Article
Does International Law Prohibit SRM?
Because they would alter the climate and could cause harm, some people wonder whether sunlight reflection methods or solar radiation modification (SRM) are banned under international law. The answer is no – no treaty that applies to SRM prohibits researching or using it, but international law does advise caution.
Key takeaways
- SRM is not banned under international law.
- No treaty that applies to SRM prohibits research, field experiments, or deployment.
- This could change, but that seems unlikely for the time being.
SRM interventions – if they were undertaken – would affect the global climate system, and thus every country on Earth. Since some effects of SRM could be harmful, the question arises: does international law prohibit SRM research, field experiments, or deployment?
International law and SRM
Simply put, international law is law among states. There are two main types of binding international law: customary international law and treaty law.
Customary international law consists of legal obligations among all states that derive from practice. For example, according to the customary “no-harm rule”, states have duties to minimise or at least reduce significant environmental harms to other states. They also have obligations to conduct environmental impact assessments where appropriate.
While customary international law is binding on all states, it lacks detail and can be open to interpretation. Most legal scholars find no evidence to suggest that customary international law categorically prohibits SRM.1
Treaty law, as its name suggests, consists of legal obligations arising from treaties signed and ratified by states. Unlike customary international law, treaty law is binding only on those states that have ratified it.2
Adoption of the Paris Agreement at the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change.
United Nations Framework Convention on Climate Change: Does not address SRM
The United Nations Framework Convention on Climate Change is the principal treaty governing climate change and the framework within which the Paris Agreement was developed, but it does not address SRM specifically.3 Instead, SRM has been addressed in piecemeal fashion by a handful of other treaties related to the environment. The table below summarises this patchwork coverage.
Are there international laws that prohibit SRM?
| Treaty | Does It Prohibit SRM? | Reason(s) |
|---|---|---|
| United Nations Framework Convention on Climate Change | No | Does not address SRM |
| Convention on Biological Diversity | No | Invitation to refrain from “geo-engineering” that might affect biodiversity (except for small-scale research), not legally binding |
| London Protocol | No | New amendment prohibiting “marine geoengineering” (with an exception for research), not in force and not applicable to SRM |
| ENMOD | No | Prohibition on “hostile” use of environmental modification techniques, not applicable to SRM |
Convention on Biological Diversity: A non-binding decision on “geo-engineering”
In 2010, states party to the Convention on Biological Diversity (CBD), which aims to protect global biodiversity, adopted a decision urging countries to prevent “climate-related geo-engineering activities [including SRM] that may affect biodiversity” – with the exception of “small scale scientific research studies” – until there is adequate scientific justification and appropriate consideration of risks and impacts.4
Some people refer to this decision as an international “moratorium”. But since it is a decision rather than an amendment, it is not legally binding – even on states that have ratified the CBD.5 Furthermore, the United States (US) is not a party to the CBD.
Regardless, most informed commentators reject the notion that the CBD prohibits SRM because its parties are under no obligation to do so.6
London Convention and Protocol: Prospective amendment does not apply to SRM
The London Convention and London Protocol regulate ocean dumping.7 In 2013, negotiators finalised an amendment to the London Protocol that would prohibit specific listed “marine geoengineering” activities with a possible exception for “legitimate scientific research”.8 As written, this amendment would apply only to ocean fertilisation, which aims to capture carbon dioxide from the atmosphere by stimulating phytoplankton blooms.
However, states that have ratified the London Protocol are currently considering whether to list marine cloud brightening as a form of marine geoengineering under the terms of the amendment.
Yet this 2013 amendment has not entered into force – only 6 of a required 36 countries have ratified it. And if it ever did enter into force and consequently became legally binding, the amendment does not currently address SRM. Further, as in the case of the CBD, the US is not a party to the London Protocol. Again, as with the CBD, legal scholars acknowledge that the London Protocol does not prohibit SRM.9
ENMOD: Only applies to hostile activities
The Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques, or ENMOD, was signed in 1977. The treaty prohibits the “hostile” use of environmental modification techniques, and such techniques would clearly include SRM.
An example of hostile environmental modification – a US military helicopter spraying Agent Orange during the Vietnam War.
(Photo: U.S. Army)Suggested uses of SRM, however, seem unlikely to be hostile in character.10 Moreover, SRM does not appear to be capable of being weaponised. In any case, ENMOD is an inactive treaty – its parties have not met since 1992 and have no plans to do so.
No prohibition on SRM, but that could change
While it might seem that international law ought to prohibit the use of SRM, neither customary international law nor any treaty does so.
Some indications of at least limited support for banning SRM should be noted. Following unauthorised balloon releases carried out in Mexico by the US start-up company “Make Sunsets” in 2022, the Mexican government announced its intention to prohibit SRM and rally other countries to take similar steps.11 And at a meeting of the United Nations Environment Assembly in 2024, African countries pushed for the “non-use” of SRM, but were unsuccessful due to lack of support.
While support for prohibiting the use of SRM may grow in the future, for now, international law poses no strong barriers to SRM.
Open questions
- Will support for an international prohibition on SRM grow?
- Could national or regional bans trigger serious international discussions?
- If an international ban were adopted, how would it be enforced?
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Endnotes
- Armeni C, Redgwell C. (2015). International Legal and Regulatory Issues of Climate Geoengineering Governance: Rethinking the Approach. Climate Geoengineering Governance Working Paper Series: 021. Available at https://jreynolds.org.
- Ratification is the process by which a state formally consents to be bound by a treaty, often through action by the national legislature.
- Note that under United States law the Paris Agreement is not a treaty as it was not submitted to the Senate for ratification. This was deliberately written and agreed as such in Paris.
- This is CBD Decision X/33.
- Brunnee J. (2002). COPing with Consent: Law-Making Under Multilateral Environmental Agreements. Leiden Journal of International Law 15: 1-52. https://doi.org/10.1017/S0922156502000018
- Williamson P, Bodle R. (2016). Update on Climate Geoengineering in Relation to the Convention on Biological Diversity: Potential Impacts and Regulatory Framework. Technical Series No. 84. https://www.cbd.int/doc/publications/cbd-ts-84-en.pdf
- The London Convention, signed in 1972, regulates ocean dumping only for specified materials. The London Protocol (to the London Convention), signed in 1996, prohibits dumping of all materials not specified. The London Protocol is intended eventually to supersede the London Convention to simplify regulation of ocean dumping.
- This amendment is contained in Resolution LP.4(8).
- Scott KN. (2023). From Ocean Dumping to Marine Geoengineering: The Evolution of the London Regime. Rayfuse, R., Jaeckel, A., and N. Klein, eds., Research Handbook on International Marine Environmental Law, 240-263. Cheltenham, UK: Edward Elgar Publishing. https://doi.org/10.4337/9781789909081.00019
- Eliason A. (2022). Avoiding Moonraker: Averting Unilateral Geoengineering Efforts. University of Pennsylvania Journal of International Law 43: 429-467. https://scholarship.law.upenn.edu/jil/vol43/iss2/3
- It remains unclear whether Mexico adopted such a ban, and there is no evidence it has undertaken any international initiative in this regard.
Thumbnail photo: AJEL
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