Great Barrier Reef waters were hottest in 400 years over the past decade, study finds

WASHINGTON (AP) — Ocean temperatures in the Great Barrier Reef hit their highest level in 400 years over the past decade, according to researchers who warned that the reef likely won’t survive if planetary warming isn’t stopped.

During that time, between 2016 and 2024, the Great Barrier Reef, the world’s largest coral reef ecosystem and one of the most biodiverse, suffered mass coral bleaching events. That’s when water temperatures get too hot and coral expel the algae that provide them with color and food, and sometimes die. Earlier this year, aerial surveys of over 300 reefs in the system off Australia’s northeast coast found bleaching in shallow water areas spanning two-thirds of the reef, according to Great Barrier Reef Marine Park Authority.

Researchers from Melbourne University and other universities in Australia, in a paper published Wednesday in the journal Nature, were able to compare recent ocean temperatures to historical ones by using coral skeleton samples from the Coral Sea to reconstruct sea surface temperature data from 1618 to 1995. They coupled that with sea surface temperature data from 1900 to 2024.

They observed largely stable temperatures before 1900, and steady warming from January to March from 1960 to 2024. And during five years of coral bleaching in the past decade — during 2016, 2017, 2020, 2022 and 2024 — temperatures in January and March were significantly higher than anything dating back to 1618, researchers found. They used climate models to attribute the warming rate after 1900 to human-caused climate change. The only other year nearly as warm as the mass bleaching years of the past decade was 2004.

“The reef is in danger and if we don’t divert from our current course, our generation will