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How could reflecting more sunlight into space lower global temperatures?

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Illustration of various geoengineering techniques to address climate change, including carbon capture and storage methods like artificial trees, industrial scrubbers, and deep ocean CO2 storage, as well as solar reflectance strategies such as sulfur aerosols, reflective crops, cloud whitening, and orbital mirrors. The scene shows these interventions applied to land, sea, and atmosphere, with labeled features explaining each process. — Geoengineering Various geoengineering proposals designed to increase solar reflectance or capture and store carbon.

Reflecting more sunlight into space is a proposed geoengineering strategy designed to lower global temperatures by reducing the amount of solar radiation absorbed by Earth’s surface and lower atmosphere. By increasing the planet's albedo—its overall reflectivity—less solar energy is converted into heat, which could theoretically offset rising temperatures caused by the greenhouse effect.12

Proposed methods to achieve this include:

Stratospheric Sulfur Injection: Creating an aerosol layer of sulfur particles in the stratosphere to scatter incoming sunlight, mimicking the cooling effects observed after major volcanic eruptions.34
Surface Albedo Modification: Altering land cover or other surface features to increase the amount of light reflected back into space.35
Cloud Whitening: Enhancing the reflectivity of marine clouds.3
Space-based Sunshades: Deploying orbital mirrors to block or deflect a portion of incoming solar energy.3

While these techniques aim to reduce heating, they remain controversial and untested, as they do not address the underlying cause of climate change: the rising concentration of carbon dioxide in the atmosphere.1