Court Analysis
La Corte Internacional de Justicia examinó el marco normativo aplicable a las obligaciones de los Estados respecto al cambio climático a partir de una interpretación sistemática del derecho internacional. Para responder a la primera pregunta planteada por la Asamblea General de la ONU, la Corte analizó tanto tratados como normas consuetudinarias, principios generales del derecho internacional y tratados relevantes en materia ambiental y de derechos humanos.[24].
La Corte identificó como parte del derecho directamente aplicable a los siguientes instrumentos y fuentes:.
• - La Carta de las Naciones Unidas, por establecer los principios de cooperación internacional en la solución de problemas globales como el cambio climático.[25].
• - Los tratados sobre cambio climático, incluyendo la Convención Marco de las Naciones Unidas sobre el Cambio Climático (CMNUCC), el Protocolo de Kioto y el Acuerdo de París. La Corte consideró que estos tres instrumentos se complementan entre sí y siguen siendo jurídicamente vigentes.[26].
• - La Convención de las Naciones Unidas sobre el Derecho del Mar (CONVEMAR), en tanto establece obligaciones sobre la protección del medio marino, también afectado por el cambio climático.[27].
• - Otros tratados ambientales, como la Convención para la Protección de la Capa de Ozono, el Protocolo de Montreal, la Convención sobre la Diversidad Biológica y la Convención de Lucha contra la Desertificación, todos considerados complementarios al régimen climático.[28].
• - El derecho internacional consuetudinario, en particular el deber de prevenir daños ambientales significativos[29] y el deber de cooperar en la protección del medio ambiente.[30].
• - El derecho internacional de los derechos humanos, por su conexión con la protección ambiental, especialmente mediante los Pactos Internacionales de 1966 y jurisprudencia de tribunales regionales.[31].
La Corte también consideró como relevantes para interpretar las obligaciones jurídicas varios principios del derecho internacional del medio ambiente:.
• - Desarrollo sostenible, como principio orientador de la implementación de medidas ambientales.[32].
• - Responsabilidades comunes pero diferenciadas y capacidades respectivas, que reflejan diferencias históricas y de capacidad entre los Estados en la lucha contra el cambio climático.[33].
• - Equidad, en su sentido jurídico, como principio aplicable dentro de los márgenes del derecho internacional.[34].
• - Equidad intergeneracional, que impone deberes hacia las generaciones futuras en la protección del clima.[35].
• - Enfoque o principio de precaución, en virtud del cual la incertidumbre científica no debe usarse como excusa para postergar medidas de protección ambiental.[36].
En contraste, la Corte concluyó que el principio de «quien contamina paga» no forma parte del derecho internacional aplicable a este caso, debido a su falta de incorporación en los tratados sobre cambio climático y su escasa recepción a nivel interestatal.[37].
La Corte rechazó la idea de que los tratados sobre cambio climático constituyen un régimen jurídico exclusivo que desplace otras normas del derecho internacional. Consideró que no existe una incompatibilidad entre dichos tratados y otras normas relevantes, ni una intención expresa de sustituirlas. En consecuencia, concluyó que el principio de lex specialis no impide la aplicación simultánea de otras normas convencionales o consuetudinarias.[38].
Asimismo, la Corte concluyó que el derecho más directamente aplicable para determinar las obligaciones de los Estados frente al cambio climático incluye instrumentos como la Carta de las Naciones Unidas, los tres tratados sobre cambio climático, la CONVEMAR, tratados ambientales conexos, normas consuetudinarias sobre prevención de daños y cooperación, el derecho internacional de los derechos humanos y una serie de principios interpretativos.[39].
International instruments that establish obligations for States
The Court reiterated that the international legal framework on climate change is mainly made up of three binding multilateral treaties: the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol and the Paris Agreement. In its opinion, the ICJ analyzed the substantive obligations emanating from these instruments and their relationship to each other, clarifying the nature and scope of the commitments assumed by States under them.[40] The ICJ explained that these treaties share a common purpose: protecting the climate system from anthropogenic greenhouse gas emissions. Although they differ in scope and specificity, the Court indicated that the three texts are complementary and mutually reinforcing. In that sense, the judges resolved that the Kyoto Protocol and the Paris Agreement should be interpreted as developments of the general provisions of the UNFCCC.[41].
Furthermore, the court stressed that principles such as common but differentiated responsibilities and respective capacities, intergenerational equity, sustainable development, international cooperation and the precautionary principle inform the interpretation of the obligations contained in these treaties.[42].
The UNFCCC establishes a series of differentiated commitments for States Parties, especially between developed countries (Annex I parties) and developing countries. Among the main obligations are:
• - Mitigation: All States must formulate, implement and update programs to mitigate climate change and report inventories of GHG emissions and removals. Annex I countries have additional obligations, including adopting policies to reduce their emissions to 1990 levels.[43].
• - Adaptation: States must facilitate adaptation to climate change through national and regional plans and programs. Developed countries are obliged to help the most vulnerable cover the costs associated with these measures.[44].
