Over the past 30,000 years, the Great Barrier Reef has come close to fully dying five times, according to a new report published in the scientific journal Nature Geoscience.

Two of the near-death experiences happened because falling sea levels exposed coral to air, and the other three events happened because rising sea levels caused sediment to blanket parts of the reef, blocking sunlight, according to Science Magazine.

Now the Great Barrier Reef is facing new threats that could wipe it out entirely, the report’s authors warn.

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"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," Jody Webster of the University of Sydney, who co-authored the paper, told AFP.

Rising ocean temperatures that cause bleaching events are the main threat against the reef today. Bleaching is when the organisms that feed coral and give it color are killed, turning it white.

Major bleaching events in both 2016 and 2017 destroyed large sections of the Great Barrier Reef. If more bleaching events occur over the next decade, the reef could lose its ability to recover.

The Great Barrier Reef is also being damaged by industrial pollution, invasive species, overfishing, plastic pollution, and ocean acidification, which is when oceans absorb too much carbon dioxide from fossil fuel emissions and then acidify.

Read More: 5 Coral Reefs That Are Dying Around the World

Unlike past catastrophic events, the reef is not being significantly affected by sea level rise, but that could change over the next century as glaciers melt, according to the team of researchers.

For the study, the scientists used sonar location to find where reefs may have once grown and then drilled 20 holes to find samples. They determined that the reef traveled extensively throughout the past 30,000 years as the sea level and other variables shifted.  

They argue that the data shows the reef is more resilient than previously thought, but that escalating stresses present a new category of risk.

"The [Great Barrier Reef] will probably die again in the next few thousand years anyway if it follows its past geological pattern," Webster told AFP.

Read More: Great Barrier Reef Is Half Dead — and Can Only Be Saved 1 Way

"But whether human-induced climate change will hasten that death remains to be seen,” she added.

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