In its advisory opinion issued in July, the International Court of Justice (ICJ) found that states have obligations to act on the climate crisis – and can face legal consequences for breaching them. 

The ruling comes six years after a group of law students from Pacific island states began a campaign to persuade the region’s leaders to take the issue of the climate crisis and human rights to the ICJ. The resulting push from Small Island States, spearheaded by Vanuatu, prompted the UN General Assembly in 2023 to call on the ICJ to issue an advisory opinion to clarify two legal issues: the obligations of states under international law to combat the climate emergency, and the legal consequences of failing to meet or breaching these obligations.

The ICJ has now confirmed that included in the obligations of states are international treaties such as the Paris Agreement, the Montreal Protocol, the Convention on Biological Diversity, the UN Convention to Combat Desertification in Those Countries Experiencing Serious Drought and/or Desertification and the UN Convention on the Law of the Sea. 

Further, the Court stated that governments have obligations under international human rights law ‘to respect and ensure the effective enjoyment of human rights by taking necessary measures to protect the climate system and other parts of the environment’.

With this opinion, the ICJ has ‘prepared a wonderful floor for domestic courts to refer to’, says Els Reynaers, Co-Chair of the IBA Environment, Health and Safety Law Committee. ‘Everyone understands that it’s not binding, but the significance of it – it was ultimately unanimous.’ She highlights that the ruling was delivered by a diverse judiciary, including judges from China, Somalia and the US. ‘It’s really reflective of a new mindset […] this is the world court setting the tone for the future,’ says Reynaers.

‘This is the start of a new era of climate accountability at a global level,’ says Danilo Garrido, legal counsel at NGO Greenpeace International. ‘The ICJ advisory opinion marks a turning point for climate justice, as it has clarified, once and for all, the international climate obligations of States, and most importantly, the consequences for breaches of these obligations.’ Garrido believes the ruling will open the door for new cases, and ‘hopefully bring justice to those, who despite having contributed the least to climate change, are already suffering its most severe consequences.’

Jessica Palairet, Executive Director at Lawyers for Climate Action NZ (LCANZ), highlights the significance of the ICJ’s statement that all countries have obligations to reduce emissions and pursue climate policies that are aligned with a goal of stabilising the global average temperature increase to 1.5 degrees Celsius above pre-industrial levels. 

The Court also clarified that these obligations are ‘rooted in international law’, she adds. ‘It’s now going to be up to domestic courts, domestic litigators like us to really put that judgment into practice,’ Palairet says. The ruling further confirmed that the climate crisis is a human rights issue, and that states have to do more to reduce emissions under international human rights law, she adds. 

‘The legal responsibility doesn’t only encompass greenhouse gas emissions, but also the conduct that leads to those emissions, [such as] continuing to produce fossil fuels, [or] subsidies that lead to an increase in fossil fuel production,’ says Bjorn-Oliver Magsig, a senior law lecturer at Victoria University and an LCANZ board member. ‘That’s a step which, for me, was a very nice surprise, that the ICJ engaged with that and said clearly that those steps by states potentially are a violation of international law.’

However, even with this opinion, Magsig says it ‘remains tricky’ to force compliance with international law. Instead, it is more likely that the ICJ opinion will have a greater impact on domestic cases. ‘We won’t see an explosion of ICJ cases on climate change,’ he believes.  

Internationally though, the impact will probably be felt in the political arena – especially for states that benefit from a rules-based order, he says. ‘If we start eroding the system in areas we think we can get away with, then other states will do the same,’ Magsig says. ‘How can we call out violations of human rights around the world if we violate human rights at home with our climate policies?’ He adds that ‘international law only works with political pressure.’

Reynaers – who’s also a partner at MV Kini in Mumbai – says that some countries may be wary of filing suits against each other, lest they ‘boomerang’ back and flag their own shortcomings. Pacific Island nations ‘will not have the same hesitation’, she adds. ‘I would imagine we would see developments or possibly cases filed by some of those countries.’

The ICJ’s opinion may also embolden NGOs and individuals to pursue litigation related to the impacts of the climate crisis – especially given that advances in science and the wealth of historical data mean such changes can be monitored and demonstrated. 

The ICJ’s ruling came just a few weeks after the Inter-American Court of Human Rights (IACHR) released its own opinion, following a request from Chile and Colombia. The IACHR opinion also recognised the existence of a human right to a healthy environment and that states have an obligation to act on the climate crisis. 

