UNEP: Working Paper on Solar Radiation Modification
Renaud de RICHTER
UNEP: Solar Radiation Modification: Scientific evidence does not support SRM as a viable climate solution - Working Paper
https://doi.org/10.59117/20.500.11822/49509
https://wedocs.unep.org/items/4154b06d-6a7a-4df0-aaa9-7472e4f7c6f5
(previous work 2023 https://www.unep.org/resources/report/Solar-Radiation-Modification-research-deployment)
Summary of findings (p 18)
• The current state of scientific knowledge does not support SRM as a viable climate response. While some SRM proposed methods—notably SAI and MCB—are receiving increasing scientific attention, they remain deeply uncertain in terms of feasibility, effectiveness and safety. They are not substitutes for climate mitigation or adaptation. Nor are they ready for deployment. UNEP underscores that the most effective and essential response to climate change continues to be deep, sustained emissions reductions, coupled with robust adaptation.
• Across all modelling studies and emerging field research, proposed SRM approaches present significant unresolved risks, including the possibility of unintended consequences, abrupt termination effects and uneven regional impacts. Modelling to date is heavily reliant on idealized assumptions and remains poorly equipped to predict real-world outcomes. Additionally, regional variability, ecosystem responses and long-term geopolitical effects are poorly understood. To support informed and responsible decision-making, integrated assessment models should more effectively incorporate interactions among biophysical systems, ecosystem responses, human behaviour and policy dynamics.
• SRM approaches require a comprehensive assessment of their readiness, feasibility, risks, impacts and trade-offs to ensure any future developments can inform decision-making. To be ethical, legitimate and responsive to real-world concerns, SRM research must address and integrate the natural, ecological, agricultural, and health and social sciences, embed co-design processes and prioritize meaningful public engagement—particularly with vulnerable and historically marginalized communities. Avoiding technocratic, top-down approaches is essential to safeguard equity and trust.
• The emerging debate around SRM also raises serious questions of justice, global equity and intergenerational responsibility. Most of the research to date has been conducted in high-income countries, with minimal participation from those most exposed to climate harms. Addressing this asymmetry requires a shift toward reciprocal capacity sharing, regionally-led research and full recognition of diverse knowledge systems—including Indigenous perspectives. Moreover, some deployment scenarios could extend over multiple decades, raising concerns about committed use, multi-generational governance and technological dependency.
• As discussions continue, there is growing agreement that early and inclusive governance is not optional—it is foundational. Without transparent, precautionary and globally coordinated governance, any increase in SRM-related activity risks outpacing our institutional capacity to manage it. Precaution does not mean paralysis—it calls for structured deliberation, ethical safeguards and clearly defined boundaries.
• UNEP stresses that SRM research should not detract attention or resources from the urgent, proven priorities of deep mitigation and adaptation. Instead, it should be approached as a limited scientific inquiry, subject to transparency, accountability and globally coordinated oversight.
• As the leading global environmental authority, UNEP sets the global environmental agenda, promotes the coherent implementation of the environmental dimension of sustainable development within the United Nations system and serves as an authoritative advocate for the global environment with a mandate to keep the environment under review. In line with this mandate, UNEP will continue to monitor developments in SRM and advise on emerging environmental risks—with a commitment to precaution, scientific integrity and inclusive dialogue.
Hawkins, David
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