As current trajectories indicate that the goals of the Paris Agreement are unlikely to be achieved, public attention is shifting towards new forms of climate policy, such as geoengineering.[1] While there are different geoengineering technologies being explored, Solar Radiation Management (SRM) is particularly controversial. SRM technologies aim to counteract global warming by intervening directly in the earth’s radiative balance by dispersing reflective particles into the atmosphere.[2] That is to say, SRM seeks to cool the earth by reflecting sunlight back into space.
While presented as a crucial response to climate change, these technologies carry significant risks.[3] Their impacts are inherently transboundary: altering atmospheric conditions in one region may disrupt precipitation patterns elsewhere, lead to biodiversity loss, and damage ecosystems, undermining food and water security.[4] These risks are unlikely to be distributed evenly, disproportionately affecting vulnerable regions in the Global South, in particular, frontline communities such as indigenous peoples, peasants, and other persons working in rural areas.[5] This would reinforce structural inequalities and exacerbate climate injustice, as those communities most affected have contributed the least to climate change.[6] Moreover, it sets us on a path of perpetual dependency, as abrupt termination would result in rapid temperature increases and potentially catastrophic consequences.[7]
Recent developments suggest that SRM is no longer purely speculative. In the United States, two startup companies have started experimenting with the release of unknown particles into the atmosphere, without clear regulatory oversight.[8] As these companies openly aim to commercialise the technology and raise the prospect of deployment within the decade[9], profound legal questions arise: who bears responsibility when interventions in the climate system cause harm beyond national borders? This contribution argues that existing international law already imposes constraints on such technologies, as clarified by the International Court of Justice (ICJ)’s 2025 Advisory Opinion on climate change. Building on this, it demonstrates that the recognition of extraterritorial obligations is essential to governing geoengineering.
No Specific International Framework: Implications following from the ICJ’s 2025 Advisory Opinion
At present, there is no specific international legal framework governing geoengineering. The lack of such specific regulation, however, does not mean that SRM technologies are permitted or can be developed in a legal vacuum.[10] Under international law, activities conducted in the stratosphere, such as the release of sulfur particles via balloons, fall within the territorial sovereignty of States.[11] By contrast, activities in outer space, such as the deployment of reflectors, are governed by a different legal regime: outer space is regarded as a common area to humanity, meaning that no State may claim sovereignty over it and that all States are, in principle, free to explore and use it (Outer Space Treaty, Art. 1).[12] SRM is therefore subjected to different legal regimes depending on where it is deployed.[13]
However, due to its potentially devastating effects on biodiversity, geoengineering is prohibited under a longstanding moratorium at the Convention on Biological Diversity.[14] Moreover, States’ rights to freely explore and engage in SRM is constrained by various norms and principles already established in international treaties and customary international law.[15]
In its 2025 Advisory Opinion on the obligations of States with respect to climate change, the ICJ clarified that a broad range of existing norms and principles apply to the protection of the climate system. The Advisory Opinion, being the most significant development in international environmental law since the adoption of the Paris Agreement, also has significant implications for SRM technologies.[16] The UN Charter, the climate change treaties (namely, the United Nations Framework Convention on Climate Change, the Kyoto Protocol, and the Paris Agreement), as well as the Convention on Biological Diversity, the UN Convention to Combat Desertfication, the Vienna Convention for the Protection of the Ozone Layer (Ozone Convention), and the Montreal Protocol on Substances that Deplete the Ozone layer all set forth binding obligations for States parties to ensure the protection of the climate system and other parts of the environment.[17] Particularly relevant in the light of SRM technologies is the Ozone Convention, which stipulates the obligation to prevent environmental damage caused by the degradation of the ozone layer (Article 2(1)).[18] The Ozone Convention’s Preamble also recalls States’ responsibility to “not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction”.[19]
