Regulating Sunlight

Solar Radiation Management (SRM), is another form of geoengineering aiming to manage and reduce incoming solar energy reaching the Earth, to counteract GHG forcing. Models indicate that the climate system reacts quickly to artificially reduced insolation, and therefore SRM is often branded as a last resort against 'dangerous' warming.

Fig.1 Illustration of geoengineering approaches (source: IPCC / Royal Society).

1. Stratospheric aerosols

1. Extensive studies have shown major volcanic eruptions to cool global temperatures over short-timescales (Fig.2). The ejection of sulphate particles in the stratosphere from eruptions causes an increase in diffused solar energy and reduction in total energy reaching the Earth. A natural analogue for the stratospheric release of sulphate aerosols. According to models cooling could start within months of release and cool significantly within decades. Thus, receiving growing traction from scientists and policymakers. 

   
   
   Fig. 2 Mean global average temperatures from 1970-2012 with major volcanic eruptions highlighted (source: Kosaka & Xie, 2013).

2. Albedo enhancement

1. Approaches that aim to enhance the reflectiveness of surfaces (land, oceans and clouds) to increase the amount of solar energy reflected into space. For instance, painting cityscape roofs white as suggested by Barack Obama in 2009, to seeding marine clouds to enhance the total of cloud condensation nuclei (CCN) present, thus increasing cloud surface area and brightness. 

3. Space reflectors

1. Roger Angel (2006), presented the idea of 100 000km wide 'sunshades' (aka space reflectors) to be placed in outer space.  Reflecting and/or blocking incoming solar radiation. Calculating that only ~2% of incoming solar radiation would have to be blocked to offset current warming. In line with calculated energy transfer figures.

Fig.3 An article headline from NY Times (source: Friedman & Thrush, 2017) 

However, a consensus within the scientific community is that SRM is bad and infeasible (I'm a little on the fence about it too). A contemporary argument for this would be the justification for the Trump administration to deny climate change (despite the arguments many USA scientists make Fig.3), disregarding the Paris Agreement and continuing fossil fuel exploitation (ie. pipeline exploration destroying indigenous lands and fracking).

Conclusion

Initially, SRM seems to be a viable climate fix. However, SRM is controversial and prone to issues surrounding governance, equity and ethics. 

However, there may be a place for SRM especially if we adopt the business-as-usual approach to climate change. SRM may 'save' us and provide us time to change current social, economic and environmental practices. In this regard, I perceive SRM to be a form of adaptation and not mitigation.