rights” sheds light on how courts should evaluate government obligations to address climate change. The question of whether the Ontario Superior Court of Justice properly characterized the Charter challenge as one that would “…impose a freestanding positive obligation on Ontario…” was central to the appeal. The Court of Appeal overturned the Superior Court’s characterization of the Charter challenge as a positive rights case, finding that, since Ontario “…voluntarily assumed a positive statutory obligation to combat climate change”, it was therefore “obligated to produce a plan and a target that were Charter compliant”. This means that once they are in place, any voluntarily imposed targets that governments decide to put in place must not violate Charter rights. 

Impact on Indigenous & Youth Rights. The appeal decision highlights the fact that with the proper evidence, courts will consider not only climate change impacts themselves, but also the disproportionate impacts of climate change on young people and Indigenous communities.

Floods or Freezing for Future Claims. If successful, Ontario v. Mathur could open the floodgates for more challenges to government climate policies or failures to meet internationally recognized climate targets. If unsuccessful, however, the case could create a chilling effect on the use of this Charter-based avenue to pursue climate change litigation.

 The Case

In 2018, Ontario repealed its previous emissions reduction target and replaced it with a new, lower target: a 30% reduction in greenhouse gas emissions by 2030. A group of youth applicants, including Indigenous youths, argue Ontario’s reduced legislated target violates their Charter rights, specifically sections 7 (life, liberty, and security of the person) and 15(1) (equality rights), claiming that climate change disproportionately affects young people and Indigenous communities. The applicants claim the target falls short of international scientific consensus, which calls for reductions of at least 45% below 2010 levels by 2030.

The Legal History

The Ontario Superior Court of Justice initially dismissed the claim in a 2023 decision, concluding that: the applicants’ case was a “positive rights” claim (a claim asking the Court to require the government to do something to benefit certain communities) and not a “negative rights” claim (asking the Court to prevent government from violating one’s rights); the government’s actions were not contrary to principles of fundamental justice under section 7 of the Charter; and section 15 of the Charter did not impose a positive obligation on Ontario to take any specific steps to combat climate change.

The applicants appealed this decision. In 2024, the Ontario Court of Appeal disagreed with the Superior Court, finding the Superior Court’s incorrect characterization of the case as a positive rights case coloured its analysis of the applicants’ claims and the matter required a new hearing. Ontario sought leave to appeal the Court of Appeal’s ruling to the Supreme Court of Canada – and Canada’s highest court denied its application. The denial of leave to appeal means the Court of Appeal’s decision to remit the case back to the Ontario Superior Court of Justice for a new hearing stands. The case will now proceed in that Court, where the Court will decide whether Ontario’s emissions target violates the applicants’ Charter rights.   

5 Key Takeaways

Ontario v. Mathur underscores the increasing legal and regulatory risks associated with climate change policies – and the need for businesses and governments to remain agile and stay apprised of emerging legal trends that could affect the environmental policies that bear on their planning and operations.

Scrutiny of Provincial Emissions Targets. Ontario v. Mathur could lead to greater scrutiny of provincial emissions reduction targets. It’s critical that companies with operations intersecting with environmental legislation be aware of emerging decisions like Ontario v Mathur, which could require governments to adopt more ambitious climate policies.

Increased Legal Risks in Climate Litigation. While Ontario v. Mathur is a Charter challenge against a government policy, not a corporate policy, it is yet another example of the growing tide of climate-related legal action in Canada – and a signal to companies to be proactive in assessing the legal risks related to climate change policies.

Alignment With International Climate Standards: Ontario v. Mathur highlights the fact that courts are considering international scientific consensus and standards, such as those outlined in the Paris Agreement. Businesses with significant carbon footprints are wise to assess their own targets in light of international standards.

Awareness & Agility in the Face of Evolving Climate Regulations. As climate change litigation progresses, governments may be forced to revise their climate policies. This pressure on governments will of course have knock-on effects for companies trying to navigate the already choppy waters of climate change legislation. Staying apprised of consequential developments and being agile, resilient, and responsive in the face of these developments are key for companies to ensure compliance with evolving regulations.

Engagement in Policy Advocacy. Consider participating in industry-appropriate policy advocacy opportunities to help shape future climate policies. By participating in the dialogue surrounding the development of emissions targets and other climate-related regulations, companies can potentially inform the development of the ever-evolving legal framework in which they operate. In addition, early and direct engagement with impacted stakeholder groups can help to alleviate climate change litigation risk and should be considered as a risk mitigation tool for major projects.

Please contact your McInnes Cooper lawyer or any member of our Environmental, Social & Governance (ESG) Team @ McInnes Cooper to discuss mitigating the risks of climate change litigation.

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