Text of the UN Framework Convention on Climate Change

Text of the Paris Agreement

Text of the Paris Decision

Relations between states are governed by law, in much the same way as are relations between citizens. Under international law it is illegal for one country to cause substantial harm to the territory of another. 

Countries consuming more than their fair share of the ‘carbon budget’ are damaging their neighbours in two important ways:

  1. They are increasing their exposure to flood, draught, food and water scarcity, disease and conflict;
  2. They are limiting their opportunities for economic development by reducing the share of carbon budget available to others.

The Preamble to the United Nations Framework Convention on Climate Change (UNFCCC) explicitly refers to obligations under general international law:

Recalling also that States have, in accordance with the Charter of the United Nations and the principles of international law … the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction.

​If a country fails to take reasonable steps to prevent such damage it is breaching international law. If the ICJ were confronted with such a case it would need to consider developing principles for:

  • the equitable sharing of the carbon budget consistent with limiting warming to 1.5 or ‘well below’ 2 degrees Celsius;
  • appropriate financial compensation for carbon creditors from carbon debtors.

See: Blueprint

The outcome of such a case might be a science-based, legally binding framework for reducing global greenhouse gas emissions at the rate required to limit warming to 1.5 or ‘well below’ 2 degrees Celsius.

​​​In some cases obligations between states are specified in treaties, along with particular enforcement mechanisms. In the absence of a  specific treaty obligation or enforcement mechanism, an alleged breach of international law may be brought before the International Court of Justice (ICJ), the principal court of the UN.

The governments of climate vulnerable countries may be reluctant to commence legal action for a variety of reasons. NGOs and civil society should consider the merits of such action for themselves, with a view to making appropriate representations. An action might take the form of an actio popularis on the basis that developing legal principles to prevent dangerous climate change would be in the interests of the wider international community.

​While the Paris Agreement brings the existing Warsaw international Mechanism for Loss and Damage under its ambit, the accompanying Decision specifically excludes liability and compensation from its scope. Consequently liability and compensation are left to be determined on the basis of general principles of law.

This section discusses the principles of international law that may be relevant to a claim by one state (or group of states) that another is failing to take sufficient steps to prevent climate change. 

Some of the principles, such as the precautionary principle and the polluter pays, may also be relevant in the context of national law. 

Countries might also consider commencing action under the UN Convention on the Law of the Sea (UNCLOS), which includes an enforcement mechanism providing for liability and compensation. As well as warming the ocean, CO2 causes it to acidify, and falls within the UNCLOS definition of ‘pollution of the marine environment.’

See: Types of Legal Action

​​Nine principles of International Environmental Law

Philippe Sands QC, in the Third Edition of his Principles of International Environmental Law​, sets out the following 7 principles that ‘are potentially applicable to all members of the international community across the range of activities that they carry out or authorise‘ and that ‘have broad, if not necessarily universal, support and are frequently endorsed in practice‘:

1. state sovereignty / the ‘no harm principle’;

2. the duty to prevent / exercise due diligence;

3. the duty to cooperate in good faith;

4. sustainable development;

5. theprecautionary principle;

6. the polluter pays principle; and

7. common but differentiated responsibility.

Breach of the first three of these principles may give rise to a free-standing cause of legal action. The latter four principles may be invoked to develop and define the scope of legal responsibility.

​​To these seven, two more may be added:

  • ​​8. equity; and
  • 9. elementary considerations of humanity.

All nine principles are pertinent to the context of climate change litigation, informing and supplementing a true interpretation of UNFCCC and the Paris Agreement. Taken together they demand that states make equitable contributions to meeting the long-term climate goal (both in terms of limiting GHG emissions and providing finance for mitigation and adaptation).

1. ​State sovereignty / ‘no harm’ principle

Arguably this principle is the foundation not just of international environmental law, but of international law generally. Recognising the interdependence of states’ rights and obligations, it consists of both right and corresponding duty:

  • the right of jurisdiction over a territory, its population and natural resources; and
  • the duty of non-intervention in the area of exclusive jurisdiction of other states.

