The Return of Not-Quite “Phantom Experts”?

On Monday, 2 December 2024, the much anticipated hearing began in the Obligations of States in respect of Climate Change advisory proceedings before the International Court of Justice. Less than a week before the start of the hearing, the Court issued a brief and unusual press release about a meeting that it held with scientists from the Intergovernmental Panel on Climate Change (IPCC). The IPCC represents the ‘scientific pillar’ of the climate change regime, with a mandate to assess scientific evidence on climate change and draw conclusions on that basis. By its own account, the IPCC prepares ‘comprehensive Assessment Reports about the state of scientific, technical and socio-economic knowledge on climate change, its impacts and future risks, and options for reducing the rate at which climate change is taking place’. UN General Assembly Resolution 77/276, by which the General Assembly requested the advisory opinion, noted ‘with utmost concern the scientific consensus expressed’ in the IPCC reports concerning the adverse impacts of human-induced climate change.

According to the Court’s press release, the purpose of the 26 November 2024 meeting at the Peace Palace was to enhance the Court’s “understanding of the key scientific findings which the IPCC has delivered through its periodic assessment reports covering the scientific basis, impacts and future risks of climate change and options for adaptation and mitigation.” The press release also listed nine IPCC scientists who were “involved in this initiative”, and indicated whether they were lead or contributing authors of various IPCC reports.

This may strike many as a welcome development. The Court’s interest in enhancing its understanding of climate change science is entirely appropriate given the potential relevance of that science to the legal questions under consideration. Moreover, the IPCC reports make up a key part of the extensive evidentiary record before the Court and will undoubtedly be referenced by participants throughout the proceedings. Nonetheless, the Court’s decision to meet privately with the scientists who authored those reports raises questions about the Court’s procedures and its approach to evidence. Above all, it is unclear why the Court decided to consult with the IPCC scientists in a closed meeting rather than eliciting testimony from these individuals as part of the formal, public hearing.

To be clear, we do not seek to challenge the importance of the Court engaging closely with relevant scientific and technical evidence. We also accept that doing so may require a “crash course” in climate science for some ICJ judges (even if only to cover foundational questions of terminology and methodology). Our primary concern relates instead to whether the good administration of justice demands a different approach than that taken by the Court on this occasion.

The ICJ Framework for Engaging With Fact and Expert Witnesses

The ICJ Statute gives the Court broad flexibility when it comes to procedure and evidence, including the responsibility “to frame rules for carrying out its functions” (art 30). This includes “making all arrangements connected with the taking of evidence” (art 48) and laying down rules of procedure for receiving testimony from “witnesses and experts” during the oral hearing (art 51). The Statute also empowers the Court to entrust any individual or body with “giving an expert opinion” (art 50). These provisions apply to contentious cases, but also to advisory proceedings to the extent that the Court “recognizes them to be applicable” (art 68). The Rules of Court provide further guidance. In particular, the Court may seek information beyond that provided by the parties for “elucidation of any aspect of the matters in issue” (art 62(1)). This includes arranging “for the attendance of a witness or expert to give evidence in the proceedings” (art 62(2)). The Rules further stipulate that witnesses and experts shall take oaths by which they swear to speak the truth (art 64) and shall be subject to examination by the parties (art 66).

These provisions provide key procedural safeguards. They ensure that parties are aware of the factual testimony and expert evidence that could affect the Court’s reasoning. In addition, party examination creates opportunities to question an expert’s methods, identify and challenge underlying presumptions, and probe the validity of the expert’s reasoning or the degree of certainty surrounding their conclusions. Taken together, these safeguards are geared towards ensuring transparency and maintaining the integrity of judicial proceedings, which should be designed to lead to fair and reasonable outcomes.

Whether one characterizes the IPCC scientists as experts or fact witnesses, it is not clear on what basis the ICJ acted in holding the 26 November meeting. Unlike the procedures set out in the Rules, this consultation did not provide any opportunity for involvement by the states and international organizations that are participating in the proceedings, and there is no indication that a transcript of the meeting was produced. While the consultation with the IPCC scientists might be deemed to fall within the broad contours of Article 62 of the Rules, this provision does not seem to contemplate private meetings between judges and experts. Nor does the Court’s brief note that its invitation to the IPCC scientists “follows United Nations General Assembly resolution 77/276” provide any clarity; the resolution does not suggest or provide a basis for such a meeting. Ultimately, the 26 November meeting instead harks back to the much-criticized past use of so-called “phantom experts” (expert fantômes).

The Court may have considered itself at liberty to inform itself in this way because this is an advisory proceeding, rather than a contentious case. In other words, the Court may have decided that it did not recognize the rules otherwise applicable to fact-finding and expert testimony as being “applicable” in this case, per Article 68 of the Statute. But a meeting with experts behind closed doors works against the good administration of justice, whether in contentious or advisory proceedings, as it precludes the participants in the proceedings from questioning the experts or taking their views into account. By issuing a press release that provided no specific information about what was discussed—or why the IPCC scientists (as opposed to other climate scientists) were invited to meet with judges—the Court ultimately deprived the states and international organizations that are participating in the hearing from evaluating or responding to whatever information the IPCC scientists conveyed to the judges. Even if that information was entirely innocuous, this is undesirable given the significance that many attach to this advisory opinion—and the importance of justice being seen to have been done.

The Court’s (Problematic) Past Practice

It is possible that the Court may have arranged the meeting with the IPCC scientists to preempt the type of criticism it has received in the past (from judges themselves and by commentators) for failing to consult experts when dealing with complex scientific or technical matters.

