Coral ill health happened in 1998 and in 2010, but the current duration of global coral die-off is no small thing: It is the longest on record and being prolonged by climate change and the current strong El Niño. National Oceanic and Atmospheric Administration (NOAA) scientists are presenting a talk on this and the outlook later this week at the 2016 Ocean Sciences Meeting, in New Orleans.

This current bleaching event began in 2014 and may well endure into 2017, the researchers said in a release. They've been monitoring and forecasting coral loss, which is being caused by heat stress from ocean temperatures as well as disease.

These losses have an impact on humans worldwide, poor and rich. On the globe, about 500 million people depend on reefs for food and as coastline protection from erosion and storms. The reefs also put about $29.8 billion into world economies annually.

"We are currently experiencing the longest global coral bleaching event ever observed," Mark Eakin at NOAA said in the release. "We may be looking at a 2- to 2½-year-long event. Some areas have already seen bleaching two years in a row."

Not only are the corals being hard hit, but some of them may not have time to recover before new bleaching events occur, said Eakin in the release.

When severe bleaching occurs, reefs erode. This eliminates fish habitat and leaves shorelines unprotected from ocean waves. The first global bleaching event on record took place in 1998 during a strong El Niño followed by a very strong La Niña. The second event was in 2010.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

-Follow Catherine on Twitter @TreesWhales