“Make Sunsets” in Mexico: Lessons for SRM Governance

There are an increasing number of for-profit private actors taking advantage of the “lack of robust and formal SRM [solar radiation modification] governance”.¹ These actors benefit from the governance vacuum, leading to “market-driven” climate governance² with avoidable negative consequences, including the public losing trust in legitimate research efforts.

One relevant case is the US-based startup Make Sunsets, a company that sells experimental “cooling credits”. They release small, high-altitude balloons into the stratosphere containing tiny amounts of sulfur dioxide, a material which forms reflective aerosol particles. These releases do not have a scientific purpose; instead, they are effectively extremely small-scale deployments of Stratospheric Aerosol Injection (SAI), framed as a measure to address climate impacts.

While Make Sunsets has now conducted tens of these releases, the one which took place in April 2023 in Baja California, Mexico had significant political implications. Deploying their balloons without prior engagement with Mexican authorities, Make Sunsets triggered significant negative reactions, including Mexico’s government announcing its intention to ban all forms of SRM experiments, including research.

Evaluating the Make Sunsets case study

In our recent article,³ No Governance Is Governance: Mapping Solar Geoengineering Discussions in Latin America & the Caribbean (LAC) published in The European Journal of Risk Regulation in 2025, we focused our attention on the LAC region and the case study of the April 2023 Make Sunsets episode.

Mainly working in Argentina, our interdisciplinary team of experts from the human and climate sciences performed a media and ethical analysis of the Mexican Make Sunsets case study.

Our media coverage analysis highlighted the diversity of perceived risk associated with SRM. Dominant narratives emphasized that Make Sunsets acted irresponsibly, without consent or scientific legitimacy. The project’s “non-research experiment” of commercialization is perceived to undermine trust in SRM research experiments. Media coverage also highlighted the lack of governance and transparency, while some outlets voiced concerns regarding unilateral actions and “climate colonialism”.

Distinguishing research and non-research experiments

Because the proposed Mexican government ban aimed to prohibit all kinds of experiments, we focused on the contested meaning of the word “experiment”, and realized that a more precise term was needed. We defined an SRM experiment as:

“a deliberate use of an SRM intervention at any scale, with either a research or non-research main aim, and without sufficient evidence of safety and/or efficacy for its regular use in […] the Earth system”.³

We distinguished two kinds of SRM experiments:

• SRM research experiments whose main aim is to resolve uncertainties about the use or non-use of SRM and build generalizable knowledge.
• SRM non-research experiments, including SRM deployment, whose main aim is to cool the Earth’s surface to address climate impacts.

We highlighted two very different small-scale SRM experiments to explain the difference: Make Sunsets is a case of a non-research experiment of small-scale SRM deployment aiming to address climate impacts, whereas SCoPEx (Stratospheric Controlled Perturbation Experiment), which aimed to “advance understanding of the risks and efficacy of SRM”,⁴ should be understood as an SRM research experiment.

The example of the Mexican government announcing the ban of undefined “SRM experiments” risks conflating research and non-research as well as responsible and irresponsible experiments. It also shows there is an ethical requirement for a neutral definition of “SRM experiment” such as the one proposed above. This would enable case-by-case identification and evaluation, grounded in independent, public ethical principles, while allowing reasonable disagreement over whether any SRM research or non-research experiment is ethically responsible.

Conclusions

The media and political reaction to Make Sunsets and our ethical analysis reveal the vital importance of a governance framework for SRM research. But what would a good framework for governance of SRM research look like?

Our work suggests two main lessons for the SRM community:

1. There is a need for an explicit and neutral definition of “SRM experiment” compatible with different sets of independent ethical principles. This would allow responsible and irresponsible SRM research and non-research experiments to be distinguished, which should help governments appropriately target their policies.
2. There is also a need for relevant actors in the LAC region to discuss and take a position on SRM regulation, oversight, and policy. The Make Sunsets case illustrates that the absence of proper regulations becomes a form of governance itself – one that benefits commercial projects outside of democratic control⁵ and leads to avoidable negative consequences, including mistrust, perceptions of neo-colonialism, and bans on potentially valuable and responsible SRM research.

The LAC region should not remain on the sidelines, as such a position could increase its vulnerability to unfair treatment – including deception, coercion, exploitation, or marginalization – in the face of emerging SRM experiments conducted without regional oversight, participation, or inclusive governance frameworks.

To ensure meaningful participation in global SRM governance, the region should strengthen its capacity, assess scientific information, and build institutional expertise. In partnership with international organizations, the LAC region has a unique opportunity to shape its own pathway in relation to SRM and contribute meaningfully to the global discussion.