Mathur v Ontario: The Ontario Court of Appeal orders rehearing of unprecedented climate case

November 4, 2024 | Christie A. McLeod, Lara Jung

On October 17, 2024, the Ontario Court of Appeal (the “ONCA”) issued its highly anticipated ruling in the case of Mathur v Ontario.[1]  In a unanimous decision, the ONCA found that the application judge wrongly interpreted the applicants’ arguments as seeking to have the court impose positive obligations on the Ontario government to combat climate change in a way that upheld their rights to life, liberty, security, and equality under sections 7 and 15 of the Charter of Rights and Freedoms (the “Charter”). The ONCA held that a correct view of the case would find that the Ontario government, by passing legislation, had voluntarily undertaken a positive obligation to address climate change in a manner consistent with the Charter.

The ONCA declined to render a final decision in the case and instead remitted the matter back to the application judge.

Decision of First Instance

The case was first heard at the Ontario Superior Court of Justice (which we discussed in a previous issue). Seven young climate activists, aged 12 and 24 at the time, filed the application, arguing that the Ontario government’s new emissions reduction target (the “Ontario Target”),  set pursuant to the Cap and Trade Cancellation Act (the “Cancellation Act”), violated young peoples’ Charter rights under sections 7 and 15. While Ontario’s previous target had required the province to reduce its emissions by 45% below 2005 levels by 2030, the new Ontario Target mandates only a 30% reduction by the same year.

With respect to section 7, the applicants asserted that the impacts of climate change, characterized by the expert evidence as “existential” risks, engaged the rights to life, liberty, and security of the person, as protected under section 7 of the Charter.[2] The argument that these risks are, and continue to be, overwhelmingly borne by youth underpinned the applicants’ related submission that, by imposing disproportionate burdens on Ontarians based on age, the Cancellation Act violated their equality rights under section 15 of the Charter. In short, the applicants submitted that the inadequate emissions targets set pursuant to the Cancellation Act would result in a disproportionate increase in climate-related threats to young people’s lives and personal security.

In her judgment released in April 2023, Justice Vermette dismissed the application, ruling that the Cancellation Act did not violate sections 7 and 15 of the Charter, as alleged by the applicants. She interpreted the applicants’ section 7 arguments as urging the court to impose positive obligations on the Ontario government to protect the applicants from the harmful effects of climate change, but declined to decide whether section 7 could be used to impose such obligations. This was based on her conclusion that any deprivation of section 7 Charter rights was not contrary to the principles of fundamental justice.[3]

Regarding the applicants’ section 15 argument, Justice Vermette held that they failed to demonstrate that the Ontario Target created a distinction based on an enumerated or analogous ground, finding that youth are disproportionately impacted by climate change, not by the Ontario Target or the Cancellation Act.

On Appeal

The three judges who heard the Mathur case on appeal held that Justice Vermette had wrongly characterized the central issue of the application as a question of positive rights.[4] The applicants were not asking the court to impose a positive duty on the state to fight climate change. Instead, they argued that by enacting the Cancellation Act and the Ontario Target, the Ontario government had knowingly and voluntarily assumed a positive obligation to address climate change.[5] The ONCA cited the established legal principle that, although the Charter does not charge governments with positive obligations to maximize every person’s right to life, liberty, and security, any legislative scheme a government enacts must be constitutionally valid and comply with the Charter.[6] In the ONCA’s view, the crux of the case was whether the Ontario Target, as part of the legislative scheme voluntarily enacted by the government, caused emissions to rise to a level that jeopardized section 7 and 15 Charter rights. If it did, the Ontario Target and Cancellation Act would be found to have violated the Charter.

In describing the errors of law made by Justice Vermette, the ONCA indirectly provided guidance for the rehearing of the case. Regarding her section 7 analysis, the ONCA reiterated that Justice Vermette’s framing of the case as one involving positive rights led her to err in her analysis of whether the risks posed to the applicants’ section 7 rights by the Cancellation Act and the Ontario Target violated the principles of fundamental justice against arbitrariness and gross disproportionality. With respect to her section 15 analysis, the ONCA held that Justice Vermette should have considered whether, in setting the Ontario Target (which she acknowledged was too low to satisfy target levels recommended by the scientific community), the Ontario government “committed itself to a level of greenhouse gas emission that will create or contribute to a disproportionate impact on the basis of an enumerated or analogous ground” under section 15 of the Charter.[7]

In addition, the ONCA confirmed that, upon rehearing the case, the judge would have jurisdiction to grant the declaratory relief sought by the applicants. Accordingly, Justice Vermette, sitting anew, would be able to declare that the Ontario Target violates Charter rights without offending the doctrine of separation of powers, and it would be open to her to provide a legal framework for a climate policy that complies with the Charter. The court could also order Ontario to enact new legislation containing a “constitutionally compliant” emissions target, which, in the ONCA’s view, the Ontario government could easily calculate based on international standards and scientific consensus on the correlation between climate change and greenhouse gas emissions.[8]

