So-called solar radiation management, dealing with the global warming problem by reflecting the Sun’s radiation away from the Earth, is usually described as a sticking-plaster technique because it doesn’t deal with the underlying issue of too many greenhouse gas molecules in the atmosphere. As CO2 builds up, the oceans become more acidic with catastrophic consequences for ocean life, for example, and no amount of reflected sun is going to change that. Also, as geoengineering solutions go, reflecting the sun may be cheap at the outset, but requires long term commitment because the sun doesn’t have an off-switch and the CO2 isn’t going anywhere (staying put for around a century per molecule).
This is perhaps the most compelling reason why it is essential that we cut carbon emissions. And it is also why geoengineering solutions that attempt to remove carbon dioxide from the atmosphere are preferable. Oliver Morton has made a detailed and thoughtful analysis of the pros and cons of different geoengineering options here.
One notable absence from much of the climate-solutions debate is the fact that almost half of global warming is now believed to be caused by non-CO2 pollutants, including ‘brown clouds’, nitrogen compounds, methane (powerful but shortlived), water vapour, low ozone… Most of these are direct health hazards quite apart from their climate change effects.
Brown clouds, or ‘black carbon’, for example, are trails of sooty particulates – the result of cow dung and other biomass being burnt in kitchens across Asia, of slash and burn across the poor world, and of dirty fires at oil and gas wells from the Canadian tar sands to Siberia. There are cities I’ve been in Asia, where breathing is a lung-searing chore and where my eyes have streamed from the pollution. It is having a measurable effect on monsoon patterns as far as Australia and the Maldives, melting glaciers and turning pristine ice grubby at the North Pole.
As far as I am aware, the only geoengineering solutions that will reduce the impact of non-CO2 pollutants are those that reflect the sun’s radiation back. Far from ideal.
Just as climate change is about more than just global warming, so greenhouse gases are about more than carbon dioxide. These gases must be included in emissions reductions and also in geoengineering labs.
Wandering Gaia 
One wrinkle in all this is that if you put the reflecting layer *below* brown cloud/black carbon etc — by putting reflectors of some sort on the surface or whitening low clouds — I’m pretty sure that you can make things worse, because the soot and muck will absorb light coming back up from the reflector as well as coming down from the sun. So some solar radiation management schemes probably need you to clean the air first…
And the trouble is, no one can effectively move reflecting layer particulates or pollution clouds to the desirable altitude or geographic location. It would be great if the brown haze clouds themselves could be moved from where they are currently increasing warming, to where they would have the most cooling effect – off the West African coast, for example. Again, this would only serve to mask the warming effect of the other greenhouse gases, so still a sticking plaster.
Most importantly, there is widespread agreement within the scientific community that the Earth’s climate is chaotic. In other words, no matter how well you know its dynamics, there will always be causative factors that may impact on it following changes thereof below an established observational limit. This boils down to the fact that, the Earth’s climate is, essentially, unpredictable and major havoc may be wrought on it if we try to preposterously steer it the way we want. Let’s not forget that every action is countered by a reaction. Safe journey !