• - Cooperation: There are cooperation obligations in scientific research, technology transfer, education and financing, especially from developed countries to developing countries.[45].
The Court indicated that the Kyoto Protocol complements the UNFCCC by imposing quantified and binding emissions reduction targets for Annex B countries. Although the second commitment period ended in 2020 and a third has not been adopted, the treaty remains in force and its provisions may still be relevant for assessing the international responsibility of States.[46].
Meanwhile, the Paris Agreement represents, according to the Court, the most recent instrument of the international climate regime, and establishes a legal framework based on nationally determined contributions (NDCs), and is aimed at keeping the increase in global temperature below 2°C, seeking to limit it to 1.5°C.
Customary international law establishing obligations for States
The ICJ affirmed that two fundamental obligations of customary international law are applicable in the context of climate change: the duty to prevent significant damage to the environment and the duty to cooperate in its protection. These general norms, according to the ruling, constitute a complement to the conventional regime on climate change and have universal validity, even for States that are not party to the relevant treaties.[54].
The duty to prevent significant harm to the environment finds its origin in the Trail Foundry arbitral award (1941) and has been reiterated in numerous ICJ decisions, including the Corfu Canal (1949), Pulp Mills (2010) and the Nuclear Weapons Case (1996). The Court reaffirmed that this obligation imposes on States the duty to prevent, by all reasonably available means, activities under their jurisdiction or control from causing significant damage to the environment of other States or to areas beyond any national jurisdiction.[55].
In the context of climate change, the Court held that the climate system is an integral part of the global environment and that the accumulation of greenhouse gases represents a risk of significant harm, even if caused by multiple actors and not attributable to a single source.[56].
On the other hand, the Court reaffirmed that the duty of prevention is fulfilled by acting with due diligence, a standard that requires substantive and procedural measures, and that varies according to the capabilities of each State.[57] Among the elements of this standard the Court cited:
• - Adoption of appropriate measures, including laws, regulatory policies and control mechanisms that ensure substantial emissions reductions and facilitate adaptation.[58].
• - Use of scientific and technological information, which implies not only applying the available knowledge, but also actively seeking new data.[59].
• - Observance of international norms and standards, including binding norms and non-binding technical guidance, such as decisions of the Conferences of the Parties.[60].
• - Consideration of differentiated capacities, which means that States with greater resources are required to exercise stricter diligence, in accordance with the principle of common but differentiated responsibilities.[61].
• - Application of the precautionary principle, which requires acting even in contexts of scientific uncertainty if there is a plausible risk of serious or irreversible damage.[62].
• - Environmental impact assessment (EIA), as an expression of the duty to identify risks before undertaking activities that may aggravate climate change.[63].
• - Notification and consultation, when planned activities may negatively affect collective mitigation or adaptation efforts.[64].
Obligations under other environmental treaties
The ICJ held that, in addition to treaties specifically aimed at climate change, there are other international legal instruments that also contribute to the protection of the climate system and are therefore relevant to determine the obligations of States with respect to this matter.[70] Among these instruments are the Vienna Convention for the Protection of the Ozone Layer, the Montreal Protocol, the Convention on Biological Diversity and the United Nations Convention to Combat Desertification.[71][70].
For example, Article 2 of the Vienna Convention establishes that States Parties must adopt appropriate legislative or administrative measures to protect human health and the environment from the adverse effects derived from human activities that may modify the ozone layer.[70].
The Montreal Protocol complements this treaty by imposing an obligation to phase out ozone-depleting substances, many of which are also greenhouse gases. The parties have reaffirmed the link between the recovery of the ozone layer and the fight against climate change, as evidenced in the Montreal Declaration of 2007.[72] These obligations were strengthened by the Kigali Amendment, which establishes specific measures to reduce hydrofluorocarbons (HFCs), with positive impacts on the climate. For the Court, the obligations derived from these treaties complement and reinforce those provided for in the UNFCCC and the Paris Agreement.[72].
On the other hand, the Convention on Biological Diversity recognizes that the conservation of biodiversity is a common concern of humanity.[72] Article 3 of the convention incorporates the customary obligation to prevent damage to the environment outside national jurisdiction, while article 5 promotes international cooperation for the conservation of biodiversity.[73] Articles 6, 7 and 8 require States to develop national conservation plans, integrate biodiversity into public policies, identify harmful processes and regulate activities that may have adverse effects, including those that generate greenhouse gas emissions.[73] The Kunming-Montreal Global Biodiversity Framework adopted in 2022 reinforces these objectives, highlighting the need to reduce the impacts of climate change on biodiversity.[73].
According to the ICJ, these obligations are complementary to those established by climate treaties, as they seek to preserve the biosphere, whose stability is directly related to climate regulation.[73].
