Ocean temperatures in Australia’s Great Barrier Reef now hottest in 400 years: What a new study says

Here is a look at the findings.

First, what are coral reefs?

Corals are essentially animals, which are sessile, meaning they permanently attach themselves to the ocean floor. They use their tiny tentacle-like hands to catch food from the water and sweep it into their mouth. Each individual coral animal is known as a polyp and it lives in groups of hundreds to thousands of genetically identical polyps that form a ‘colony’.

Corals are largely classified as either hard coral or soft coral. It is the hard corals that are the architects of coral reefs — complex three-dimensional structures built up over thousands of years. “Unlike soft corals, hard corals have stony skeletons made out of limestone that are produced by coral polyps. When polyps die, their skeletons are left behind and used as foundations for new polyps,” according to NOAA.

Coral reefs, also referred to as “rainforests of the sea”, have existed on the Earth for nearly 450 million years.

Why are coral reefs important?

Coral reefs have a crucial role in marine ecosystems. Thousands of marine species can be found living on one reef. For instance, “the Great Barrier Reef contains over 400 coral species, 1,500 fish species, 4,000 mollusc species and six of the world’s seven sea turtle species”, according to a report by the Natural History Museum. Research has shown that there could be millions of undiscovered species of organisms living in and around reefs.

These massive structures also provide economic goods and services worth about $375 billion each year. More than 500 million people across the world depend on coral reefs for food, income and coastal protection from storms and floods. Coral reefs can absorb up to 97% of the energy from waves, storms, and floods, which prevents loss of life, property damage, and soil erosion.

What are the findings of the study?

A group of scientists at universities across Australia drilled cores into the coral and, much like counting the rings on a tree, analysed the samples to measure summer ocean temperatures going back to 1618.

Combined with ship and satellite data going back around a hundred years, the results show ocean temperatures that were stable for hundreds of years began to rise from 1900 onwards as a result of human influence, the research concluded.

From 1960 to 2024, the study’s authors observed an average annual warming from January to March of 0.12 degree Celsius per decade.

Since 2016, the Great Barrier Reef has experienced five summers of mass coral bleaching, when large sections of the reef turn white due to heat stress, putting them at greater risk of death.

These summers were during five of the six warmest years in the last four centuries, the study showed.

“The world is losing one of its icons,” said Benjamin Henley, an academic at the University of Melbourne and one of the study’s co-authors. “I find that to be an absolute tragedy. It’s hard to understand how that can happen on our watch in our lifetime. So it’s very, very sad.”

The last temperature data point, from January to March of this year, was the highest on record and “head and shoulders” above any other year, Henley said.

(With inputs from Reuters)