Oh dear. There seems to be an unquenchable penchant for techno-fixes that invariably (i) have no economic rationality, and (ii) overlook many important facets of the problem. This is definitely the case with the “hey, why don’t we just build a big sunshade?” idea.
Aside from the absolute impracticality of the proposal (by the time anything of the sort could be achieved, the Earth would be so far gone it wouldn’t really matter), and aside from the economic insanity (it would cost far more than other more plausible ways to cut back on CO2 emissions) there’s the tiny problem of ocean acidification.
As 80% of our oxygen (you know, the stuff we need to breath in order to stay alive) comes from phytoplankton in the oceans, and as these tiny creatures are very sensitive to the acidity level of their aquatic environment, and as CO2 dissolving into water forms carbonic acid, the “sunshade way up there in space” idea is irrelevant because we’d still be making the oceans more and more acidic and thus killing the phytoplankton we rely on for life itself.
And these are just three of the many very obvious problems associated with the heavenly parasol concept.
Really, people, let’s stop playing Star Trek and get a grip on reality. Because climate change is a serious problem and won’t be solved by pretending there can be superficial tech quick-fixes.