Corals around the world are turning white, a dangerous “bleaching event” that’s being triggered by climate change and a burgeoning El Niño. Scientists have seen this sort of thing before, but this event appears to be the worst yet.


The U.S. National Oceanographic Administration (NOAA) has officially declared a global bleaching event, reports Nature News. It’s the third time scientists have seen such a thing, but this particular bleaching trend—where warmer waters cause reefs to let go of the algae that colors them—is expected to worsen over the coming months.




Graphic credit: NOAA



The NOAA explains the bizarre phenomenon:



Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.



In 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters centered around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined.



That said, not all bleaching events are caused by warm water, as witnessed by the 2010 Florida Keys bleaching event where water temperatures dropped 12 degrees F below normal.


Bleached corals (Photo credit: J. Roff/CC BY-SA 3.0) ·



Nature News explains more about the current bleaching event:



Reefs in parts of the Pacific, the Indian and the Atlantic oceans have now turned white. By the end of the year, the bleaching could affect more than a third of the world’s coral reefs and kill more than 12,000 square kilometres of them, NOAA estimates. “We’re in shock and awe of what’s happening,” says Ove Hoegh-Guldberg, a marine scientist at the University of Queensland in Brisbane, Australia. “It’s a doozy of an event.” Bleached corals are more vulnerable to stressors such as disease that can kill them. In 1998, the biggest bleaching event in history led to the death of 16% of the world’s coral reefs.


NOAA started to notice that something was happening back in 2014, when parts of the Pacific, including the Hawaiian islands, began experiencing mass coral bleachings. Warmer ocean temperatures, and an El Niño that’s got the potential to become the worst on record, are creating a very volatile situation.




Image credit: NOAA

NOAA models predict that, by mid-2016, the bleaching will have spread through most of the world’s coral-bearing regions.


Read the entire article at Nature News. And check out the NOAA’s Coral Reef Watch.

