On the Science-Coloured Glasses of the ICJ: Harmfulness, Wrongfulness, and Climate Accountability

The ICJ gave a thoroughly science-based reading of State obligations with respect to climate change in its Advisory Opinion on Climate Change. This, in and of itself, is not very surprising considering the standard practice of domestic and human rights courts in climate cases, which are also known for heavily citing and relying on scientific evidence, mainly from the reports of the International Panel on Climate Change (IPCC). The Advisory Opinion, nevertheless, stands out, first, as compared to the ICJ’s own previous environmental case-law, and second, for the way in which the Court is paving the way towards establishing state responsibility for climate harm with climate science evidence. 

The Opinion suggests that scientific evidence is no longer a nuisance that should be avoided by the Court’s reasoning as much as possible (see the majority’s findings in Pulp Mills), or an extra-legal knowledge that is irrelevant for deciding the legal controversy. Long gone the days when members of the bench argued that adjudging science-heavy legal questions (in the material case, whether Japan’s whaling program can be deemed scientific in nature) is “more suited to scientists rather than lawyers” (see Separate Opinion of Judge Sebutinde in Whaling). Nor did the Court deem sufficient to pay only symbolic gestures towards scientific authority. Instead, it engaged with climate science meaningfully, assigning a central role to scientific knowledge in how the Court made legal sense of the climate crisis.

Despite unanimous acceptance of climate science at large, judges had slightly different takes on climate science evidence, as transpires from several individual opinions. The main point of contention among members of the bench lies in whether the Court went far enough in relying on climate science. Judge Yusuf deems that the Court’s reasoning as “scientifically ill-grounded” (Separate Opinion, §16) for stopping short of legally recognizing what scientific evidence, in his view, suggests for States’ responsibility for climate harm. Judge Nolte defended the Opinion’s approach to conceptualizing wrongful acts and Judge Xue would have preferred more extensive legal reliance on per capita emission data provided by the IPCC. 

Undoubtedly, the Court spared no efforts in weaving together legal and scientific knowledge in translating the “more than legal problem” (§ 456)  of climate change to the language of international obligations and state responsibility. This short contribution will comment on how the Court was balancing factual and legal aspects in operationalizing the duty to prevent harm to the climate system and will discuss the ways in which climate science informs the content of legal concepts, with a special focus on how scientific evidence now may pave the way to a new legal paradigm of climate accountability.

1. Science as the Backbone of the Judicial Findings

References to climate science runs through the Opinion as a consistent thread. With its 76 references to the term “science” or “scientific” across the 133 pages, the Opinion indeed reads like the Court is openly using climate science knowledge as the main compass for navigating the uncharted waters of state responsibility for climate harm. 

This was possible likely due to the pre-hearing meeting the Court held with members of the IPCC. The goal of the day-long exchange was “to enhance the Court’s understanding of the key scientific findings” which the IPCC has delivered through its periodic assessment reports. Even though the exact questions and answers were not revealed to the public, it seems plausible that but for this substantive engagement with leading scientists, climate science could hardly fly so high in Court.

Having declared that IPCC reports “constitute the best available science on the causes, nature and consequences of climate change” (§74), the Court went on reiterating the main findings of these reports (see pages 35-38), which is a standard practice of domestic courts in climate cases.  What is more surprising is that the ICJ also used IPCC science as the starting point for basic definitions, such as “the climate system” or “mitigation”, even though these very terms are also defined in climate treaties (but the legal definitions come only second in the Opinion after the respective scientific definitions, see §75 and §85). 

The science-coloured glasses of the ICJ also enabled giving a holistic solution to the problem before it. Given the scientific fact that the climate crisis is inextricably linked to other human-enhanced planetary challenges, such as the ecological crisis or desertification, the Court included the Convention on Biological Diversity and the Convention to Combat Desertification among “the most directly relevant applicable laws” – on the basis of primarily scientific justifications (§325, §331). 

Climate science evidence also serves as the main epistemic justification for reaching almost every novel conclusion as to the content of legal obligations. Climate science lays the foundations for several key legal findings, including:

• that the harm prevention principle is applicable in the context of climate change and poses corresponding obligations for all States (§137), 
• that the standard of due diligence must be stringent, as every fraction of the degree matters (§ 245), and “may also become more demanding in the light of new scientific or technological knowledge” (§284),
• that the determination of “significant harm to the climate system and other parts of the environment” must take into account the IPCC reports, which identify “harms associated with climate change as including sea level rise, extreme weather events and severe consequences for ecosystems and biodiversity” (§278),
• that risks caused by GHG emissions should be assessed as part of States’ EIA obligations, including “their possible downstream effects” (§298),
• that the ‘primary’ temperature goal of the Paris Agreement is 1.5C, and notes that this interpretation is the one that is consistent with best available science (§224),
• that State efforts to “enhancing adaptive capacity, strengthening resilience and reducing vulnerability to climate change” must also conform to best available science (§258), 
• that scientific evidence informs what measures are deemed necessary within the meaning of Article 194 (1) (§334), and
•  that sea-level rise is “not without consequences for” the right to self-determination (§357).

2. Harmfulness vs Wrongfulness of Emissions 

A particularly consequential finding of the Opinion pertains to operationalizing the duty of prevention in the climate context. In this respect I will focus only on the Court’s firm distinction between harmful emissions (in the ordinary, and scientific, sense) and wrongful emissions (in the legal sense). This element in the reasoning reveals how the ‘scientific’ and ‘legal’ narrative on climate change can conflict with each other, even though they relate to the same element of the factual reality, namely, the effects of anthropogenic emissions, and, therefore, necessarily have an interface. 

