Australia’s Great Barrier Reef has had five near-extinction events in the past 30,000 years, researchers said Monday.

And while this suggests the reef may be more resilient than once thought, it has likely never faced an onslaught quite as severe as today, they added.

“I have grave concerns about the ability of the reef in its current form to survive the pace of change caused by the many current stresses and those projected into the near future,” said Jody Webster of the University of Sydney, who co-authored a paper in the journal Nature Geoscience.

To conduct the study, scientists used underwater sonar to locate places on the sea floor where corals may have grown in the past. Then, they drilled 20 holes, extracting rock cores that contained fossil corals and sediments deposited over the past 30,000 years.That time period spans both the ice age and the modern era, providing a clear picture of how the reef responded to past climate changes.

The cores also contain evidence of the conditions that led to the episodic die-offs. Changes in sea level exerted the strongest influence on reef growth and demise, although species composition, reef location and water quality also played important roles.

During these swings, the reef faced death events, but survived the ups and downs by shifting and growing at different depths.

Today, though, with a faster changing climate, the Great Barrier Reef simply might not be able to keep up.

The reef “probably has not faced changes in sea surface temperature and acidification at such a rate,” Webster said. Rates of change “are likely much faster now — and in future projections.”

The World Heritage-listed site, which attracts millions of tourists, is reeling from successive bouts of coral bleaching due to warming sea temperatures linked to climate change.