Worst Bleaching Event: Entire Southern Hemisphere Likely To Bleach This Year, NOAA Says

The United States' National Oceanic and Atmospheric Administration (NOAA), the body that monitors the risk of coral bleaching in the world, has warned that the entire Southern Hemisphere is probably going to bleach this year.

Worst Bleaching Event

For the previous nine months, the world has frequently broken land-based heat records. However, February broke a particularly worrying milestone for the ocean: average global sea surfaces reached the highest temperatures ever recorded for any month since at least 1979, according to the Copernicus Climate Change Service. 

NOAA said El Niño conditions and climate change are contributing to the world's fourth catastrophic coral bleaching disaster. 

"We are literally sitting on the cusp of the worst bleaching event in the history of the planet," said Derek Manzello, the coordinator of NOAA's Coral Reef Watch.

Following the world's hottest summer on record last year, the Caribbean had its worst documented bleaching episode. 

The last global bleaching happened between 2014 and 2017, when experts estimated that around 15% of all reefs had severe coral deaths. 

The bleaching killed nearly a third of the coral on the Great Barrier Reef.

In the Southern Hemisphere, where summer is closing and ocean temperatures are at or near their yearly high, there is literally bleaching all over the place.

Manzello pointed out that in order to declare a bleaching episode "global," scientists must examine coral in all three major oceans: the Atlantic, Pacific, and Indian.

Scientists utilize sea surface temperature data and satellite pictures of reefs to assess bleaching. Based on current research, Manzello believes the world is "already there."

Coral Bleaching

Corals form symbiotic relationships with small algae that live in their tissues; in exchange for this hardened home, the algae provide food to the coral via photosynthesis in their chlorophyll cells, which generate green and brown pigments. 

However, significant ocean warming can stress the coral to the point where they eject these symbiotes, depriving the coral of a vital food source and its brilliant colors.

This procedure does not necessarily kill coral, but it might impair their development and reproduction, leaving them susceptible to disease. 

As bleaching events become more frequent with less recovery time in between, the long-term outlook for the Great Barrier Reef is getting increasingly grim, according to Terry Hughes, a coral researcher at James Cook University in Australia.

"Reefs that bleached in 2017 or 2016 have had only five or six years to recover before being hit again this summer-assuming they escaped bleaching during  the 2020 and 2022 episodes," he added. 

Historically, bleaching events and other disturbances, such as ocean acidification, have devastated nearly half of the Great Barrier Reef's coral.

In 2022, a brief period of low heat allowed coral to grow and recover, and scientists recorded the highest levels of coral cover across two-thirds of the Great Barrier Reef in over 36 years. 

Scientists believe that the only way to avoid worst-case scenarios for coral reefs and the environment is to quickly transition from fossil fuels to renewable energy. 

Reducing land-based pollution and overfishing are also important for reef preservation.