By Alia Hassan, Director of International Policy
As calls for governance of Solar Radiation Modification (SRM) intensify, the German Environment Agency (Umweltbundesamt, or UBA), Germany’s central environmental authority, has added its voice with a detailed and cautionary report. While UBA holds no direct enforcement power, it plays an important advisory role within the German government, providing independent scientific assessments to inform environmental policymaking. The comprehensive new report, titled “Solar Radiation Modification (SRM): Concepts, Risks and Governance of Intervention in the Global Climate System,” provides a detailed and cautionary overview of SRM proposals, especially Stratospheric Aerosol Injection (SAI), which it warns could result in destabilizing and unjust global outcomes if deployed. The authors call for a strong international non-use agreement on SRM, citing environmental, geopolitical, and ethical risks. They argue that SRM is not a form of climate action and caution against the redirection of mitigation and adaptation resources toward solar geoengineering research. The report also provides an extensive review of potential legal frameworks, including the Convention on Biological Diversity (CBD), which it cites as establishing a “de facto moratorium” on SRM-related outdoor activities.
In line with the three reports released by the European Commission in December last year, the UBA report adopts a precautionary approach to SRM and expresses serious concerns about normalization through research. Notably, however, while the European Commission reports emphasize the need for careful, transparent, and inclusive approaches to SRM research, the UBA report calls for a complete ban on SRM deployment, including field experiments, and insists that any regulation of research activities must first be grounded in a legally binding ban.
While the Alliance for Just Deliberation on Solar Geoengineering (DSG) shares many of the UBA’s concerns about premature or unregulated SRM experimentation, it differs on the pathway to precaution and governance. The report’s recommendation that no SRM research should be permitted unless preceded by a general ban — reflects a highly restrictive legal framework that may be impractical and even counterproductive in the international context. In practice, securing a binding international ban on SRM would be politically complex and unlikely to gain consensus, particularly given the diverging views among major powers and the lack of universal participation in frameworks like the CBD. Conditioning all research regulation on such a ban risks delaying or obstructing the development of oversight mechanisms for small-scale, non-deployable experiments. It could also drive research into private and unregulated spaces, undermining transparency and democratic accountability.
DSG acknowledges the potential for research to drive acceptance, but we also believe that transparent, inclusive, and bounded small-scale experiments can help inform global governance without opening the door to deployment. A blanket prohibition conflates research with implementation and could discourage precisely the type of rigorous, publicly accountable investigations that are needed to assess risk and avoid unilateral deployment.
The report also gives significant normative weight to the CBD’s “de facto moratorium.” While this is an important reference point, it is not legally binding and lacks universal participation. The United States, for example, has never ratified the CBD — and in the current political climate, it remains unlikely to do so. With the possibility of renewed skepticism toward international climate cooperation in key countries, building global governance around a moratorium that excludes major powers risks creating a fragmented and ineffective oversight regime.
It is also worth noting that while the report describes various SRM techniques—including Marine Cloud Brightening (MCB), Cirrus Cloud Thinning (CCT), and surface albedo modification—the governance and legal analyses focus almost exclusively on SAI. This focus may inadvertently conflate the broader SRM landscape with the most controversial and globally scaled approach, but different techniques carry different levels of risk, impacts, and governance challenges — and should therefore preferably not be governed through a one-size-fits-all framework. Small-scale, localized interventions like MCB may require different oversight mechanisms than more globally oriented approaches like SAI.
One notable omission from the UBA report is the perspective of the Global South. While it rightly raises concerns about SRM’s risks and geopolitical implications, it does not meaningfully acknowledge the voices, priorities, or vulnerabilities of countries most affected by climate impacts — many of which have also been historically excluded from shaping climate and technology governance. Proposing a global research ban without meaningful consultation and inclusion of these voices risks repeating that marginalization and undermining the legitimacy of any resulting framework. DSG emphasizes that any conversation on SRM must center equity and inclusion, particularly for communities in the Global South that stand to be disproportionately impacted by both climate change and any potential responses to it.
Finally, the report argues that SRM is not a form of climate action. While SRM is not a substitute for emissions reduction or adaptation, it is inherently climate-relevant—and that is precisely why research, governance and inclusive public engagement are needed. Dismissing it as “not climate action” risks oversimplifying a complex and evolving debate and could delay the development of necessary ethical, equitable, and globally representative governance frameworks.
Rather than calling for a total research ban, DSG believes it is more pragmatic to build international consensus around principles of precaution, transparency, and equity. One illustrative approach is the UK’s ARIA ( Advanced Research and Invention Agency) program*, which is currently supporting small-scale SRM research projects aimed at improving our understanding of key physical and chemical processes, such as aerosol behavior and cloud interactions. While some of these studies explore techniques that could theoretically be scaled, their current scope is explicitly limited to early-stage inquiry under rigorous and clearly defined ethical and governance standards, not to pilot deployment or demonstrate operational feasibility. Importantly, ARIA also funds social science and interdisciplinary research, including work on governance, public engagement, and ethical implications. This reflects an understanding that SRM is not only a technical issue, but one that must be examined through the lenses of justice, inclusion, and global equity. These types of carefully bounded efforts illustrate how it is possible to conduct research without crossing into normalization or unregulated advancement — and could serve as a model for how science and governance can evolve responsibly, in tandem. ARIA reflects the kind of ethically grounded, globally conscious research pathway that DSG views as compatible with precaution.
Ultimately, the UBA report is an important contribution to the global SRM debate. The examples provided by initiatives like ARIA demonstrate that it is possible to engage in science that informs governance without endorsing deployment or undermining precaution. But the report’s approach may benefit from greater realism about where the international system stands today, and a more differentiated view of how science and governance can evolve in parallel.
*Full disclosure: DSG’s Executive Director currently serves on ARIA’s Oversight Committee for the program on Exploring Climate Cooling Options in an independent advisory capacity. The views expressed here reflect DSG’s institutional position and not those of ARIA.