Its application to cross-border pollution was first considered by the Trail Smelter Arbitral Tribunal in 1941. Sulphur Dioxide emissions from a smelting plant in Canada (owned by a Canadian company) were causing substantial damage to land in the US. The Tribunal held the Government of Canada responsible for the damage on the basis that no state may permit activity on its territory which causes serious injury to another.

On the same principle, if State A permits greenhouse gas emissions on its territory on a scale which cause significant harm within State B, State B has a good cause of action against State A. In practice the principal challenges for an action brought on this basis are likely to be causation and attribution, i.e.:

  • Can State B prove the damage can be attributed to climate change?
  • If so, can State B prove that State A has made a substantial contribution to climate change?

Until recently these issues were considered to be substantial impediments to an action for breach of the no harm principle. Advances in climate science, however, and the approach Courts have taken to causation in domestic cases in the Netherlands and the US, are now prompting a reassessment of this view.

In the absence of agreed, legally-binding limits, the principles for attribution will need to be developed through the courts on the basis of equity (see Blueprint).

Despite the basic principle of territorial jurisdiction, States may apply their environmental laws extra-territorially where:
a) the subject is a company registered or incorporated in that state; or
​b) activities in another state are having, or are likely to have, effects in that state.

The UK, in other words, could require BP to comply with UK environmental law in respect of all of its operations; and any country likely to be affected by BP’s operations might apply its laws to BP.

​​2. Duty to prevent / due diligence

​The duty to prevent is closely related to the ‘no harm’ principle. Indeed many would argue they are one and the same. The International Court of Justice has confirmed the legal status of the duty to prevent harm to other states or areas beyond their jurisdiction (see opposite).

The duty is incorporated within the UNFCCC: the Preamble refers to it directly as a principle of international law, and Article 3(3) obliges Parties to take preventative measures on the basis of the precautionary principle.

If the duty to prevent and the ‘no harm’ principle can be distinguished, it is on the following basis: an action brought on the basis of the duty to prevent requires proof neither of causation nor of harm that has already occurred. It is enough for State A to show that State B is taking insufficient steps to protect State A from harm. If, for example, States A, B, C, D and E can show that:

i) they are at serious risk of harm if average global warming exceeds 1.5 degrees Celsius; and that

ii) State F is taking insufficient steps to prevent warming exceeding 1.5 degrees Celsius,

then, under general principles of law, States A, B, C, D and E have a good cause of action against State B.

Put another way, States have a legally binding duty to prevent harm to other states from their GHG emissions; a duty, which arises independently of the UNFCCC process and the Paris Agreement.

On what basis would the adequacy of Party F’s NDC be assessed?

UNFCCC directly incorporates a number of relevant principles of law, the most significant of which are:

the precautionary principle; and


The question for the court might therefore be framed as follows:

In light of the precautionary principle, and principles of equity, is Party F’s NDC adequate to discharge its duty to prevent climate induced harm to Parties A, B, C and D?

For all the talk of the voluntary nature of NDCs, it appears we have a legally binding framework for GHG emissions after all (albeit one which requires development through the courts). 

See further: 

the Precautionary Principle and Equity (below)


The Structured Expert Dialogue (SED), established at COP18 to review the adequacy of the climate change long-​term goal, concluded in May 2015 that ‘in some regions and vulnerable ecosystems, high risks are projected even for warming above 1.5 degrees Celsius. We are therefore of the view that Parties would profit from restating the long-term goal as a ‘defence line’ or ‘buffer zone’, instead of a ‘guardrail’ up to which all would be safe.’

This conclusion helps define the duty to prevent in the context of climate change. Reinforced by the incorporation of the 1.5 degree Celsius target in the Paris Agreement, States are now, almost certainly, under a legal obligation to the more vulnerable regions of the world to exercise due diligence in preventing warming exceeding 1.5 degrees.

