An Airborne Sunshade to Protect Arctic Sea-Ice

The airborne sunshade is a similar concept to the “space sunshade”, but flying at 10-20 km altitude in the lower stratosphere, as opposed to 1.5 million km out in space. It is potentially both much less expensive and much more targetable than the space sunshade. It consists of a fleet of specialised aircraft, typically lighter-than-air, with a high-albedo surface for reflecting solar radiation back into space. Komerath et al (2017, https://doi.org/10.4271/2017-01-2143) proposed the “Aerostatically Balanced Reflector” (ABR), a circular solar reflector sheet, suspended from multiple dual skinned hydrogen balloons. Morrey (2022, https://patentscope.wipo.int/search/en/detail.jsf?docId=WO2023209319) proposes pairs of airships which unroll a flat envelope as they ascend to the lower stratosphere, increasing their surface area by up-to 100 times. A pair of 250m-long airships could deploy a flat envelope up to 10 km wide, with an area of 2 square kilometres. Solar radiation absorbed by open ocean during the June to August period, can explains up to 80% of the variability in minimum sea-ice extent (Huang 2019 https://doi.org/10.1029/2019GL084204), due to the strength of the “ice-albedo feedback” mechanism. In Arctic applications, the airborne sunshade is the only geoengineering system able to shade open-sea exposed during the early part of the Arctic melt season. By shading the relatively small areas of open sea, the airborne sunshade can use the ice-albedo feedback to its advantage. Early results from a simple empirical model will be presented. These indicate the area of sea-ice preserved in September could be up to 50 times the area of open sea shaded May - July. An intervention using 8,000 of the above envelopes could increase minimum sea-ice extent by up-to 10% in the first year of operation.