‘For the first time, the IACHR establishes standards for States regarding the prevention, mitigation and reparation of climate-related harm, and affirms that climate change may constitute a violation of human rights,’ writes Manuel Frávega, an officer of the IBA Environment, Health and Safety Law Committee, in a briefing. 

Similarly to the ICJ, the IACHR also found that states must take steps to curb the climate crisis and refrain from conduct that would lead to setbacks or delay action, including the adoption of regressive measures. ‘This [advisory opinion] is part of the growing phenomenon of climate litigation at the global level and represents a significant precedent in Latin America,’ concludes Frávega, who’s also a partner at Beccar Varela in Buenos Aires.

The author would like to thank the IBA’s Legal Policy & Research Unit for their assistance with this article.

Image credit: Valmedia/AdobeStock.com

IBA President Jaime Carey stated, ‘The establishment of the IBA ICC Moot Court is rooted in the conviction that it plays a vital role in educating the next generation of international lawyers, who will continue the fight against impunity for the gravest international crimes […] I am delighted that a new MOU is in place.’

Carsten Stahn, Professor of International Criminal Law and Global Justice at Leiden University and Chair of the IBA ICC Moot Court Competition Organising Committee, said, ‘In times like these, the IBA ICC Moot Court is more needed than ever to educate the lawyers of the future. We are delighted to continue this wonderful collaboration with the IBA. The agreement reflects our strong partnership and mutual commitment and provides an invaluable basis for the years to come.’

Read more about the Memorandum of Understanding and the Competition here.

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Israeli Air Force fighter jets head for Iran, June 2025. IDF Spokesperson's Unit / CC BY-SA 3.0

With no UN mandate and little disclosed intelligence, US and Israeli airstrikes on Iran have sparked global concern not just over war, but over the very rules meant to prevent it.

In June, long-simmering tensions erupted into open warfare when Israel launched ‘Operation Rising Lion’, targeting Iran’s nuclear facilities, military bases and senior officials. Israel justified the strikes as a pre-emptive measure based on intelligence. Tehran retaliated immediately, unleashing missiles and drones at Israeli cities and strategic sites.

The exchange marked the first open state-on-state attacks between the two adversaries, shattering long-held red lines.

Beyond military sites, Israeli strikes reportedly targeted a state television station, media workers and civilian nuclear scientists, killing at least 224 people, mostly civilians. The attacks claimed several high-ranking Iranian military officials and scientists involved in the nuclear programme. Iranian attacks left 24 dead in Israel.

The crisis deepened when the US launched ‘Operation Midnight Hammer’. Employing advanced munitions, Washington deployed precision airstrikes against Iran’s most secure nuclear sites in Fordow, Natanz, and Isfahan. The White House framed the operation as both a defence of US interests and an act of support for Israel, a key ally.

‘Last night, history changed,’ Danny Danon, Permanent Representative of Israel to the United Nations, told the UN Security Council after the US strikes. ‘The United States, the leader of the free world, removed the greatest existential threat facing the free world...Just like our Operation Rising Lion, this was not a war of choice; this action was a necessity, it was a righteous act.’

Legally, the US and Israel defended their dramatic strikes by invoking the right to pre-emptively attack an adversary believed to be on the verge of a nuclear breakthrough. They contended that intelligence indicated Iran was in the final stages of assembling a nuclear device, thus presenting a 'last window of opportunity' to act, even absent an immediate, active attack. The specifics of this intelligence remain largely undisclosed by Israel.

Yet, this justification triggered a heated debate and an immediate pushback from international law experts and arms control monitors. ‘These attacks represent a blatant act of aggression and a violation of jus cogens norms – peremptory rules from which no derogation is permitted,’ a group of UN human rights experts said in a statement citing the UN Charter’s prohibition on the initiation of use of force. The experts noted that 'there is no evidence whatsoever that Iran intends to imminently attack the US or Israel with a nuclear weapon.'

The International Commission of Jurists says Israel’s use of armed force violated Iran’s sovereignty and territorial integrity, posing a major threat to international peace and security. The core legal debate around both US and Israeli strikes hinges on interpreting and applying Article 2(4) and Article 51 of the UN Charter, which govern the ban on the use of force and the right to self-defence. ‘Pre-emptive strikes are always a violation of international law unless authorised by the UN Security Council,’ says Mary Ellen O'Connell of the Law School at the University of Notre Dame, Indiana. ‘That obviates attacking in anticipation of or to pre-empt an attack that is not yet occurring.’ She says the strikes on Iran did not constitute self-defence nor possess such authorisation.

