Historic International Court Decisions on Climate

The International Court of Justice (ICJ) and the Inter-American Court of Human Rights (IACtHR) each recently determined that States must do more to address climate change. The IACtHR affirmed the human right to a healthy climate. The ICJ affirmed that all States have legal obligations to reduce Greenhouse gas emissions. These landmark opinions provide authoritative interpretations of existing international law, underscoring the legal duties of States in addressing the climate crisis and its devastating environmental and human rights impacts, and offering guidance for future legal action and accountability. 

Both courts expressed deep concern about the climate emergency. They declared that States have legal duties that include establishing national climate frameworks, setting mitigation targets and adaptation plans, and instituting effective enforcement mechanisms.

Highlights of the Inter-American Court of Human Rights Opinion

Following an unprecedented number of submissions from civil society, academics, States, and international organizations, the IACtHR issued its Advisory Opinion on Climate Change and Human Rights. The climate emergency is defined, according to the Court, by the urgency of effective action, the severity of its impacts, and the complexity of the response required. Therefore, the court emphasized that States must abstain from any behavior that sets back, delays, or undermines the results of measures necessary to protect human rights from climate-related harms. 

Interpreting the principle of prevention, the court concluded that States are obliged to exercise enhanced due diligence in the face of climate change. Moreover, States’ duties include enacting domestic legislation to guide both State and private actors, grounded in the best available science as well as traditional, local, and Indigenous knowledge systems. 

The court referred to the imperative prohibition against causing massive and irreversible damage to the environment. From the right to a healthy environment, it derived the human right to a healthy climate, imposing specific obligations on States. Moving beyond a purely human-centered view, the IACtHR highlighted nature and its components as rights-holders, which contributes to a development model that respects planetary boundaries (the earth’s natural limits) and safeguards enough vital natural resources for both current and future generations.  

The court addressed a wide range of substantive and procedural rights at risk in the context of the climate emergency, including the right to life, personal integrity, health, private property, adequate housing, freedom of movement and residence, water, food, work, social security, education, democracy, science, access to information, public participation, access to justice, and the right to defend human rights. 

“The Advisory Opinion issued by the IACtHR elevates the protection of environmental defenders,” says Luciano Coco Pastrana, ELAW Defenders Team Attorney. “The Court affirms the autonomous nature of the right to defend human rights and recognizes environmental defenders as rights-holders who, because of their work, are entitled to specific protections. Drawing on the Escazú Agreement, the opinion reinforces States’ obligations to ensure participation, transparency, and protection, making Escazú a key interpretive source in the Court’s jurisprudence. This opinion positions the defense of the environment not only as a matter of public interest, but as a fundamental pillar of democratic and climate governance across the Americas.”

Highlights of the International Court of Justice Opinion

The ICJ gave its advice on two questions referred to it by the UN General Assembly:

• What are the legal obligations of States regarding climate change caused by anthropogenic greenhouse gas emissions?

• What are the legal consequences of non-compliance by a State with those legal obligations?

The Court considered the written and oral submissions of many States, international organizations, and civil society organizations before issuing its Advisory Opinion on July 24, 2025. The Advisory Opinion unanimously affirmed that States have legal obligations under climate change treaty law to undertake collective measures to reduce greenhouse gas emissions to meet the 1.5 °C standard for temperature increase. In doing so, States must take adequate measures that align with the principle of common but differentiated responsibility et le precautionary principle.

The Court also opined that States have a legal obligation to submit regular Nationally Determined Contributions required under the UN climate convention framework, which should be progressive – meaning increased efforts and measures to reach the 1.5°C standard. The Court held that States have a legal obligation to cooperate to achieve the temperature limitation of 1.5°C. Additionally, the Court, having examined customary international law, opined that States are legally obligated to prevent significant harm to the environment and to the climate system, as well as to ensure that their actions and omissions do not cause harm to other States through their greenhouse gas emissions.

Addressing the second question of legal consequences for non-compliance, the Court said that a State in breach of any of its climate obligations is internationally responsible for a wrongful act, which implies the duty to cease the wrongful actions or omissions, to guarantee they don’t repeat the actions, and to provide full reparation to injured States. 

Overview

These opinions demonstrate how different branches of international law are interconnected, as the courts elaborated on existing duties under human rights treaties, environmental conventions, customary law, and principles of international law. They all inform and strengthen States’ climate obligations. 

“These Advisory Opinions will certainly shape the global legal landscape for future climate action,” says ELAW Attorney Letícia Aleixo. “They will serve as vital references for domestic courts and policymakers, and set the stage for civil society to demand government and corporate responsibility in addressing climate change.” 

ELAW collaborates with our partners in diverse ways to protect the climate, including:

• Filing cases to keep fossil fuels in the ground;
• Shutting down dirty power plants that do not meet legal standards for operation; and
• Improving policies to ensure the consideration of the comprehensive costs of dirty energy when permitting new projects, to help countries make way for renewable energy.

We have much work ahead to unpack these opinions and collectively strategize to ensure that these landmark interpretations of international law result in on-the-ground changes to protect the climate and repair the harm done to communities, especially those who have done the least to cause the problem while suffering the most devastating impacts. ELAW will facilitate spaces for our partners to exchange strategies as they delve into these decisions in greater detail.

We are eager to step up our efforts to help our partners leverage the authority and influence of these two advisory opinions to strengthen their cases in courts around the world to hold governments and corporations accountable and enact effective climate protection policies.

Sincèrement,

Dr Lalanath de Silva
Directeur exécutif
Alliance mondiale du droit de l'environnement

Further Reading:

IACtHR Advisory Opinion in English

IACtHR Advisory Opinion Website

IACtHR Advisory Opinion in Spanish

Read what colleagues at AIDA are saying about the IACtHR Advisory Opinion

ICJ Advisory Opinion