The potential merits and drawbacks of atmospheric geoengineering using aerosols are still hotly debated, but most concern the direct impact of injected aerosol on atmospheric energy balance and chemistry. However, one recent study looks at a secondary, potentially unwanted, effect of stratospheric aerosol geoengineering on sky brightness. Charlie Zender, University of California, Irvine, models the night-time light intensity observed at ground level in urban and rural areas, incorporating natural light e.g. from stars, and light from anthropogenic sources e.g. street lighting, with and without effects from additional stratospheric aerosol from large-scale injection. In urban areas, back-scattered (artificial) light from injected aerosol increases the night-time sky brightness by 25-95%, ‘glowing out’ starlight and potentially impacting on day-night ‘circadian’ rhythms in humans and other animals, a factor implicated in several conditions including sleep disorders, depression and, potentially, some cancers. Even in rural areas, the increase in scattering of incoming starlight is sufficient to darken the skies significantly, meaning far fewer stars would be visible. Further work on the model will investigate the impact of aerosol injection only in certain regions e.g. over polar regions.

Read the full article by Sarah McQuate here