Can we test geoengineering?

Abstract

Solar radiation management (SRM), a form of geoengineering, might be used to offset some fraction of the anthropogenic radiative forcing of climate as a means to reduce climate change, but the risks and effectiveness of SRM are uncertain. We examine the possibility of testing SRM through sub-scale deployment as a means to test models of climate response to SRM and explore risks prior to full-scale implementation. Contrary to some claims, this could provide meaningful tests of the climate's response to SRM within a decade. We use idealized simulations with the HadCM3L general circulation model (GCM) to estimate the response to SRM and signal-to-noise ratio for global-scale SRM forcing tests, and quantify the trade-offs between duration and intensity of the test and it's ability to make quantitative measurements of the climate's response to SRM forcing. The response at long timescales would need to be extrapolated from results measured by a short-term test; this can help reduce the uncertainty associated with relatively rapid climate feedbacks, but uncertainties that only manifest at long timescales can never be resolved by such a test. With this important caveat, the transient climate response may be bounded with 90% confidence to be no more than 1.5 C higher than it's estimated value, in a single decade test that used roughly 1/10th the radiative forcing perturbation of a CO 2doubling. However, tests could require several decades or longer to obtain accurate response estimates, particularly to understand the response of regional hydrological fields which are critical uncertainties. Some fields, like precipitation over land, have as large a response to short period forcing as to slowlyvarying changes. This implies that the ratio of the hydrological to the temperature response that results from a sustained SRM deployment will differ from that of either a short-duration test or that which has been observed to result from large volcanic eruptions.

Dealing with the uncertainties of climate engineering: Warnings from a psychological complex problem solving perspective

“…This is especially true given the long time perspectives in the climate change problem as with larger time frames, the vagueness of predictions increases [39]. Coming back to the example of an SRM field test, if our decision maker decides to carry it out only for a short duration, effects would need to be extrapolated from the effects found during the time frame of the test, yielding significant uncertainties [35]. Thus, the uncertainties that are associated with the climate models he bases his predictions on make it more difficult to control the complex system.…”

“…Therefore, with such a test, a trade-off decision would be needed between the duration of it, the magnitude of it and the uncertainty of any estimated climate response: "Accurate estimates at a local scale would require greater time or larger forcing". If our decision maker wants to restrict the magnitude of the test (for example, because with larger forcings, the line between field test and full implementation becomes blurry, possibly also threatening his relations with neighboring states) he would want to plan many years ahead: ".accurate estimates could require several decades or longer" [35].…”

Bridging the Gaps in Interdisciplinary Research on Solar Radiation Management

“…States cannot be sure of what would be their "optimal" level of SRM, since there is deep uncertainty about how costs and benefits from an SRM intervention will be distributed, because their climate impacts are uncertain. Even if SRM were to be deployed, it would be very challeng ing to confidently detect and attribute the effects that it might have had on the climate (Stone et al 2009, MacMynowski et al 2011. Due to the inherently variable nature of the earth's climate, it can take decades to detect and attribute even fairly large global signals, as has been the case for the global warming signal (Stone et al 2009).…”

Ambivalence in calculating the future: the case of re-engineering the world

“…Several researchers have also stressed the extreme difficulty of determining SRM's impact on climate change, even if large field experiments are conducted (e.g. Blackstock and Long 2010;MacMynowski et al 2011). Nevertheless, scientific attempts to assess SRM's future are intense and can be exemplified by extensive appraisals by the Royal Society (Shepherd et al 2009;cf.…”