Likewise, recalling the Legality of the Threat or Use of Nuclear Weapons Advisory Opinion[20] and the Pulp Mills judgment[21], the ICJ held that under customary international law, States have the duty to prevent significant harm to the environment by acting with due diligence and to use all means at their disposal to prevent activities carried out within their jurisdiction or under their control from causing significant harm to the climate system and other parts of the environment (Principle of Prevention). Because all States share a common interest in protecting global environmental commons such as the atmosphere, they are under an erga omnes obligation (i.e., an obligation which is owed to the international community as a whole) to safeguard the climate system, in particular by preventing significant transboundary harm.[22] The ICJ confirmed that a breach of these obligations constitutes an internationally wrongful act, giving rise to an “entire panoply” of legal consequences.[23]
Importantly, the ICJ rejected the argument that wrongful conduct in the context of climate change is cumulative in nature. While climate change is caused by cumulative emissions, it remains possible to determine each State’s total contribution to global emissions and thus attribute responsibility.[24] What constitutes a wrongful act is not the emissions as such, but actions or omissions that cause significant harm to the climate system in breach of a State’s international obligations.[25] This has direct implications for geoengineering. For instance, a State deploying SRM measures that alter precipitation patterns in another State, causing drought or crop failure, could incur responsibility for breaching its obligation to prevent transboundary harm. Attempts to justify such acts, for example, on the grounds of necessity (Art. 25 Articles on State Responsibility for Internationally Wrongful Acts), arguing that geoengineering measures were required to avert severe climate impacts, would be subject to strict conditions. Given the inherently transboundary and uneven impacts of SRM, this threshold would be difficult to meet in practice. Moreover, in a 2023 report, the Human Rights Council cautioned that, given the practical and scientific uncertainty of the hypothetical benefits of SRM technologies, these “speculative technologies” cannot be considered viable mitigation or adaptation measures.[26] Rather, the current focus of climate action should be on deploying existing, safe measures and technologies in line with a rights-based approach and the findings of the Intergovernmental Panel on Climate Change.[27]
Human Rights Law: Applicability and Limitations
Geoengineering also raises fundamental questions under International Human Rights Law, since these technologies have the potential to cause significant and long-lasting impacts on the environment and the enjoyment of human rights, including the rights to life, health, housing, food, and a clean, healthy, and sustainable environment.[28] According to the ICJ’s Advisory Opinion, the human right to a clean, healthy, and sustainable environment is inherent in the enjoyment of other human rights.[29] “Consequently, in so far as States parties to human rights treaties are required to guarantee the effective enjoyment of such rights, it is difficult to see how these obligations can be fulfilled without at the same time ensuring the protection of the right to a clean, healthy and sustainable environment.”[30]
Traditionally, human rights have been interpreted territorially, with States’ obligations confined to individuals within their borders. However, this approach is increasingly challenged in light of the transboundary consequences of climate change, mainly due to the enormous gaps in protection it results in.[31]
As expressed in the 2011 Maastricht principles on Extraterritorial Obligations, “obligations of a global character are set out in the Charter of the United Nations and human rights instruments to take action, separately, and jointly through international cooperation, to realise human rights universally”.[32] While the Maastricht Principles in themselves are not legally binding, they were explicitly “drawn from international law (…) with a view to advancing and giving full effect to the object of the Charter of the United Nations and international human rights”.[33] The UN Charter lists as one of its purposes “to achieve international co-operation in solving international problems of an economic, social, cultural, or humanitarian character, and in promoting and encouraging respect for human rights and for fundamental freedoms…”.[34] All states that are members of the United Nations have ratified the UN Charter and committed to perform this treaty “in good faith”.[35] For member states of the United Nations, the international cooperation to achieve the goals of the organisation is thus not a choice but a legally binding commitment that they have made.[36]
