4th global coral reef bleaching event underway as oceans continue to warm: NOAA

Mass coral reef bleaching can subject coral to mortality without intervention.

April 15, 2024, 5:21 PM

As the world's oceans experience unprecedented rising temperatures, significant coral bleaching has been reported across the globe, according to experts.

On Monday, the National Oceanic and Atmospheric Administration (NOAA) reported the fourth global bleaching event on record and the second in the last 10 years.

"From February 2023 to April 2024, significant coral bleaching has been documented in both the Northern and Southern Hemispheres of each major ocean basin," Derek Manzello, Ph.D., NOAA CRW coordinator, said in a press release Monday.

A scuba diver checks coral reefs in the Red Sea off the southern Israeli resort city of Eilat on June 12, 2017.
Menahem Kahana/AFP via Getty Images, FILE

According to the National Ocean Service, warmer ocean temperatures can result in expulsion of algae that live in the coral tissue. This leaves the coral completely white, known as coral bleaching. Coral bleaching does not necessarily mean corals will die, according to NOAA, which noted that corals can recuperate if the strain on their ecosystems is reduced.

At a local level, storms, disease, sediments and changes in salinity can cause corals to bleach, however, mass bleaching, when several varieties of coral reefs are bleached, is largely caused by increased sea temperatures, according to the Australian Institute of Marine Science.

Last month, the average global sea surface temperature reached a record 69.93 degrees Fahrenheit, according to the Copernicus Climate Change Service.

This photo taken on Dec. 6, 2020 and released by Reef Explorer Fiji shows fish swimming through the coral on Fiji's Coral Coast.
Victor Bonito/REEF EXPLORER FIJI/AFP via Getty Images, FILE

Since early 2023, mass bleaching of coral reefs has been confirmed in the Atlantic, Pacific and Indian oceans, basins including parts of Florida and the U.S. Coastline, the Caribbean, Central America, South America, Australia, the South Pacific, the Persian Gulf, coasts of East Africa, as well as Indonesia, according to the NOAA report.

"As the world's oceans continue to warm, coral bleaching is becoming more frequent and severe," Manzello said. "When these events are sufficiently severe or prolonged, they can cause coral mortality, which hurts the people who depend on the coral reefs for their livelihoods."

Coral bleaching does not necessarily mean corals will die, according to NOAA, which noted that corals can recuperate if the strain on their ecosystems is reduced.

In 2019, NOAA and the National Academies of Sciences published the study Interventions to Increase the Resilience of Coral Reefs, which provided "resilience-based management practices" and heightened the importance of coral restoration.

Underwater photo of bleached corals on a coral reef in the Maldives.

"We are on the frontlines of coral reef research, management and restoration, and are actively and aggressively implementing the recommendations of the 2019 Interventions Report," Jennifer Koss, director of NOAA's Coral Reef Conservation Program (CRCP), said in the release.

In 2023, a heatwave in Florida spurred an "unprecedented" coral bleaching event in the region that "started earlier, lasted longer and was more severe than any previous event in that region," according to NOAA.

A buoy in Manatee Bay, Florida, reported an ocean temperature of 101.1 degrees in July 2023, according to meteorologists at the time.

In response, NOAA enacted the Iconic Reefs program to attempt to offset the effects of global climate change on the local coral reefs by moving coral nurseries to deeper, cooler waters and deploying sunshades to protect corals in other areas, according to NOAA.

This year's global coral bleaching event follows previous confirmed events in 1998, 2010 and 2014-2017, according to NOAA.

ABC News' Dan Peck contributed to this report