Have you considered something different for climate; mass production of climate change resistant (ie heat/acid) photosynthetic plankton and releasing to ocean?
i'm always a skeptic of muddling too much with nature (as opposed to just getting out of natures way and letting it do it's thing) Maybe its because I've read too much science fiction, but the first scenario that pops into my head is that we engineer some super plankton that grows out of control and smothers the ocean, not letting light filter down, and basically killing all ocean life. Kinda like a green ice-9 if you will...
A comforting thought for this sort of thing is that it would have happened naturally already, if it were possible at all. We can assume that we're broadly in a 'low energy state', and there's no tiny change that will cause a massive permanent shift. Similarly, Ice-9 can't be real or Earth would be covered in it, and we weren't going to set the atmosphere on fire at Trinity because Earth's already been hit by huge asteroids that didn't.