The world’s coral reefs are undergoing a fourth mass die-off, driven by rapidly accelerating global heating. As Julian Cribb explains, the science is clear – and the political failure to respond is not defensible.

The corals of the world are telling us something that most government and politicians – whether through corruption, fear or impenetrable ignorance – are unwilling to divulge: our planet is now heating at catastrophic rates.

“Before the 1980s, mass coral bleaching and mortality events due to heat stress were rare. In the last four decades, these events have become increasingly frequent and severe. Ocean warming is now the foremost threat to coral reefs worldwide,” says an international team of scientists, after completing the most extensive survey of the world’s coral reefs ever.

The world is currently in the grip of the fourth great coral die-off of modern times. Researchers at NOAA’s Coral Reef Watch unit are tracking killer ocean temperatures at fine scale and in real time. They have recently completed an exhaustive study of the third great coral wipe-out, which took place between 2014-2017, when 80 per cent of the world’s corals bleached and 35 per cent died. As the planet heats, they fear the current episode may prove worse.

Corals are formed from a delicate partnership between the reef-building coral animals and their symbiotic algae – zooxanthellae – which feed them. When water temperatures rise above 32 degrees C, the partnership breaks down, the algae depart and the corals die unless cooler water quickly brings them fresh algae to nourish them. Demonstrably, the algae know things about the Earth’s changing climate that most politicians do not, or else pretend not to. They are a glaring red........

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