Cloud reflectivity modification

Marine cloud brightening is a proposed solar radiation management climate engineering technique that would make clouds brighter, reflecting a small fraction of incoming sunlight back into space in order to offset anthropogenic global warming. Along with stratospheric aerosol injection, it is one of the two solar radiation management methods that may most feasibly have a substantial climate impact. The intention is that increasing the Earth's albedo, in combination with greenhouse gas emissions reduction, carbon dioxide removal, and adaptation, would reduce climate change and its risks to people and the environment. If implemented, the cooling effect is expected to be felt rapidly and to be reversible on fairly short time scales. However, technical barriers remain to large-scale marine cloud brightening. There are also risks with such modification of complex climate systems.

Marine Cloud Brightening is based on phenomena that are currently observed in the climate system. Today, emissions particles mix with clouds in the atmosphere and increase the amount sunlight they reflect, reducing warming. This 'cooling' effect is estimated at between 0.5 and 1.5°C, and is one of the most important unknowns in climate. Marine Cloud Brightening proposes to generate a similar effect using benign material (e.g. sea salt) delivered to clouds that are most susceptible to these effects (marine stratocumulus).

Most clouds are quite reflective, bouncing incoming solar radiation back into space. Increasing clouds' albedo would increase the portion of incoming solar radiation that is reflected, in turn cooling the planet. Clouds consist of water droplets, and clouds with smaller droplets are more reflective (because of the Twomey effect). Cloud condensation nuclei are necessary for water droplet formation. The central idea underlying marine cloud brightening is to add aerosols to atmospheric locations where clouds form. These would then act as cloud condensation nuclei, increasing the cloud albedo.

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