... Currently around 30% of the sun’s rays that reach Earth are reflected back to space by white surfaces, largely our polar ice. Sea ice reflects sunlight better than any known natural surface, bouncing around 90% back up; at the other end of the scale, the dark open ocean reflects just 6% of sunlight and absorbs 94%. With Arctic sea ice rapidly declining, replacing one with the other is expected to see global warming accelerate. Unless, that is, we find another white surface that can do the job. There have been many suggestions for artificial reflective surfaces: launching mirrors into...