Climate Change at the International Court of Justice

On 23 July 2025, the International Court of Justice (ICJ) delivered a unanimous advisory opinion on the Obligations of States in Respect of Climate Change (PDF).

The advisory opinion marks the first time that the ICJ, the United Nations’ principal judicial organ, has examined the international legal framework applicable to climate change.

The ICJ opinion largely rejects the arguments put by major emitters of greenhouse gases (historical and current), including the UK. The 15 judges adopted an expansive interpretation of states’ obligations. Despite being non-legally binding, the advisory opinion has significant implications for national climate policies and international climate negotiations. It also opens new pathways for international and domestic litigation against governments.

This briefing presents the origins of the proceedings, summarises the ICJ’s key findings and outlines domestic and international reactions.

The origins of the advisory opinion Grassroots youth movements

The initiative to request an ICJ advisory opinion on climate obligations began with grassroots youth movements in the Pacific islands, driven by concerns about the long-term impacts of climate change on their communities. An advisory opinion from the ICJ serves to clarify and interpret the law to guide state actions. The expectation was that greater legal clarity would help encourage stronger climate action.

UN resolution

The ICJ can provide an advisory opinion on questions of international law at the request of certain UN organs or specialized agencies. Following a successful diplomatic campaign led by the small Pacific island nation of Vanuatu, the UN General Assembly adopted resolution 77/276 in March 2023, formally requesting the opinion of the ICJ.

Adopted by consensus (an unprecedented outcome), the resolution was co-sponsored by the UK, alongside 130 other countries. The UK’s Deputy Permanent Representative to the UN, James Kariuki, explained that “an ICJ Advisory Opinion may help to refocus efforts to deliver on climate commitments in this critical decade”.

ICJ proceedings

The ICJ was tasked with addressing two questions:

• to determine the obligations of states applicable to climate change
• to set out the legal consequences of violating climate change obligations

The proceedings had the highest level of participation in the ICJ’s history (PDF): 96 States and 11 international organizations presented oral statements during public hearings in The Hague in December 2024. Sharp differences appeared between high-emitting states (past and present), which interpreted climate obligations restrictively, and climate-vulnerable countries, which argued for broader legal duties and stronger accountability. The UK argued for a narrow interpretation of legal climate obligations, emphasising the primacy of climate treaties.

The ICJ’s 133-page advisory opinion, while neither legally binding nor related to a specific dispute, carries substantial legal and political weight.

The ICJ’s is the third advisory opinion on climate change issued by an international tribunal, following advisory opinions from the International Tribunal for the Law of the Sea (PDF) in May 2024 and the Inter-American Court of Human Rights (PDF) in July 2025.

What did the ICJ say? Climate change poses an existential threat

The ICJ acknowledged “the urgent and existential threat posed by climate change” (para 73), drawing on Intergovernmental Panel on Climate Change reports as the “best available science” (para 74).

Global warming must remain below 1.5°C

The ICJ held that the Paris Agreement creates legally binding, enforceable, duties. It also affirmed that the decisions of the Conference of the Parties (COP) carry legal weight (para 184).

The ICJ set the goal of keeping global warming below 1.5°C above pre-industrial levels as the standard for all climate policies (para 224). It also said that countries have limited discretion when designing their national climate plans: these must become more ambitious over time (para 241) and help meet the collective temperature goal (para 245). The ICJ also made clear that states must take measures to adapt to the impacts of climate change (para 210).

States must regulate fossil fuels

The ICJ noted that producing and consuming fossil fuels, granting exploration licences for fossil fuels or providing subsidies for fossil fuels could amount to a violation of international law (para 427).

In a joint declaration accompanying the unanimous opinion of the 15 judges, two judges said that achieving the 1.5°C goal requires that no new fossil fuel extraction projects be developed (PDF). They also considered that environmental impact assessments for such projects must include the emissions released when the fuels are later burned (known as ‘Scope 3 emissions’).

The advisory opinion was referenced in domestic proceedings a week after its publication (PDF), in an appeal against the South African Government’s decision to authorise Shell’s offshore oil and gas project.

States must cooperate

The ICJ stressed that international cooperation is a legal obligation (para 308). This includes providing financial assistance at a level that makes it possible to meet the temperature goal (para 265). Other legally-binding forms of cooperation include technology transfers and capacity-building (para 262).

States must prevent environmental harm

The ICJ said that climate change is not only governed by treaties like the Paris Agreement. It confirmed the existence of a customary duty to prevent harm to the climate system (para 273). This means that all states, whether or not they are a party to a climate treaty, are under a duty to take action to achieve “deep, rapid and sustained” cuts in emissions (para 282). This duty requires regulating corporations (para 282).

