I have no doubt that many regular readers of this fine little blog also subscribe to to the journal of Atmospheric Chemistry and Physics.
For those of you who, in some weird and unlikely parallel universe, might have missed it, the latest edition contains a nice summary (equations included at no extra charge) of all the clever ways we can suck carbon emissions back to the levels of the stone ages ... or something like that.
All currently mooted geoengineering options are quantified and evaluated for effectiveness.
Launching sunshades would be highly effective, but unfortunately we would need to send 31000 square kilometers of sunshades up into space every year, which would require 135000 rocket launches every year. The sunshades solution would counteract the radiative effects caused by our current rate of carbon output. Interestingly, the analysis concludes that this solution would be our best, and most staggeringly expensive, option.
The second best option would be seeding the stratosphere with reflective aerosols, although an unintended consequence would be global drought. As a second place-getter solution it rather sucks, if you ask me.
After those big hitters, all other options would need to be used in combination to make a serious difference. In other words, effectiveness plummets when it comes to the various flavors of carbon sequestration, for example, which are touted quite frequently and with much optimism by our government and by our fossil fuel businesses.
The radiative forcing potential of different climate geoengineering options - refer pg 2575, subsection 3.1.1 for Sunshades in space