Coral reefs are facing "mass extinction" as changing ocean currents continue to cause widespread bleaching events, a study has found.
The new study, published in the journal Oxford Open Climate Change by researchers at the Global Coral Reef Alliance, found that several major coral reefs around the world suffered extreme bleaching in 2023, suggesting that climate change is altering ocean circulations, exacerbating the effects.
"Coral reefs, the most vulnerable of all ecosystems, began to bleach and die from high temperatures starting in the 1980s," the paper's lead author and director of the Global Coral Reef Alliance, Thomas Goreau, said in a statement. "Most coral around the world has been killed, and survivors can't take more warming. The sudden rise in global temperature during 2023 further imperils coral reefs, and indicates large-scale changes in ocean circulation are underway, causing positive feedback that amplify global warming, which are not included in IPCC models."
Extreme temperatures across the world are the main cause of coral bleaching—a process that causes corals to become white, completely losing their once-vibrant colors. The process is brought about by stressors that take a huge toll on a coral's health. And as the world's climate warms, drastic temperature changes are occurring more regularly. Bleaching alone does not cause death, but it can increase the likelihood of it happening.
The new study focuses on 2023, which was the hottest year on record. Researchers identified coral reef bleaching hotspots, using ocean temperature data gathered from satellite observations.
They discovered that 2023 marked the worst-ever year for coral bleaching in the Northern Hemisphere. They also estimate that the Southern Hemisphere will see its worst year yet in 2024.
In 2023, widespread coral bleaching occurred across the Caribbean, the east and west coasts of Mexico, Central America, Kiribati, Fiji and Eastern New Guinea, the study showed. In these areas "near total bleaching and severe coral reef death" was reported.
The longest duration of extreme temperatures occurred in the area along "Haiti-Jamaica-Nicaragua-Honduras-Costa Rica," the study reported.
By looking at satellite sea surface data, they found that changes in temperatures were largely due to a shifting of ocean currents.
They reported that major warm currents continued to increase in temperature during 2023. This indicates that warm water coming from the tropics to colder regions has quickened as climate change worsens. While this keeps the topics cool, it is causing an excess of heat in polar regions, the study reported.
The potential mass extinction of coral reefs is hugely concerning, as they are vital to their ecosystems. They provide a home to native wildlife, and also protect shorelines from storms.
In many areas, they are also hugely beneficial to the economy, as with the famous Great Barrier Reef in Australia. One of the worst bleaching events was on Australia's Great Barrier Reef between 2016 to 2017, which caused bleaching across 91 percent of the reef.
Research like this new study helps scientists learn more about bleaching events, and how best to prevent it.
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