Similarly, Article 28 of the Universal Declaration of Human Rights (UDHR) envisages a structure of the international community that is conducive to full implementation and enjoyment of human rights, reflecting the obligations as per the United Nations Charter.[37] Following the entry into force of the UN Charter and the adoption of the UDHR, global obligations have had their expression in individual human rights treaties, declarations, UN resolutions, and other soft law instruments.[38] For instance, the International Covenant on Economic, Social, and Cultural Rights (ICESCR), which prescribes States parties “to take steps, individually and through international assistance and cooperation” (Art. 2(1)).[39] This obligation of international cooperation has to be read in light of the object and purpose of the ICESCR, which is the full realisation of economic, social, and cultural rights.[40] A territorialist interpretation would therefore be contrary to the purpose of the Covenant.[41] This is also the approach of the Committee of Economic, Social, and Cultural Rights (CESCR), which has held that the ICESCR contains extraterritorial obligations, “following from the fact that the obligations of the Covenant are expressed without any restriction linked to territory or jurisdiction”.[42]
Today, extraterritorial obligations are increasingly referenced in the United Nations and other international law instruments, and there is even evidence of growing recognition by states.[43] States are therefore expected to ensure that activities under their jurisdiction or effective control do not cause environmental harm or human rights violations in other States.[44] By analogy, this reasoning can be extended to SRM. Extraterritorial obligations would provide an important basis for regulating these technologies: States could be held responsible for transboundary harm resulting from interventions in the climate system.[45]
At the same time, the legal recognition of extraterritorial obligations remains contested. At the regional level, the European Court of Human Rights held in Duarte Agostinho that States do not exercise extraterritorial jurisdiction in the context of climate change.[46] The case law of the ECtHR is very clear: while a State may exercise effective control over the ‘source’ of transboundary risk and harm produced by greenhouse gas emissions (produced from activities within its territory), it lacks effective control over the victims of such risk or harm (as they are situated outside its jurisdiction). Paradoxically, this results in the situation where harmful conduct can be attributed to a State under the general rules of international law, yet this State’s jurisdiction cannot be established under the European Convention on Human Rights.[47]
This creates a discrepancy with other systems, such as the Inter-American Human Rights System and the United Nations, where such obligations have been recognised in the context of the right to a clean, healthy, and sustainable environment.[48] This discrepancy reflects a recurring asymmetry, whereby extraterritorial approaches are primarily advanced by states from the Global South, while states from the Global North, where the largest emitters are based, resist them.[49] In Duarte Agostinho, the ECtHR expressly ruled out the opportunity to adopt a different understanding of extraterritorial jurisdiction, inspired by approaches from the Global South.[50]
Conclusion
Geoengineering, and SRM in particular, is constrained by various norms and principles of international customary law, international environmental law, and human rights law. At the 2010 Conference of the Parties under the Convention on Biological Diversity, States recognised the need for science-based, global, transparent and effective regulatory mechanisms for geoengineering as a prerequisite for its potential development and deployment. Today, however, geoengineering is rapidly moving from speculative science towards implementation without regulation. If SRM technologies are to be developed or deployed, relying solely on territorial interpretations of States’ obligations will be insufficient.
The emerging era of geoengineering and the associated transboundary human rights challenges represent a turning point for international law, particularly concerning the recognition and consolidation of extraterritorial obligations. The Maastricht Principles and the ICJ’s Advisory Opinion provide an important starting point for holding governments accountable for extraterritorial human rights violations on the basis of their existing obligations under international law.[51] They emphasise that States must ensure that their decisions, actions, and omissions do not, directly or indirectly, infringe upon human rights beyond their borders.[52]
Although extraterritorial obligations derive from existing international law and are increasingly recognised by international institutions and States alike, their recognition as legally binding remains contested, particularly in the Global North, where the majority of historical emissions and transboundary environmental harm originate. This reflects a broader imbalance within international climate governance, in which States most responsible for climate change continue to resist legal frameworks that could expand accountability. Recognising extraterritorial obligations is essential not only in the context of geoengineering, but also to address the current gaps within international human rights law and to ensure that human rights treaties effectively fulfil their intended purpose. If we are to respond effectively to climate injustice, the recognition and effective enforcement of extraterritorial obligations are necessary in an era of increasing transboundary harm driven by climate change and geoengineering technologies.