A State may discharge the obligation of prevention by, for example, legislative, administrative or other action necessary for enforcing the laws (see International Law Commission’s Draft articles on Prevention of Transboundary Harm from Hazardous Activities, with commentaries, 2001).

3. The duty to co-operate in good faith​

Whereas the ‘no harm’ principle and the duty to prevent are substantive, outcome based obligations, the duty to co-operate in good faith over shared resources is, essentially, an obligation of procedure, reflected in Principle 7 of the UNEP Draft Principles 1978 (see opposite).

As the ICJ has stated in the Gabcikovo-Nagymaros Project Case 1997 it also requires that states apply a treaty: ‘in a reasonable way and in such manner that its purpose can be realised’.

In the context of climate change the duty implies that States should inter alia:

  • Define their common objectives;
  • Co-operate in good faith towards realizing those objectives;
  • Exchange information and consult each other regarding actions which may impact on those objectives; and
  • Develop common mechanisms for adapting to and mitigating the consequences of climate change.

While the UNFCCC process is the de facto mechanism through which Parties implement the duty to co-operate over climate change, it is worth noting that obligations to exchange information and consult over GHG emissions arise independently of the UNFCCC process and the Paris Agreement. A failure to engage in good faith with others over national GHG emission reduction targets should be construed as a breach of this principle.​

​4. Sustainable development

​Sustainable Development is the principle that integrates considerations of economic development with environmental protection. As such it might be regarded as the founding principle of the international community (as reflected in the 2015 Resolution of the UN General Assembly: Transforming Our World: the 2030 Agenda for Sustainable Development.)

Crucially ‘sustainable development’ is not simply a generalised aspiration, it is a principle with legal consequences (as recognised in judgements of the ICJ and WTO).

The legal content of the principle is as follows:

  • As a matter of law, economic development must be reconciled with environmental protection (Gabcikovo-Nagymaros case; Shrimp / Turtle case; Iron Rhine arbitration);
  • Development projects demand practical measures to prevent or mitigate environmental harm (Iron Rhine arbitration);
  • ​The interests of future generations must be taken into account (​Brundtland Report, Advisory opinion on The Legality of the Threat or Use of Nuclear Weapons).

In relation to common resources, equitable principles may need to be invoked both to determine ‘fair shares’ as between states and between generations: indeed the Preamble the Paris Agreement urges Parties to respect and promote ‘intergenerational equity’ in taking action on climate change: See Blueprint.

One interesting legal question is the extent to which the rights of future generations may be enforced through the courts. There is a good argument that a key component of the right to family life is a healthy environment for one’s children and grand-children. On that basis individuals as well as NGOs might find a basis for bringing actions on behalf generations to come. 

5. The precautionary principle

The precautionary principle, as set out in Principle 15 of the Rio Declaration, is really just the legal formulation of a common sense proposition for managing risk: preventative steps should reflect both an event’s probability and its impact. If the consequences of an adverse event would be severe, you take steps to guard against it, even while the probability of it occurring remains relatively low.  

Unlikely as it seems to me that my London house will burn down, in the event that it did, the financial consequences would be so serious that it makes sense to insure against the risk (indeed my lender requires me to do so). For a national government, even if there’s just a 1% chance of an epidemic of avian flu, that’s probably a sufficient reason to stock-pile anti-viral medications. Let’s say there was a 40% risk of an epidemic, and that the US government, in full knowledge of this, failed to prepare. Most likely it would bear legal responsibility for the consequent, avoidable loss of life to its citizens. Likewise, if there were a scientific consensus of a 60% chance of a meteor striking the earth in the next 50 years, with sufficient force to kill hundreds of millions of people, obliterating a number of small island states, lack of scientific certainty could not excuse (morally or legally) governmental inaction.

Some in the US have challenged the principle (fearing it might be used to justify protectionist trade measures), and the ICJ has not specifically invoked it in its judgements. Nevertheless it has been widely incorporated into environmental treaties (including the UNFCCC), and, in practice, it is a necessary corollary of the ‘duty to prevent’ / ‘principle of due diligence’. 

