So many of the comments here talk about using abundant solar energy as a solution to the atmosphric CO2 problem. But unfortunately, solar energy isn't even close to providing the energy we need for home-heating, transport and industry.

We have to start from where we are: we can't just warp into a future where Dyson Spheres are realistic. We have less than thirty years. I suspect it's actually already too late. Using solar to reduce Gallium, so we can use the Gallium to reduce CO2, while we continue burning hydrocarbons because the solar is all being used to reduce Gallium (or solve hashes), doesn't look to me like the way forward.