[1] Karl Mathiesen and Corbin Hiar, ‘The Strange and Totally Real Plan to Blot Out the Sun and Reverse Global Warming’ (Politico Magazine, 21 November 2025) <https://www.politico.com/news/magazine/2025/11/21/stardust-geoengineering-janos-pasztor-regulations-00646414> accessed 4 May 2026; Bart Crezee, ‘Ijsmeesters van het Hoge Noorden’ (De Groene Amsterdammer, 1 April 2026) <https://www.groene.nl/artikel/ijsmeesters-van-het-hoge-noorden> accessed 4 May 2026
[2] James Temple, ‘How One Controversial Startup Hopes to Cool the Planet’ (MIT Technology Review, 10 December 2025) <https://www.technologyreview.com/2025/12/10/1129079/how-one-controversial-startup-hopes-to-cool-the-planet/> accessed 4 May 2026
[3] Center for International Environmental Law, ‘US-Israeli Start-Up Announces Reckless Solar Geoengineering Experiments from April 2026’ (28 October 2025) <https://www.ciel.org/news/us-israeli-start-up-announces-reckless-solar-geoengineering-experiments-from-april-2026/> accessed 4 may 2026
[4] UNHRC, Advisory Committee ‘Impact of New Technologies Intended for Climate Protection on the Enjoyment of Human Rights’ UN Doc A/HRC/54/47 (10 August 2023) [15-16]; Center for International Environmental Law, ‘US-Israeli Start-Up Announces Reckless Solar Geoengineering Experiments from April 2026’
[5] UNHRC ‘Impact of New Technologies’18
[6] UNHRC ‘Impact of New Technologies’18
[7] Center for International Environmental Law, ‘US-Israeli Start-Up Announces Reckless Solar Geoengineering Experiments from April 2026’
[8] Mathiesen and Hiar, ‘The Strange and Totally Real Plan to Blot Out the Sun and Reverse Global Warming’
[9] Center for International Environmental Law, ‘US-Israeli Start-Up Announces Reckless Solar Geoengineering Experiments from April 2026’
[10] UNHRC Advisory Committee ‘Impact of New Technologies’ 31
[11] Gerd Winter, ‘Climate Engineering and International Law: Last Resort or the End of Humanity?’ (2011) RECIEL,280
[12] Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (adopted 27 January 1967, entered into force 10 October 1967) Art. 1; Ibid., 282
[13] Ibid. 285
[14] Conference of the Parties to the Convention on Biological Diversity, ‘Biodiversity and Climate Change’ (Decision X/33, 29 October 2010), para 8(w)
[15] Ibid. 285; UNHRC Advisory Committee ‘Impact of New Technologies’ 29, 31
[16] Maria Antonia Tigre, Maxim Bönnemann and Antoine De Spiegeleir, ‘The ICJ’s Advisory Opinion on Climate Change’ (Verfassungsblog, 24 July 2025) <https://verfassungsblog.de/the-icj-advisory-opinion-on-climate-change/>accessed 4 May 2026
[17] Obligations of States in respect of Climate Change (Advisory Opinion)2025 <https://www.icj-cij.org/sites/default/files/case-related/187/187-20250723-adv-01-00-en.pdf accessed 11 May 2026> 113-128
[18] Vienna Convention for the Protection of the Ozone Layer (adopted 22 March 1985, entered into force 22 September 1988) Art. 2(1)
[19] Ibid. Preamble
[20] Legality of the Threat or Use of Nuclear Weapons (Advisory opinion) 1966 <https://www.icj-cij.org/sites/default/files/case-related/95/095-19960708-ADV-01-00-EN.pdf 29
[21] Case Concerning Pulp Mills on the River Uruguay 2010 < https://icj-web.leman.un-icc.cloud/sites/default/files/case-related/135/135-20100420-JUD-01-00-EN.pdf >101
[22] Obligations of States in respect of Climate Change 439-441
[23] Ibid. 445
[24] Ibid. 429
[25] Ibid. 430-431
[26] UNHRC ‘Impact of New Technologies’ 10, 29
[27] Ibid. 10
[28] UNHRC Advisory Committee ‘Impact of New Technologies’ 6, 29
[29] Obligations of States in respect of Climate Change 393
[30] Ibid.
