Why Climate Science Matters for International Law

The International Tribunal for the Law of the Sea (ITLOS) issued an advisory opinion on May 21, 2024, in response to a request submitted by the Commission of Small Island States on Climate Change and International Law (COSIS). While various aspects of the advisory opinion have already been discussed in this joint blog symposium, this post focuses on a feature of the opinion that has so far received little emphasis: the strong role of science in the advisory opinion. Scientific reports on climate issues, as well as reports on the state of the ocean, its ecosystems, and the relevance of the ocean for climate change, play a central role in the opinion. In the remainder of this post, I discuss the process that led the tribunal to base the opinion on the various scientific reports consulted and argue that the use and interpretation of scientific research can facilitate and improve court decisions. In the context of this advisory opinion, ITLOS utilizes climate science to clarify a number of concepts, to classify and prioritize the legal problems posed, and to make its opinion more robust and assertive in the context of the climate emergency.

As a prelude, it is important to revisit the questions posed by COSIS to clarify the obligations of State Parties to the Convention. Question a) referred to States’ obligations to prevent, reduce and control marine pollution in relation to the deleterious effects resulting or likely to result from climate change and ocean acidification caused by anthropogenic greenhouse gas (GHG) emissions into the atmosphere. Question b) related to the protection and preservation of the marine environment in relation to climate change impacts, including ocean warming, sea level rise, and ocean acidification.

ITLOS recognized that these questions “necessarily have scientific aspects” which it had to consider (para. 46). The tribunal focused first on the science regarding climate change, for which it relied on the “authoritative” reports of the Intergovernmental Panel on Climate Change (IPCC). (para. 47-51). It accepted the definitions provided by the IPCC (para. 52-54) and acknowledged the critical role the ocean plays in regulating the climate system (para. 55-57). Furthermore, it highlighted the negative effects of anthropogenic GHG emissions on the ocean (para. 57-65). Finally, the tribunal noted that climate change is a threat to humanity, particularly for vulnerable people and/or communities living near the coasts (para. 66). These scientific elements allowed the tribunal to support and anchor its notable opinion.

The central role of the IPCC reports on climate change

Before entering into the heart of its opinion and to clarify the use of certain terminology, the tribunal explained that “given the fact that the terms “climate change”, “greenhouse gas emissions” (hereinafter “GHGs), and “ocean acidification” do not appear in the International Convention of the Law of the sea, it (the tribunal) will use these terms as they are defined in relevant legal instruments relating to climate change or in authoritative scientific works, such as the reports of the Intergovernmental Panel on Climate Change (IPCC)” (para. 157 as used in para. 52, 54, 60 and 68).

By way of introduction to its opinion, the tribunal also explained what the IPCC affirmed in its 2023 Synthesis Report that human activities, principally through GHGs “have unequivocally caused global warming” (para. 54). ITLOS elaborated on this point by referencing the IPCC glossary to explain that GHGs are “[g]aseous constituents of the atmosphere, both natural and anthropogenic” that “absorb infrared radiation, emitted by the Earth’s surface, the atmosphere and clouds”, and “[t]hey emit in turn infrared radiation in all directions including downward to the Earth’s surface” (para. 54-55). ITLOS underscored that anthropogenic GHG emissions “have increased since the pre-industrial era, driven largely by economic and population growth, and are now higher than ever”, and “led to atmospheric concentrations of carbon dioxide, methane and nitrous oxide that are unprecedented in at least the last 800,000 years” (para. 54). In this regard, ITLOS noted that the IPCC defines the term “anthropogenic” as “[r]esulting from or produced by human activities” (ibid).

However, none of these elements would be useful to the tribunal if it had not also emphasized the validity of this information. To do so, it presented the level of confidence that the IPCC places in the scientific elements.

