Scientific evidence to guide ICJ's decision on climate change

The global community is closely watching as the International Court of Justice (ICJ) prepares to issue its advisory opinion on states’ responsibilities under international law to safeguard the climate system.

Following persistent efforts for environmental justice, several of the world’s most climate-vulnerable countries primarily small island developing states and least developed nations had their opportunity to present their case at The Hague last December.

During the ICJ’s advisory proceedings on climate change, testimonies drew upon climate science, traditional and indigenous knowledge, and firsthand experiences of living through a changing climate.

As the court’s decision looms, experts and scientists have submitted compelling evidence highlighting issues such as global warming, rising sea levels, cyclones, and impacts on human security presented by states calling for urgent and robust climate action.

A coalition of Pacific Island nations, led by Vanuatu and supported by law students and diplomats, asked the ICJ to clarify the obligations countries have to combat climate change, the legal consequences of failing to act, and what constitutes “significant harm.”

Frustrated with the slow and often disappointing progress at climate summits like the Conferences of the Parties (COPs), these vulnerable nations brought their case to The Hague, seeking stronger accountability.

However, during the December hearings, wealthy, high-emitting countries relied on existing climate treaties the very frameworks that guide COP negotiations, to resist calls for enhanced climate commitments.

In recent years, there has been a surge in climate-related lawsuits and growing involvement from legal experts and courts in environmental issues.

Groups such as children, elderly women, and NGOs have taken legal action to push for stronger climate measures and demand environmental justice.

But what exactly is environmental justice (EJ)? In 2021 and 2022, the United Nations Human Rights Council and General Assembly formally recognized the human right to a clean, healthy, and sustainable environment.

The UN Development Programme (UNDP) has also crafted a global strategy on EJ aimed at boosting accountability and safeguarding environmental rights worldwide.

Environmental justice is both a social movement and a framework of principles focused on ensuring that everyone has the right to a healthy environment and equal protection against environmental hazards.

This encompasses rights such as access to natural resources, protection from environmental damage, and freedom from disproportionate harm caused by environmental laws, policies, or regulations.

EJ further includes the right to obtain environmental information and participate in decisions affecting the environment.

The movement aims to tackle environmental inequalities that disproportionately affect marginalized communities, including issues arising from hazardous waste, resource extraction, land use, and discriminatory practices like redlining where essential financial services are denied to neighborhoods with high populations of racial and ethnic minorities.

In the latest edition of the International Institute of Sustainable Development (IISD) Earth Negotiations Bulletin, Shaina Sada and Elisabeth Holland highlight testimonies presented at The Hague.

They note that the anticipated ICJ advisory opinion on climate change aims to clarify states’ obligations to safeguard the climate system and the legal repercussions under international law for neglecting these duties.

The call for the ICJ advisory opinion was driven by Pacific youth witnessing the effects of climate change on their islands and oceans, frustrated by the slow political response.

In response, Vanuatu led a coalition to advance the case through the United Nations.

The Intergovernmental Panel on Climate Change (IPCC) reports provide comprehensive summaries of global climate science.

Since their start in the early 1990s, these reports have evolved from recognizing the possibility of human influence on the climate to the clear and definitive attribution of climate change to human activities, as stated 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,” noted Sada and Holland.

Building on the scientific foundation of the IPCC reports, states incorporated a broad range of additional knowledge in their testimonies.

This included cultural, Indigenous, and local knowledge, firsthand accounts, expert analyses, and peer-reviewed research published after the completion of AR6.

The Earth's temperature has risen across land, oceans, and the atmosphere.

The IPCC AR6 found that the global atmosphere has warmed by an average of 1.1°C since pre-industrial times.

Many states, including Sri Lanka, emphasized the strong scientific consensus on the causes and consequences of global warming.

They highlighted that the increase in human-caused greenhouse gas (GHG) emissions, mainly from fossil fuel combustion, is the clear driver of rising temperatures, a point underscored by countries like Kenya.

Nine member states of the Commission of Small Island States on Climate Change and International Law (COSIS) stressed the urgent necessity to phase out fossil fuels to meet global climate targets.

As temperatures climb, sea levels rise due to thermal expansion and melting ice on land.

The Melanesian Spearhead Group highlighted how those least responsible for GHG emissions suffer the greatest impacts.

Sea-level rise is expected to continue for centuries, posing severe challenges for current and future generations as well as coastal ecosystems.

The issue of intergenerational equity was a key focus, with Sierra Leone underscoring the importance of addressing this alongside efforts to meet the Sustainable Development Goals (SDGs).

The accelerating pace of sea level rise was also addressed in the context of state sovereignty.

The Pacific Islands Forum (PIF) rejected the idea that coastal flooding could nullify state sovereignty, arguing instead that international law must ensure states can continue to exist despite rising seas.

The combined effects of sea level rise, warming, and cyclones are overwhelming the adaptive capacity of communities in atoll nations.

Testimonies from Tonga, Tuvalu, and the Pacific Community highlighted how major emitters have failed to uphold the principle of common but differentiated responsibilities and have not fulfilled climate finance promises to help vulnerable countries adapt.

Climate change poses significant risks to human safety and security.

Sudan shared experiences of resource shortages and displacement caused by environmental stress.

Palestine emphasized that ongoing military activities contribute to rising emissions and that living under occupation complicates efforts to adapt to climate change.

The World Health Organization (WHO) testified that future climate impacts are expected to displace millions and deepen poverty levels.

The ICJ heard how climate change effects such as warming, extreme weather events, and rising sea levels have already caused devastating harm and will continue to do so.

In 2024, the year these testimonies were presented, global temperatures reached 1.55°C above pre-industrial levels for the first time, surpassing the critical 1.5°C threshold and underscoring the urgent need for action.

Pacific Island Students Fighting Climate Change told the court, “International law must serve as a compass for justice and responsibility… the pursuit of climate justice requires determining the obligations of states, but it is incomplete without the requisite legal consequences.”

The world now awaits the ICJ’s advisory opinion, hopeful for a decisive ruling grounded in the extensive scientific evidence and powerful testimonies shared during the proceedings.