In the context of climate change UNFCCC Art. 3(3) is explicit that the precautionary principle should be applied:

The Parties should take precautionary measures to anticipate, prevent or minimize the causes of climate change and mitigate its adverse effects.

There is, of course, no serious scientific doubt that global warming is already occurring, nor that serious and irreversible damage is becoming increasingly severe. Nevertheless the precautionary principle will support legal action on climate change by helping to determine the scope of the ‘duty to prevent / duty of due diligence’, reinforcing the point that states are legally bound to take action which leaves a low probability of the long-term temperature goal being exceeded. 

The Structured Expert Dialogue (SED), established at COP18 to review the adequacy of the long-​term goal, concluded in May 2015 that:

in some regions and vulnerable ecosystems, high risks are projected even for warming above 1.5 degrees Celsius. We are therefore of the view that Parties would profit from restating the long-term goal as a ‘defence line’ or ‘buffer zone’, instead of a ‘guardrail’ up to which all would be safe.

The 1.5 degree Celsius target is now embedded in the Paris Agreement. On this basis the duty to prevent demands that high polluting states take precautionary measures to prevent the target being exceeded. If they fail to do so they will potentially be liable for the consequences to vulnerable states.​​​

6. The Polluter Pays

​Legal​ responsibility for harm caused to others is one of the mainstays of the modern life. Imagine a world in which drivers were unaccountable for the accidents they cause; or doctors could remove the wrong lung with impunity; or an architect miscalculate the foundations for a bridge without being liable etc, etc. Legal responsibility is not just a mechanism for compensating those who suffer injury; it’s a harm prevention strategy incentivising due care and diligence towards others.

It is unfortunate that this basic principle, which is generally taken for granted as elementary and indispensable, has not been applied where it’s needed most: those who profit from the development and exploitation of fossil fuels, generally do so believing ‘someone else’ will pay the price. 

It’s not that the international community has failed to recognise the significance of making the polluter pay. Indeed in 1972, the OECD asserted that this was the ​principle for encouraging ‘rational use of scarce environmental resources.’ In the same year Principle 22 of the Stockholm Declaration committed states to further developing international law ‘regarding liability and compensation for the victims of pollution and other environmental damage‘. 

Since then ‘the polluter pays’ has been widely referenced as a general principle of law. The Rio Declaration 1992,Principle 16 states that: ‘National authorities should endeavour to promote the internalization of environmental costs and the use of economic instruments, taking into account the approach that the polluter should, in principle, bear the cost of pollution.‘ ​A number of international treaties (such as the International Convention on Oil Pollution Preparedness, Response and Cooperation, 1990​; the Protocol on civil liability and compensation for damage caused by the transboundary effects of industrial accidents; ​and the ​Protocol on Preparedness, Response and Co-operation to Pollution Incidents by Hazardous and Noxious Substances, 2000) expressly refer to the ‘polluter pays’ principle as ‘a general principle of international environmental law’. Art. 191(2) of the EU’s 2007 Lisbon Treaty states that EU environmental policy shall be based on the principle (inter alia) that ‘the polluter should pay’.

In practice, however, the principle has not been applied in a way that would encourage the rational use of the atmosphere and carbon sinks. Indeed the very opposite has been happening. ​A 2015 IMF Report, ‘Counting the Cost of Energy Subsidies‘, concludes that the failure to internalise the environmental costs of fossil fuels amounts to an annual subsidy of $5.3 trillion (that’s $10 million a minute). Such a figure implies a market distortion on an astronomical scale; and a systematic failure to implement the principle of the ‘polluter pays’ in the context of climate change.

Addressing this situation gives rise to a number of questions:

  • How do you ‘make the polluter pay’?
  • Who is the polluter?
  • Is the polluter legally liable for loss and damage?

How do you ‘make the polluter pay’? 

