Mass Coral Bleaching Is Latest Sign of Incredibly Hot Oceans

Once vibrant corals turning bone white highlights something scientists have been saying for years: the oceans are heating up dangerously.

This week, the US National Oceanic and Atmospheric Administration announced a global coral bleaching event. Too much heat is the main cause of coral bleaching — and there are more worrying signs as the latest ocean-surface readings show temperatures are on the rise.

“This is big,” said John Abraham, professor of thermal sciences at the University of St. Thomas. People are realizing just “how important the oceans are as the measurement metric for climate change.”

Every day, for more than a year — barring a tiny blip last spring — the global average sea-surface temperature has been at a record seasonal high in data that go back to 1979. And those historical records haven’t just been narrowly surpassed, they’ve been obliterated.

Hotter oceans matter for all sorts of reasons beyond their impact on coral reefs. They exacerbate sea-level rise as warmer water expands. They restrict the supply of oxygen to marine life and are pushing fish toward the earth’s poles or deeper waters. They’ve been linked to the rise of marine bacteria called Vibrio, which can cause vibriosis in humans, bringing symptoms such as fever, diarrhea, vomiting, and, in some cases, it can kill. And last year, high sea-surface temperatures helped push scientists to raise their forecast for Atlantic hurricanes.