Arctic sea ice might be preserved if its albedo could be increased. To this end, it has been proposed to spread hollow glass microspheres over the ice. We assess the radiative forcing that would result, by considering the areal coverages and spectral albedos of eight representative surface types, as well as the incident solar radiation, cloud properties, and spectral radiative properties of hollow glass microspheres. Hollow glass microspheres can raise the albedo of new ice, but new ice occurs in autumn and winter when there is little sunlight.
In spring the ice is covered by high-albedo, thick snow. In summer the sunlight is intense, and the snow melts, so a substantial area is covered by dark ponds of meltwater, which could be an attractive target for attempted brightening. However, prior studies show that wind blows hollow glass microspheres to the pond edges. A thin layer of hollow glass microspheres has about 10% absorptance for solar radiation, so hollow glass microspheres would darken any surfaces with albedo >0.61, such as snow-covered ice.
The net result is the opposite of what was intended: spreading hollow glass microspheres would warm the Arctic climate and speed sea-ice loss. If non-absorbing hollow glass microspheres could be manufactured, and if they could be transported and distributed without contamination by dark substances, they could cool the climate. The maximum benefit would be achieved by distribution during the month of May, resulting in an annual average radiative forcing for the Arctic Ocean of −3 Wm−2 if 360 megatons of hollow glass microspheres were spread onto the ice annually.