The Continuing Challenge Of Causation In Climate Litigation

As climate litigation develops both domestically and internationally, the issue of causation remains contentious. In short, "causation" in this context refers to the nexus between a particular government or private actor's conduct, or lack of conduct, and the harms alleged to be suffered by the claimants or those they represent.

Causation issues permeate climate litigation. This is because the causes of climate change are generally seen as raising enormous factual complexity and engaging many multiples of actors. For example, in 2024, The Hague Court of Appeal allowed the appeal in Milieudefensie et al. v. Royal Dutch Shell, a class action alleging that Royal Dutch Shell plc ("Shell") owed a duty of care to Dutch citizens in relation to climate change. In quashing the claim, The Hague Court of Appeal accepted Shell's position that a court-mandated reduction in certain of Shell's indirect emissions would be "ineffective" in reducing global CO2 levels; other actors would simply replace Shell in the value chain. As detailed in our previous bulletin, when Milieudefensie announced its intention to appeal this result to The Hague Supreme Court, it stated in part that "[h]ow other companies are behaving is irrelevant", and that courts should be focusing instead on "accountability" and "action".

Earlier this year, the International Court of Justice released its advisory opinion on international law obligations in respect of climate change (the "ICJ Opinion"). As part of its analysis, the International Court of Justice referred to the challenges of causation issues in climate claims, noting its receipt of submissions that causation is "impossible" to establish in this context, and submissions that causation should accordingly be "presumed". Here, the International Court of Justice broke causation issues into two parts — first, whether a given climatic event is attributable to human-caused climate change, and, second, whether the damage is attributable to a particular actor. The International Court of Justice concluded that the second prong — attribution to a particular actor — although raising difficulties, was not legally "impossible", and should be left to be established through the adjudication of particular cases.

This conclusion tracks the thinking of two of Canada's appeal courts in climate litigation against public actors. In 2023, the Federal Court of Appeal allowed the appeal in La Rose v. Canada, a constitutional challenge to the federal government of Canada's legislative response to climate change. Canada sought to strike the claims against it in part because of causation issues; Canada argued that there was no nexus between the harms alleged to be suffered and the legislation impugned in the proceedings. Although the Federal Court of Appeal agreed with Canada that, as presently constituted, the plaintiffs' pleadings "lack[ed] the focus necessary" for a constitutional challenge, it granted the plaintiffs leave to address the pleadings deficiencies through amendment.

In doing so, the Federal Court of Appeal referred to the prospect of a government "shell game" in response to climate litigation. In essence, the Court of Appeal recognized that a government could resist constitutional liability either on the basis that a proposed claim is "too broad" (and therefore unmanageable in any trial context) or "too specific" (and therefore unable to be usefully analyzed in isolation). The Federal Court of Appeal concluded that the answer to this problem was twofold: first, to recognize that, in complex societies, problems arise from "a host of social, economic, legal, and practical influences"; and, second, to leave factual determinations to be determined in particular cases through the mechanism of a trial.

Causation was also a key issue in Mathur v. Ontario, a 2024 case in which the Ontario Court of Appeal permitted a challenge to the constitutionality of Ontario's emission reduction target and plan to proceed to trial. In the underlying decision, the Ontario Superior Court concluded that the problem of "collective action" had to be considered in climate change cases at the stage of causation assessment. It found that an unduly narrow approach to causation would "impede collective action and hinder the solving of global problems". On appeal, the Ontario Court of Appeal did not disturb this conclusion — indeed, it found that the Ontario Superior Court had erred in making other causation-based findings apparently in conflict with it. Additionally, the Ontario Court of Appeal rejected Ontario's argument that the kind of constitutional relief sought — a "constitutionally compliant" target — was "impossibly" vague and imprecise. The Ontario Court of Appeal, in essence, deferred this issue to the trial judge, citing clarity in scientific consensus on climate change, as well as remedial flexibility in constitutional litigation.

Following the Federal Court of Appeal's decision in La Rose, the La Rose plaintiffs amended their pleadings, and the federal government again moved to strike the claim. However, the parties in that proceeding reached an agreement based on further amended pleadings, and the matter is proceeding to trial. The new framing of the La Rose action now tracks the plaintiffs' approach in Mathur — the La Rose plaintiffs focus on the federal government's climate target itself as being allegedly unconstitutional.

A different result has been reached more recently in Lho'Imggin v. Canada, a constitutional climate challenge brought by certain Dini Ze' (or Head Chiefs) of the Wet'suwet'en. The Lho'Imggin case, like the La Rose case, was initially struck without leave to amend by the Federal Court. The appeal from this decision was heard concurrently with the La Rose matter, with the Federal Court of Appeal allowing, in both cases, the plaintiffs a further opportunity to amend their pleadings.

In September of this year, the Federal Court disposed of Lho'Imggin following a further motion to strike the plaintiffs' amended claim. In allowing the strike motion, the Federal Court stressed that the Lho'Imggin plaintiffs' challenge was to over 17 statutes and 20 regulations, implicating, in an unprecedented way, approximately 1,900 legislative provisions. The Federal Court concluded that the plaintiffs' case was "still obscured by an effusive and broad pleading by virtue of the sheer scope of the [impugned] laws". It held that the plaintiffs "must clearly plead which measures contribute to the deprivation of their protected rights and how those measures cause the alleged deprivation".

The Federal Court in Lho'Imggin also considered the import of the ICJ Opinion on the plaintiffs' case. The ICJ Opinion is advisory and does not directly impose legal obligations on states. However, the plaintiffs relied on the ICJ Opinion in support of a novel claim that the Crown was in breach of customary international law. While the court did not foreclose the possibility that customary international law provided a further, novel basis for the plaintiffs' claim, it concluded that the plaintiffs' pleading was currently deficient in this regard as well. It allowed the federal government's strike motion, but permitted the plaintiffs yet a further opportunity to amend.

These court analyses show that there is judicial appetite in Canada for taking on causation considerations unique to constitutional climate claims, with an eye toward favouring the concrete, trial-based adjudication of particular cases where the alleged legal wrong is properly pleaded.

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