The International Court of Justice (ICJ) said on Wednesday that climate change was an "urgent and existential threat" and countries had a legal duty under international law to prevent harm from their planet-warming pollution.

"It only confirms the immensity of the challenge we face and the importance of climate action and the Paris Agreement, and it also reaffirms the need of taking collective and ambitious action," Anna-Kaisa Itkonen, a spokeswoman for the European Commission, told a press conference of the ruling.

In a historic advisory opinion, which is not legally binding but carries political and legal weight, the ICJ said countries breaching their climate obligations were committing a "wrongful act".

Itkonen said the commission, the European Union's top executive body, had taken note of the opinion and was currently "looking into the details" of what it entailed.

Brussels would "stay the course" in its push to achieve climate neutrality by 2050, she added.

Earlier this month the EU unveiled its long-delayed target of cutting greenhouse gas emissions by 90 percent by 2040, compared to 1990 levels. But it built in contested new flexibilities to win over the most sceptical member states.