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The world's largest coral bleaching event is now underway

Coral reefs around the globe are currently suffering through a significant bleaching event, a consequence of unprecedented ocean heat levels driven by the climate crisis. 

According to a joint statement by the National Oceanic and Atmospheric Administration (NOAA) and the International Coral Reef Initiative (ICRI), over half of the world’s coral reef areas are affected. 

Unprecedented coral bleaching

With extensive bleaching impacting at least 53 countries across various oceans, this event could mark the most severe coral bleaching event in recorded history.

“It is likely that this event will surpass the previous peak of 56.1% soon,” said Derek Manzello, the coordinator for NOAA’s Coral Reef Watch program. “The percentage of reef areas experiencing bleaching-level heat stress has been increasing by roughly 1% per week.”

Bleaching deprives corals of their energy source

Coral bleaching occurs when corals, stressed by elevated water temperatures, expel the symbiotic algae living within their tissues. These algae not only give corals their vibrant colors but also transfer a large part of their energy through photosynthesis. 

Without the algae, the corals lose their coloration, turning stark white, while being deprived of an essential energy source, leading to weakened health and potentially mass mortality if conditions do not improve.

World’s fourth bleaching event on record

This event is the world’s fourth documented global bleaching event, following previous occurrences in 1998, 2010, and from 2014-2017. Over the past year, regions experiencing significant bleaching include vast areas such as Florida, the wider Caribbean, Mexico, Brazil, Australia, the South Pacific, the Red Sea, the Persian Gulf, Indonesia, and the Indian Ocean, encompassing locations like the east coast of Africa and the Seychelles.

Researchers at the Center for Island Research and Environmental Observatory (CRIOBE) are diligently studying coral ecosystems to develop strategies for resilience. Under the guidance of PhD student Laetitia Hédouin, these teams are identifying and genetically analyzing corals that exhibit resistance to thermal stress. These corals are then grown in coral nurseries to study their resilience capabilities in comparison to other colonies.

Record ocean heat

Professor Ove Hoegh-Guldberg, a renowned climate scientist specializing in coral reefs at the University of Queensland, had predicted this mass bleaching event months in advance. 

“We knew sea temperatures were increasing rapidly, but not at this speed. The worrying issue is that we don’t know how long this massive temperature change is likely to last,” said Professor Hoegh-Guldberg.

Recent records have shown that the last 12 months have been the warmest in recorded history, with ocean temperatures reaching new highs. Data from the European Commission’s Copernicus Climate Change Service confirmed record-high global sea surface temperatures for February and March. 

Coral bleaching alert maps

In response to the escalating threat, scientists at NOAA’s Coral Reef Watch program have introduced three new alert levels on their coral bleaching alert maps to better monitor and assess the scale of underwater warming.

The arrival of La Niña 

Looking forward, the potential arrival of La Niña between June and August could offer some relief. This cooler climate phase might help reduce ocean temperatures, providing a respite for the beleaguered reefs. 

However, Manzello warned that, despite potential cooling, past La Niña years have still experienced bleaching events. He voiced specific concerns for the reefs around Florida and the Caribbean as the summer approaches, highlighting the vulnerability of these areas to even slight increases in seasonal warming.

Australia’s Great Barrier Reef

The dire situation of coral reefs is further highlighted by extensive bleaching on Australia’s Great Barrier Reef, the world’s largest coral reef system. 

Following aerial and underwater surveys, a mass bleaching event was officially confirmed by the Australian Institute of Marine Science (AIMS) and the Great Barrier Reef Marine Park Authority.

Climate change is the primary threat to coral reefs

“The increasing frequency and extremity of marine heatwaves driven by climate change, is testing the tolerance levels of coral reefs,” said Selina Stead, the CEO of AIMS. 

“Climate change is the biggest threat to coral reefs worldwide and this global confirmation illustrates just how extensive its impact has been across the last 12 months.That is why it is critical the world works to reduce carbon emissions. It is also important to ensure coral reefs are well managed at local and regional levels.”

The UN Environment Programme has issued a stark warning: without significant reductions in emissions, the planet is on track to experience nearly 3 degrees Celsius of warming above pre-industrial levels within this century. This escalation in temperature poses a dire threat to global ecosystems, particularly coral reefs.

Scientists have projected that with a 2-degree Celsius increase in global temperatures – a threshold that could be reached by 2050 – about 99% of coral reefs worldwide are expected to perish. The loss of these reefs would be catastrophic, not only for marine biodiversity but also for human communities. 

Coral reefs are in critical condition 

Coral reefs are crucial habitats for marine life, while also providing essential services to people. They buffer coastal areas against flooding from storms and rising sea levels and are fundamental to the livelihoods and food security of approximately a billion people around the world.

David Ritter, CEO of Greenpeace Australia, emphasized the critical condition of these marine ecosystems, arguing that reefs are confronting an “existential danger.” He pointedly blamed “the main culprits fueling global warming: fossil fuel companies, and the governments who prop up this industry.”

“We are running out of runway to avoid irreversible climate disaster and must act quickly to ensure an immediate end to new fossil fuels,” he concluded.


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