Presuming said miracle is possible, geoengineering at a scale capable of "solving" climate change would be a massive gamble. Humanity's ability to model the climate simply isn't at a point where we could say with any confidence what the long-term effects of any particular geoengineering "solution" would be, and short of an abrupt technological singularity, won't be for centuries. Without any appeal to moral judgments whatsoever, it's safe to say geoengineering would only be seriously attempted out of total desperation and signal persistent unresolved issues.