After clarifying the issues to be determined, the ONCA concluded it was not the appropriate body to decide the case and remitted it back to Justice Vermette. The ONCA concluded its judgment by inviting the appellants to amend their pleadings to include issues raised by the interveners, including the rights of Indigenous peoples under s. 35 of the Constitution Act, so that these issues may be considered at the rehearing of the case.[9]

Takeaways & Conclusion

For decades, there has been a scientific consensus that our world is warming due to human actions, yet global emissions continue to increase. In Canada, national emissions increased by 16.5% between 1990 and 2022.[10] The newly released United Nations Emissions Gap Report details that the world is headed towards 3.1°C of warming by 2100 based on the mitigation effects implied by current policies.[11] This is significantly higher than the global commitments set out in the Paris Agreement to limit global warming to well below 2°C above pre-industrial levels, and to pursue efforts to further limit warming to 1.5°C to reduce the risks and impacts of climate change.[12]

Young people face the greatest threat to their futures due to our governments’ ongoing failures to reduce emissions and limit global warming. By bringing this case, the applicants have drawn important attention to the climate crisis and how it disproportionately impacts youth and future generations, as well as the inadequacy of the Ontario government’s emissions reduction target.

The unanimous decision by the ONCA serves as a warning to governments across Canada that climate legislation is not exempt from the requirement to adhere to the Charter. Legislative efforts to combat climate change, including setting or modifying emissions targets, cannot infringe on Charter rights. By passing the Cancellation Act and publishing an emissions reduction target, the Ontario government committed to take action on climate change and is obligated to ensure that these actions comply with the Charter.

At the Ontario Superior Court of Justice, Justice Vermette firmly rejected the Ontario government’s argument that the Ontario Target was “meaningless.”[13] The ONCA echoed Justice Vermette’s finding that Ontario’s failure to set a more stringent emissions target contributed to an increase in the risk of death and security of the person.[14] With this ruling, governments may face challenges in convincing courts that their policies and actions do not contribute to climate change.

The Mathur decision also confirms that climate policies are reviewable by the courts. Judges are empowered to declare legislation as violative of the Charter but are not obligated to provide direction to the government on how to remedy the violation. Regarding climate legislation, the ONCA implied that governments should have no difficulty calculating and setting emissions targets that align with international requirements and comply with the Charter. The ONCA echoed Justice Vermette’s finding that, to align with climate science, the Ontario government would need to reduce its 2005 emissions by approximately 52% (i.e., 22% more than the 30% reduction outlined in the Ontario Target) by 2030. The gap between the science-based target and the Ontario Target was described as “large, unexplained and without any apparent scientific basis.”[15]

Both Mathur judgments demonstrate the courts’ acceptance of the overwhelming evidence that climate change poses real and urgent threats to future generations, and align with the Supreme Court of Canada’s finding that the climate crisis “poses a grave threat to humanity’s future.”[16] This recent decision offers hope to the applicants for a successful outcome in the rehearing of this case and may inspire additional lawsuits challenging the adequacy and constitutionality of climate targets and policies across the nation.


[1] Mathur v Ontario, 2024 ONCA 762 (“Mathur: 2024 ONCA”).

[2] Mathur v Ontario, 2023 ONSC 2316 at para 167 (“Mathur: 2023 ONSC”) .

[3] Mathur: 2024 ONCA, at para 47.

[4] Mathur: 2024 ONCA, at para 49.

[5] Mathur: 2024 ONCA, at para 5.

[6] Mathur: 2024 ONCA, at para 40.

[7] Mathur: 2024 ONCA, at para 58.

[8] Mathur: 2024 ONCA, at para 70.

[9] Mathur: 2024 ONCA, at para 78.

[10] Government of Canada, “Greenhouse Gas Emissions” (last modified 2 May 2024), online: <www.canada.ca/en/environment-climate-change/services/environmental-indicators/greenhouse-gas-emissions.html>.

[11] United Nations Environment Programme, “Emissions Gap Report 2024: No more hot air… please! With a massive gap between rhetoric and reality, countries draft new climate commitments” (2024), at 33, available for download online: <https://doi.org/10.59117/20.500. 11822/46404>.

[12] “Paris Agreement to the United Nations Framework Convention on Climate Change”, (12 December 2015), TIAS No 16-1104, 3156 UNTS 54113, at Article 2(1)(a).

[13] Mathur: 2023 ONSC, at para 123.

[14] Mathur: 2024 ONCA, at para 62.

[15] Mathur: 2023 ONSC, at para 146; Mathur: 2024 ONCA, at para 23.

[16] References re Greenhouse Gas Pollution Pricing Act, 2021 SCC 11, at para. 2.

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