SRM Bans and Moratoria: Calls to Restrict Solar Geoengineering Activities

In the early 1970s, controversy arose over “recombinant DNA” (rDNA), an emerging technology that involved the combining of genetic material from different species.¹ The use of rDNA held tremendous promise for advances in science and medicine but triggered serious concerns about potential public health, safety, and environmental hazards. To address these concerns, in 1974 researchers adopted a moratorium on certain experiments using rDNA technology.¹

Like rDNA, SRM (solar geoengineering) has the potential to provide immense benefits while also posing considerable risks. While SRM is not banned under international law, participants in discussions about SRM have proposed an array of moratoria or bans on different aspects of the technology over the past two decades. What are these proposals, and how would their adoption affect the development of SRM?

Bans and moratoria

Moratoria and bans are two types of prohibition, defined as an act that forbids something. A moratorium is a temporary prohibition, while a ban is a permanent one.

They both involve ordering a stop to an activity but have different purposes. A ban is intended to stop something from happening indefinitely because it is regarded as morally impermissible or because it is considered to pose unacceptable risks.

By contrast, a moratorium is intended to pause an activity to learn more about the risks associated with it and/or to reduce tensions to allow for bargains to be struck.² However, a moratorium might also reflect a partially successful attempt to ban something.

As types of prohibition, moratoria and bans both vary in important ways. Any prohibition must specify its scope, or the range of activities it covers, as well as the actors to which it applies.

Additionally, a moratorium must specify the conditions under which it could be lifted. Conditions for lifting can vary from permissive, for example, once a short period of time has passed, to restrictive, for example, only after very demanding or vaguely specified criteria have been met.

At the extreme, conditions can be so onerous or undefined that they are impossible to meet in practice – in this instance, a moratorium may constitute a de facto ban. This occurred, for example, in the case of germ line gene therapy.^3,4

Calls for a moratorium on SRM activities

Over the years, there have been several calls or proposals for moratoria on SRM, as summarised in the table below.

In 2010, parties to the Convention on Biological Diversity (CBD) adopted Decision X/33 inviting countries to consider prohibiting “climate-related geo-engineering activities [including SRM] that may affect biodiversity”,  except for carefully regulated small-scale field experiments. This non-binding decision specified that such a prohibition could be lifted if there was adequate governance, scientific justification, and consideration of risks. In effect, the parties to the CBD called on countries to consider adopting such a moratorium. To date, no countries have done so.

More than a decade later, the non-governmental Climate Overshoot Commission recommended that countries adopt a moratorium on SRM deployment and large-scale outdoor experiments. More precisely, such a moratorium should apply to any intervention posing a risk of “significant transboundary harm”, that is, harm to other states’ environments and areas beyond their national jurisdiction. Like CBD Decision X/33, the recommended moratorium would be lifted if doing so was supported by a strong scientific knowledge base and an adequate governance framework.

At the end of 2024, the Group of Chief Scientific Advisors to the European Commission recommended pursuing two separate but related moratoria. First, they called for an “EU-wide moratorium” on SRM, with an exception for carefully regulated small-scale outdoor experiments, to be lifted only if there is a scientific and political consensus to do so. Second, they advocated for a global “non-deployment agreement” in the longer term that would prohibit interventions by states and private entities but allow for carefully controlled small-scale outdoor experiments; no conditions for lifting were specified. The European Commission is currently reviewing these recommendations.

Calls for a ban on SRM

There have also been several more restrictive proposals to prohibit SRM. Most of these would impose self-described bans. While proponents of an International Non-Use Agreement on Solar Geoengineering do not describe it as such, in failing to specify conditions for lifting (and in other ways), their proposal would amount to a de facto ban. These proposals are summarised in the table below.

Starting in the mid-2010s, several US state legislatures have considered bills that would ban all outdoor SRM interventions, and this number has surged recently.⁵ Although they vary somewhat in their specifics, all these bills employ language and articulate concerns tied to the chemtrails conspiracy theory community – their promotion appears to be loosely coordinated by networks of conservative activist groups. Penalties for violating these bans can be significant. Tennessee has passed one of these state-level bills.

In 2022, a group of academics called for countries to adopt an International Non-Use Agreement (NUA) on Solar Geoengineering.⁶ Signatories to the NUA would commit to prohibit public research funding for SRM, outdoor experiments, patent rights, deployment including that of technologies developed by third parties, and the “institutionalisation” of SRM as a policy option in international bodies.

Although its proponents contend that “the duration of such a non-use agreement … would remain open to political debate and further decision-making”, they specify no pathway for lifting the prohibition while declaring that: “At its core would be the mutual assurance of its signatories that they would not develop or deploy solar geoengineering technologies in the future”.⁶ As such, the NUA is best understood as a ban. At the time of writing, no countries have adopted it.

In addition, it is worth noting that in 2022 the Mexican government announced its intention to ban SRM, although it remains unclear whether it has done so.

Implications of these proposed bans and moratorium

If imposed, the bans discussed above – US state-level bans as well as the NUA – would have variable effects. To the extent that state-level bans are targeting outdoor interventions, which their sponsors believe are taking place but are not in fact occurring, they would have (and, in the case of Tennessee, are having) little practical impact.

The NUA, however, is more grounded and comprehensive than these state-level bans. By seeking to ban not just outdoor interventions but also public funding for research, patent rights, and the “normalisation” of SRM, adoption of the NUA could have a severe chilling effect on research.

In contrast, the various moratoria might support expanded research on SRM. By prohibiting deployment and large-scale field experiments, while explicitly carving out exceptions for small-scale research including outdoor experiments, such moratoria could reassure sceptical publics that deployment is neither happening nor permitted. They might help create a safe space for researchers to learn more about the risks and potential benefits of SRM and possible ways of addressing its governance challenges.

The consequences of CBD Decision X/33 have been primarily political. Specifically, it has prompted some actors to push for restrictive measures on SRM, and it has been framed misleadingly as a de facto moratorium by some groups.

Prospects

In 1975, a year after the moratorium on rDNA was adopted, scientists met at a conference in Asilomar, California, where they judged that the risks associated with rDNA were manageable and agreed to lift the moratorium under strict guidelines.^1,7 In the decades since, rDNA technology has proven to be enormously beneficial for public health and entail minimal risk.

The case of rDNA suggests that a carefully designed moratorium might help ease fears and enable responsible research. For those opposed to expanded research, however, a more restrictive moratorium or ban is likely to be preferred. Ultimately, both types of prohibition reflect an underlying desire to proceed with caution, a sentiment that is widely shared across the SRM community.

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