Why This Matters Solar geoengineering seeks to cool Earth’s temperature by reflecting incoming sunlight back into space, but effects on the environment and public health are uncertain. Several private companies are beginning to develop and use these methods, raising concerns about the lack of oversight. Key Takeaways Solar geoengineering methods might mitigate Earth’s rising temperatures, but effects are highly uncertain. More research and field testing of solar geoengineering methods would improve understanding of effects. Limited understanding of outcomes may heighten geopolitical risks and complicate governance.