​Taxation, the creation of carbon markets and legal liability may all serve to internalise the costs of activities generating social risk: it is not a case of either / or and the different approaches are complementary. A local government, for example, confronting a high accident rate on a road system, might introduce a road tax as a nudge towards public transport and to generate funds for road safety measures. That wouldn’t exempt a driver, who pays the tax, from liability for a specific accident they cause or contribute to. On the same principle, carbon taxation should not be seen as an alternative or substitute for legal liability.

Looked at another way, if taxes were sufficiently high to internalise costs, and to compensate victims, no legal liability would actually arise. Uncompensated loss and damage, therefore, represents the inadequacy or shortfall in taxation (or carbon trading schemes) to be addressed through the courts: the more effective the taxation the narrower the role for legal liability.

Conversely the less effective taxation is at making the polluter bear its social and environmental costs, the greater the potential legal liability. On the basis of the IMF’s stated methodology for determining subsidies (​’[The paper] focuses on the broad notion of post-tax energy subsidies, which arise when consumer prices are below supply costs plus a tax to reflect environmental damage and an additional tax applied to all consumption goods to raise government revenues.‘]) the $5.3 trillion annual subsidy arguably offers a rough estimate of the annual potential legal liability of polluters.  

For the most part, however, there has been little effort to enforce the principle of the ‘polluter pays’ through the courts.

Who is ‘the polluter’?

Everyone has a ‘carbon footprint’. That does not make everyone a ‘polluter’. In order to function as an economic tool, polluters should rather be identified as the principal economic operators profiting from the polluting activities. Such an approach is supported by the OECD Recommendations of 1992, 1(2):

‘On grounds of economic efficiency and administrative convenience, it is occasionally appropriate to identify the polluter as the economic agent playing a decisive role in the pollution, rather than the agent actually originating it. Hence a vehicle manufacturer could be deemed the polluter, although pollution results from the vehicle’s use by its owner. Similarly, a pesticide producer could be the polluter, even though the pollution is the outcome of proper or improper use of pesticides.’ 

Recent research has shown that the 90 largest corporate investor-owned and state-owned producers of fossil fuels and cement are responsible for nearly two thirds of global GHG emissions. The fact that there are vast number of actors emitting some level of greenhouse gases prevents neither identification of the major polluters, nor assessment of the scale of their responsibility for loss and damage. 

Does the principle make the polluter liable for loss and damage?

As a principle of international, environmental law ‘the polluter pays’ principle does not necessarily make the polluter liable for loss and damage. Rather it requires states to impose conditions which make the polluter bear the social and environmental cost to its activities. ​Thus, in so far as State X is subsidising polluting activities within its jurisdiction, State Y might invoke the polluter pays principle in bringing an action against State X (e.g. on the basis of a breach of the duty to prevent).

Nevertheless the principal may be relevant to private international law in the following respects:

Imposing on governments an obligation to facilitate private legal action against polluters (particularly in conjunction with Rio Declaration, Principle 13 etc);

As evidence of the policy considerations to be considered in the course of a private legs action against a polluter.

See also: Causation.

​Our political and economic system is founded on obedience to the economic incentive. For as long as polluters can profit from polluting, while displacing the social and environmental costs onto others, market forces all but guarantee environmental destruction. Making the polluter pay is critical to changing course.​

7. Principle of Common but Differentiated Responsibility

The principle of common but differentiated responsibility (CBDR) implies three things:

  1. That all states share in the responsibility to protect and restore the earth’s ecosystem;​​
  2. That individual country responsibilities differ according to national circumstances; and ​
  3. That the precise extent of an individual country’s responsibilities may be determined on the basis of equitable principles (including historic responsibility for environmental problems).

Significantly the principle is directly incorporated into both the UNFCCC and the Paris Agreement. In conjunction with principles of equity, therefore, it provides the conceptual framework for determining Party contributions towards meeting the ultimate objective of UNFCCC.

What, then, is the relationship between CBDR, principles of equity and the ‘Nationally Determined Contributions’ (NDCs), which are also required by the Paris Agreement? 