Scientifically speaking, every tonne of GHG emissions contributes to global emissions, which mix up in the atmosphere, and collectively, cause harmful climate impacts well beyond the State of origin. However, the Court points out that “the internationally wrongful act in question is not the emission of GHGs per se” only those that contravene international law obligations. (§427). As a result, with the words of Judge Nolte, “only a limited amount of all anthropogenic GHG emissions since industrialization has been caused by wrongful acts.“ (Declaration of Judge Nolte, §27)

This conceptualization of the unlawful State conduct, although is in line with the approach of the European Court of Human Rights in KlimaSeniorinnen – which also assessed domestic climate policies, and resulting GHG emissions, as part of States’ positive obligations under human rights law – was not fully backed by all judges despite being adopted unanimously.

 Judge Yusuf finds this reconstruction of the relevant processes problematic, calling it “completely detached from empirical realities and the scientific findings relating to the causes and consequences of climate change” (Separate Opinion, §8.) He concludes that the Opinion’s finding that “climate change is inherently a consequence of activities … of all States (emphasis added) is scientifically ill-grounded”(§16). 

It is argued here, however, that rejecting the harmfulness of the emissions of all States disregards the scientific fact that every tonne of emissions (regardless of its source) has equal warming potential (and hence, harmful). This is not to say, of course, that all States’ emissions are equally blameful or wrongful – but the difference between them lies in the normative part of the wrongfulness calculus and not in the scientific dimension of harmfulness.

Moreover, Judge Yusuf focuses his legal inquiry on IPCC data confirming a disparately bigger portion of emissions of the Global North compared to developing States as far as historical emissions are concerned (§15). In his reading, these data would justify a system of State responsibility for climate harm that is proportionate to the respective State’s cumulative emissions, including historical emissions dating back to 1850. In contrast, Judge Nolte invokes IPCC data showing a growing share of emissions post 1990 in all anthropogenic emissions, which by now has reached the same order of magnitude than emissions prior 1990 (42%-58%, respectively, see §25 of his Declaration). This is possible given that current emissions are now dominated by emerging economies, and not by historically high emitting States from the Global North. 

These competing judicial narratives building on different sets of equally robust scientific data highlights the importance of the broader question of the appropriate role of scientific knowledge in adjudication. As I argued elsewhere, even though scientific evidence is crucially relevant and can (and should) inform the judicial decision on legal responsibility for climate harm, climate science alone cannot answer the legal question directly, nor such answer is dictated by climate science. Evidence needs to be legally contextualized and interpreted for purposes of answering the legal question put before a court. The hard limit, in this respect, lies in that the judicial narrative on factual processes should not contradict robust climate science knowledge. Doing so would undermine the epistemic legitimacy of the reasoning. Nevertheless, the presence of scientific evidence cannot exempt judges from their task of undertaking normative considerations in deciding (science-heavy) legal dilemmas.  

After all, the Court seems to strike a careful balance between scientific and normative components in reconstructing the legally relevant process leading from anthropogenic GHG emissions to harmful climate impacts. The Opinion remains within the bounds of epistemically legitimate reasoning when distinguishes the harmfulness of emissions from their wrongfulness. Equating the two would have “scientized” the issue of state responsibility to an excessive extent by eliminating the normative aspects of the (essentially legal) calculus. 

3. Attribution, Causation: Climate Science in Future Contentious Cases

The Court, thus, preserves the role of normative assessment in the assessment of the wrongfulness of an act. Nevertheless, it swings the door wide open to finding the responsibility of individual States (or group of States) established for climate harm in future contentious proceedings – and the chances of success of such claims will, for a large part, hinge on climate science. Relevant scientific questions include causal determinations and assessing whether the respective State took measures that are reasonable, appropriate and necessary to prevent harm to the climate system. 

The Court finds that “the rules on State responsibility admit the possibility of determining the responsibility of States in the climate change context” (§431), and the extent of liability must be established “in concreto” (§437), that is, individual contentious proceedings. 

The success of climate damage claims hinges on whether the respective court is willing to accept climate attribution science, a field of climate research that studies whether individual climate impacts, such as extreme weather impacts, can be attributed to anthropogenic climate change (impact attribution), or even further back to individual emitters, based on their share from the global emissions (source attribution). The Advisory Opinion openly welcomes the insights deriving from attribution science. It finds, first, that source attribution studies can have bearing on a State responsibility, by emphasizing that ”it is scientifically possible to determine each State’s total contribution to global emissions, taking into account both historical and current emissions” (§429). Moreover, it also acknowledges impact attribution by citing IPCC data “clearly linking the human contribution to climate change to observed increases in heatwaves, flooding and drought” (§437).

While attribution science causally links a portion of emissions to certain harmful impacts and the sources of emissions, respectively, legal causation must still be established separately  in the context of state responsibility. This requires the demonstration of a causal link between a wrongful act and a specific climate harm. Importantly, the Court stresses that finding a causal nexus “is not impossible” and will have to be done in each case “through an in concreto assessment” (§438). The difficulties presented by scientific uncertainty burdening causal evidence “must be addressed as and when they arise in light of … the evidence presented to the Court”  (§437). 

The findings on the possibility of establishing state responsibility for climate harm may seem progressive, surprising or even radical to some. Yet, there exists robust scientific evidence that is capable of establishing causality. Any friction is not between the logic of (climate) science and the logic of (international) law, but rather between two legal worldviews: the old paradigm of climate impunity and the new paradigm of climate accountability.