Case for Assessment of Solar Radiation Modification
by William J. Ripple
We are facing an imminent, irreversible climate crisis—an undeniable global emergency that threatens the very foundation of life on Earth. Reducing greenhouse gas emissions is essential, but no amount of current reduction can undo the warming impact of past and present emissions. According to the United Nations IPCC, the Earth is expected to keep warming for decades in all projected climate change scenarios. As we outlined in our recent 2024 State of the Climate Report, every fraction of a degree of warming leads to more extreme impacts on ecosystems and human communities, with the threats of feedback loops and irreversible climate tipping points looming ever closer. While reducing greenhouse gas emissions remains the bedrock of climate action, it is unlikely that these efforts alone will be enough. Considering this, Solar Radiation Modification (SRM)—a set of techniques that can reflect a portion of sunlight back into space to cool the planet—has gained attention as a potential tool for limiting peak warming.
SRM could help alleviate some of the most dangerous climate impacts while we continue to cut emissions and remove carbon dioxide from the atmosphere. Current projections suggest that even the most aggressive emissions reductions might not keep global warming below several degrees. SRM may offer a buffer, potentially giving vulnerable communities time to adapt while longer-term solutions are refined. This is not to say SRM is without risks; it could have unintended side effects, potentially altering regional climates and impacting weather patterns. However, dismissing SRM research and assessment could leave humanity unprepared as climate risks escalate beyond current mitigation capabilities.
Critics of SRM rightly caution that its use could introduce serious governance challenges. Who decides if, when, or how to deploy SRM? Could powerful nations exert control over its use, potentially worsening global inequalities? The concerns are real, and to avoid the risks associated with uninformed or unilateral decision-making, thorough research, planning, and an internationally inclusive discussion are essential.
Responsible SRM research and assessment would enable a deeper understanding of its potential benefits and limits, helping society make balanced, scientifically-informed choices. Ethical, transparent, and interdisciplinary research and assessment, with broad input from the Global South and other often-marginalized communities, would help create an equitable framework for future SRM discussions.
There is a moral imperative here. Entering the SRM decision-making process without sound science would be dangerous. Ignoring SRM research today may leave future generations with fewer options and less clarity about their potential impacts. While SRM is far from a perfect solution, refusing to investigate it responsibly could have significant consequences in an increasingly uncertain climate future.
For these reasons, we need to approach SRM research and assessment as a possible important tool—one that could make a crucial difference in minimizing climate harm. By working on SRM now, we take a proactive approach, preparing for all scenarios and safeguarding humanity’s ability to make informed, ethical decisions on climate change.
The editorial featured here may or may not be consistent with the views of the writer’s affiliations or with those of the other individual AWS members.
The following open letter is from more than 110 physical and biological scientists studying climate and climate impacts about the role of physical sciences research, including the central role it plays in effective governance. The letter affirms the importance of proceeding with responsible research to objectively evaluate the potential for SRM to reduce climate risks and impacts, to understand and minimize the risks of SRM approaches, and to identify the information required for governance. While not addressed in this letter, any decisions to actively use SRM would also need to be preceded by work to address the complex legal, ethical, and political aspects of making such a decision.
An open letter regarding research on reflecting sunlight to reduce the risks of climate change.