Updated Apr 15, 2024 - Energy & Environment

World's fourth global coral bleaching event is underway, NOAA says

Bleached corals in the waters of Raja Ampat Regency in east Indonesia's West Papua region in 2023.

Bleached corals in the waters of Raja Ampat Regency in east Indonesia's West Papua region in 2023. Photo: Lillian Suwanrumpha/AFP via Getty Image

Coral reefs around the world are experiencing a "significant" bleaching event driven by record-breaking ocean heat from human-caused climate change, the National Ocean and Atmospheric Administration (NOAA) warned on Monday.

Why it matters: It's the fourth global bleaching event on record, and the second in the last decade. Bleaching threatens the reefs, which are vital harbors for marine biodiversity and major drivers of fishing and tourism revenue for countries across the globe.

  • The previous bleaching events were recorded in 1998, 2010 and between 2014 to 2017.

Threat level: NOAA and the International Coral Reef Initiative (ICRI) said bleaching has been documented in at least 53 countries, territories and local economies in both hemispheres since early 2023.

  • Derek Manzello, NOAA's Coral Reef Watch coordinator, told Axios' Andrew Freedman that 54% world's coral area has experienced bleaching-level heat stress over the last year.
  • He said that figure is growing by roughly 1% every week and that the current bleaching event could become the largest on record if it surpasses the previous peak of 56.1%.

What they're saying: "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," Manzello added.

How it works: Bleaching occurs when coral stressed from environmental changes loses the photosynthetic algae, or zooxanthellae, they need to survive.

  • Bleached corals are more vulnerable to disease and mortality, per NOAA.
  • Coral faces an elevated risk of starvation and disease while bleached but can survive if conditions quickly return to normal. If not, mass coral deaths are likely to occur, leading to the potential collapse of entire reef ecosystems.
  • Mass events are defined as significant bleaching being recorded in all three ocean basins that host coral reefs — the Pacific, Indian and Atlantic — within a year.

The big picture: NOAA warned last month marine heatwaves are expected to continue to bleach coral around the world.

  • Australia's Great Barrier Reef, the world's largest coral reef ecosystem, could be among the areas hardest hit, the agency said at the time.
  • ICRI said the current widespread coral bleaching event across the Great Barrier Reef is the fifth mass event the reef has suffered in the last decade and the seventh on record.
  • The coral in the Florida Keys were extensively damaged from a long-lasting and severe marine heat wave last year even after NOAA and other organizations went to extraordinary lengths to save them.

Go deeper: Earth has its warmest March on record, beating 2023's milestone

Editor's note: This story was updated with additional context.

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