[31] Sara L Seck, ‘Climate Justice and the ETOs’ in M Gibney, G Erdem Türkelli, M Krajewski and W Vandenhole (eds), The Routledge Handbook on Extraterritorial Human Rights Obligations (Routledge 2022) 421
[32] Maastricht Principles on Extraterritorial Obligations of States in the Area of Economic, Social, and Cultural Rights (2011) Principle 8(b)
[33] Sigrun Skogly, ‘Global Human Rights Obligations’ in M Gibney, G Erdem Türkelli, M Krajewski and W Vandenhole (eds), The Routledge Handbook on Extraterritorial Human Rights Obligations (Routledge 2022) 27
[34] Joint reading of Charter of the United Nations (adopted 26 June 1945, entered into force 24 October 1945) Article 1(3) and Arts. 55 and 56
[35] Vienna Convention on the Law of Treaties (adopted 23 May 1969, entered into force 27 January 1980), Art. 26
[36] Skogly, ‘Global Human Rights Obligations’, 29
[37] Universal Declaration of Human Rights, UNGA Res 217 (10 December 1948) Art. 28; Ibid. 28
[38] Ibid. 28
[39] International Covenant on Economic Social and CulturalRights (adopted 16 December 1966, entered into force 3 January 1976) Art. 2(1); Ashfaq Khaflan, ‘Development Cooperation and Extraterritorial Obligations’ in M Langford and A Russel (eds) The Right to Water Theory, Practice and Prospects (Cambridge University Press 2012) 8
[40] UN Committee on Economic, Social and Cultural Rights (CESCR), General Comment No 3: The Nature of States Parties’ Obligations (Art. 2(1)) UN Doc E/1991/23 (1990) 9
[41] Khaflan, ‘Development Cooperation and Extraterritorial Obligations’, 5
[42] UNCESCR, General Comment NO 24 on State Obligations Under the International Covenant on Economic Social and Cultural Rights in the Context of Business Activities UN Doc E/C.12/GC/24 (2017) 27
[43] Wouter Vandenhole, Gamze Erdem Türkelli, Mark Gibney and Markus Krasjewski, ‘Introduction’ in M Gibney, G Erdem Türkelli, M Krajewski and W Vandenhole(eds), The Routledge Handbook on Extraterritorial Human Rights Obligations (Routledge 2022) 2.
[44] UNHRC Advisory Committee ‘Impact of New Technologies’ 41
[45] UNHRC Advisory Committee ‘Impact of New Technologies’ 58
[46] Armando Rocha, ‘States’ Extraterritorial Jurisdiction for Climate-Related Impacts’ (Verfassungsblog, 12 April 2024) <https://verfassungsblog.de/states-extraterritorial-jurisdiction-for-climate-related-impacts/> accessed 4 May 2026
[47] Rocha, ‘States’ Extraterritorial Jurisdiction for Climate-Related Impacts’.
[48] Obligations of States in respect of Climate Change [393]; The Environment and Human Rights, Advisory Opinion OC-23-17, Inter American Court of Human Rights Series A No 23(15 November 2017), [47]; UNHRC Res 48/13UN Doc A/HRC/RES/48/13 (18 October 2021); UNGA Res 76/300 (1 Augustus 2022)UN Doc A/RES/76/300 ; Patricio Trincado Vera, ‘Rights of Nature in the Inter-American Court of Human Rights: Understanding the Econcentric Approach to the Right to a Healthy Environment’ (2024) RECIEL; Baïna Ubushieva and Christophe Golay, ‘The Human Right to A Clean, Healthy and Sustainable Environment: Understanding Its Scope, States’ Obligations And Links with Other Human Rights’ (2024) Geneva Academy.
[49] Rocha, ‘States’ Extraterritorial Jurisdiction for Climate-Related Impacts’
[50] Melanie Murcott, Maria Antonia Tigre and Nesa Zimmermann, ‘What the ECtHR Could Learn from Courts in the Global South’ (Verfassungsblog, 22 March 2022) <https://verfassungsblog.de/what-the-ecthr-could-learn-from-courts-in-the-global-south/> accessed 4 May 2026
[51] Greenpeace International and Center for International Environmental Law, Extraterritorial Obligations in the Context of Climate Change (2015) https://www.ciel.org/wp-content/uploads/2015/06/ETOs_CC_16Jan15.pdf accessed 4 May 2026
[52] Ibid.