The Cap and Trade Cancellation Act (CTCA) was enacted by the province of Ontario in 2018. It repealed the Climate Change Mitigation and Low-Carbon Economy Act, which had established an emission reduction target of 37% below 2005 levels by 2030 in the province, and implemented a revised target of 30% below 2005 levels by 2030. In response, Ecojustice assisted seven youth environmental activists who filed an application against Ontario, contesting the constitutionality of CTCA. The Applicants argued that the revised target did not adequately address the risks associated with climate change, thereby violating the rights of Ontario youth and future generations as protected by sections 7 and 15 of the Canadian Charter of Rights and Freedoms. They contended that their section 7 right to life, liberty, and security of the person was infringed due to the perilous and existential threats posed by climate change to the lives and well-being of Ontarians. The Applicants maintained that their section 15 right to equality was violated because the revised target created a distinction based on age, imposing a greater burden on younger Ontarians who would endure the long-term impacts of climate change. They sought a declaration that the revised target was unconstitutional and an order requiring Ontario to establish a revised emissions target grounded in scientific principles, consistent with Ontario’s commitments under the Paris Agreement.

On April 15, 2020, Ontario filed a motion seeking to dismiss the case on the grounds that the claim was not justiciable. Ontario argued that determining emissions reductions was inherently political and thus unsuitable for judicial review. On November 12, 2020, Justice Brown of the Ontario Superior Court denied the motion, finding that it was not immediately apparent that the revised target would be immune from court scrutiny. 

In September 2022, the lawsuit proceeded to a hearing on its merits before the Ontario Superior Court. On April 14, 2023, Justice Vermette of the Ontario Superior Court determined that while the Applicants’ claim was justiciable, there was no violation of the Applicants’ sections 7 and 15 Charter rights. Regarding section 7 of the Charter, Justice Vermette found that the province’s revised target for reducing greenhouse gas (GHG) emissions was not arbitrary, as it was linked to the objective of GHG reduction under the CTCA. With respect to section 15 of the Charter, Justice Vermette concluded that the provision did not impose a positive obligation on the provincial government to take any specific actions to combat climate change. The Ontario Superior Court, therefore, dismissed the case. 

The applicants appealed to the Court of Appeal for Ontario in May 2023. On October 17, 2024, the Court of Appeal for Ontario released its decision unanimously in favor of the appeal. The Court found that the applicants’ case was not a positive rights case but rather a negative rights case because they were not requesting that Ontario implement specific climate change actions. Instead, they contended that the greenhouse gas emissions targets set by the Minister under the CTCA violated their Charter rights. In other words, by enacting the CTCA, the Ontario government voluntarily assumed a positive statutory obligation to combat climate change in a way that complies with the Charter. Given the lack of a complete evidentiary record, the ONCA declined to determine the applicants’ case on its merits and remitted the application for further consideration by the lower court.

On December 16, 2024, Ontario sought leave to appeal the Court of Appeal's decision to the Supreme Court of Canada. On May 1, 2025, however, the Supreme Court denied leave, leaving the Court of Appeal’s order remitting the matter to the Ontario Superior Court for a new hearing on the applicants’ Charter claims in place. 

Before that rehearing occurred, Ontario enacted legislation repealing provisions of the Cap and Trade Cancellation Act that were central to the litigation. The applicants then moved to reopen the appeal, arguing that the Court of Appeal should decide additional constitutional issues in light of the repeal. 

In Mathur v. Ontario, 2026 ONCA 561, released on August 5, 2026, the Court of Appeal dismissed that motion. The Court held that reopening the appeal was not justified and that the appropriate next step remained further proceedings before the Superior Court, which would determine, among other things, whether the case could continue notwithstanding the repeal of the impugned legislative provisions.

Mathur et al. v. His Majesty the King in Right of Ontario

<p>This entry was provided by the Sabin Center for Climate Change Law. Please see the terms of use for citation and licensing of third party data.</p>

Mathur et al. v. His Majesty the King in Right of Ontario - complaint

Filed

Canada

Ontario

The Climate Litigation Database

Find climate change litigation data and indicators for {text}.

{text} litigation

Sabin Center for Climate Change Law provides Climate Litigation Database, a comprehensive database of US and Global climate change caselaw

Quickly and easily search through the complete text of thousands of climate change law and policy documents from every country.

Search the Climate Litigation Database

An aim to achieve a quantifiable outcome within a given time-frame, set by an institution such as a national government.

Policy instruments are techniques or tools used by governing authorities to promote certain policies in order to achieve predetermined goals. Put simply, instruments are how a government tries to achieve its goals, with this taxonomy being focused on national policy instruments.

