First they converted five-thousand year-round homes into summer rentals.  The number of Airbnbs and zoning regulations filled the ponds with nitrogen and cyanobacteria, stuff that evolved 2.7 billion years ago. You stare at a sign that says keep kids away from scum. You think, something is desperately wrong, but folks just shrug, elated that the remaining ponds are six degrees hotter.  A woman in a bathing suit reads the same sign. “I’m glad I won’t be around to see what happens!” she says, snapping swimming goggles over hair the color of spider silk. She details her upcoming trip to a coral…