Is an ICJ Advisory Opinion on climate change a big deal? Yes, it is!

By Francesco Sindico - posted on 25 July 2025

Today we know that if a State, or a private actor under its jurisdiction, acts in a way that can lead to significant harm to the climate system (for example by keeping fossil fuel subsidies) they are going through a red light and they are acting not only in an irresponsible manner, but they are going against the law.

In this post, Professor Sindico offers his initial reflections on why the ICJ Advisory Opinion on climate change is important to a non-lawyer audience. A second, related post offers further normative thoughts on the judgment, which can also be found on the Strathclyde Law Blog. 

Is an International Court of Justice Advisory Opinion a big deal?

Let us assume you are into football (I am). This is like the World Cup or the Euros for football. Or maybe you are into films, who is not? This is like the Oscars! The ICJ is the World Cup or the Oscars of international law. So, yes, it is a big deal!

Having been part of the final of the World Cup, even if just from the sidelines (or, a bit more ambitiously, by entering into the pitch at the very last minute – wink to the fact I was the last one to take the floor on 13 December 2024 before the judges asked their very important questions) on behalf of the International Union for the Conservation of Nature legal team (led by Christina Voigt) fills me with joy and pride, especially considering the very progressive and balanced Opinion rendered by the Court.

So, what has the ICJ said that is so important? International lawyers navigate this kind of language on a daily basis. Erga omnes, customary law, due diligence, non refoulement are their bread and butter. But for the other disciplines, and other people out there, they mean very little, so let me try and break it down in very simple (maybe too simple) words through an analogy.

Until this week, it was not entirely clear that passing through a red light was illegal. But now, thanks to the Advisory Opinion, all drivers (States and private actors) know that driving without care and passing through a red light can be illegal. Does that mean that from one day to the other all drivers will stop at a red light? No, but they will think twice about it. If you are a responsible driver (State or private actor) you now know that: a) you have to stop at the red light and b) you will face a penalty if you pass through the red light. Whilst the way the red light rule is enforced, and irresponsible drivers are prosecuted, is a completely different in national and international law, with the latter closely related to international politics and power, still today we know something we did not know yesterday. Today we know that if a State, or a private actor under its jurisdiction, acts in a way that can lead to significant harm to the climate system (for example by keeping fossil fuel subsidies) they are going through a red light and they are acting not only in an irresponsible manner, but they are going against the law.

Instead of immediately starting to question the effectiveness of such a law and being cynical and sceptical (see the Channel 4 anchorman interviewing one of the students who led the charge for the Advisory Opinion), let us stop for a moment and celebrate those who kickstarted this process and kept the momentum going over the past six years. Let us see the Advisory Opinion of the ICJ as a foundation to build hope for future climate justice.

You can see the Advisory Opinion online (together with a summary from the Court itself). IUCN World Commission on Environmental Law’s reaction to the release of the Advisory Opinion is available on its website.