Risk is the potential for adverse consequences resulting from the dynamic interplay between (climate-related) hazards, exposure, and vulnerability of affected human or ecological systems.

Groups  of people who are adversely affected by climate change or the response to it

A set of principles, processes, and practices that build economic and political power to shift from an extractive economy to a regenerative economy.

Justice is the ethical and political framework that addresses fairness, including issues of responsibility, rights, and structural inequity.

Renewable energy means all forms of energy produced from renewable sources in a sustainable manner.

Fossil fuel is a generic term for non-renewable energy sources such as coal, fossil gas, and oil (including crude oil, and petroleum products), that can be used for electricity and heat generation. Fossil fuels are hydrocarbons formed from pressurised and heated organic material buried over millions of years.

Molecules in the atmosphere that play a key role in the greenhouse effect by trapping heat radiating from Earth’s surface.

Area of the economy in which actors engage in identical or related activities.

In human systems, the process of adjustment to actual or expected climate change and its effects, in order to moderate harm, increase resilience or exploit beneficial opportunities. In natural systems, the process of adjustment to actual climate change and its effects; human intervention may facilitate adjustment to expected climate change and its effects.

The management and allocation of funds, assets and investments to meet various objectives

People who are less able to respond to the effects of climate change due to having limited financial or physical assets

A tax advantage is a fiscal incentive where the government reduces or exempts selected activities, goods or actors from taxes.

A subsidy is a direct or indirect payment to individuals or businesses, typically provided as a government cash payment or a specific tax reduction.

Tradable permits are market-based tools that grant permission for specific activities, frequently used to regulate emissions. These permits can be issued within a trading system to manage environmental impacts.

A target to reduce the prevalence of a greenhouse gas over a specific time frame

A commitment to balance GHG emissions with removal by a certain point in time, effectively reducing the net emissions to zero

Hot temperature extremes are daily maximum temperatures  that were exceeded on average once in a decade or once in 50 years, and includes heatwaves.

The release of heat-trapping gases, primarily from human activities such as burning fossil fuels, agriculture and industry.

A long-lived, colourless gas, chiefly emitted from fossil fuel combustion, deforestation and cement production.

Actions to reduce emissions in energy generation and supply.

Risks to the ecosystem health of the marine environment, including ocean warming, ocean acidification, and ocean deoxygenation, harming biodiversity, species health, ecosystem services, and coastal community livelihoods.

Extreme weather refers to events where a weather variable exceeds (or falls below) a threshold. Meaning it is significantly different from the average or usual weather pattern.

Terrestrial means "of the earth" and relates to the risks to ecological system that includes all living organisms and their interactions within land-based environments, such as forests, grasslands, and deserts.

Fossil gas, commonly known as natural gas, is a fossil fuel consisting chiefly of methane with smaller amounts of other hydrocarbons and trace gases, found in underground deposits.

People with different national or cultural traditions from the dominant population

Social and cultural groups that share collective ancestral ties to the lands and natural resources where they live, occupy or from which they have been displaced

People whose health, both mental and physical, makes them more vulnerable to the effects of climate change

This sector involves the wholesale and retail selling of goods.

This sector involves activities to move goods and people, alongside the storage of products.

This sector creates and distributes information and entertainment through television, radio, print, and digital platforms.

This sector involves activities that impart knowledge and skills to individuals, including formal schooling, vocational training and educational support.

Activities of government agencies and institutions that provide public services, enforce laws and manage public resources.

This sector includes firms and individuals offering specialised expertise in fields such as law, accounting, consulting, science and engineering.

Any substance with chemical properties that can cause physical harm to people or damage the environment, including ammonia, carbon monoxide, phosphine, chlorine, arsenic, cadmium, mercury, pesticides, dioxins, microplastics, benzene, asbestos, aflatoxins, fluoride, methanol, and toxins from marine sources.

Slow onset events evolve gradually from incremental changes over many years or from increased frequency or intensity of recurring events. As defined in the Cancun Adaptation Framework (2010), slow onset events include risks and impacts from rising temperatures, desertification, biodiversity loss, land and forest degradation, glacial retreat, ocean acidification, sea level rise, and salinization.

The cryosphere is the frozen part of the Earth—it includes sea ice, glaciers, snow, and ice sheets. It helps regulate the climate and weather by reflecting sunlight. Rising temperatures are causing melting, leading to sea ice loss, glacier collapse, and glacier landslides and avalanches. This threatens the livelihoods of around 700 million people who rely on the cryosphere for food, water security, and cultural practices.

Mathur et al. v. His Majesty the King in Right of Ontario - complaint

Target

Policy instrument

Risk

Impacted group

Just transition

Renewable energy

Fossil fuel

Greenhouse gas

Economic sector

Adaptation/resilience