A major new study looking at 30,000 years of the Great Barrier Reef’s history shows the world’s largest living structure to be especially resilient. But scientists aren’t sure if that strength in the past can be called upon for today’s climate change challenges.
Using data collected from 16 points across the reef over a period of 10 years, the study found what the scientists call five separate “death events” from which the Reef bounced back. However, the latest man-made conditions are unique in the reef’s history.
The first of these incidents dates back to an event 20,000 years ago known as the Last Glacial Maximum (LGM). The Earth was a mostly cold and dry place during this period of history, when the world’s glaciers were at their greatest. With so much ice, the world’s oceans dramatically shrank—sea levels were 387 feet (118 meters) below where they currently sit.
The water got so low that the reef’s coral became exposed to the open air, meaning they got hit with increased solar radiation, changes in temperature from day to night and even an influx of freshwater through rain. It all adds up to an effect called subaerial exposure that rapidly leads to coral bleaching.
Massive subaerial exposure has happened a couple of times in the reef’s history. During another occurrence 22,000 years ago, the reef responded to this existential threat by moving further into the sea. While coral died en masse through these sub aerial exposures, the Great Barrier Reef as a whole is able to move laterally at between 7.87 inches (0.2 meters) and almost 5 feet (1.5 meters) a year.
The Reef struggled with period of rapid deglaciation 17,000 and 13,000 years ago, respectively. Getting too deep into the ocean can increase the amount of carbon dioxide the coral is taking in, which can also lead to mass bleaching. Just as the Reef moved into the ocean, it responded to the deglaciation by lurching itself closer to the land.
The last of these death events occurred 10,000 years ago and had nothing to do with glaciers. Rather, the threat came from below. There was a massive increase in sediment which worsened the water quality surrounded the coral.
While the Great Barrier Reef has been able to survive these challenges, the current threats look like a combination of many of these events. Rising ocean levels would increase the carbon dioxide, rising ocean temperatures would change the type of fish that live there or any reef.
“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,” says University of Sydney’s Associate Professor Jody Webster, who led the decade-long study, in a press release.
Another problem is that at least in terms of global warming, humans can move with a far greater efficiency than nature. For a couple of degrees to make a difference to the Great Barrier Reef, 10,000 years of warming had to happen. Now, humans are expected to raise temperatures by 0.7 degrees in a hundred years.
Some scientists want to use a little bit of human ingenuity to help coral along though. There’s currently a movement to edit coral genes with CRISPR to make them more resilient to upcoming changes.