Climate change is a human rights problem

The ICJ recognized that the human right to a clean, healthy and sustainable environment (which the UK does not treat as legally binding) is “essential for the enjoyment of other human rights” threatened by climate change (para 393).

Land lost to sea level rise may not mean the loss of statehood

The ICJ addressed the challenges that sea level rise poses to low-lying states and vulnerable communities. It recognized that states continue to hold legal rights over their maritime zones and the resources within them, even if coastlines shift (para 362). The Court also acknowledged the existential threat faced by small island states and clarified that the loss of land territory as a result of sea level rise does not necessarily mean that a state ceases to exist (para 363).

State responsibility applies to climate change

The ICJ confirmed that the general rules of state responsibility apply to climate change (para 420). It rejected the arguments that the complex, global nature of climate change makes it impossible to apply these rules.

This means that if a state breaches its climate obligations, it must provide reparation, including through compensation (para 452). It might also be required to revoke all administrative, legislative and other measures contributing to the breach (para 447). In establishing this, the ICJ set out a framework for holding states accountable for climate damages.

What were the reactions? UK Government

The UK took an active part in the proceedings, submitting written statements in March 2024 (PDF) and August 2024 (PDF) and giving an oral statement in December 2024 (PDF). It argued that climate treaties, especially the Paris Agreement, are the main source of binding obligations. It rejected claims that human rights law or the customary duty to prevent environmental harm apply to the climate system. It held the minority view that the rules on State responsibility were not relevant to the Court’s questions.

Commenting on the advisory opinion after its publication, an FCDO spokesperson said that the UK remained committed to addressing climate change:

Tackling climate change is and will remain an urgent UK and global priority. Our position remains that this is best achieved through international commitment to the UN’s existing climate treaties and mechanisms (…) We will continue to collaborate closely to create the conditions for greater ambition and action, including with Brazil as it prepares to host COP30, and will tackle the climate crisis in a way that makes the British people better off.

Official Opposition

The Shadow Foreign Secretary, Dame Priti Patel, compared the climate advisory opinion process to the one that led to the “Chagos surrender”. She expressed concerns that the ICJ was “destroying the sovereign rights of national governments”:

The ICJ has lost its core purpose and is now joining political campaigns and bandwagons based upon ideological obsessions on issues such as reparations and destroying the sovereign rights of national governments.

Questions about historic reparations

Some press reports expressed concerns that the advisory opinion “opened the door to Britain being sued over its historic contribution to climate change”. Asked to comment on this risk, Secretary of Business and Trade Jonathan Reynolds said that the UK should not “apologise or pay reparations” for leading the Industrial Revolution. In the UK’s written comments to the ICJ (PDF), it responded to other states’ references to the UK’s contribution to climate change by arguing that such statements did not account for the UK’s climate leadership:

These [suggestions]… are made without any attempt to analyse the degree and effect of the UK’s considerable efforts in recent decades in respect of, in particular, mitigation of its own emissions and the financing of the mitigation and adaptation initiatives of other States.

United Nations

The UN Secretary General, António Guterres, welcomed the “historic” advisory opinion as “a victory for our planet, for climate justice, and for the power of young people to make a difference”.

Mary Robinson, the first female President of Ireland and former UN High Commissioner for Human Rights, said the advisory opinion was “a powerful new way to protect people from the devastating impacts of climate change” and said it would “deliver justice for the harm already caused”.

Climate vulnerable states

The possibility of financial compensation for climate harms has been welcomed by many climate justice activists, including in vulnerable states.

After the decision, Vanuatu’s climate adaptation minister, Ralph Regenvanu, said his country would take the ICJ ruling to the UN General Assembly and “pursue a resolution that will support implementation of this decision”. He explained that, for Vanuatu, “the opinion is both shield and sword: a shield affirming its right to survival and a sword compelling the world’s major emitters to act in line with science and justice.”

France

In a press release issued by the Ministry of Foreign Affairs, France noted the advisory opinion and reaffirmed its “unwavering commitment to the ICJ”. It said that it “will continue working ambitiously to achieve its climate goals and to support its partners”.

Germany

Germany’s Federal Environment Minister said: “mitigating climate change is a universal obligation for all countries. Germany has long accepted this responsibility”.

United States

When asked about the advisory opinion, a spokesperson for the White House said: “As always, President Trump and the entire administration is committed to putting America first and prioritising the interests of everyday Americans.”

China

A Chinese government spokesperson said the advisory opinion was consistent with “the long-standing stance and proposition of developing countries, including China”, adding that China was a leader in emissions reduction and green technologies.

About the author:

Dr Leslie-Anne Duvic-Paoli is the Parliamentary Thematic Research Lead for International Affairs and National Security. She is a Reader in environmental law at King's College London and represented the African Union in the ICJ proceedings on the climate advisory opinion.