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Cost of Climate Change

International Court of Justice Issues Landmark Climate Opinion

“The Court hopes that its conclusions will allow the law to inform and guide social and political action to address the ongoing climate crisis.” – ICJ Advisory Opinion, para. 456

In a historic and unanimous ruling, the International Court of Justice (ICJ) has issued its Advisory Opinion on the legal responsibilities of nation states to address climate change. This decision, requested by the United Nations General Assembly in 2023, clarifies for the first time what international law demands of countries and what legal consequences may follow if they fail to act.

Background to the Request

The United Nations General Assembly formally asked the ICJ to weigh in on two questions:
1. What obligations countries have, under international law, to protect the climate system and the environment from human-caused (anthropogenic) greenhouse gas emissions?
2. What are the legal consequences for states that have caused significant harm to the climate, particularly concerning vulnerable nations such as small island states, and individuals of present and future generations?

Over 150 countries and international organizations submitted written or oral arguments—more than in any case in the ICJ’s history. The Court held public hearings in December 2024 and delivered its Advisory Opinion on July 23, 2025.

The United States position

In their submissions, major emitters like the United States, China and Saudi Arabia opposed any actions beyond existing treaties.

The United States rejected the idea that it could be legally responsible for reparations related to historical greenhouse gas emissions.

“Emissions that occurred before the creation of specific climate obligations do not constitute internationally wrongful acts.”

In a statement released when he pulled the United States out of the Paris Agreement for the second time, President Donald Trump proclaimed, “It is the policy of my Administration to put the interests of the United States and the American people first in the development and negotiation of any international agreements with the potential to damage or stifle the American economy.  These agreements must not unduly or unfairly burden the United States.”

Canada’s Position

Canada also opposes the idea of obligations being applied to actions taken prior to formal agreements, but endorses the non-punitive and collaborative compliance mechanisms under the United Nations Framework Convention on Climate Change and Paris Agreement

The Court’s Descions

The Court’s opinion sets out a comprehensive list of obligations under both treaty law and customary international law. These include:

Obligations under Climate Treaties

  • Reduce greenhouse gas emissions and take steps to adapt to climate impacts.
  • Wealthier nations need to lead the way in emission reductions and climate action.
  • Cooperate internationally, in good faith, toward shared climate goals.
  • Submit, update, and follow through on national climate plans (Nationally Determined Contributions or NDCs).
  • Pursue efforts to limit warming to 1.5°C, consistent with global goals.
  • Provide financial and technological support, especially to developing countries.

Obligations under Customary International Law

  • Prevent significant environmental harm caused by activities within their jurisdiction.
  • Act with due diligence and take reasonable measures to stop damaging emissions.
  • Cooperate continuously and in good faith with other nations.

Other Treaty Obligations

States are also bound by agreements on the ozone layer, biodiversity, desertification, and ocean protection, all of which require safeguards against climate-related harm.

Human Rights Obligations

The ICJ emphasized that climate protection is a human rights issue. States must also protect fundamental rights such as health, life, and housing, which are threatened by climate change.

What Happens When States Fail to Act?

When states violate their climate obligations, they commit an internationally wrongful act. They must:

  • Stop the wrongful conduct.
  • Assure others of non-repetition.
  • Make full reparation—environmental restoration, financial compensation, or symbolic acts—if a clear link between harm and action can be shown.

Even when multiple countries contribute to climate harm, each may be held accountable for its share. Climate change’s complexity does not erase responsibility.

Addressing Vulnerable Nations and Peoples

Small island states, developing countries, and future generations are often most impacted. The Court affirmed that international law applies equally, regardless of a state’s size or wealth.

Determining Blame and Causation

The Court accepted the difficulty of attributing climate damage, but stated modern science can track national emissions histories. Legal responsibility involves:

1. Scientific causation – Linking emissions to events.
2. Legal causation – Linking state actions to resulting harm.

Both types of causation can be proven through case-specific evidence. Climate harm may be shared, but so is legal accountability.

Global Responsibility and Legal Principles

The Court declared climate protection a legal obligation owed to the entire international community. All treaty members have a right to hold one another accountable.

Final Reflections: Law in the Climate Era

This ruling marks a turning point. Inaction on climate is no longer just poor policy—it is a violation of international law. The ICJ called on governments to let law guide real-world solutions.

Links of Interest:

Top image credit: Press room at the ICJ – Screenshot from the ICJ website

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