The principal function of Public International Law is to regulate conduct between nation states (although it may engage other actors in various ways). From the first principle of ‘sovereignty of states’ it follows that states have a responsibility to respect the sovereignty of others. That, in turn, imposes on all states a duty to ensure that activities within their jurisdiction do not cause substantial harm beyond their borders. A failure to do so is a breach of international law.

Prima facie ​anthropogenic climate change is the archetype case for an action in public international law, based on the duty to prevent harm to others. The UNFCCC specifically refers to the duty in its Preamble, confirming the principle’s relevance to climate change.

Historically States have brought actions based on this duty where the threat has been minor compared to that posed by climate change (e.g. air pollution causing damage to a discrete area of farm-land). What explains the lack of legal action to date, in particular from states on the record as considering climate change ‘an existential threat’?

It is not, of course, that states are unaware of their rights (a number of climate vulnerable states made declarations asserting these rights on signing the UNFCCC). Rather the explanations for inaction appear to be as follows:

1. ​potential claimants are nervous about the repercussions of bringing an action against those on whom they depend on for finance and trade;
2. given that all states are, to some extent, emitters of greenhouse gases, there is uncertainty about how the principle would be applied in practice; and
3. states have been hoping to address climate change comprehensively through the UNFCCC process rather than the courts.

The limits of the UNFCCC are now clear; potential claimants might spread the political risk by bringing an action jointly, or simply seeking an advisory opinion from the ICJ; and the Court would be bound to apply the principle on the basis of equity and the precautionary principle.

In practice, enforcement of international obligations is likely to occur through a combination of international organisations, state and non-state actors. The main subjects of international law, however, are states. Generally speaking, to have standing a state must be able to show it is an ‘injured state’, which it can do on the basis that it is specially affected by an obligation owed to a group of states or the international community as a whole (see International Law Commission’s 2001 Articles on State Responsibility, Art. 42).

Some obligations, however, are considered to be of such fundamental importance that they apply as between all members of the international community: these are described as obligations ​erga omnes. In respect of such an obligation a state (or group of states) may bring a claim on behalf of the international community as a whole – an ​actio popularis.

The obligation to preserve a safe climate may be considered the archetype of an obligation ​erga omnes. On that basis it is open to any state or group of states to bring an action for breach of the duty to prevent (recognising that the more immediately climate vulnerable countries have the most obvious motivation to do so).

The ICJ is the principal court of the UN. It has jurisdiction where:

1. state parties refer a specific dispute;
2. a dispute is referred via a compromise clause in a treaty;
3. relevant state parties have agreed to submit to its jurisdiction more generally (72 countries have done so, including India, Marshall Islands, Mauritius, UK, Canada Australia, but not US, China or Russia); or
4. the UN General Assembly, Security Council, or specialised agency (such as the World Meteorological Organisation, International Maritime Organisation or World Health Organisation) request an advisory opinion.

Assuming theICJ were asked to determine the scope of Country X’s duty to prevent in relation to GHG emissions, it would need to determine a general formula for doing so. Most likely this would involve equitable distribution of a carbon budget, determined on the basis of consistency with the long-term temperature goal. Consequently an ICJ judgement has the potential to deliver a generalised framework for binding, country greenhouse gas (GHGs) emissions (with far greater ease than the UNFCCC process).

See further:

• Principles of Public International Law
• Carbon Budgets, Equity and Attribution

GHGs threaten the marine environment in two ways:

1. by warming the oceans beyond the adaptive capacity of many forms of ocean life; and
2. in the case of CO2, by acidifying the oceans, jeopardising the ocean food chain, and the livelihoods and food security of those who depend on it.

State use of the oceans is governed principally by the UN Convention on the Law of the Sea (UNCLOS).

UNCLOS Art. 1(4) defines ‘pollution of the marine environment‘ in broad terms, applicable to the emission of GHGs.

States are obliged to protect and preserve the marine environment generally (Art. 192), and specifically to take all measures necessary to ‘prevent, reduce and control’ pollution of the marine environment.

​UNCLOS, in other words, imposes on states a clear, legal obligation to avoid damaging the marine environment through the emission of GHGs.

In contrast to UNFCCC, UNCLOS explicitly provides for liability and compensation, requiring that States ensure the availability of ‘prompt and adequate compensation’ in relation to damage to the marine environment caused by those within its jurisdiction (UNCLOS Art. 234).

UNCLOS Article 287 provides a choice of procedures for dispute resolution (to be determined by Party declaration):

1. the International Tribunal for the Law of the Sea;
2. the International Court of Justice;
3. an arbitral tribunal constituted in accordance with Annex VII;
4. a special arbitral tribunal constituted in accordance with Annex VIII for one or more of the categories of disputes specified therein.

In the absence of a declaration a Party is deemed to have elected arbitration, and where two or more Parties have chosen different options, the dispute will go to arbitration, unless they otherwise agree.

It might conceivably be argued that, in light of the UNFCCC framework, UNCLOS should not be applied to the emission of GHGs: ​lex specialis derogat legi generali (the specific law overrides the general).

