Facilitative, non-punitive compliance machinery has a stronger theoretical basis now than ever before. Previously competing rationalist and managerial approaches to compliance come together in an interdependent world where we are confronting challenges that affect all States, including climate change, pandemic prevention and high seas conservation. In these contexts it is inherently rational for all States to play their part in addressing shared challenges by implementing their commitments; facilitative implementation and compliance arrangements on the model seen in the Paris Agreement will assist and support them in their efforts. The author investigates the benefits of the Paris Agreement model for compliance provisions in new international treaties including Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction (BBNJ), the international agreement on pandemic preparedness and response, and the plastics pollution treaty.

INTRODUCTION

In the penultimate chapter of his book New Zealand Constitution, Professor Harris remarks that ‘[m]odern international law creates normative expectations of what the country should consider providing in domestic law in respect of large areas of generic human activity’. Indeed, international law increasingly regulates matters that are central to domestic public policy. States have become answerable internationally for activity in domains such as healThpolicy, resource management and environmental protection that were previously effectively reserved to the administration of national governments. As a result, international courts and tribunals increasingly find themselves in a position where they must address such matters of domestic public policy in order to resolve international disputes. Further, the applicable international legal rules are often lacking in specificity. The international adjudicatory response has been to engage in the formulation of standards and tests governing states’ regulatory activity in finer grain.

The development of regulatory standards can notably be seen in international dispute settlement in the specialised fields of trade and investment protection, in disputes concerning riparian rights, and in the law of the sea, including specifically in areas including international health protection and the law on transboundary harm. International adjudicatory bodies’ identification of regulatory standards is by nature ad hoc, and the standard articulated in each case depends on the law that is being applied. However, commonalities are becoming apparent. For instance, the standards frequently take the form of requirements for regulatory coherence, specifying that there be rational relationships between states’ regulatory measures and their legitimate objectives. There is considerable debate about whether such standards should go further to incorporate requirements of proportionality between states’ regulatory actions and their effects on other states’ legal interests. While proportionality might in theory make for better balancing of competing interests it is doubtful that states would wish to subject themselves to the required oversight. Indeed, international law may be too far removed from the daily life of affected populations to offer the institutional mechanisms that would be needed.

International law scholars have worked hard to explain the emergence of regulatory standards, describing these standards withreference to ideas of ‘standards of review’ and ‘methods of review’, and in terms of ‘deference’ to domestic legal authorities.

Scientific disputes pose new challenges within the rationalist conception of adjudication in the international setting. Important factual elements of such disputes are acknowledged as unknowable, and so it becomes difficult to maintain a strict traditional rationalist conception of adjudication as a process where the law is applied to the facts. As a result, scientific disputes are generating renewed attention to rules about evidence and proof in international courts and tribunals.

The scientific disputes discussed in this book are ‘live’ policy cases where complainants want respondents to change their conduct. These cases differ from other disputes where complainants are seeking only compensation or the restoration of their dignity. At the national level it has been suggested that policy disputes call for a modification to traditional adversarial procedure. This is precisely what is taking place in international courts and tribunals, as they increasingly experiment with a wide range of methods for investigating central aspects of these scientific disputes.

Among the results of this experimentation is a greater reliance on expert evidence. Here, complex problems begin to arise. Many of the legal rules that are applicable will have been crafted with scientific uncertainty in mind. They may incorporate tests according to which a state is required to conduct itself as ‘necessary’ in the circumstances, or take steps based on ‘sufficient’ scientific evidence, for example. International courts and tribunals will need the close assistance of experts to interpret and apply these tests in different contexts.

The importance of co-operation between disputing parties

Co-operation between the disputing parties will often be key to the successful resolution of a scientific or technical dispute, and may also allow for a calibrated application of the precautionary principle that may not be as achievable through adjudicatory dispute settlement. Whether or not disputants ultimately do co-operate effectively cannot by any means be guaranteed, but judicial prompting may assist. The two awards in the well-known Trail Smelter Arbitration (US v. Canada) provide an early demonstration of how helpful it may be to allow time for co-operative study of how to address or ameliorate a problem, here the distribution of sulphur dioxide from the Canadian smelter at Trail through cross-border currents in the upper air. In its first award the Tribunal decided that three consultants would be appointed for the gathering of meteorological observations, and prescribed a temporary emissions limitations regime. In its second award the Tribunal was then in a position to lay down a detailed and permanent regime.

Adjudicatory proceedings may be just one of the stages through which a dispute proceeds, and it is part of the function of an international court or tribunal to take this into account in deciding how to deal with a case. The practical significance of scientific and administrative co-operation is apparent upon considering the various high-profile international disputes involving scientific uncertainties introduced in the pages that follow.

The previous chapter dealt with two procedural avenues that could be helpful in dealing with situations where it is asserted that new scientific evidence requires an international adjudicatory decision to be reconsidered. However, it was found that neither the revision procedure nor the doctrine of nullity offers the type of process that may be needed. This final chapter therefore proposes the institutionalisation of reassessment proceedings for disputes involving scientific uncertainty, drawing on experience in the WTO in the Continued Suspension of Obligations cases. Additionally the chapter addresses the application of the rules on res judicata in subsequent proceedings in scientific cases.

‘Reassessment’ proceedings would be concentrated on assessing an original respondent's compliance with its international legal obligations at the point in time after new scientific research has been invoked. A number of factors point to the need to treat the idea of reassessment with caution. There are obvious problems in providing what would be an opportunity for a reasonably full rehearing. Making use of such a procedure would consume considerable resources, and the procedure is open to abuse. The issues lying behind ongoing litigation in disputes involving potential future harm may in some instances be social and political, and ongoing litigation may not be the best way to resolve them. Further, for all concerned it is most desirable to make an enduring decision at the time of the original proceedings.

