According to a new landmark opinion of the International Court of Justice (ICJ) on the obligations of states with respect to climate change, the world must phase out fossil fuel production to achieve the goals of the Paris Agreement—and this isn't just a scientific demand, it’s a legal imperative.

The ICJ advisory opinion came about because of a United Nations General Assembly resolution requesting it, which itself resulted from a sustained diplomatic effort by the small island state of Vanuatu and a grassroots campaign by the Pacific Island Students Fighting Climate Change.

The Court’s first major finding was that the UN climate treaties (the UN Framework Convention on Climate Change, the Kyoto Protocol, and the Paris Agreement) are not the only laws applicable to the climate crisis. It found that multiple sources of law impose legal responsibilities on states, from duties of customary international law to prevent significant transboundary environmental harm, to international human rights law. Such a ruling is significant because these other sources of law, in particular the obligation to prevent significant environmental harm, may form a stronger legal basis for fossil fuel production phase outs than current obligations under the Paris Agreement.

The second major finding was that the 1.5°C goal is the agreed legally binding temperature target under the Paris Agreement. This is important because the impacts of global warming of 2°C are much worse than those at 1.5°C, and because no new oil and gas fields or coal mines are permissible under pathways consistent with 1.5°C.

Early in its opinion, the ICJ clarified that fossil fuel production is included in the scope of conduct that can potentially be in breach of international law. International legal obligations relating to climate change don’t only cover conduct that itself directly results in greenhouse gas (GHG) emissions (e.g. fossil fuel combustion), but can cover ongoing ‘production, licensing and subsidizing’ of fossil fuels (para. 94).

Later in the opinion, the ICJ was even clearer on this point, specifically stating that a state’s fossil fuel production, fossil fuel consumption, granting of fossil fuel exploration licenses, and the provision of fossil fuel subsidies ‘may constitute an internationally wrongful act which is attributable to that state’ (para. 427).

The significance of this cannot be underestimated. It opens the door for international litigation against states that expand their fossil fuel production or do not phase it out consistently with the 1.5°C temperature limit. Since the Court also found that climate change obligations are so-called ‘erga omnes’ obligations, meaning all states have an interest in compliance, any country can bring a case against a fossil fuel producing nation at the ICJ, including those not directly harmed.

Importantly, the standard to which states are held when it comes to fossil fuel phase out varies with their capabilities. According to the ICJ, ‘the capabilities of states are a key factor…for the determination of the appropriate standard of due diligence in a particular situation’ (para. 290). However, even a state with lesser capabilities or insufficient resources is required ‘to take all the means at its disposal to protect the climate system in accordance with its capabilities and available resources’ (para. 291). Capabilities are not a “get out of jail free card”, in other words.

Where states commit a breach of international law, and this breach can be causally linked to particular climate harm, they can be held liable for reparations, including restitution (restoring the situation to how it was before the harm occurred, such as through ecosystem restoration or fixing infrastructure), compensation (financial compensation of the harm), or satisfaction (for example, formal apologies or declarations that an internationally wrongful act was committed).

States committing internationally wrongful acts will also be liable for ‘performance’ and ‘cessation’. That is, even though a breach has been committed, they must continue to adhere to their obligations and cease the internationally wrongful act(s). For instance, if an oil and gas exploration licence has been issued in breach of international law, that state would likely be ordered to cancel that licence, and phase out its production in line with the 1.5°C goal.

Downstream impacts of fossil fuel production, licensing, and subsidies must also be taken into account. Under the due diligence obligation to prevent environmental harm, the court makes clear that the combustion emissions from burning extracted fossil fuels must be considered in the Environmental Impact Assessments (EIAs) of fossil fuel projects. This is a big deal because EIAs typically focus only on the emissions that occur in operating an oilfield, such as from fueling support ships or powering rigs. But about 75% of the GHG emissions associated with a barrel of oil occur when the fuel is ultimately consumed, such as in a car or aeroplane.

The separate Joint Declaration of Judges Bhandari and Cleveland goes into the issue of fossil fuel production in even more depth. ICJ Declarations are where individual judges, or groups of judges, wish to record a clarification or emphasize certain points made in the main judgment. They hold less weight than the main opinion but are still an important and persuasive source of law.

The two judges further clarify the point that states must phase out fossil fuels. They said that the stringent due diligence obligations to implement nationally determined contributions (NDCs) under the Paris Agreement and prevent significant transboundary harm require states to adopt and enforce regulations including phasing out the production and use of fossil fuels, transitioning away from fossil fuels, and regulating fossil fuels in a manner that does not undermine global cooperation to achieve these goals, including with respect to subsidies.

Judges Bhandari and Cleveland also noted that NDCs, which are due this year, must address fossil fuel production. According to Judges Bhandari and Cleveland, States' NDCs must address all fossil fuel production, licensing and subsidy activities in a manner consistent with achieving the 1.5C temperature goal. An IISD report contains guidance for states in this regard.

The ICJ’s opinion is not legally binding, but it carries considerable legal weight and political legitimacy. It is likely to influence future domestic and international climate change litigation, shape negotiations under the UN climate talks, provide new leverage to vulnerable states seeking accountability and climate justice, and embolden civil society activism.