SRM: In space … more about the environmental impacts

To expand upon my last blog, I feel it is necessary to provide more detail about the environmental implications of space-based methods of solar radiation management.  I am therefore going to explore how much we actually know about the likely effects on the ozone and global climate.

Ozone

The role of changes in the ozone layer needs to be further understood.  I have been unable to track down any quantitative studies that project the extent to which sun shielding could decrease ozone production; this is primarily a stratospheric photochemical process reliant on solar radiation thus it is important that impacts of reducing radiation are explored.  Regardless, Ross and Toohey (2008) have indicated that the ozone is under significant threat due to this method, simply due to launching sunshields into orbit.  As much as 20% losses of ozone have been estimated due to this aspect alone.  Reductions in the ozone are liable to have huge implications climatically, ecological and on human health and agriculture.  

Climate projections

As previously mentioned, Lunt et al. (2008) modelled the effects of restoring global temperatures to that of pre-industrial levels, such that they were able to assess how far a space-based SRM world deviates from a pre-industrial world in relation to a future world of increased CO2 levels.  The results of the study concluded that despite restoring global temperatures, the SRM world differed significantly from a pre-industrial world in the following ways:

• Reduced latitudinal temperature gradient, compounded by cooler tropics
• Hydrological cycle intensity reduced most notably in the tropics
• Arctic sea-ice declined
• Seasonality of temperatures weakened
• The ENSO responded with reduced amplification
•  The Atlantic Ocean overturning strengthened

The impacts of such changes could have significant ecological and human repercussions most notably in the tropical and polar regions.  However, comparatively the study indicated that the changes liable to occur solely from increased atmospheric CO2 would be far more dramatic and detrimental. The diagram indicates the differences in projections of temperature, sea ice depths and precipitation between an SRM world (a,b,c) and a 4 x pre-industrial CO2 world (d,e,f).  For each of the three environmental variables, the diagram highlights that the SRM world (a,b,c) shows substantially less deviation from pre-industrial values.

Adapted from Lunt et al. (2008)

This study, despite being one of few fully-coupled ocean-atmosphere dynamic GCM models applied to such studies, is still limited; lacking incorporation of what would be significant vegetation, stratosphere and ozone feedbacks. Thus this study is far from conclusive in suggesting that a sun-shielded world is the better of two evils.

Other impacts related to this method such as plant productivity and solar power will be assessed later in the blog as there are also significant in relation to other SRM methods.

Conclusion

In the first instance perhaps sun-shielding doesn’t appear to be all that damaging environmentally, relative to not implementing SRM.  However, very little in depth research has been done into distinct regional impacts, and all lack incorporation of essential feedback systems.  Perhaps such projections are beyond our present modelling capabilities, but what is important is that where and how severe the effects of space-based SRM is still largely unknown and further investigation is required, results of lone studies such as Lunt et al. (2008) are not strong enough to condone such methods.