How could increasing Earth’s reflectance lower the heating effect of sunlight?

Increasing Earth’s reflectance—a strategy known as geoengineering—aims to reduce the amount of solar radiation absorbed by the planet, thereby lowering the heating effect of sunlight on the surface and the lower atmosphere.1

Several proposed methods seek to achieve this by altering the planet's albedo, or reflectivity:

• Stratospheric Sulfur Injection: This involves dispersing sulfur particles into the stratosphere to create an aerosol layer. This layer would scatter incoming sunlight back into space, mimicking the cooling effects observed after major volcanic eruptions.32
• Marine Cloud Whitening: This process proposes spraying seawater mist into the air to increase the brightness and coverage of marine clouds. The resulting salt crystals would reflect more solar radiation and act as condensation nuclei to further enhance cloud reflectivity.34
• Surface and Orbital Modifications: Other concepts include increasing ground-level albedo or deploying orbital mirrors or sunshades in space to block or reflect sunlight before it reaches the atmosphere.3

While these proposals aim to offset rising temperatures, they remain highly controversial and untested, as they do not address the root cause of climate change, such as rising carbon dioxide concentrations, and carry significant risks of unintended consequences.1