By Shaina Sadai and Elisabeth Holland

The International Court of Justice (ICJ) advisory opinion on climate change seeks to clarify States’ responsibilities to protect the climate system, and legal consequences under international law for failing to do so. In 2024, nations and international organizations from around the world submitted written and oral testimony to the Court. These testimonies were informed by climate science, traditional and Indigenous knowledge, and firsthand accounts of experiences under a changing climate. Here we discuss some of the evidence included in these powerful testimonies related to warming, sea level rise, cyclones, and human security from States seeking strong climate action.

The request for an ICJ advisory opinion originated from efforts of Pacific youth who saw the impacts of climate change on their ocean and island homes and felt dismayed with the lack of urgency in the political process. Vanuatu formed a coalition to move the case through the UN.

Evidentiary base and the use of science

The Intergovernmental Panel on Climate Change (IPCC) reports summarize global climate change knowledge. In the decades since their inception in the early 1990s, the reports’ conclusions regarding the certainty of human impacts on the climate evolved from acknowledging the potential for human influence to the strong and unequivocal statement of human responsibility in the IPCC Sixth Assessment Report (AR6). The body of scientific knowledge within the reports has expanded dramatically, documenting compelling consistency of climate impacts among myriad lines of evidence.

Complementing the scientific knowledge in the IPCC reports, States drew from additional expansive knowledge to build their testimonies. This included cultural, Indigenous, and place-based knowledge, firsthand testimonies, expert reports, and peer-reviewed studies published since AR6 concluded.

Rising heat

Earth’s temperature has increased on land, in the ocean, and in the atmosphere. IPCC AR6 concluded Earth’s atmosphere has warmed on average 1.1°C since preindustrial times. The certainty of the scientific consensus on the causes and outcomes of warming was cited by many States, such as Sri Lanka. The rise in human-induced greenhouse gas (GHG) emissions, primarily from burning fossil fuels, unequivocally drives rising temperatures, as noted by States including Kenya. Speaking to State responsibilities, testimony from the Commission of Small Islands States on Climate Change and International Law (COSIS), on behalf of its nine member States, discussed the urgent need to phase out fossil fuels to meet international climate goals.

The global oceans have stored over 90% of Earth’s accumulated heat. Ocean heat accumulation is accelerating, resulting in tropical cyclone intensification, rising sea levels, and marine heatwaves which wreak havoc on coastal ecosystems and compromise food security. Last year’s advisory opinion from the International Tribunal for the Law of the Sea (ITLOS) acknowledged these vast impacts, and States such as Seychelles included extensive evidence for them in ICJ testimonies.

Extreme events

Intensifying tropical cyclones have profound impacts, particularly on island nations. During tropical cyclones, waves and storm surge, compounded by rising sea levels, cause most of the damage. The devastating impacts of intensifying tropical cyclones were emphasized in numerous testimonies. Tropical Cyclone Pam had a lasting impact on women in Vanuatu and displaced half the population of Tuvalu. Tropical Cyclone Winston caused deaths, injuries, and economic hardship in Fiji. Tropical Cyclone Gita destroyed homes and cultural landmarks including Tonga’s parliament building. Oral testimony from The Bahamas communicated the devastation of Hurricane Dorian, which killed 200 people, displaced 10,000, and destroyed 9,000 homes. Many of these testimonies emphasized the minimal emissions responsibility of impacted States and the need for accountability and action from high-emitting countries.

Sea level rise: Accounting for responsibilities

As temperatures rise, thermal expansion and melting land ice drive rising sea levels. The Melanesian Spearhead Group described the strong cultural and spiritual connection peoples of the Pacific have to their environment, and the detrimental effects of sea level rise on their wellbeing. They testified to the disproportionate impacts on people who bear little responsibility for GHG emissions.

Sea levels will continue rising for centuries, presenting stark challenges for present and future generations and coastal ecosystems. The question of intergenerational equity is crucial, as Sierra Leone testified, noting the related need to achieve the SDGs. The rapid acceleration of sea level rise over time was also discussed in relation to state sovereignty. Testimony from the Pacific Islands Forum (PIF) rejected the notion that coastal inundation could disrupt State sovereignty, instead stressing that international law should allow for the continuation of States in the face of rising sea levels.

Human security and limits to adaptation

The combined impacts of sea level rise, warming, and cyclones are pushing communities beyond the limits of adaptation in atoll countries. This was highlighted in testimonies from Tonga, Tuvalu, the Pacific Community, and others as illustrating the failure of high-emitting States to comply with the principles of common but differentiated responsibilities – and deliver climate finance commitments to support adaptation efforts in vulnerable countries. 

The challenges of climate change have broad implications for human safety and security. The Sudan testified to people’s experiences with resource scarcity and displacement. Palestine testified that military activity drives increasing emissions and that living under occupation poses extraordinary challenges to climate adaptation. Testimony from the World Health Organization (WHO) points to projected future climate impacts displacing millions of people and exacerbating poverty.

Looking ahead

Testimonies submitted to the ICJ demonstrate how the effects of climate change, including warming, extreme events, and rising sea levels have devastating impacts which will continue into the future. In 2024, the year in which testimonies were submitted, the global average temperature was 1.55°C above pre-industrial levels, marking the first temporary exceedance of 1.5°C and underscoring the need for urgent action.

Pacific Island Students Fighting Climate Change noted in their closing statement that “international law must serve as a compass for justice and accountability.…The pursuit for climate justice requires determining the obligations of States but is incomplete without the requisite legal consequences.” As we await the ICJ’s advisory opinion we feel hopeful for a strong outcome – informed by the myriad lines of evidence presented in the powerful testimonies heard by the Court.

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This article was written by Shaina Sadai (Mount Holyoke College) and Elisabeth Holland (Brown University).

This Guest Article is part of a project that seeks to raise awareness and build momentum and knowledge around the ICJ advisory opinion on obligations of States in respect of climate change and to promote a better understanding of the implications of the advisory opinion among sustainable development decision makers.