There is another problem to solve, which is cooling the Earth. What does it take to shield the Earth from Sun so less solar power reaches the Earth? Is there such technology?
"Tin foil". Arranged in the right shape, and spun to maintain positioning at L1. About a million square kilometers give or take should do it, plus ancillary things like positioning thrusters etc.
Call it five to ten million metric tons, if we're using ultrathin kapton with sputtered aluminum. Launch costs alone would be in the upper billions to low trillions, combined with construction and maintenance, probably 1-2 trillion as a lowball estimate.
N.B. this only reduces power by a factor of 0.1%, about 1 W/m^2!
