2025 was a crucial year for international climate law and human rights. Two advisory opinions (AOs) were issued, one by each of the International Court of Justice (ICJ) and the Inter-American Court of Human Rights (IACtHR). These two AOs form a possible new “evidence” perspective to the standard of proof requirement, capable of ensuring broader protection of human rights.

The ICJ has confirmed that States are legally obliged to protect the climate system for both present and future generations; greenhouse gas (GHGs) emissions are directly linked to adverse impacts on fundamental rights; and that climate damage is compensable under international law through restitution, compensation, and satisfaction. It also assessed fundamental remarks in relation to issues of attribution and causation, referring to climate change, by emphasizing that a failure to exercise regulatory due diligence can be ranked as an internationally wrongful act and, therefore, attributable to a State.

Traditional international law has often required a sufficiently direct and certain causal nexus between the wrongful act and the injury suffered by the Applicant—a standard nearly impossible to meet, given the diffuse and cumulative nature of climate change.

However, the ICJ observed that it is scientifically possible to determine each State’s total contribution to global emissions, taking into account both historical and current emissions, and considers that rules on State responsibility admit the possibility of determining the responsibility of States in the climate change context.

The ICJ ’emphasizes that the internationally wrongful act in question is not the emission of GHGs per se, but the breach of conventional and customary obligations pertaining to the protection of the climate system from significant harm resulting from anthropogenic emissions’ by translating it into failure to exercise regulatory due diligence’ [para 427].

The existing legal standard for establishing causation can be applied to establish causation between the internationally wrongful act (non-compliance with States’ obligations to protect the climate system from harm caused by anthropogenic GHG emissions) and the damage suffered by States as a result of such a wrongful act.

Causation plays a role in determining reparation. Since reparation implies the existence of damage, causation must be established between the State’s wrongful act and the particular damage suffered by the injured individuals.

On the other hand, the IACtHR delivered its own transformative AO, explicitly recognizing the right to a healthy climate as an autonomous fundamental right on par with rights to life, health, and dignity [para 300].

It emphasized that due diligence remains the central criterion for assessing state responsibility: States must demonstrate that they have taken all reasonable measures within their power to prevent climate harm and protect this fundamental right [para 231-237].

The IACtHR notes that the strict application of certain general provisions on evidentiary matters could represent an unjustified obstacle to effective access to justice in climate litigation [para 552]. Against this backdrop, the IACtHR gives new ways of interpretation of the evidentiary rules based on the principles of availability of evidence, procedural cooperation, pro persona, pro natura, and pro actione, to interpret provisions concerning the admissibility, reliability, and assessment of evidence flexibly and to avoid them becoming unjustified procedural barriers for victims, by guaranteeing access to appropriate proof such as satellite evidence in view of its probative pertinence in the context of the climate emergency [para 556].

Both Courts have underlined the need to adopt a more flexible way of interpreting the causal nexus between States’ conduct and individual harms, given its crucial role in assessing victimhood in human rights violations derived from climate change.

This development can have concrete consequences, considering the increasing cross-fertilization working in international human rights law. Even the ECHR jurisprudence, in assessing applicants’ victim status, has recalled that “causation must always be regarded in the light of the factual nature of the alleged violation and the nature and scope of the legal obligations at issue.” [para 435]

The convergence of these two AOs has the potential to mutually reinforce frameworks that strengthen victims’ positions in climate litigation. As these principles filter through domestic legal systems and inform future litigation, we may be witnessing the beginning of a new era in which individuals will no longer need to reach an especially high threshold to be able to demand accountability under international law, by expanding admissibility criteria and allowing individuals to be recognized as victims of climate change.