[floatrock]

Blocking out the sun whether by a sunshade or light controlled nuclear winter/"artificial volcano" has the downside that it hurts agricultural production. And food production needs to increase anywhere by 25% to doubling by 2050, depending on which population growth hockey stick charts you look at.

[chr1]

That's assuming we block all the sunlight, but what we need to do is reduce sunlight in places like sahara, antarctica, middle of australia, and increase in places that are too cold. This can be achieved by satellites orbiting at lower level, or even stratospheric balloons. We do not need this to cover significant portion of earth surface, just enough to nudge winds in the right direction and change the humidity. Since the greenhouse effect from humidity and clouds is much larger than the effect from CO2, we can get much nicer climate even without reducing atmospheric CO2.