Thread by @JohnHKnox

On July 23, the International Court of Justice issued its advisory opinion on climate change. Here’s a somewhat lengthy thread on what I see as its main points – what it did (and didn’t) decide. 1/24

https://x.com/CIJ_ICJ/status/1948043424168288643

Before starting, I want to emphasize that, on the whole, this is a very strong opinion. I’ve heard from many observers and participants that it’s better than they had dared to hope. 2/24

We should take a moment to thank, especially, the Pacific island youth who began this process; Vanuatu, which had the courage to push it forward; and the many civil society actors that supported it. Without them, this would not have happened. 3/24theguardian.com/world/2025/jul…

So, on to the case. Recall that ICJ advisory opinions aren’t legally binding, but courts and other bodies that pay any attention at all to international law treat them as persuasive. The weight of persuasiveness here is increased by several factors, including . . . 4/24

. . . the opinion is unanimous; it aligns itself wherever possible with opinions of other int’l bodies; and, perhaps most important, on virtually every issue, it stays within the mainstream range of opinion of States – albeit usually at the progressive end of the range. 5/24

In 2023, the UN General Assembly asked the ICJ two questions: (a) what are States’ obligations under international law to protect the climate system? (b) what are the legal consequences for States when they have caused significant harm to the climate? 6/24 press.un.org/en/2023/ga1249…

In its advisory opinion, the ICJ made clear – repeatedly – that it saw its job as setting out the international legal framework for States generally, and NOT as addressing the responsibility of individual States. That, it said, would have to be left to specific cases. 7/24

With that preamble, let’s get to the opinion. Again, I won’t try to describe everything! (For example, I’m leaving the law of the sea to others.) On the first question – what are the relevant international legal obligations? – I see 7 points as especially important. 8/24

First, the ICJ rejected the “lex specialis” argument. The US and some others argued that the climate treaties, especially the 2015 Paris Agreement, were the only relevant int'l law. The ICJ’s rejection should end this specious argument for good. 9/24

Second, the ICJ rejected the argument (again, by the US and others) that the climate treaties don’t require much. Much of the debate has been over Paris article 4, which requires each State to submit its own "nationally determined contribution" (NDC) to mitigation. 10/24

The ICJ said that each State has to “do its utmost to ensure that the NDCs it puts forward represent its highest possible ambition” to achieve the goal of the agreement and that, collectively, States have to ensure that the NDCs are capable of achieving that goal. 11/24

The ICJ also said that, based on Paris itself and later statements by the Paris Conference of Parties, the relevant goal is to limit global warming to 1.5°C. Perhaps needless to say, States’ NDCs do not currently come close to achieving that goal. 12/24unepccc.org/emissions-gap-…

Third, and relatedly, the ICJ said that Paris Agreement parties have to make their “best efforts” to actually do in practice what their NDCs say that they will do. That means that they must be proactive and pursue measures that are reasonably capable of achieving the NDCs. 13/24

Fourth, the ICJ said that under customary international law, States must make their best efforts to avoid significant environmental harm. So even States that withdraw from Paris (like the US) have duties to mitigate and adapt, including through international cooperation. 14/24

Fifth, the court said that the effects of climate change can significantly impair the enjoyment of human rights. Human rights law therefore requires States to take necessary measures to protect the climate system. This language supports the many rights-based climate cases. 15/24

Sixth, the ICJ said that the human right to a clean, healthy and sustainable environment – recognized in 2022 by the General Assembly - is “inherent in” and “essential for” the enjoyment of other human rights. This solidifies its standing in intl law. 16/ news.un.org/en/story/2022/…

Seventh, States must take their human rights duties into account when implementing their duties under climate (and other environmental) treaties, and vice versa. Like much else in the opinion, this language will be cited by advocates in many cases and forums going forward. 17/24

That brings us to the 2d question, on “legal consequences” for States. The ICJ made clear that it only addressed the consequences of breaches of legal obligations, thus avoiding the interesting but controversial issue of potential liability for harm caused by legal conduct. 18/24

The ICJ again rejected lex specialis, and said the whole body of int'l law on state responsibility applies. That means the full panoply of remedies, including compensation, may be available, depending on the nature of the breach – but there has to have been a breach of some kind.

The ICJ joined many other courts in rejecting the argument that just because a State is not the sole cause of climate change, it cannot be held responsible. And it made clear that States could be responsible because they failed to regulate private sources of harm. 20/24

In highly quotable language, the ICJ said that such an "internationally wrongful act" may occur through a State's failure to take appropriate action to protect the climate system from GHG emissions, including fossil fuel production, consumption, or subsidies. 21/24

Finally, I want to highlight that the Court did NOT provide guidance on the critical issue of how to determine States’ individual shares of responsibility. This will no doubt continue to be the subject of intense debate in international and domestic forums. 22/24

In closing, the ICJ said int'l law has an important but limited role. “A lasting and satisfactory solution requires human will and wisdom . . . to change our habits, comforts and current way of life in order to secure a future for ourselves and those who are yet to come.” 23/24

Still, it is worth celebrating this opinion, the judges who worked hard to reach unanimity (how hard? individual judges filed 12 separate opinions!), and, most of all, the advocates who fought with conviction and creativity to get to this point. 24/24 bbc.com/future/article…