Here’s one solution to the population problem: In 1967 Buckminster Fuller patented a giant floating geodesic sphere enclosing a city, hoping to reduce the economic and environmental costs of using land for housing. Each sphere would be a mile in diameter, enclosing an enormous volume of air that would be warmed by the sun, enabling it to carry buildings bearing thousands of people. The structural weight of even a half-mile sphere would be a thousandth the weight of the air inside, and heating the air even 1 degree would raise the whole structure like a hot-air balloon. By opening and closing polyethylene “curtains,” the occupants could keep the sphere floating at a chosen altitude. The cities could be tethered to mountaintops or float freely, enabling them (for example) to travel to disaster sites in a matter of days, and permitting humans to “converge and deploy around Earth without its depletion.”

“Cloud Nine is probably possible, but even Bucky didn’t expect to see one soon,” writes J. Baldwin in BuckyWorks: Buckminster Fuller’s Ideas for Today (1996). “He offered it as a jarring exercise, intended to stimulate the imaginative thinking we’re going to need if the billions of new Earth citizens predicted to arrive soon are to have decent housing.”