Furthermore, the Convention to Combat Desertification establishes explicit links with the UNFCCC and recognizes that combating desertification can contribute to the achievement of global climate goals. According to article 1, desertification is the result of natural and human factors, including climate change and climate variability, and affects the geosphere and biosphere. Articles 4 and 6 establish obligations to adopt integrated approaches that consider physical, biological and socio-economic aspects, as well as specific commitments by developed countries to support developing countries in combating desertification and its related effects, such as drought. Furthermore, Article 8 encourages States to coordinate their actions under this convention, the UNFCCC and the Convention on Biological Diversity. Fulfilling these obligations directly contributes to the protection of the climate system, in particular through the conservation of the geosphere and hydrosphere. [74].
Implementation of the United Nations Convention on the Law of the Sea
The International Court of Justice affirmed that the United Nations Convention on the Law of the Sea (UNCLOS) is relevant in the context of climate change given that anthropogenic emissions of greenhouse gases have detrimental effects on the marine environment, which represents more than 70% of the planet and more than 95% of the biosphere.[75] In particular Part XII of UNCLOS, relating to the protection and preservation of the marine environment, was highlighted as of special importance.[75].
The ICJ noted that the International Tribunal on the Law of the Sea (ITLOS) had already issued an advisory opinion in May 2024 on the obligations of States with respect to marine pollution derived from GHG emissions, and considered it pertinent to take into account its jurisprudence to maintain the coherence of international law.[75].
The Court concluded that anthropogenic GHG emissions constitute marine pollution as defined in article 1, paragraph 1, paragraph 4 of UNCLOS, since they involve the introduction of substances or energy that may have harmful effects on the marine environment.[76] Article 192 imposes on States the obligation to protect and preserve the marine environment, both through positive action and by preventing its degradation.[76] Given the serious and irreversible risk posed by climate change, the ICJ affirmed that the standard applicable due diligence is strict.[76].
The Court also recognized that the sovereign right of States to exploit their natural resources in accordance with their environmental policies, contemplated in Article 193, is conditioned by the duty to protect the marine environment.[77].
Article 194 obliges States to take all necessary measures, individually or collectively, to prevent, reduce and control marine pollution, using the best practical means available and considering their capabilities.[77] According to the Court, these measures must be evaluated in accordance with objective criteria, including the best available science and the national circumstances of each State.[77] Likewise, it determined that activities that generate GHG emissions are also covered by Article 194, paragraph 2.[77].
Article 197 of UNCLOS establishes the obligation to cooperate on an ongoing basis in the development of standards and good practices to protect the marine environment.[78] This obligation is complemented by articles 200 and 201, which require promoting scientific studies and sharing relevant data.[78] For its part, article 206 requires States to carry out environmental impact assessments when there are reasons to believe that activities under their jurisdiction may cause significant harmful changes to the marine environment. This obligation extends to areas outside national jurisdiction.[78].
Obligations under international human rights law
The Court affirmed that the adverse effects of climate change undermine the effective enjoyment of various human rights. In this sense, he explained that the environment constitutes a precondition for the exercise of such rights, given that it sustains human life and the well-being of present and future generations.[82] This interdependence is reflected in the preamble of the Paris Agreement, which calls on States to consider their human rights obligations when taking climate measures.[82].
The Court recognized that the right to life, enshrined in instruments such as the International Covenant on Civil and Political Rights (ICCPR) and the Convention on the Rights of the Child, can be compromised by climate-related events, such as rising sea levels, droughts or natural disasters.[82] It also noted that the application of the principle of non-refoulement may prevent a person from being repatriated to a country where they face serious risks due to climate change.[83].
Regarding the right to health, the Court highlighted its protection under the International Covenant on Economic, Social and Cultural Rights (ICESCR) and other instruments. He emphasized that this right is threatened by air, water and soil pollution, and that States must guarantee healthy environmental conditions for its enjoyment.[83].
The impact on the right to an adequate standard of living, which includes access to food, housing and drinking water,[84] and the right to private, family and home life, was also highlighted, especially when States do not adopt sufficient adaptation measures.[84].
Groups such as women, children, indigenous peoples and people in vulnerable situations face greater risks. The Court observed that States must design mitigation and adaptation measures with a focus on human rights, substantive equality and non-discrimination.[84].
The ICJ recognized that the right to a clean, healthy and sustainable environment is a fundamental human right, inherent to the enjoyment of other rights. This right has been proclaimed in regional instruments, such as the African Charter on Human and Peoples' Rights, the Protocol of San Salvador and the Arab Charter on Human Rights.[85].
In addition, more than one hundred States have incorporated it into their constitutions or national legislation.[85] The United Nations General Assembly formally recognized it through resolution 76/300 of 2022, highlighting its connection with other rights and its importance for its effective enjoyment.[85].
The Court concluded that this right derives from the interdependence between human rights and environmental protection, which is why it should be considered part of the international legal corpus on human rights.[85].
Regarding the territorial scope of application of human rights treaties, the Court reiterated that States must respect their obligations even when they exercise jurisdiction outside their national territory.[86] This interpretation has been confirmed in advisory opinions and previous rulings of the Court itself, as well as by oversight bodies such as the Human Rights Committee.