Abstract
Solar geoengineering has been suggested as a tool that might reduce damage from anthropogenic climate change. Analysis often assumes that geoengineering would be used to maintain a constant global mean temperature. Under this scenario, geoengineering would be required either indefinitely (on societal time scales) or until atmospheric CO2 concentrations were sufficiently reduced. Impacts of climate change, however, are related to the rate of change as well as its magnitude. We thus describe an alternative scenario in which solar geoengineering is used only to constrain the rate of change of global mean temperature; this leads to a finite deployment period for any emissions pathway that stabilizes global mean temperature. The length of deployment and amount of geoengineering required depends on the emissions pathway and allowable rate of change, e.g. in our simulations, reducing the maximum approximately 0.3°C per decade rate of change in an RCP 4.5 pathway to 0.1°C per decade would require geoengineering for 160 years; under RCP 6.0, the required time nearly doubles. We demonstrate that feedback control can limit rates of change in a climate model. Finally, we note that a decision to terminate use of solar geoengineering does not automatically imply rapid temperature increases: feedback could be used to limit rates of change in a gradual phase-out.
Highlights
Much of the discussion on solar radiation management (SRM; variously sunlight reflection methods) either implicitly or explicitly assumes that it would be used to maintain an approximately constant global mean temperature, e.g. restoring to pre-industrial, or avoiding temperature rising above some threshold
We consider the different representative concentration pathways (RCPs) [22,23] that are frequently used as standard scenarios to explore future anthropogenic climate change [24], and explore how the choice of emissions pathway and the value chosen for the maximum allowable rate of temperature change affect both the duration and the amount of SRM deployment
Carbon dioxide released to the atmosphere can affect the Earth’s climate for millennia [33], in the absence of methods used to accelerate the removal of CO2 from the atmosphere, CO2 emissions commit us to millennia of altered climate
Summary
Much of the discussion on solar radiation management (SRM; variously sunlight reflection methods) either implicitly or explicitly assumes that it would be used to maintain an approximately constant global mean temperature, e.g. restoring to pre-industrial, or avoiding temperature rising above some threshold This includes almost all SRM simulations to date, including early work [1] and both steady-state and transient experiments G1–G3 in the current GeoMIP simulations [2,3]; some recent papers have been even more explicit, using feedback to maintain a particular temperature [4,5]. In our GCM simulations, we adjust this estimate each year based on feedback of the global mean temperature to maintain a roughly constant rate of temperature increase; this feedback compensates for any differences between the simple model and the GCM This approach—combining prediction and correction— captures the situation that would be faced in actual implementation, where we do not have the option to re-run a simulation in order to tune the amount of SRM
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Schedule a callMore From: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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