Is the Great Barrier Reef resilient or at risk?

Australia’s Great Barrier Reef is in imminent danger from climate change. Or is it?

Recent studies on the health of this wonder of the world, the largest coral reef system in the world, suggest that the impacts climate change will likely have on the reef aren’t fully understood.

Scientists agree that global warming is a serious threat to the Great Barrier Reef.

Rising ocean water temperatures are known to be causing more severe coral bleaching episodes. The GBR has experienced several mass coral bleaching events in recent years, including one last year.

At the same time, the extent of coral cover at the GBR has expanded in some areas. And there are signs that some species of coral may be able to withstand the changing conditions fairly well.

Mike Emslie, Principal Research Scientist at the Australian Institute of Marine Science, acknowledged the uncertainty in the Great Barrier Reef’s outlook.

“People with different agendas will tell you different stories about the state of the Great Barri Reef,” Emslie explained in an interview with Public Parks. “But it’s not black and white and it is somewhere in the middle there.”

Contrasting research

GBR experts admit that it’s a mixed picture—warming ocean temperatures threaten the reef’s health, while many scientists are discovering that certain coral species that call the GBR home are probably fairly capable of withstanding the onslaught for some time.

Two different recent studies reflect these differences in perspectives.

Late last year, researchers at Australia’s University of Queensland and Newcastle University in the United Kingdom published a study in the journal Science warning that Pacific Ocean reef systems like the GBR are “unlikely to keep up” with changes brought by global warming.

The research team ran modeling that showed climate change leading to localized extinctions of some vulnerable coral species. Modeling that showed even moderate global warming caused by greenhouse gas emissions showed seriously negative repercussions for some corals.

“Our modeling for this moderate emissions scenario shows we would expect to see profound reductions in reef health and an elevated risk of local extinction for thermally sensitive coral species,” Dr. Liam Lachs of Newcastle University said in an overview.

The modeling was based on a Palau reef system, but the findings applied to Pacific Ocean coral in general.

At the same time, the authors of this study were careful to admit that there are plenty of unknowns. “We acknowledge that considerable uncertainty remains in the ‘evolvability’ of coral populations,” Lachs clarified in his report.

Then there’s the contrasting view.

A study issued earlier this year by another team, led by scholars from Queensland University and the Commonwealth Scientific and Industrial Research Organization (CSIRO), argued that predictions on the extent of coral bleaching at the GBR in the future are likely overblown. That take was published in the journal Nature Geoscience.

By changing the way future heat stress is measured, those researchers found it was possible that surviving coral colonies could be double what other methodologies found in estimating Great Barrier Reef coral bleaching trends from 2030 to 2050.

Emslie told Public Parks that it’s not unusual for two different GBR-related studies to reach such separate conclusions. The difference, he said, is subtle but important.

Emslie said multiple analyses of climate change’s impact on the Great Barrier Reef find that the system might prove fairly resilient in the short- to near-term. The concern is the longer-term impacts that global warming will have, he said.

Resilience at the Great Barrier Reef means “you can absorb the impacts of disturbances, maintain all the necessary ecological functions, and then recover to the state that you were prior to the disturbance,” he said.

“At the moment, yes, the GBR has the ability to do all of that,” Emslie added. “It is resilient, it is bouncing back. But its continued ability to do so must be seriously questioned at this point.”

Fish and coral migrations

Research that Emslie worked on discovered that the composition of fish colonies at certain parts of the Great Barrier Reef was changing due to climate change.

Just as studies found tropical fish are starting to migrate to higher latitudes in the Northern Hemisphere, Emslie and his colleagues found that fish colonies are shifting their GBR ranges. These changes are likely being driven by how different species of coral are migrating across the GBR system due to changes in ocean temperatures.

Emslie said the change is being driven by where certain species of coral are moving to and/or concentrating.

“The biggest changes that we’ve seen in the diversity of reef fishes on the GBR are due to changes in the coral assemblages following these disturbances,” he said.

Great diversity in coral colonies remains. But the degree to which certain species are concentrated in certain areas is changing, and this is driving the changes they’re seeing in fish colony compositions, Emslie told us.

“Something the size of the GBR, it’s quite complex, so there’s a lot of change going on but it’s different in different places,” he said. “The diversity of corals is still there, it’s just that the composition of them has changed through time.”

A report issued just a month ago warned of catastrophic levels of coral bleaching at the Great Barrier Reef. The team behind that report assessed the impact of a mass bleaching event that happened in early 2024.

Heritage in danger

Determining the extent to which global warming threatens the Great Barrier Reef is important.

The Great Barrier Reef was designated a Natural World Heritage Site by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) in 1981.

UNESCO is now threatening to slap a dreaded “World Heritage Site in Danger” label on the GBR. Australia strongly opposes the move, fearing that it could potentially harm tourism to the Great Barrier Reef.

Australia’s government has convinced UNESCO to hold off for now.

The Australian Institute of Marine Science (AIMS) gathers data that will inform the UNESCO decision. Thus, Emslie declined to take a position on this question.

The Australian government is expected to present to UNESCO a Reef 2050 Water Quality Improvement Plan this year. The draft document is to outline a strategy for addressing runoff from the Australian continent that’s thought to be contaminating portions of the GBR.

A general reef protection progress report was supposed to be handed to UNESCO at the beginning of this month. Then an overarching “state of conservation” report is expected to be turned in by February 1, 2026.

At that point, UNESCO says it will consider proposals to downgrade the Great Barrier Reef’s World Heritage status again.