For example, in the 2010 judgment in Pulp Mills (Argentina v Uruguay), Judges Al-Khasawneh and Simma harshly criticized the Court in a joint dissenting opinion for having failed to make use of experts to “adequately assess and weigh complex scientific evidence” presented by the parties (see paras 3-5). Since Pulp Mills, parties have largely moved away from the practice of appointing scientific experts as counsel, and the Court has heard a handful of cases over the past decade involving party-appointed experts (see, e.g., Whaling in the Antarctic, Croatia v Serbia, Certain Activities/Construction of a Road, and Waters of the Silala). This has allowed the Court to develop better procedures for organizing the submission of expert reports and the examination of experts during the oral hearing, which in turn has arguably helped the Court to engage more effectively with scientific evidence. The Court also took the rare step of appointing its own experts in Maritime Delimitation in the Caribbean Sea and the Pacific Ocean (Costa Rica v Nicaragua)  and at the compensation phase of the Armed Activities case.

The joint dissenting opinion in Pulp Mills also put a spotlight on the Court’s occasional practice of consulting experts informally, without informing the parties or giving them any opportunity to review, comment on or question the views of these so-called ‘phantom experts’. Judges Al-Khasawneh and Simma observed that this practice deprived the Court of the advantages of transparency, openness, and procedural fairness to the detriment of the good administration of justice. Yet the 26 November meeting with the IPCC scientists differed from past consultations with undisclosed ‘phantom experts’ only in that the Court announced the meeting and named the participants. This provided a veneer of transparency without addressing the underlying substantive concerns surrounding informal discussions between experts and the bench.

The View from Strasbourg

It should be noted that some other international courts and tribunals also engage with experts outside of the main public hearing. For example, the Annex to the Rules of Court of the European Court of Human Rights (ECtHR) provides for ‘investigative measures’ that allow the ECtHR to gather additional evidence, including expert views (Rule A1). Yet while a fact-finding hearing with experts in Strasbourg may be undertaken in camera, it is typical for party representatives to attend the hearing and for a verbatim record to be kept. Moreover, the views of such experts will often be set out in the judgment. This was the case, for example, in Dániel Karsai v Hungary (App No. 32312/23), a case decided in June 2024 concerning assisted suicide. In that instance, the Chamber decided proprio motu to hear evidence from two experts. The fact-finding hearing, which took place in the presence of the parties’ representatives, was held the day before the public hearing; the judgment then described the expert testimony in detail (see paras 44-57). A similar approach was taken in Abu Zubaydah v Poland (App No. 7511/13), which also involved a fact-finding hearing with experts in camera the day before the public hearing. The 2014 judgment included extensive ‘extracts’ from the testimony provided (see paras 298-332). This approach appears to accord better with the good administration of justice than does an informal meeting that excludes the participants in a case. Notably, as Corina Heri has pointed out, the ECtHR did not choose to hold a fact-finding hearing with climate experts in connection with its recent climate change cases, including Verein KlimaSeniorinnen Schweiz and Others v Switzerland (App No. 53600/20). Nonetheless, the ECtHR’s approach to seeking expert testimony through fact-finding hearings is an approach that the ICJ might consider adopting and that the relative flexibility of its Rules could likely accommodate, at least in the context of advisory proceedings.

A Better Way Forward?

One can speculate about why the Court organized an informal briefing with the IPCC scientists rather than arranging for the IPCC scientists to give evidence in the proceedings pursuant to Article 62(2) of the Rules. It is possible that the Court sought to avoid the logistical challenges that might have accompanied the inclusion of live testimony by experts in what is already a complicated two-week hearing involving dozens of participants. It likely would have been unwieldy and impractical to allow participants in the advisory proceedings to take part in the questioning of the IPCC scientists, if they had been called to testify. There is, however, no clear reason why the Court could not have limited the questioning to judges.

Alternatively, the Court could have found other ways to enhance transparency. It could have produced a transcript of the informal discussion between the judges and the experts and provided the transcript to the participants in the advisory proceedings, in advance of the hearing. This would have allowed the participants to understand which issues required further briefing or clarification, in the judges’ opinion. It would have also allowed the parties to comment on the transcript in their oral pleadings. Another possibility might have been to submit questions or requests for clarification relating to the IPCC reports to the IPCC scientists in advance. The responses by the experts (provided in writing or orally) could have been made part of the case file. Ultimately, the irregular nature of the 26 November meeting may reflect the fact that judges simply did not want to expose their relative lack of expertise when it comes to climate science, despite the fact that most of us would likely require straightforward guidance if asked to assess or rely upon the complex climate models found in the IPCC reports.

These questions relating to how the ICJ engages with experts and how it makes use of third-party reports carry importance beyond the climate change advisory opinion. For example, the ICJ is increasingly asked by parties to credit the findings and conclusions of international commissions of inquiry and UN fact-finding bodies, especially in cases dealing with armed conflict and alleged violations of human rights and international humanitarian law. One of us has suggested previously that the Court should take a more proactive approach in calling the authors of such reports to testify, especially to explain choices about methodology or to clarify or fill in evidentiary gaps. But that proposal contemplates public testimony as part of the formal hearing, not informal consultations with the authors of such reports behind closed doors. And if that latter scenario seems obviously inappropriate, one should ask why the Court’s decision to hear from the IPPC scientists in a closed meeting is any less fraught.

The ICJ currently faces a number of challenges that call for creative responses. The new reality of ‘mass’ participation in ICJ cases is a clear trend, not only in the context of advisory proceedings that attract a substantial number of participants but also in contentious cases that attract ‘mass intervention’ by third parties. Legal questions that are intertwined with scientific assessments also pose difficulties. All of this demands a degree of flexibility and pragmatism on the part of the Court, which finds itself busier than ever. Innovative solutions should ultimately be measured against the core principles of transparency and fairness. In this case, the Court’s decision to meet with the IPCC scientists risks falling short of that mark.