Illustration of the different proposed methods of reflecting more sunlight to reduce Earth's temperature
Solar radiation modification (SRM), or solar geoengineering, is a type of climate engineering (or geoengineering) in which sunlight (solar radiation) would be reflected back to outer space to offset human-caused climate change. There are multiple potential approaches, with stratospheric aerosol injection being the most-studied, followed by marine cloud brightening. SRM could be a temporary measure to limit climate-change impacts while greenhouse gas emissions are reduced and carbon dioxide is removed[1] but would not be a substitute for reducing emissions.
Studies using climate models have generally shown that SRM could reduce many adverse effects of climate change. Specifically, controlled stratospheric aerosol injection appears able to greatly moderate most environmental impacts—especially warming—and consequently most ecological, economic, and other impacts of climate change across most regions. However, because warming from greenhouse gases and cooling from SRM would operate differently across latitudes and seasons, a world where global warming would be offset by SRM would have a different climate from the world where this warming did not occur in the first place, mainly as the result of an altered hydrological cycle. Furthermore, confidence in the current projections of how SRM would affect regional climate and ecosystems is low.[1]
SRM would pose environmental risks. In addition to its imperfect reduction of climate-change impacts, stratospheric aerosol injection could, for example, slow the recovery of stratospheric ozone. If a significant SRM intervention were to suddenly stop and not be resumed, the cooling would end relatively rapidly, posing serious environmental risks. Some environmental risks may remain unknown.
Governing SRM is challenging for multiple reasons, including that several countries would likely be capable of doing it alone.[2] For now, there is no formal international framework designed to regulate SRM, although aspects of existing international law would be applicable. The most common concern about SRM is that its research and evaluation might undermine reductions of greenhouse gas emissions. Issues of governance and effectiveness are intertwined, as poorly governed use of SRM might lead to its highly suboptimal implementation. Thus, many questions regarding the acceptable deployment of SRM, or even its research and development, are currently unanswered.
At the 6th UN Environmental Assembly (UNEA 6) February/Mar 2024 in Nairobi, Switzerland failed for the second time with a proposal to hold a discussion on “Solar Radiation Management” (SRM) measures in an international body begin. There will still be no structured global debate on the possible use of geoengineering techniques. The countries mistrust each other and argue about the scope and aim of an investigation. Meanwhile, other actors are creating facts. The US, Saudi Arabia and Japan spoke out against a generally accessible knowledge base at the multilateral level.[3]
^ abTrisos, Christopher H.; Geden, Oliver; Seneviratne, Sonia I.; Sugiyama, Masahiro; van Aalst, Maarten; Bala, Govindasamy; Mach, Katharine J.; Ginzburg, Veronika; de Coninck, Heleen; Patt, Anthony. "Cross-Working Group Box SRM: Solar Radiation Modification" (PDF). Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press. p. 221-222. doi:10.1017/9781009325844.004. In Climate Change 2022: Impacts, Adaptation and Vulnerability [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke,V. Möller, A. Okem, B. Rama (eds.)].
^Gernot Wagner (2021). Geoengineering: the Gamble.
^Goswami, Urmi (March 2024). ""Solar Geoengineering" Die Sonne für das Klima verdunkeln? Staaten streiten – die ersten Unternehmen schaffen Fakten". FocusOnline. Retrieved 29 March 2024.
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