Some legal experts defended the strikes on grounds that a status of conflict had already existed between Israel and Iran and that waiting for an attack on Israel to materialise could be catastrophic and therefore the strikes were justified. O'Connell, however, counters that international law defines armed conflict as an exchange of organised armed fighting, a condition absent when Israel attacked on 13 June. ‘The US joined the fighting and attacked a nuclear site. It was acting collectively with Israel but equally had no right to resort to force. International humanitarian law did apply at that point but would also prohibit the attack on the nuclear site for several reasons,’ she explains. ‘The nuclear site had no role in the fighting between Israel and Iran. It was well known that no weapons existed there or would exist there for months or years.’

Federica D'Alessandra, Co-Chair of the IBA’s Rule of Law Forum, explains that assessing the legality of such actions hinges on whether Iran was actively assembling a nuclear weapon at that moment, justifying a ‘last window’ response. ‘International law does however permit the use of force in “anticipatory self-defense”, but under strict conditions of imminence – alongside respect for the jus ad bellum principles of necessity and proportionality,’ she says.

Conflicting intelligence, including US assessments from March, complicates a definitive conclusion, leading to divided expert opinions as full justification rests heavily on Israel's undisclosed intelligence. ‘It’s important to underscore that legality of the use of force does, in large part, depend on whether the threat was assessed as imminent, contextually or temporally, which Israel has said it was,’ says D'Alessandra. ‘However, the burden does fall on the state using force to demonstrate the imminence of the threat and to advance sufficient information to support its legal justification.’

As for nuclear sites, D'Alessandra says that under jus in bello, which addresses the lawful use of force during hostilities, striking facilities used purely for civilian purposes would be illegal. Conversely, if those facilities were ‘dual-use’; meaning they were being employed for the production of a nuclear weapon, in violation of Iran's non-proliferation obligations, and the threat was deemed imminent, then they would constitute a legitimate military target.

On the targeting of scientists or civilians, D'Alessandra said the legality of striking nuclear scientists depends on whether they directly participated in hostilities. This requires a case-by-case assessment of their work's direct contribution to military action and its significant threat to the opposing party. 'If Iran was actively pursuing a nuclear weapon, and those scientists’ work was essential to the weapon production, then they would have constituted lawful military targets as they would have been considered as actively involved in hostilities based on their conduct, thus losing protections associated with their civilian status,' she says, 'otherwise, their targeting would have been unlawful.'

French President Emmanuel Macron acknowledged that the US strikes lacked a legal framework, but nevertheless said there was ‘a legitimacy in neutralising Iran's nuclear structures’. A joint statement by France, Germany and the United Kingdom similarly justified the US attacks. Critics contend these statements represent a political justification of the objective, rather than a legal defence of the means used.

‘The attacks on Iran cannot be seen as legitimate,’ says the Stockholm International Peace Research Institute, an independent Swedish think tank. The group highlighted the civilian casualties of those attacks. ‘The attacks against Iran’s civilian nuclear sites amount to aggression that violates international law, as do the Israeli assassinations of Iranian nuclear scientists, some in their residences. International humanitarian law prohibits attacks directed against civilians and civilian objects,’ says O'Connell. ‘Only members of the armed forces and civilians directly participating in the armed conflict hostilities are lawful targets.’

D'Alessandra says it’s hard to see how media workers or a TV station could be a legitimate target for either side. ‘War propaganda does not amount to active participation in hostilities, and the targeting of journalists without a lawful military justification is a serious breach of the laws of war,’ she says. ‘Media facilities and journalists are a protected civilian category under the laws of war – based on their status – and do not lose their protection unless their activities amount to active participation in hostilities.’

The strikes lacked a UN mandate and clear self-defence justification and carried significant humanitarian and environmental risks, making their legality a subject of global condemnation. ‘Respect for international law has plainly taken another blow,’ says O'Connell, referring to the dozens who lost their lives, those who were injured and the environment that has been damaged ‘pointlessly and unlawfully’.

‘Treaties are the way to end weapons programmes. Not violence,' she says.