In July this year, the battle to combat climate change entered a new phase. It was then that the United Nations’ highest court issued a landmark opinion stating governments had a legal duty to protect the environment.
According to ClientEarth, a non-profit group of lawyers that has built a formidable reputation for holding governments and companies to account over climate change, nature loss, and pollution, the decision could have wide implications not only for official policy, but also for businesses and investors.
“The court found that the protection of the environment is a precondition for the enjoyment of human rights, which is crucial … The court was at pains to make that this isn't just about the climate, it's about nature as well,” says Adam Weiss, Chief Programmes and Impact Officer at ClientEarth.
“With governments held accountable, there is more incentive for them to enforce regulation on businesses and to create new, stricter rules.”
In its ruling, the International Court of Justice (ICJ) said that “states have a duty to prevent significant harm to the environment by acting with due diligence and to use all means at their disposal to prevent activities carried out within their jurisdiction or control from causing significant harm to the climate system and other parts of the environment”.https://www.icj-cij.org/sites/default/files/case-related/187/187-20250723-pre-01-00-en.pdf
Climate change treaties, such as the Paris Agreement, set out binding obligations for countries which have signed them, on issues including the mitigation of greenhouse gas emissions, promotion of climate change adaptation measures and support for biodiversity.
Court cases
The ruling opens the door to more legal action to ensure these obligations are met. To date, over 3,000 climate cases have been filed in 60 countries. ClientEarth has been involved in many of them. This year alone, the actions it brought saw Dutch carrier KLM found liable for making misleading climate-related claims in its marketing, the UK government’s climate strategy declared not fit for purpose and Portugal abandoning plans to build a new airport.
So far, the majority of court cases have targeted government bodies, but that could change, Weiss says.
“Basically, the International Court of Justice has opened up the possibility that there can be lawsuits between countries because of the damage caused by climate change,” he explains.
Thus, a poor country suffering the impacts of climate change could in theory sue a rich country which contributed to environmental deterioration. An international court could then rule that the rich country should stop the detrimental actions, and, on an exceptional basis, could possibly even award compensation.
“I think the ICJ opinion strengthens the hand of anyone trying to bring an attribution kind of case because what the opinion says is it's theoretically possible”” Weiss says.
Yet because such cases would be complicated and difficult to bring to court, a more probable consequence would be more action against companies – which in 2024 were the targets of just 20% of all climate-related litigation.Global trends in climate change litigation: 2025 That, in turn, will have consequences for financial markets.
We are likely to see more “people who are responsible for corporate conduct being held to account for whether their actions line up with their words and, more importantly, whether their actions add up to what we need to do to reach the Paris goals,” Weiss says.
“We will see that certain business models are simply not viable anymore… If I were working for a finance company, my investment in a fossil fuel company [would start] to look shakier because one of those companies is going to be held liable and have to pay damages. And if I were a bondholder in a country that's violating climate laws in a really obvious way, I might be thinking about that as well.”
Led by China and Europe
Of course, in order to be effective, the ICJ ruling needs to be adhered to – as is not always the case with international laws, which don’t have the same enforcement mechanisms as national legislation.
With climate issues currently seeing some pushback from governments – notably in the US – there could be reason to think the ruling will be ignored. But Weiss is cautiously optimistic.
One reason for optimism is that “the EU and China are increasingly invested in international law”. For China, this presents an opportunity to secure global leadership on the environmental stage.
Another encouraging sign is that the ruling was unanimous – a rarity in the history of the ICJ, suggesting broad international support.
Furthermore, the ICJ is not alone. Its judgment chimes in with last year’s European Court of Human Rights (ECHR) ruling, in the so-called Klima case, that the Swiss government violated the rights of its citizens by not doing enough to combat climate change. This year, meanwhile, the ECHR found that Italy violated the rights of the inhabitants of an area near Naples by not addressing toxic waste pollution.
“This brings together this idea that there is a human right to a clean and healthy environment and states have obligations to meet it,” Weiss says. “This is the most advanced thinking on the relationship between human rights and climate. So I'm expecting big rulings coming in the future.”
All in, momentum is building for tighter regulation on climate issues and closer monitoring, as well as more public spending.
“States have to take mitigation measures, they have to get greenhouse gas emissions under control, including by regulating the activities carried out by private actors. And that is going to be held up to a best effort standard,” Weiss says. “I might argue that the opinion means everything for business and investments.”
