There have been a spate of articles recently outlining the alarming coral destruction event currently underway including a story from the Guardian with interviews from prominent scientists from NOAA's Reef Watch program.
Evidentially this is the third event in the last 20 years or so and this one is by far the worst. It's estimated that the kill rate could be upwards of 40% of all the coral reefs on earth. Let me say that again: 40 percent dead, extinct, poof! One expert with the non-profit group Reef Watch asserts that the bio-diversity loss could rival the last mass extinction.
El Niño the Culprit
El Niño occurs when the waters of the equatorial Pacific warm to a certain threshold temperature that helps foster unusual weather patterns, often very distant from the point of origin. The event that's happening now is the strongest in years and may well last until next summer. It's believed that climate change is accelerating the pace and severity of El Niño. Also the chemistry of the oceans is dynamically changing and becoming more acidic.
All of these favors are combining to drive this coral bleaching destruction.
Hawaii Especially Hit Hard
With the previous two bleaching events Hawaii was largely spared from the most damaging coral effects. But not this time. According to NOAA scientists this event actually started in Hawaii in 2014 and has damaged even pristine virtually untouched reefs of the Northwestern Hawaiian Islands. Here's a link to more info from NOAA.