Certainties and confidence in climate science

The opinion, on numerous occasions, relied on the certainties, uncertainties and the level of confidence concerning the various scientific information handled by the tribunal (para. 62 – 66, 175, 209). Indeed, the tribunal used the IPCC’s own evaluation of its degree of certainty of data on the seriousness of climate change and its impacts on the ocean in two ways. First, the tribunal used the IPCC’s “very high confidence” in its evaluation of adverse impacts from climate change to conclude that there is “broad agreement within the scientific community that if global temperature increases exceed 1.5°C, severe consequences for the marine environment would ensue” (para. 241 f.). Second, the tribunal used varying degrees of certainty in certain forms of scientific knowledge to present its view concerning the need to apply the principles of prevention and precaution, urging States to take preventive measures even in the absence of absolute scientific certainty (para. 212 and 213). The tribunal used here the same tools for measuring occurrences used by the IPCC: the degree of probability or improbability. This point constitutes an especially strong element of the opinion–the tribunal anchored its opinion in the IPCC’s scientific reports, which have been documenting the evidence of increasing climate change and the deterioration of the climate system since 1988 (para. 241 and 242).

Underlining the role of the ocean on climate change

The opinion highlighted two critical points on the relationship between climate change and the ocean. First, the tribunal explained that the ocean plays a crucial role in the regulation and stability of the climate system. Second, the tribunal explained that, due to increasing warming, the ocean is suffering severe consequences. The tribunal went on to explain the negative “chain” effects caused by the degradation of the marine environment: acidification, sea-level rise, the disappearance of marine ecosystems, and the consequent disruption in climate regulation (para. 57). To demonstrate that its findings were logical, rigorous, and based on the best available science, ITLOS relied on the 2019 IPCC Report, which confirmed that the ocean is “a fundamental climate regulator on seasonal to millennial time scales” (para.  55). According to the tribunal, the report indicated that the accumulation of anthropogenic GHGs in the atmosphere has had numerous effects on the ocean. With respect to ocean warming, ITLOS emphasized –as the IPCC does– that “the dominant effect of human activities is apparent not only in the warming of global surface temperature, but also in … the warming of the ocean” (para. 58).

Climate Change is a threat and exacerbates several vulnerabilities

These findings supported another key pronouncement made by ITLOS, regarding the risks climate change poses, not only to the marine environment, but also for populations, especially the most vulnerable.

On this point, ITLOS stated that the 2023 IPCC report concludes that “[r]isks and projected adverse impacts and related losses and damages from climate change escalate with every increment of global warming” (para 62). The risks “are higher for global warming of 1.5°C than at present, but lower than at 2°C” (para 62). According to these findings, the “[i]ncreasing frequency of marine heatwaves will increase risks of biodiversity loss in the oceans”. In particular, “[w]arm-water corals are at high risk already and are projected to transition to very high risk even if global warming is limited to 1.5°C.” (para 62).

ITLOS noted also that climate change is a threat to human well-being, particularly for vulnerable people and/or communities living near the coasts (para. 66): “[v]ulnerable communities who have historically contributed the least to current climate change are disproportionately affected (high confidence)” (2023 Synthesis Report) (para. 66). Additionally, the tribunal stated that “[c]limate hazards are a growing driver of involuntary migration and displacement” and that “[c]limate-related illnesses … and threats to mental health and well-being are increasing,” again drawing on the IPCC reports (para. 66). the tribunal thus noted that climate change represents an existential threat and raises human rights concerns.

Protecting and preserving “marine environment” from adverse effects

The scientific evidence presented by the tribunal provides a solid basis for its conclusions on State obligations to prevent, reduce, and control climate pollution. ITLOS emphasized that, according to its fourth preambular paragraph, one of the main goals of the Convention is to establish a legal order for the seas and the ocean that will promote the protection and preservation of the marine environment (para. 195). In light of this objective, ITLOS identified the relevant provisions of the Convention and examined their application in the context of climate change. The Tribunal concluded by delineating specific obligations of States Parties to prevent, reduce and control pollution of the marine environment arising from climate change and ocean acidification. To do this, the Tribunal relied on article 194 of the Convention, which imposes an obligation on States to address all sources of marine pollution (para. 189). The best available scientific knowledge, contained in the IPCC’s reports, allowed the tribunal to reach these conclusions.