Only 2% Of Great Barrier Reef Has Escaped Coral Bleaching, Study Finds

Reef scientists have called for urgent action on climate change or humanity could have a very different underwater world by midcentury.

The Great Barrier Reef has been walloped by warming seas time and time again, and scientists now say almost the entire span of the natural wonder has been hit with coral bleaching in recent years, a troubling figure that amplifies the warning bells about the effects of climate change happening right now.

A new study, published Friday in the journal Current Biology, found just 2% of the Great Barrier Reef has escaped bleaching over the past 30 years. The first major mass bleaching in 1998 prompted dire warnings from coral biologists, who said warming seas amounted to an underwater apocalypse for delicate coral ecosystems.

But climate change has since continued largely unabated, and professor Terry Hughes, a lead author of the report and the director of the ARC Centre of Excellence for Coral Reef Studies, said bleaching events that used to be “unprecedented or very rare” are now commonplace.

“Five bouts of mass bleaching since 1998 have turned the Great Barrier Reef into a checkerboard of reefs with very different recent histories, ranging from 2% of reefs that have escaped bleaching altogether, to 80% that have now bleached severely at least once since 2016,” Hughes said in a statement.

That 98% of the reef has been hit with calamitous bleaching is significant. The Great Barrier Reef is the largest living structure on the planet, stretching nearly 1,500 miles and comprising more than 3,000 individual reefs.

In this undated photo provided by the Great Barrier Reef Marine Park Authority, Hardy Reef, part of the Great Barrier Reef, is viewed off the coast of Australia.
In this undated photo provided by the Great Barrier Reef Marine Park Authority, Hardy Reef, part of the Great Barrier Reef, is viewed off the coast of Australia.
Jumbo Aerial Photography/Great Barrier Reef Marine Park Authority via Associated Press

The study adds that bleaching events need to be considered as a series of ailments rather than one-off catastrophes to determine how corals can recover over time. Interestingly, the authors found that areas of the Great Barrier Reef that were hit with a mass bleaching event before were more tolerant to future stressors, while the most vulnerable reefs were those that hadn’t been suffered bleaching in recent years.

The accumulation of bleaching events over several decades “highlights the grave risk that without immediate global action on greenhouse gas emissions, more frequent and more severe bleaching events will continue to undermine the resilience of coral reef ecosystems,” the authors said.

Corals are particularly vulnerable to climate change. Warmer waters linked to the phenomenon can effectively cook the delicate structures, causing reefs to bleach as the once-colorful polyps turn bone white when the algae that feeds them leave their skeletons. If temperatures return to normal, the corals can recover over time, but if waters stay warm for too long, stretches of reefs that took decades to grow can die.

Bleached reefs can recover, but it takes years. Scientists have long warned that back-to-back mass bleaching events, like those in 2016, 2017 and 2020, don’t give corals enough time to heal.

Reef fish swim above recovering coral colonies on the Great Barrier Reef off the coast of Cairns, Australia, in 2019.
Reef fish swim above recovering coral colonies on the Great Barrier Reef off the coast of Cairns, Australia, in 2019.
Lucas Jackson/Reuters

The forecast for the planet’s corals is bleak. A recent report found the world lost 14% of its corals from 2009 to 2018 due to heat waves linked to climate change. That figure is huge, effectively amounting to about 4,500 square miles of reef, or more than all of the living coral off the cost of Australia, including the Great Barrier.

The latest study comes amid the United Nations climate summit, COP26, in Glasgow, Scotland, where world leaders and dignitaries are attempting to hash out the planet’s best hope for averting the worst effects of climate change.

Hughes said Friday that how reefs like the Great Barrier fare depends on humanity getting its act together to limit greenhouse gas emissions, although he stressed there is still time for the world to act. Australia, however, has largely refused to sign on to pledges to abandon coal mining and limit methane emissions, instead releasing vague plans to rein in emissions by 2050s that have been lambasted by scientists.

“Where the reef ends up depends on how much warmer it gets,” he told The Guardian. “If we stabilize at 1.5 degrees [Celsius], which is unlikely, the reef might be OK. … While we are not going to see the Great Barrier Reef like it was 20 years ago, we can still have a reef if countries can reduce greenhouse gas emissions in the next decade.”