One of the more exotic potential solar radiation management geoengineering technologies is the placement of sunshades in space to reflect or deflect solar radiation, either by lifting these reflectors into orbit around Earth or at the Lagrangian L1 point between the sun and Earth. A new article by Takanobu Kosugi is a very thorough assessment of the potential effectiveness of this scheme, as well as potential perils that the technology might pose to societies in the next century, Takanobu Kosugi, Role of Sunshades in Space as a Climate Control Option, 67 Acta Astronautica 241-253 (2010) (subscription required). This would be an excellent reading for graduate students or law students.

Among the key take-aways from the study:

1. According to theoretical calculations, sunshade technology could reduce 1.8% of total solar radiation inflows, offsetting warming associated with a doubling of atmospheric carbon dioxide concentrations;
2. Sunshade research is at a “germinal” stage, with large uncertainties in terms of the characteristics of such technologies, including critical issues e.g. the mass of sunshades required to reduce a certain among of solar radiation inflows;
3. The cost of space launching of sunshades is projected at $6000/kg. currently; however, technological progress could ultimately reduce costs to $20/kg. assuming that the materials for sunshades could be extracted from the moon or an asteroid;
4. For all scenarios involving the sunshade mass-effectiveness coefficient and equilibrium climate sensitivity (which likely ranges from 2-4.5C, but could even reach approximately 6C), deployment of sunshades are expected to become cost-effective for initial deployment in the middle of this century, a point at which temperatures are projected to have risen 2C above pre–industrial levels. Assuming climate sensitivity of 3C, sunshade deployment could reduce total societal costs by $240 billion; if climate sensitivity ultimately proves to be 6C, cost savings could rise to $1.9 trillion;
5. There is a potential “termination problem” associated with deployment of sunshade technology, i.e. the potential for abrupt temperature rises if use of sunshades was suspended for any reason, especially in cases where the mass-effectiveness coefficient is low. The study indicates that with low mass-effectiveness coefficient, the termination of sunshade deployment in 2125 could result in temperatures increasing by between 0.14C-1.28C based on different assumptions of climate sensitivity. However, the study also emphasizes that even with temperature sensitivity of 6C, the temperature rise after termination is less than the 0.2C per decade temperature increase anticipated under a business as usual scenario without deployment;
6. Continuous investment in research and development of $14 billion annually over the next quarter century would be a reasonable expenditure for sunshade technology.

This article could generate substantial class discussion. Some potential questions include:

1. While the article doesn’t address moral hazard questions, are they related to the “termination problem” cited by the author?;
2. Given the substantial costs projected for R&D for sunshade technologies, how does one assess opportunity costs vis-a-vis either other geoengineering schemes or mitigation/adaptation responses?;
3. Does the sunshade approach pose any of the potential negative side effects that might be posed by other SRM approaches, e.g. changes in regional precipitation patterns, impacts on the ozone layer, etc. If not, would this obviate some of the potential governance problems associated with other SRM (or CDR) approaches?;
4. What treaties might be relevant in terms of governing sunshade R&D or deployment?

Related posts:

1. Geoengineering and Solar Radiation Management
2. Geoengineering: The Potential Role of Solar Radiation Management Schemes
3. Ethics of Geoengineering Video Interviews
4. Can We Test Geoengineering Without Potential Consequences?
5. The Impact of Climate Geoengineering on Crop Yields