It’s come to this. With Earth at its hottest point in recorded history, and humans doing far from enough to stop its overheating, a small but growing number of astronomers and physicists are proposing a potential fix that could have leaped from the pages of science fiction: the equivalent of a giant beach umbrella, floating in outer space. The idea is to create a huge sunshade and send it to a far away point between the Earth and the sun to block a small but crucial amount of solar radiation, enough to counter global warming. Scientists have calculated that if...