In 2016, an eight-month marine heat wave kept surface temperatures in the Coral Sea about 1 degree Celsius warmer than usual. Researchers now say that slight increase caused nearly 30 percent of coral in the Great Barrier Reef to start dying.
The most catastrophic die-offs occurred where temperatures rose the highest. In those spots, coral died immediately from heat stress. Bleaching events, which are linked to warming, killed even more coral, albeit more slowly. Of the 60 percent of coral colonies that experienced heavy bleaching, only 1 percent survived after eight months.
These colonies might be able to regrow, but researchers said the chances of a full recovery are "poor." They noted that many of the survivors of this heat wave are still slowly dying because they're now more susceptible to disease and that even the fastest growing species of coral would take at least a decade to pop back up.