SRM: In space ...

Reading up on this aspect of SRM has been somewhat surreal, with phrases such as ‘lunar glass’, ideas inspired by Saturn’s rings, not to mention the immense scales (temporal and spatial) and quantities necessary to reduce solar insolation by the 2% that estimations state will counteract CO2 induced climate warming.  The prospect of taking the engineering power of man beyond the confines of our own planet is also a daunting prospect (I actually find this idea terrifying, and can’t help the images of Futurama, Star Wars and Dr Who reverberating round my head!).  How do people feel about blasting 10 trillion reflective discs, 1.5 million km into space (Royal Society, 2009) … 1 million at a time … every minute … for more than 30 years … ? – this sounds crazy but the science behind this is real!


How would it work?

One thing is sure, that sun shields would be effective.  By placing reflective or refractive material, be that discs or dust particles into orbit around the earth, the solar energy entering the Earth’s system will be reduced.  There is no physical limit on the extent of reduction (unlike other SRM methods which I’ll cover later), this may become very important if the critics’ fears are realised and geo-engineering diminishes societies desire to cap and reduce CO2 emissions; the more CO2 in the atmosphere, the more solar reflection/refraction is required, thus in this scenario, opportunity for expansion is crucial.


Feasibility?

This method, however, becomes less feasible when the logistics are considered.  The cost of implementing and maintaining such technology is posing to be a difficult balance.  The mass of sunshields is proportional to solar reduction and the cost of launching increases with mass.  Subsequently, various technologies have been developed such that a smaller mass of sunshields can produce the same solar degree of reduction, but these technologies are dramatically more expensive to engineer, thus until in-situ space production is possible, this remains a drastically expensive option (McInnes, 2010).   The expense of a proposal such as that posed by Angel (2006) is estimated to cost in the region of $100 billion per year, which exceeds current global financial investments in renewable energy technologies by an entire order of magnitude (Robock, 2008).  This solution is financially unfeasible.

This method also contradicts claims that SRM can be used as a quick fix in a climate emergency.  As highlighted earlier, it is evident that initiation of such technology will take decades to implement.  Thus, if this option is further explored, it suggests that we’re committing ourselves to a future of climate manipulation, rather than preparing ourselves for an emergency.


Risks?

Such engineering may lie outside the Earth’s system, but that doesn’t mean it evades environmental side effects.  These include: ozone depletion, changes in regional climate and reduced primary production, it could even compromise the efficiency of renewable solar energy capture.  Modelling these methods has been explored, however, not too a degree adequate enough to fully appreciate the extent of the possible side effects.  One model by Lunt et al. (2008) in comparison with pre-industrial climate, describes significant temperature reductions at the tropics and warming at high latitudes resulting in a reduced latitudinal temperature gradient.  Subsequent reductions in sea ice were also simulated, along with intensity reduction of the hydrological cycle, intensification of Atlantic Ocean overturning and less variability in ENSO.  That said, the authors claim that this deviation from pre-industrial climate is less than we're experiencing in a climate warmed by CO2.

Conclusion:

These methods are imaginative and exciting, but completely unpractical, for financial and logistical reasons if not due to the possible side effects.