Five times in the history of life on Earth the corals have perished, swept from the board by conditions hostile to nearly all life. Each time, it has taken them millions of years to evolve anew. Each mass death of corals has been accompanied by the mass deaths of most other species, on land and at sea.

Corals are the traffic light that warns of planet-wide catastrophe ahead. And the light is glaring red.

Like the wildfires searing the world’s forests and grasslands, like the vanishing of insects, birds and large mammals the corals are another unambiguous signal that humans are riding a runaway train to our own ultimate destruction. Yet our fossil-fuelled governments and corporations heap coals into the engine, keep down their heads and deliberately ignore onrushing disaster.

That the sixth Great Death of corals is now upon us is plain from the evidence piling up around the world. The US National Oceanic and Atmospheric Administration’s Coral Reef Watch has warned the world is now in its fourth global cycle of bleaching since 1998 – an ominous crescendo.[1]

Coral bleaching has been reported in reefs extending across Florida, the Caribbean, Brazil, the south Pacific, the Middle East, west Indonesia and East Africa. Australia’s Great Barrier Reef is undergoing its fifth mass bleaching event in eight years with over 80% of the reef hit by bleaching-level heat stress in 2024, the highest ever seen. [2]

NOAA’s Coral Reef Watch uses satellites to monitor ocean temperatures on the world’s reefs

The data spell disaster for humanity in both the short and the long term. Coral reefs are estimated to generate around US$9.8 trillion in economic activity annually from fishing, tourism and ecosystem services. They support around 500 million livelihoods in 100 countries around the planet and supply a significant part of the world’s food. Their loss would be the economic equivalent of losing three world car industries. Yet most governments and corporates are accelerating it.

Additionally, coral reefs provide barrier protection for many heavily-populated coastlines which will be exposed to major flooding from storms, tsunamis and sea level rise as the reefs break up. Corals also absorb a significant amount of atmospheric carbon dioxide – and their loss eliminates an important brake on global heating, projecting the Earth more rapidly into a Hothouse state where large animals and humans struggle to survive.

As in the previous five events, the loss of corals heralds extinction on a global scale.  

Corals first emerged around 542 million years ago in the oceans of the Precambrian era. Over the next half billion years they underwent five major extinction events, followed by long lags of 5 to 20 million years before they managed to evolve anew. Ancient species, such as the once-plentiful rugose corals, were wiped out in the Great Death of the Permian era, and remain lost forever.

Corals are not a single creature, but a partnership between the coral polyps and their symbiotic zooxanthellae, from which they obtain most of their nutrient energy. When this partnership is severed – by hot, toxic, anoxic or acidic sea water or disease – the coral expel the algae and blanch. Unless the algae rapidly reoccupy them, the coral polyps starve and die and the whole colony perishes, leaving only the whitened skeletons of ‘hard corals’ in the graveyards photographed by wondering tourists, blind to the tragedy unfolding before their very eyes.

Coral colonies also sustain a host of other life, including fishes, molluscs and sea plants, creating living marvels such as the Great Barrier Reef. Their loss is thus accompanied by the loss of thousands of other species, and travels all the way up the food chain reaching even birds and land animals, including humans.

It is the very fraility of the bond between the coral polyps and their zooxanthellae that renders them such a vital signaller of thermal and chemical disaster in the oceans – and thus, on the planet as a whole. They are not ‘just corals’, as so many scientifically-illiterate politicians, media and ‘opinion influencers’ seem to regard them. They are the premonition of global catastrophe.

The warning was made clear in 2008 by Australian coral reef scientist Dr Charlie Veron in his book “A Reef In Time: The Great Barrier Reef from Beginning to End” in which he charted the rise and likely fate of the world’s largest coral reef system over the past 25 million years. Veron is appalled at the failure of successive government to act. “Public uncertainty, in combination with pressure from groups with vested interests, has prolonged government inaction… and this delay is already having far-reaching consequences. The Great Barrier Reef will be among the first in a long line of dominoes to fall,” he said.[3]

The last two major coral extinctions, the K/T (65my ago, when the dinosaurs disappeared) and the Toarcian (180my ago) took out over 90 per cent of coral species. [4]

Scientists are concerned that, thanks to human agency, chemically polluting both atmosphere and oceans, a sixth has now been triggered. One that will affect our own chances of survival on a habitable planet.

Professor Ove Hoegh-Guldberg, a pioneer of coral research who was among the first to link bleaching to global heating, told The Guardian: “It’s a shock. We clearly have to prevent governments from investing in fossil fuels, or we won’t have a chance in hell [to save reefs].”

And Professor Terry Hughes has waged a one-man campaign on Twitter (or X) condemning successive Australian governments for their disinformation about the state of the reef, while they consistently approve new fossil energy developments that will speed its demise. [5]

These informed voices go unheeded as the crisis unfolds. The corals are telling us our time on Earth may well be up, if we do not heed the warnings they provide. They pose an even more profound question: are human still intelligent enough to survive… or not? 

Ends

Julian Cribb AM is an Australian science writer and author of six books on the human existential emergency. His latest book is “How to Fix a Broken Planet” (Cambridge University Press, 2023).

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[1] https://www.noaa.gov/news-release/noaa-confirms-4th-global-coral-bleaching-event

[2] https://x.com/ProfTerryHughes/status/1780350823509196836

[3] https://www.themonthly.com.au/issue/2008/may/1315812848/julian-cribb/committed#mtr

[4] https://www.sciencedirect.com/science/article/abs/pii/S0921818121002320

[5] https://twitter.com/ProfTerryHughes