Given the potential consequences of climate change and the danger of reaching an irreversible “tipping point”, it is argued that all options should be carefully considered. Sending giant mirrors into space to reflect solar radiation away from the Earth is one such option.
The problem is that many of these geoengineering methods are taboo, and researchers don’t have enough information to make a definitive decision about which options are still viable. A 2021 report by the National Academies of Sciences, Engineering, and Medicine and a report by the Council on Foreign Relations advocate further research and related governance of solar geoengineering methods (i.e., stratospheric aerosols, artificial rainfall, or cirrus thinning). These reports ignored solar geoengineering methods using large space mirrors.
Space mirrors are about the size of Brazil and could be located at the Lagrangian point between the Earth and the Sun L1. While they are still seen as an unfeasible and costly idea in science fiction, they have not yet been rigorously analysed in light of current advances in space technology. Other ideas for reflecting sunlight to cool the Earth include placing objects into the Earth’s atmosphere, which could have secondary effects on the biosphere on a global scale, a major concern of public opinion. The placement of space mirrors 1.5 million kilometres away in space (albeit outside the Earth’s biosphere) may entail other governance and risk considerations that should be weighed against the potential benefits.
The RAND Corporation recently conducted a review of geoengineering technologies, discussing the geopolitical risks associated with geoengineering implementation and the inability of existing legal mechanisms to manage these risks. The review included space mirrors. However, the paucity of published studies requires reliance on 15-year-old literature to determine costs, technology readiness, and side effects. For reference, a 2006 feasibility study estimated that a fleet of metre-class spacecraft could be developed and deployed in 25 years, with a lifespan of 50 years and at a cost of trillions of dollars.
The problem is that many geoengineering methods have been so taboo that there is not enough information to make a clear decision on which options are viable.
What are the risks? In relation to US national security, solar geoengineering in general has a first-mover advantage, being able to “set the thermostat” and commercialise the service, even against adversaries with any negative impact. China has invested heavily in technologies that can be used for geoengineering (e.g., artificial weather), putting it in the lead. Even if the U.S. does not plan to implement space mirrors or solar geoengineering options, the impacts of other players implementing these options could negatively affect U.S. international relations, the economy, and the regional climate. Experts agree that there are concerns about the weaponisation of this technology and that, without further research, there remains significant uncertainty about efficacy and safety.
Since space is a contested operational domain (PDF), some new considerations have also emerged. Space norms are still being developed and codified, and tensions between the major space powers may affect the geopolitical feasibility of implementing large-scale projects such as Space Mirror. For example, will the project be undertaken by a single state or a coalition of states or non-state actors?
What are the benefits? The attraction of solar geoengineering technology is that it provides a viable stopgap measure to halt temperature rise while continuing to reduce greenhouse gas emissions. They will especially serve as an emergency option if current climate mitigation and adaptation efforts are insufficient to stop existing climate hazards. Beyond that, some experts see dual-purpose space mirrors as a potential new source of renewable energy (i.e., space solar). They also see space mirrors as a possible commercial market that could sustain implementation.
In addition to established notions of risk and reward, these considerations may change based on new concepts and technologies that have been recently developed. A team of researchers at the Massachusetts Institute of Technology (MIT) has proposed a geoengineering concept similar to space mirrors, which proposes a series of reflective bubbles that can be assembled and moved in space. In terms of space capabilities in general, the cost of space launch campaigns required to implement large space mirrors could be significantly improved through cheaper, reusable launch capabilities like SpaceX’s Starship. It is also worth considering engineering advances such as the recent launch of the Hexagonal Folding Mirror as part of the James Webb Space Telescope, which makes the 6.5-metre mirror lightweight and compact enough for launch.
The risks and benefits are still very theoretical, and there are many details that deserve closer examination to help policymakers evaluate these technologies and prepare for scenarios in which other entities use them. First, new insights into the feasibility of different approaches to implementing space mirrors may be needed, given today’s technology and infrastructure, effectiveness, and life-cycle costs. A second area that could benefit from more research is broadly the area of associated risks. This includes the assessment of environmental risks and how they differ from other solar geoengineering approaches; the risks to space-based systems in a contested space environment under existing space governance; the risks posed by the implementation of space-scope approaches by different participants; and the risks posed by the generation of large amounts of space debris at the end of the life of a space-scope.