[cbacba]

you're missing the most crucial problem there sidew. granted you have some serious concerns but you didn't catch the most serious yet.

when talking of modifying large surface areas there is the albedo concern. Sand can be as high as 0.4 in albedo, which is the reflection of light/energy back out into space. Solar panels could be as low as 0.02. Note that 1.0 is a perfect mirror while 0 is a perfect black body absorber.

Earth has a nominal 0.30 albedo, most of which comes from clouds. Unfortunately, oceans tend to run about 0.03 albedo and that is over 75% of the surface.

Global temperature balance is a function of several items which include solar radiation coming down, albedo (which eliminates some of that energy), and the atmosphere which restricts somewhat the escape of that energy. As an example, variations in albedo measured over the last 20 years indicates changes and variations that reach 10% and this relates to almost twice the forcing of a co2 doubling - something that has yet to happen.