Sunshades in Solar Orbit and other seeming pie in the sky ideas to mitigate Climate Change

It seems pretty obvious to me that we are not going to be able to prevent enough of the Climate Change taking place as a result of the near doubling of the CO-2 in our atmosphere since the start of the Industrial Age (or Antrhopocene, if you prefer). The process is too far along, and there is no way human civilization is going to immediately shut down all fossil carbon use.  
  

So, we will have to take various global-scale macro-engineering steps, sooner or later. This idea, of building sun shades at the Solar LaGrange point (see link below) is one that will probably engender a reaction of (almost literally) "pie in the sky" from most people, but, apparently, space engineering folks have looked at it pretty carefully and it actually is likely to be feasible.

http://en.wikipedia.org/wiki/Space_sunshade 
  

One issue this kind of macroengineering, direct redress of solar heating, does not deal with is the acidification of the oceans. So it would have to be coupled with other measures, especially, the rapid move away from fossil carbon fuels, in order to be effective. We all know our long addiction to fossil carbon simply has to come to an end, and the sooner the better. We can't just keep on spending the millions of years long sequestration of carbon that our planet has accomplished (for good reason), without dire consequences. 
  
But combined measures likely actually could stop major further warming of the Earth, and, gradually, at least, the oceans could be protected. (We will also have to stop expecting them to supply unlimited amounts of wild fish; that era, too, is all but over). And we humans need to get busy working on, and funding the work on, all plausible efforts. 
  
One of which may be helped by this recent discovery: possibly far superior method of producing hydrogen for engine fuels (hydrogen can also be used as a jet fuel).  Of course the combustion of hydrogen just yields water. And there is no danger of using up all the oxygen; even if all the fossil carbon on Earth were burned, it would have less than a few tenths of a percent effect on oxygen content of the atmosphere, and even that would be temporary; the Earth's oxygen surplus is built into its bioregulatory systems very robustly). Using hydrogen as a manufactured fuel, as long as fossil carbon isn't involved in making it, is climate-friendly. It's also the case that oxygenic photosynthesis converts water into oxygen, so artificial processes that directly convert hydrogen and oxygen into water are fairly readily offset by the natural systems of the Earth.

https://richarddawkins.net/2015/04/new-discovery-may-be-breakthrough-for-hydrogen-cars/

Another possible temperature mitigation is aerosolization of sea water by ocean going vessels, which could greatly increase, well, fog, over the ocean surface. This is already a major regulatory mechanism by which the Global Feedback System (Gaia) keeps the Earth very much cooler (about 40° C cooler) than it would be in the absence of life: much of the surface mist over the ocean results from bacteria in the water. Anyway, the technology to do this is already in development. But this, too, does nothing about the encroaching acidification of the oceans, which cannot be ignored. 
  

Some people reflexively balk at "geoengineering," but I think we absolutely must consider all options. We have done a LOT of geoengineering since we started burning coal, oil, and natural gas on a massive scale, and it promises to wreck our world as cozy and comfortable habitat for humanity. Either we get smart, and think these things through carefully, control for all effects, and proceed cautiously to do what has to be done, or we fail, and billions will likely die in the catastrophe that ensues. That's the choice. Reflexive rejection of "geoengineering" is not an option.