As promised: stratospheric sulphate aerosols vs. cloud brightening (Jones et al., 2010)

Jones et al. (2010):

Employing the HADGEM2-AO GCM to conduct 60 year simulations, this study sought to establish how these two methods compared in terms of climate impacts.

In summary:

Both techniques were able to sufficiently reduce global temperatures, though Stratospheric sulphates were considered more effective.  The variation between the two was most evident in the geographic distribution of these changes ...

Largely it would be considered that the stratospheric method produced more uniform changes in forcing, and thus the distribution of climatic effects deviated far less from the temperature equivalent natural conditions. The diagrams below the deviation of rainfall for the two methods, with each varying in terms of distribution and magnitude, though it is clear that the marine cloud method produces the most severe deviation. 

                                          (a) SO2

                                         (b) Marine clouds

The uneven and very regionally focussed climate perturbations induced by marine cloud brightening, is also reflected in changes in sea ice extent.  The increase in sea ice extent was far less for this technique than when compared to the more globally distributed effects of stratospheric sulphate injections.  

What the authors draw from these results is that the effectiveness and nature of climatic changes induced by these methods is largely dependent on distribution and location of application.  

Conclusions

The marine cloud method in this study used what is considered to be a reliable and efficient seeding regime, but it restricts application to the eastern coasts of the Pacific ocean and the south Atlantic and therefore more anomalous climatic outcomes and inefficiency.  Though marine cloud seeding regimes could be more global, they are still restricted and such regions (as the ones used in this study), if more efficient, would still dominate the forcing.  Comparatively stratospheric aerosol applications can be much more widely applied, and the nature of stratospheric circulation aids such distribution, yielding in this model more desirable climatic outcomes.