This is the sixth such event the reef has experienced in recorded history.

As ocean temperatures raise due to global climate change, coral reefs around the world have been experiencing a greater frequency of bleaching events. These events occur when the water becomes too warm, forcing coral to expel algae and turn white, leaving them vulnerable to disease and death. As large populations of plants and animals, both under and above water, call reefs home, mass bleaching events can be potentially catastrophic for ecosystem stability.

One of the largest, most well-known reefs in the world, Australia’s Great Barrier Reef, experienced another bleaching event this year. This is the sixth bleaching event the reef has suffered in recorded history, and the fourth one since 2016. According to a report from the Great Barrier Reef Marine Park Authority, nearly 91% of all of the coral in the reef experienced at least partial bleaching due to rising temperatures.

The relative frequency of bleaching events in the last several years has been extremely concerning for marine biologists. While coral can recover from bleaching, it takes time and ideal conditions, neither of which they have been receiving.

“Even the most robust corals require nearly a decade to recover,” Jodie Rummer, associate professor of Marine Biology at James Cook University told CNN.

“So we’re really losing that window of recovery. We’re getting back-to-back bleaching events, back-to-back heat waves. And the corals just aren’t adapting to these new conditions.”

Unfortunately, there are no quick ways to ensure the health of the reef. The only true solution is to ensure the global climate does not worsen.

“To give our reef a fighting chance, we must deal with the number one problem: climate change. No amount of funding will stop these bleaching events unless we drive down our emissions this decade,” said CEO of the Climate Council Amanda McKenzie.