[greedo]

Rooftop solar isn't viable in a large portion of the world, and solar is much better served in mega deployments. Scale matters.

That said, if you look at the total amount of energy consumed worldwide, the grow rate of this energy consumption, the amount currently generated by renewables, and the growth rate of renewables, it's pretty obvious that there's no realistic way to cut emissions 50% in a decade. Absolutely none short of a global war that devastates both modern society and reduces world population by 25%.