‘Unprecedented mass coral bleaching’ expected in 2024, says expert | Coral

Record-breaking land and sea temperatures, driven by climate collapse, are likely to cause “unprecedented mass coral bleaching and mortality” through 2024, according to a pioneering coral scientist.

The impact of climate change on coral reefs has reached “uncharted territory”. Prof Ove Hoegh-Guldbergfrom the University of Queensland, Australia, leading to concerns that we may be at a “tipping point”.

The upper ocean is undergoing unprecedented changes in conditions, ecosystems and communities that can be traced back to the 1980s, when mass coral bleaching first appeared. In a paper published in the journal ScienceUS and Australian researchers say that historical data on sea surface temperatures, spanning four decades, suggest that this year’s extreme marine heatwaves could be a precursor to a mass bleaching and coral mortality event across the Indo-Pacific in 2024-25.

Mass coral bleaching occurs when delicate corals are stressed due to factors including heat, causing them to lose their brown microbial algae and turn them white. At low stress levels, the algae can return to corals in a few months. But a lot Caribbean Islands reef areas recently experienced historically high sea temperatures that started one or two months earlier and lasted longer than usual.

Crucially, 2023 is the first year of a potential pair of El Niño years, with the warmest average February to July global sea surface temperature on record. Since 1997, each occurrence of these El Niño pairs has resulted in a global mass coral bleaching event.

Hoegh-Guldberg, whose work helped shape the world’s understanding of the risks to the ocean’s richest ecosystems, said: “The likelihood is that sometime in the next 12 to 24 months we will see El Niño combine with warm ocean temperatures and have a very large impact.

“We are literally in uncharted territory, which we know very little about and don’t know how to respond to and I think we are dangerously exposed.”

“We don’t know what the implications of such an increase in temperature are,” the scientist said from Dubai, where he Police 28 climate summit. “We may see storms that are even bigger than the ones we’ve seen. These are the hottest temperatures ever on land and sea.”

Hoegh-Guldberg added: “If it’s going to be ‘summers from hell’ type of thing, many of us fear that it could be a tipping point that we’re past, meaning we can’t come back. We do not know what the implications of such a rise in temperature are.”

Mass bleaching and coral mortality events in the Indo-Pacific, which will lead to long-term damage to ecosystems and the millions of people in Earth’s tropical regions who depend on them, could worsen unless greenhouse gas emissions are reduced, he said.

The small brown algae that live in coral are very sensitive to temperature changes. “Just like us, as humans, there is a set temperature at which we feel good. But then one or two temperatures above that, and you’re dead. This is on a planetary scale. It’s a shock.”

Earth experienced its hottest day since 1910 in July 2023, as well as its warmest month for upper sea temperatures.

Hoegh-Guldberg said: “What we do know, from 40 years of history, is that there is a very strong, close relationship between this amount of energy in the system and the violence of storms and the impact on biological systems. It is very well established.”

As coral reefs bleach and die, the habitats that many associated reef species depend on disappear, leading to ecosystem collapse. This could undermine as much as 25% of marine biodiversity, say the researchers.

He urged policymakers and world leaders to “move faster and with more determination than ever before” to reduce greenhouse gas emissions and to “trust the science” to guide us.

“This is a science-based engineering problem,” Hoegh-Guldberg said. “We have to set the parameters. We need to define the way our planet works and do it in record time. Because we have resources, we can do it. But we have to be smart and involve everyone. And make sure we get a system that’s going to cool the planet for a while, or at least not increase for a while.”