The Preamble to the Paris Decision notes ‘with grave concern’ the gap between aggregate NDCs, and the total emission reductions required to meet the long-term goal. The words are stark recognition of the inadequacy of aggregated NDCs in terms of the UNFCCC’s ultimate objective. It would therefore be contrary to the purposes of UNFCCC if the Paris Agreement were to ‘set-in-stone’ or indemnify such inadequate commitments and the Vienna Convention 1969, Art. 31(1) calls for an interpretation that avoids such a consequence. Such an interpretation is easily arrived at.

NDCs are not intended to override the principles of CBDR and equity in determining Party responsibilities. General principles of the UNFCCC, the Convention’s overall object and purpose (Vienna Convention 1969, Article 31(1)​, as well as general rules of international law (Vienna Convention 1969, Article 31(3)(c)) dictate that Country emissions conform to these principles. More specifically Article 4(3) of the Paris Agreement mandates that NDCs reflect Parties’ ‘common but differentiated responsibilities and respective capabilities.’

In contrast to the Montreal Convention or the Kyoto Protocol, for example, the concept of NDCs imposes on Parties procedural rather than substantive obligations. It does not, in other words, provide a mechanism for determining the content of Party emission reductions (this was considered to be beyond the scope of the political process). Rather it requires Parties to:

a) plan a long-term emission reduction pathway;

b) share the plan with others; and

c) periodically review and increase the ambition of the pathway.

Essentially NDCs (and the Paris Agreement) may be thought of as giving effect to the procedural ‘duty to co-operate in good faith.’ The mere submission of an NDC, however, is plainly insufficient to discharge a Party’s substantive ‘duty to prevent’ or its ‘duty of due diligence’. Since the Paris Agreement does not provide a top-down mechanism for determining such duties, a formal challenge would need to be conducted on the basis of general principles of the UNFCC and international law, i.e. a claim to the ICJ, alleging breach of these duties, invoking principles of equity and CBDR to determine their proper scope.  

See: Blueprint

8. Equity

​​​The principle of equity demands that general considerations of justice and fairness are taken into account in the development and application of international law.

More precisely, following the ICJ ruling in the North Sea Continental Shelf Cases, ICJ, 1969, equitable principles will be applied to determining the appropriate use, delimitation or division of natural resources in the absence of a specific rule to the contrary.

The case provides a paradigm for how the ICJ might define the duty to prevent in the context of GHG emissions (if called upon to do so). Since the Paris Agreement does not provide a mechanism for determining the content of NDCs, the Court would need to apply equitable principles and CBDR in determining a country’s obligations. Such an approach is reinforced by the terms of the UNFCCC and the Paris Agreement​, which highlight equity as the basis for protecting the climate system and the reduction of GHG emissions.

How might equity be interpreted in this context? A number of approaches have been proposed. The Intergovernmental Panel on Climate Change (IPCC), for example, reviews equitable principles and frameworks in its Fifth Assessment Report (2014). It proposes ‘four key dimensions’:

  • Responsibility
  • Capacity
  • Equality, and
  • the Right to Sustainable Development.

The Report goes on to describe two different types of implementing framework:

  • Resource-sharing frameworks which establish a basis for sharing the agreed global ‘carbon budget’; and
  • Effort-sharing frameworks which aim at sharing the costs of the global climate response.

As the IPCC notes, it is not, however, a case of ‘either / or’. The ‘duty to prevent’ imposes obligations on states both to:

limit their own GHG emissions; and

finance the mitigation and adaptation efforts of others.

An equitable framework will need to reflect the interrelationship between both sets of obligations. For further discussion on how this might be elaborated see:

See: Blueprint

9. Elementary considerations of humanity

​​Corfu Channel Case, ICJ, 1949: Obligation to notify others of existence of a minefield in territorial waters derives from ‘elementary considerations of humanity’.​

​Effect of treaty prior to entry into force

Vienna Convention 1969, Article 18: ​Even prior to its entry into force States are obliged not to defeat the objects and purposes of a treaty they have signed.​