Albedo Variability Limits Potential Detection of Engineered Increases in Reflected Sunlight

Proposals for engineering the climate system by increasing reflection of sunlight away from Earth raise many complex questions. A fundamental scientific question is whether an engineered increase in reflectivity (albedo), either from short-duration field experiments or from prolonged implementation of a “solar radiation management” (SRM) scheme, would be detectable with the current global climate observing system. We have estimated notional detection limits through analysis of satellite observations of incoming and reflected solar radiation. High-precision, uninterrupted observations of solar radiation facilitate detection of very large albedo increases, but interannual albedo variability overwhelms the maximum increases estimated to be achieved by the leading proposed schemes. An abrupt global-average albedo increase < 0.002 (comparable to a ~0.7 W m-2 reduction in radiative forcing) would be unlikely to be detected within a year, given a 5-year prior record. Three-month experiments in the equatorial zone, a potential target region for stratospheric aerosol injection, and in 1º (latitude/longitude) regions of the subtropical Pacific, potential targets for marine cloud brightening, have detection limits ~0.03 and 0.2, respectively. In summary, although very large albedo increases are potentially detectable, interannual albedo variability overwhelms the maximum conceivable increases associated with the leading proposed SRM schemes.

REFERENCE: Seidel, D. J., G. Feingold, A. R. Jacobson, and N. Loeb, 2014: Detection limits of albedo changes induced by climate engineering. Nature Climate Change, 4, 93-98. doi:10.1038/NCLIMATE2076.