Drilling a coral skeletal core on the Great Barrier Ree. Credit: Anne Hoggett, Lizard Island Research Station, Copyright holder: Tom DeCarlo. Used with permission.
The
Great Barrier Reef is under critical pressure, with warming sea temperatures
and mass coral bleaching events threatening to destroy the remarkable
ecology, biodiversity, and beauty of the world's largest coral reef, according
to new research.
"Highest ocean heat in four
centuries places Great Barrier Reef in danger," published in Nature 8
August, led by University of Wollongong (UOW) Honorary Fellow and University of
Melbourne Lecturer Dr. Benjamin Henley, provides evidence of the impact that
rising sea surface temperatures have had, and will continue to have, on
Australia's ecological jewel.
The research reconstructs 400 years of
summer sea surface temperatures in the Coral Sea. The results chronicle extreme
recent ocean heat that has led to mass coral bleaching on the Great Barrier
Reef.
UNESCO's World Heritage Committee
recently handed down its final decision on the state of the Great Barrier Reef,
declining to list the Reef as in danger. However, the scientists have pushed
back and say, based on their new evidence, the Great Barrier Reef is absolutely
in danger.
Removing a skeletal core from a coral colony in
the Coral Sea. Credit: Tom DeCarlo, Tulane University
Dr. Henley and his team combined
sea surface temperature reconstructions using geochemical data from coral cores
previously collected from the region. They also analyzed climate model
simulations of sea surface temperatures, run with and without climate change,
finding that human-caused climate change is to blame for the rising
temperatures in the region.
The recent mass bleaching events
coincide with five of the six hottest years in the new 400-year-long record. In
the years 2024, 2017 and 2020, the Coral Sea reached 400-year highs, with 2024
being the warmest on record by a large margin.
The recent heat events in 2016,
2004, and 2022, were the next warmest three years on record. The impact on the
Great Barrier Reef's unparalleled ecology and biodiversity over repeated
sequences of mass coral bleaching is devastating.
"When I plotted the 2024 data
point, I had to triple check my calculations—it was off the charts—far above
the previous record high in 2017. I could almost not believe it. Tragically,
mass coral bleaching has occurred yet again this year," Dr. Henley said.
"In the absence of rapid,
coordinated and ambitious global action to combat climate change, we will
likely witness the demise of one of Earth's most spectacular natural wonders.
"When you compile all of the
evidence we have, it's the inevitability of the impacts on the reef in the coming years that really gets to
me."
Professor Helen McGregor, from
UOW's Environmental Futures, who is the second author of the study, said urgent action is needed to prevent devastation of one of the
world's most important ecosystems.
"There is no 'if, but or
maybe'—the ocean temperatures during these bleaching events are unprecedented
in the past four centuries."
"The Great Barrier Reef is
facing catastrophe if anthropogenic climate
change is not
immediately addressed. The very corals that have lived for hundreds of years
and that gave us the data for our study are themselves under serious
threat," Professor McGregor said.
"Our climate model analysis
confirms that human influence on the climate system is responsible for the
rapid warming in recent decades," said Dr. Henley, who undertook most of
the study as a post-doctoral researcher at UOW, where he is now an Honorary
Fellow.
"Without urgent intervention,
our iconic Great Barrier Reef is at risk of near-annual bleaching from high
ocean temperatures. The Reef's fundamental ecological integrity and outstanding
universal value are at stake.
"We have many of the key
solutions to stop climate change; what we need is a step change in the level of
coordinated national and international action to transition to net zero.
"We can never lose hope. Every
fraction of a degree of warming we avoid will lead to a better future for the
human and natural systems of our planet.
"We hope that our study equips
policymakers with more evidence to pursue deeper cuts in greenhouse gas
emissions internationally."
Coral bleaching occurs when stress
causes the corals to expel the algae that live in their tissue. The algae give
corals their vibrant colors and without them the coral's white skeleton is
exposed.
Stress from environmental
disturbances and declining water quality can lead to bleaching, but recent warming
in sea temperatures has led to bleaching on a mass scale. Corals can
recover from bleaching events if the stress trigger, such as extreme ocean
warming, is reduced for a significant period. The reef has experienced five
major mass coral bleaching events since 2016.
While the Great Barrier Reef is the
world's largest coral reef system, the groundbreaking research has implications
for coral reef systems throughout the world, highlighting the link between the
long-term trajectory of extreme ocean temperatures and the ecological health
and biodiversity of these complex and crucial ecosystems.
Researchers from Securing Antarctic's Environmental Future, UOW, University of Melbourne, The University of Queensland, the Australian Institute of Marine Science, Tulane University (U.S.), and Columbia University (U.S.) contributed to the paper.
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