Among those closely following the case is University of Auckland law professor Caroline Foster, who served as legal counsel for the International Union for the Conservation of Nature.

Reflecting on the two weeks of oral hearings, Foster describes the experience as "almost surreal."

No state is linking what’s happening before the ICJ to what's happening in world trade law.

During a roundtable discussion, the environmental law expert highlighted key arguments and critical omissions from the hearings.

The urgent need to update and renovate international trade law went noticeably unmentioned, according to Foster.

"No state is linking what’s happening before the ICJ to what's happening in world trade law," she says. "Given that collective measures to address climate change most certainly require major renovations in this area, this is really lacking from the dialogue." 

Another significant question raised during the roundtable discussion, organised by the European Society of International Law, was the issue of insurance and climate damage.  

"Reparation for climate damage is a massive challenge," says Foster. 

"When we look at what recent disasters have done to the insurance underwriting market and how thin the world's insurance arrangements are, as well as the increase in severe weather events and other major episodes that will stem from climate change, states are going to have to put their thinking caps on about how our system of reparation, as set out in the law on state responsibility, can operate in this context." 

Strong arguments emerging from the submissions included the customary law obligation to prevent environmental harm, also known as the 'no harm' rule.

This principle of international law requires countries to prevent, reduce and control the risk of environmental harm to others.

"What I saw in the oral pleadings confirms that both treaty and customary international law are seen as relevant, almost universally," Foster says. "Most states take the customary obligation around no harm and prevention seriously." 

However, a few countries argued that they would have had to be historically aware of the risk of harm from emissions for such law to apply.  

Russia said harm from emissions had to be scientifically established and foreseeable, and that humanity had become aware of the issues only in the 1990s.  

Switzerland said there had been reasonably robust knowledge from 1990 about the adverse effects of greenhouse gases - and unequivocal knowledge from 2023. France argued in a similar vein, and the US said there was awareness of the impacts today. 

But several other countries, including Vietnam, Antigua and Barbuda, Solomon and Marshall Islands, Micronesia, and Samoa, presented compelling evidence that countries were aware of the harmful effects of emissions dating back to at least the 1960s.  

Foster says most countries continue to appreciate the significance of the Paris Agreement goal to limit global warming to 1.5°C.

"However, China and Russia argued that 1.5-2°C constitutes a target range. And Saudi Arabia preferred to emphasise ‘stabilising greenhouse gas concentrations’." 

Intergenerational equity was a key theme during the hearings, with submissions from nations like Saint Vincent and the Grenadines arguing that states have duties to act as trustees of the climate system for future generations.  

"Submissions also touched on the concept of due regard for long-term effects of state conduct," Foster says. 

The ICJ's advisory opinion, expected this year, may not be binding but it could provide guidance to combat climate change and determine the responsibilities of countries for historic emissions under international law. 

Foster’s hope is that it will help set the tone for governments, businesses and people around the world to invest maximum efforts in getting to a zero-carbon world.

“The ultimate aim would be to bring the global temperature back below 1.5C above pre-industrial levels.”

Professor Caroline Foster was one of several expert panellists who discussed the ICJ climate change advisory proceedings at an event organised by the European Society of International Law. It’s available to view.