Advancing climate change litigation involves overcoming significant hurdles to promote justice and alter human behaviors for the benefit of society and the environment. During this challenging process, litigants, legal professionals, scientific experts, and judges encounter difficulties in cross-disciplinary communication. The Union of Concerned Scientists (UCS) has introduced a new resource, Climate Science in Legal Contexts: A Glossary of Key Terms for Lawyers, to help ease this journey.
In numerous climate change-related trials and appeals, attorneys must adeptly present factual evidence and analyses with the help of climate scientists, ecosystem specialists, physicians, engineers, and other experts. A case in point is Held vs. Montana, where youths filed a lawsuit against their state government for alleged constitutional rights violations. The plaintiffs’ legal team introduced testimony from two climate scientists, two ecologists, environmental policy leaders, a pediatrician, a psychiatrist, an energy engineer, and a tribal leader. Beyond standard witness preparation, this case demanded effective collaboration and communication between lawyers and scientists on complex topics like scientific consensus, anthropogenic climate change, and greenhouse gas emissions.
The complex terminology introduced in climate change litigation can be overwhelming. This is where the UCS glossary proves invaluable.
Vocabulary challenges in two prominent court proceedings
The UCS glossary is a tool designed to facilitate clearer communication across disciplines, enhancing outcomes in climate change litigation. This was evident in two significant recent court proceedings.
1. The 2025 ICJ Opinion: In its 2025 Advisory Opinion on climate change, the International Court of Justice (ICJ) interpreted the Paris Agreement’s “1.5°C above pre-industrial levels” provision. The ICJ aimed to apply the “best available science” as outlined in the Paris Agreement.
As part of a team of environmental lawyers from a leading international organization, I contributed to a brief submitted to the ICJ. Some lawyers initially suggested describing this provision as a “threshold” and “tipping point” for the global climate system. However, I advised them to consider that atmospheric scientists view the effects of temperature increases as a continuum, with harmful effects extending both below and above 1.5°C. Additionally, climate scientists study thresholds or tipping points at various temperatures for different natural systems.
The legal team adjusted the brief to align more closely with climate science. The UCS glossary’s details on “best available science,” “1.5° Celsius,” “threshold,” and “tipping point” would have been beneficial for the lawyers. The glossary could also provide valuable insights for judges and their clerks. The ICJ’s interpretation incorporated climate science terms like “scientific consensus,” “target,” “threshold,” and “goal,” ultimately concluding that the 1.5°C threshold is the agreed primary temperature goal under the Paris Agreement.
2. Held v. Montana Case: This case involved 16 plaintiffs aged 2 to 18 who sought a ruling from Montana courts on whether a statute restricting environmental reviews for permits violated their state constitutional right to a “clean and healthful environment.” The plaintiffs’ legal team relied on extensive scientific analyses of climate systems. The UCS glossary, with its sections on climate models, public health, and cultural heritage, would have been beneficial throughout the litigation for expert witnesses, attorneys, and judges.
The court’s findings included statements such as:
- “There is overwhelming scientific consensus that Earth is warming as a direct result of human GHG emissions, primarily from the burning of fossil fuels,” and
- “Children are uniquely vulnerable to the consequences of climate change, which harms their physical and psychological health and safety, interferes with family and cultural foundations and integrity, and causes economic deprivations.”
In 2024, the Montana Supreme Court upheld the trial court’s findings. The concept of “overwhelming scientific consensus” was not a standard for constitutional interpretation. Instead, the court used a different vocabulary, concluding that the constitutional right to a “clean and healthful environment” encompasses a stable climate system.
The judges demonstrated a strong grasp of climate science terminology, aided by the scientific experts’ understanding of legal concepts. Multidisciplinary decisions are possible, and the UCS glossary contributes to achieving this goal.
From glossary to actions
The UCS glossary aims to assist lawyers in understanding scientific concepts frequently encountered in climate litigation, helping them assess expert evidence accurately and avoid misinterpretations in court. This glossary also provides insight into the broader implications of climate change litigation.
For example, the glossary explains “attribution science” and its significance. Lawyers should deepen their understanding of these scientific tools developed through complex climate models and statistical analyses. How will this understanding impact climate change litigation’s effectiveness in promoting justice and behavioral change?
Legislators might attempt to protect polluters from liability for damages identified through attribution science. This outcome depends partially on public awareness and efforts to translate scientific findings into policies. Moreover, will judges recognize standing in lawsuits against polluters, consider expert evidence based on attribution science, and order remedies aligned with scientific evidence? This is influenced by the training materials available for judges, similar to resources in other scientific fields. Despite this need, the Federal Judicial Center in 2026 removed a draft chapter on climate change from its scientific evidence manual.
Another example is the glossary’s definition of “vulnerability,” crucial in successful climate change litigation by Montanan youths and Swiss elderly women before the European Court of Human Rights (ECHR). Plaintiffs’ lawyers demonstrated these groups’ susceptibility to health impacts from climate changes. However, Montana quickly enacted a law excluding certain fossil fuel projects from environmental reviews. Likewise, the Swiss parliament rejected the ECHR’s ruling, and the Council of Europe issued a weak review of Switzerland’s compliance. While enhancing understanding among lawyers is crucial, implementing protective changes remains vital for climate justice.
Multidisciplinary thinking in education and litigation
The UCS glossary is a valuable tool for advancing interdisciplinary approaches in teaching environmental law, policies, and impacts, as well as in environmental litigation and regulations.
As an adjunct professor at the University of Illinois, with graduate degrees in law, applied mathematics, and economics, I teach students across various disciplines, including law, environmental sciences, medicine, public health, and more. These students learn that sustainability is interconnected with social, economic, and environmental systems, supported by science and law. They often engage with unfamiliar fields of evidence, analysis, and recommendations, contributing their expertise to develop multidisciplinary sustainability solutions.
Universities should promote education for multidisciplinary action on climate change and sustainability, emphasizing vocabulary comprehension and term understanding. Graduates in all fields should not only recognize sustainability challenges but also collaborate effectively to implement solutions.
Collaboration and communication across disciplines are also vital for climate change and environmental lawyering. I have collaborated with scientists, engineers, physicians, and other experts on litigation and regulatory proceedings for UCS and other organizations, including work with the World Commission on Environmental Law and community groups in Spain and Portugal.
While the glossary is valuable for education and legal work, deeper challenges persist, including political attacks on science and the rule of law, alongside disinformation campaigns. The federal EPA’s February 2026 rescission of the endangerment finding highlights the need for effective climate litigation. Cases range from appellate reviews of agency actions to state cases on public nuisance and human rights claims. Despite some lawyers’ reluctance towards science and quantitative analysis, climate litigation, like the Montana case, demonstrates that science-informed actions are possible. Continued efforts by UCS and others are essential.
The UCS glossary is a crucial, timely, and beneficial resource. It represents a significant step toward enhanced multidisciplinary understanding, addressing climate change, and promoting sustainability.
