During summer 2017 a large swath of Australia’s Great Barrier Reef—normally a riot of electric oranges, reds and other colors—turned ghostly pale.
Unusually warm water temperatures, partly due to global warming, had caused the corals to expel from their tissues the symbiotic algae that provide them with food and give them their brilliant hues. It was the second mass-bleaching event to hit the reef in as many years. Together, the back-to-back events hit two thirds of the reef.
Image: NASA