Cases involving scientific knowledge and the risk of future harm raise a host of new problems in connection with evidence, proof and the finality of adjudicatory decision-making. Indeed, international rules relating to evidence and proof in international courts and tribunals are evolving as a result of the increasingly high incidence of such disputes. Increased use is being made of different methods for the taking of expert evidence; the rules on the allocation of the burden of proof are coming under scrutiny; and the rules ensuring the finality of international adjudication require consideration. This book explores and evaluates the procedural developments that are taking place and assesses further steps to be taken, particularly with a view to recognising and accommodating the precautionary principle.

According to the precautionary principle, action to counter a serious threat to human health or the environment should not be delayed merely because of scientific uncertainty. The need to protect human life or health and the environment should be assumed, once certain thresholds are crossed. Proving that harm will occur is not required. This approach sits awkwardly with the usual precepts of adjudication, which revolve around the proof of fact. The challenge is for adjudicators to make reasoned decisions that pay due heed to the harm that is threatened in every dispute, despite the absence of perfect knowledge.

The judgments and awards of international courts and tribunals provide points of stability in international politics, permanently allocating resources and responsibility according to law. They offer disputing parties a decision that will enable them to close down their disputes and move on. They also reinforce the status of the law and help to clarify and develop its content. The finality of international adjudication is important in enabling international courts' and tribunals' decisions to fulfil these systemic functions. For judgments and awards dependent on continually advancing scientific research there is thus an awkward problem. Within a relatively short period of time it is always possible that new scientific evidence could show a judgment or award to have been based on erroneous factual foundations.

The principle of finality should not be seen as an end in itself. Appropriately circumscribed processes of review are also an essential aspect of international adjudication. International law has always readily accommodated the need for procedures allowing the rectification, interpretation and even the revision of judgments and awards. On rare occasions, express provision is also made by an international court or tribunal for a decision to be revisited, as in the Nuclear Tests cases (Australia v. France) (New Zealand v. France). There are also other case-specific rubrics under which the parties might return to the courtroom. In the Case concerning the Gabčíkovo-Nagymaros Project (Hungary/Slovakia), Slovakia invoked Article 5(3) of its Special Agreement with Slovakia in 1998.

The exercise of the international adjudicatory function in disputes involving scientific uncertainty may meet its greatest test in relation to the allocation of the burden of proof. The traditional rule on the burden of proof has the potential to provide a high degree of predictability in international adjudication, yet there may arise cases where fairness calls strongly for an international court to reassess or adjust the allocation of the burden of proof. This may especially be so in the light of the precautionary principle. This chapter investigates the origins and the logic of the rule on burden of proof, establishing its parameters and the desirable directions for its future development. Chapter 6 then explores the potential for a modification in the articulation or application of the existing rules on burden of proof, in order to permit the reversal of the burden of proof to give effect to the precautionary principle.

The rule on the allocation of the burden of proof that is applied in international courts and tribunals is that the party making an assertion must prove that assertion: actori incumbit probatio. The rule derives from the rule applying in civil trials in Roman law: ei incumbit probatio qui dicit non qui negat. According to the maxim reus in exceptione fit actor, a party relying on an exception in the substantive law will attract the burden of proving the applicability of the exception or defence. Thus, as Rosenne has written:

A close engagement with the science, and with the testimony of scientific experts, is becoming an inevitable feature of the international adjudication of disputes involving potential harm to human health or the environment. Even the most traditional of the international courts, the International Court of Justice, has been giving careful consideration to this issue. Greater use of the diverse procedures addressed in the previous chapter, particularly the consultation of experts appointed by a court or tribunal, will require a revisitation of the fundamental tenets of international adjudication. Perhaps the most central of these tenets is that the tribunal to which a dispute is submitted alone has the authority to take a binding decision on the issues raised by a case, and that a tribunal's findings must be based on its own convictions.

The need for tribunals to be alert to the possibility of inadvertent delegation to experts was emphasised by White in 1965. White underlined that the role of the independent expert was limited to assisting a tribunal in the establishment or elucidation of matters of fact. In principle, it is the tribunal and not the expert who is tasked with identifying the relevance and significance of the factual aspects of a case. Thus Sandifer has emphasised ‘the importance of limiting the use of experts to questions susceptible to resolution by reference to reasonably well established scientific and technical standards’.

Sound decision-making is essential in an international legal system where submission to jurisdiction is voluntary and many of the interests at stake are important, sensitive and complex. International courts and tribunals must carry out their functions thoroughly and on the basis of a full understanding of the facts. They must ensure that they are in a position to appreciate the disputed policy choices made by the states appearing before them, and to perform their role wisely with a view to the stability and development of the law, as well as to the importance of ongoing relations between the parties. The task of the international adjudicator today is not simply to choose between two competing conceptions of the facts presented in adversarial fashion.

As a result of the closeness of law and fact in the type of dispute that is the subject of this book, international adjudication is changing. Most obvious and most fundamental is the shift in the role of expert witnesses. The complexity of the science requires heavy consultation with experts, and considerable reliance on their testimony. Inevitably, it seems, experts will be drawn into questions of legal interpretation through their involvement in the application of legal terms. The insights offered by a scientific expert will help determine the application of a legal concept such as ‘necessity’ or ‘reasonableness’ in the case at hand – and in the course of this process the scientific expert's advice will also come to shape the development of the conventions and usages on which the established meaning of the legal concept of ‘necessity’ or ‘reasonableness’ in the context of the provision in question will be based.