Does Testing Really Equal Deployment?

In a memorable 2010 article titled "A Test for Geoengineering?," Alan Robock and others argued that, because the climate system is highly complex, interconnected, and characterized by a low signal-to-noise ratio, a convincing test of SRM must be planetary in scale, and thus "geoengineering cannot be tested without full-scale implementation" (p. 530). Now David Keith, Ken Caldeira, and two other colleagues have challenged this assertion. In "Can We Test Geoengineering?," these authors contend that smaller scale experiments, while incapable of providing definitive answers regarding the effects and effectiveness of global SRM deployment, nevertheless would generate very useful information on the likely costs and benefits of implementation. They write,

an initial test (or sub-scale deployment phase) could provide important tests of the climate's response to geoengineering within a decade, although accurate estimates could require several decades or longer. Testing cannot eliminate uncertainty about the risks posed by geoengineering, but testing by modulation could improve understanding of risks of geoengineering and might also constrain our estimate of the climate's sensitivity to CO2.

Since last year, the idea that SRM testing and SRM deployment would be identical in practice has been conventional wisdom, which in turn has had a discernible chilling effect on SAI and other climate engineering research proposals. With this conventional wisdom challenged, we may begin to see a greater willingness to consider and fund smaller scale experiments to establish a body of empirical evidence. Such observations would serve as an essential foundation on which to base future decisions about additional testing and possible deployment.