This is a very dangerous concept and I will tell you why.
As I have said elsewhere on this blog, anywhere else I can and to everyone who will listen to me (a small but important minority), we have lost our sense of who and what we are and where we fit in the continuum of life on Earth. We do not understand the effects we have on the biosphere and cannot comprehend the degree to which we are interconnected with everything, living or not, on the only home we have – Spaceship Earth. We tend to think that we are special, so special that we can think, design and work our way out of any problem we may encounter, especially if we might cause problems ourselves – as unlikely as that may seem to us.
Experience tells a very different story. Our attempts to design, build and manage complex systems such as equitable economic systems, corruption-free political systems, healthy and sustainable food production systems, global peace initiatives, sustainable energy supply systems and many others have, over time, degenerated into at least partial, sometimes catastrophic, failure. Effects from a number of these human-designed systems have had and continue to have massively disruptive impact on natural systems such as climate, terrestrial and oceanic food chains, agricultural soils as well as the on-going realities of poverty and war.
So, having disrupted the global climate system to the point of threatening our very existence, we now think we can design and build fixes to re-stabilize it to something like it was naturally before the industrial revolution. And we think we can re-design plants and animals to better suit them for use by humans without disturbing the myriad species with which they currently interact in the wild.
Now a bit from the author of the article referenced above:
In his new book, A Case for Climate Engineering, [Canadian environmental engineer David] Keith says that geoengineering is a “brutally ugly technical fix.” He cheerfully admits that he has a lot of qualms about it as a technology that could have dangerous and unintended consequences, and that it doesn’t address the root cause of climate change: the buildup of greenhouse gases in the atmosphere.
“I think the important point is that it’s not hard to do, that all the hard questions are about whether we should do it, who controls it, how well it works.”
. . . and what if it doesn’t (work) but does have those “dangerous and unintended consequences”? Who we gonna call . . . Ghostbusters??
If we really are intent on placing mirrors in orbit around the earth, rather than having them face the sun so we can “control” the amount of radiant energy reaching Earth, I would vote for turning them around so we could look up into the sky and see ourselves for the fools we really are.