A powerful El Niño combined with rising temperatures is wreaking havoc on the world’s coral reefs, causing what federal scientists say is the longest die-off event on record.

The National Oceanic and Atmospheric Administration, whose researchers are expected to present their findings Friday at a meeting on coral reefs, concluded that the global coral bleaching event that started in 2014 in the western Pacific Ocean could extend well into 2017.

Related: NOAA: Latest El Nino is now tied for strongest ever

“We are currently experiencing the longest global coral bleaching event ever observed,” Mark Eakin, NOAA’s Coral Reef Watch coordinator, said in a statement. “We may be looking at a 2- to 2½-year-long event. Some areas have already seen bleaching two years in a row.”

Coral bleaching happens when corals are stressed by conditions such as high water temperatures brought on by El Niño and global warming, prompting the corals to expel algae that live in their tissues. Without the algae, corals lose a significant source of food and are more vulnerable to disease.

The worst bleaching events have often coincided with El Niño events – created when the equatorial waters of the Pacific Ocean warm significantly. The first widespread mass bleaching occurred during the 1982-83 El Niño, while a record El Niño in 1997-98, caused the first global bleaching event. A second global bleaching event occurred in 2010, during a less powerful El Niño.

Related: Monster El Nino expected to shape this winter's weather

NOAA forecasters in January concluded the current El Niño is now as strong as the one in 1997-98. It began in March 2015 and the World Meteorological Organization announced this week that it had peaked and would weaken in the comings months before fading away in the second quarter.

Along with coral bleaching, this El Niño has been blamed on a more active cyclone season in the Western North Pacific and Eastern North Pacific basins, drought in Central America as well changing weather across North America – including forecasts of above-average precipitation across the southern tier of the United States and above-average temperatures in the North and West, the WMO said.

According to Eakin, the record-long bleaching may make it impossible for corals in some parts of the world to recover before they are hit again.

NOAA coral scientists point out that reefs that bleached in 2015 in the Caribbean and Florida Keys have just started to recover, but may start bleaching all over again as early as July. Eakin also notes that in the Pacific, corals in Fiji’s near shore waters are bleaching with lots of dead coral for the second consecutive year, and could be worse than last year.

Related: Worst of this El Nino expected in coming months

The 1998 bleaching event may offer a guide of what to expect. Severe bleaching in Southeast Asia followed by 12 years of recovery allowed some of the more rapid growing, branching corals to grow back. However, the slower growing corals that build the backbone of reefs did not recover. In 2010, the same area was hit again, killing off newly grown branching corals and many of the surviving massive corals.

“The 2010 Southeast Asia event was only six years ago,” said Eakin. “We're seeing global bleaching again now. Research shows that the frequency of mass bleaching events is increasing because of global warming. The corals are being hit again and again.”

The loss of reefs to bleaching can have dire economic and environmental consequences. Reefs are some of the world's most important ecosystems, supporting more species than any other marine environment, including 4,000 fish species. About 500 million people also depend on the reefs for food and protection, with reefs contributing $29.8 billion to the world economies each year, NOAA said.