With the help of machines that resemble snow cannons, salt particles are whirled up from the ocean's surface and propelled to altitudes up to 300 meters/1.000 feet. The wind then captures these particles, and transports them into higher atmospheric layers. Upon reaching a cloud, water binds to the salt, leading to increased particle concentration and smaller droplets. "These are more effective at scattering light" explains atmospheric physicist Anna Possner from Goethe University Frankfurt, "what leads to a drop of temperature in the region below the clouds of 0.5 to 1.5°C."
What sounds like science fiction, along with stratospheric aerosol injection, is a proposed solar geoengineering technique that would reflect a small fraction of sunlight back into space in order to offset global warming. The method theoretically is said to pose minimal environmental risk, as the salt particles would remain within the clouds only for a few days before returning to the ocean during rainfall. The process is primarily intended for use over the sea without affecting land masses. According to the scientist the greatest effect is expected above the sea, as the dark ocean would otherwise absorb a lot of solar energy.
While localized studies, among others in the region of the Great Barrier Reef in Australia, have demonstrated its efficacy, broader implications and potential side effects necessitate further investigation. "There are still many uncertainties surrounding the global deployment of this method," acknowledges Possner.
To address these uncertainties, an extensive research project in the United States has convened experts from across the globe. This initiative, started by an international workshop in 2022, aims to evaluate the potential and risks associated with marine cloud brightening. Recently published in the journal "Science Advances," this project underlines the importance of integrating various disciplines, from physics to ethics, in shaping future research directions.
As the project unfolds, Possner emphasizes the necessity of rigorous field experiments and a holistic research approach. While initial assessments have focused on the physical and climatological aspects, ethical, social, and political considerations remain largely unexplored. Indeed, ethicists caution against viewing geoengineering as a substitute for reducing greenhouse gas emissions, stressing the moral imperative to prioritize the well-being of present and future generations.