Geoengineering: The world's largest control problem

Solar geoengineering (or Solar Radiation Management, SRM) refers to any intentional, large-scale manipulation of the Earth's incoming solar radiation to offset some of the effects of anthropogenic greenhouse gases, reducing the associated risks from climate changes. Examples of such methods are injecting aerosols into the stratosphere or increasing marine cloud reflectivity, both of which would reflect some sunlight back to space. There are many serious concerns associated with any such approach, and also many challenges. One often overlooked aspect in geoengineering research is that this is a control problem, requiring (a) feedback of the observed climate state to manage significant uncertainty in both the radiative forcing and the climate's dynamic response to this forcing, and (b) optimization of the distribution of radiative effect to minimize regional disparities as well as side-effects from the geoengineering implementation. We present recent progress on control for this challenging problem, building on [1, 2], and discuss open research gaps. This is the first time an explicit external feedback loop has been implemented in a fully coupled general circulation model of the Earth's climate.