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' scheme, would be detectable with the current global climate observing system. High-precision, uninterrupted satellite observations of solar radiation facilitate detection of very large albedo increases, but interannual albedo variability overwhelms the aspirational increases associated with 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 1 degree latitude by 1 degree longitude regions of the subtropical Pacific, potential targets for marine cloud brightening, have detection limits ~0.03 and 0.2, respectively.