Such an argument fails on two grounds:

1. Ocean acidification is outside the mandate of the UNFCCC (which makes no mention of it);
2. In any event UNFCCC does not impose specific emission reduction commitments (which therefore remain subject to general principles of law and the requirements of other relevant treaties).

This section does not describe proactive legal action (i.e. a legal action taken to challenge directly activity contributing to climate change). Rather it provides an overview of the legal framework relating to trade restrictions, imposed for the purpose of tackling climate change.

​As the WTO Appeal Hearing in United States – Standards for Reformulated and Conventional Gasoline, WTO makes clear, ​trade restrictions designed to promote cleaner forms of energy are, in principle, permissible under the WTO regime.

​The Preamble  to the Marrakesh Agreement Establishing the World Trade Organization begins with an acknowledgement that rules of trade should support the objective of sustainable development and should seek to ‘protect and preserve the environment’.

GATT, Article XX allows WTO members to take measures ‘necessary to protect human, animal or plant life or health’ or ‘relating to the conservation of exhaustible natural resources’, as long as the measures do not constitute ‘arbitrary or unjustified discrimination’ or ‘a disguised restriction on trade.’

As as is evident from the WTO case United States – Standards for Reformulated and Conventional Gasoline, as long as a measure is genuinely intended to prevent climate change it is likely to be covered by Article XX (g) (i.e. that it relates to the conservation of exhaustible natural resources).

The case concerned a US regulation (Regulation of Fuels and Fuel Additives – Standards for Reformulated and Conventional Gasoline), enacted by the US Environmental Protection Agency, pursuant to the Clean Air Act 1990, to control toxic and other pollution caused by the combustion of gasoline manufactured in or imported into the United States. In respect of both reformulated gasoline and conventional gasoline, 1990 baselines are an integral element of the regulation’s enforcement process. Brazil and Venezuela argued that the rule contravened the WTO free trade regime.

The first instance WTO Panel concluded that clean air was a ‘natural resource’ that could be depleted; and therefore that a policy to reduce the depletion of clean air would be covered by Article XX(g).

​In practice the more difficult issue for the Country applying the policy may be demonstrating that it does not cause ‘unjustifiable discrimination’ between countries. In this case the US did not make available to foreign refiners the same provision allowed to domestic refiners to determine an individual baseline for 1990, arguing that this was impractical. The WTO Appellate Body disagreed on this point, and consequently found a violation of Article III(4). However the Body went out of its way (on page 29 of the judgement) to emphasise that this finding:

does not mean, or imply, that the ability of any WTO Member to take measures to control air pollution or, more generally, to protect the environment, is at issue.

The Appellate Body adopted a similar approach in the‘Shrimp / Turtle’ case of 1998. There, again, it held that a US requirement that imported shrimps be harvested using a specific device to prevent turtle by-catch:

1. was covered by the exemption of Article XX(g);
2. but had been applied in a way that was discriminatory.

In particular the Body focussed on the failure of the US to engage in negotiations with exporters regarding the requirement, and  to consider alternatives that might serve an equivalent purpose.

​The broad principles emerging from these cases seem reasonably clear:

1. WTO Members may introduce rules restricting imports where the purpose of the rules is to prevent climate change;
2. The rules must be applied in a way that is fair between countries, and not overly prescriptive where different approaches might reasonably be considered to serve the same purpose;
3. It may be appropriate to enter into negotiations with affected Parties regarding the rules and their potential impacts on exporters.

In private law, actions which cause damage to the person or property of another will generally constitute a tort or ‘delict’, giving the injured party the right to sue the perpetrator.

Private international law concerns the application of private law to cross-border cases.

On this basis individuals or communities suffering climate change loss and damage should have multiple claims against the major polluters, covering not just the costs of climate change damage incurred, but also the costs of adaptation. If successful, such actions would:

1. ensure victims of climate change are appropriately compensated; and
2. provide accountability and responsibility for climate change loss and damage, harnessing investment towards clean technologies.

Potential claimants have been deterred from bringing claims by the perceived complexities of issues such as causation and attribution.

This section will provide an overview of:

• how claims in private law might work in practice; and
• what countries can do, in terms of domestic legislation, to ensure their citizens are supported in bringing claims in private law.

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The prudence standard of the Act can easily support a decision not to continue to hold or invest in fossil fuel companies. The risks and rewards now offered by such securities are asymmetric, in the sense that the foreseeable rewards are not likely to be equal to the foreseeable risks. The risk that, at some unknown and unknowable, yet highly likely, point in the future, markets will begin to adjust the equity price of fossil fuel company securities downward to reflect the swiftly changing future prospects of those companies, is as serious as it is immense. Moreover, the possibility of that adjustment being a swift one is also a serious risk. A decision to linger in an investment with such an overhanging risk, and expect to time one’s exit before the danger is recognized in the market, is a strategy hard to fit within the concept of prudence.

Whether the duties of care, skill and caution today compel a decision not to hold or invest in fossil fuel companies can ultimately only be answered by a court, which always looks back in time, and therefore can be subject to the force of hindsight.

At some point down the road towards the red light of 2 degrees C, however, it is entirely plausible, even predictable, that continuing to hold equities in fossil fuel companies will be ruled negligence.‘ Bevis Longstreth, 2016.