International Law and Climate Change – Federal Court Decision in Lho'Imggin v. Canada

The Federal Court’s recent decision in Lho'Imggin v. Canada adds further guidance to existing case law regarding how governments in Canada may potentially face liability for climate change. Specifically, the decision raises implications for how international law can affect climate lawsuits in Canada.

In its decision, the Federal Court struck a climate-related claim against the Canadian federal government, for the second time, for not disclosing a reasonable cause of action. However, the Federal Court allowed the plaintiffs to amend their claim to plead a common law tort claim against Canada for an alleged breach of customary international law. It did so based on consideration of the International Court of Justice’s (“ICJ”) recent advisory opinion on the Obligations of States in Respect of Climate Change (the “ICJ Opinion”), which had addressed the legal obligations of states to mitigate climate change.    

Background on Customary International Law

The ICJ is the principal judicial body of the United Nations and is empowered to provide advisory opinions on legal questions. The ICJ can address matters of customary international law, which is a source of international law that arises from legal norms that develop through widespread and consistent practice that states follow out of a sense of legal obligation. Over time, these norms can crystallize into binding rules of law, even in the absence of treaties or other formal instruments.

The ICJ Opinion was released in July 2025, and notes the customary duties on states to prevent significant harm to the environment, to co-operate for the protection of the environment, and to protect human rights. These obligations extend to transboundary harm and require states to avoid activities under their jurisdiction that cause significant damage to the environment of another state.  The ICJ Opinion makes certain pronouncements with implications not only for states, but also for private actors such as corporations subject to state jurisdiction. For example, the ICJ was “of the view that a risk of significant harm may also be present in situations where significant harm to the environment is caused by the cumulative effect of different acts undertaken by various States and by private actors subject to their respective jurisdiction or control, even if it is difficult in such situations to identify a specific share of responsibility of any particular State.” The ICJ Opinion identifies obligations of states to regulate the activities of private actors, noting that states may be responsible for failing to take necessary measures to limit emissions caused by private actors under their jurisdiction. Among other things, the ICJ Opinion found that customary international law imposes obligations on states to protect the environment from human-made greenhouse gas (“GHG”) emissions.

Canadian courts, in particular the Supreme Court of Canada in Nevsun Resources Ltd. v. Araya,  have recognized the significance of customary international law within Canadian law. In Nevsun, three Eritrean workers claimed damages against a Canadian mining company for alleged breaches of customary international law resulting from being indefinitely conscripted through Eritrea’s military service, and forced to work at a mine in Eritrea under violent, cruel, inhuman, and degrading conditions. The mine was owned by a Canadian company, which sought to strike the pleadings, contending that claims grounded in customary international law could not succeed in Canada. A majority of the Supreme Court in Nevsun disagreed and allowed the claim to proceed to trial. The Supreme Court held that customary international law is automatically incorporated into domestic law even in the absence of legislation. It found it was not “plain and obvious” that the plaintiffs in that case could not bring forward a tort claim based on alleged breaches of customary international law against a Canadian mining company operating in Eritrea.

Federal Court’s Decision in Lho'Imggin v. Canada

Lho'Imggin v. Canada concerns a claim against the Canadian federal government, similar to other Canadian climate lawsuits against governments we have previously written about. The claim was brought by two Head Chiefs of certain houses that comprise one of five hereditary Indigenous Clans constituting the Wet’suwet’en First Nation. The plaintiffs pleaded that the federal government has no existing or planned legislative or policy initiatives to enable Canada to achieve the GHG emission reductions that the plaintiffs alleged are required. In addition to alleging a breach of section 7 of the Charter of Rights and Freedoms, the plaintiffs raised the significance of the ICJ Opinion.

The Federal Court struck the plaintiffs’ claim for failing to disclose a reasonable cause of action.  However, the Federal Court granted leave to the plaintiffs to amend their claim. With respect to a claim alleging a common law tort for a violation of customary international law, the Federal Court referenced the Nevsun decision for the notion such a claim was possible. The ICJ Opinion, while not binding in Canadian courts, may be considered and “[i]nternational legal principles may legitimately be invoked in domestic litigation when claimants are affected by actions that contravene customary norms or international treaty obligations.” In this way, Lho'Imggin v. Canada affirmed the potential viability of novel tort claims based on alleged breaches of a customary international law obligation to protect the environment from human-made GHG emissions.

Looking Forward

Decisions like Nevsun and Lho’Imggin v. Canada reflect a judicial willingness within domestic Canadian law to consider international norms, including international environmental norms such as an obligation on states to protect the environment from GHG emissions as stated in the ICJ Opinion. It stands in contrast to the treatment of similar claims in the United States. For example, the United States District Court for the District of Montana in Lighthiser et al. v. Trump et al. recently dismissed a claim challenging three presidential Executive Orders that encouraged fossil fuel development and directed federal agencies to unwind climate-related policies. While the American court acknowledged that the Executive Orders being challenged will exacerbate the harms of climate change, it held it did not have jurisdiction to address the matter, but rather that the “Plaintiffs’ compelling case for redress must be made to the political branches or to the electorate”. 

For further information on this recent decision, please contact the author or any member of our Litigation and Dispute Resolution Group.

The author would like to thank Josephine Hu, Articling Student-At-Law, for her assistance in writing this Update.