The conclusions from a series of scientific surveys of the Great Barrier Reef bleaching event — an environmental assault on the largest coral ecosystem on Earth — are in, and scientists aren’t holding back about how devastating they find them.

Australia’s National Coral Bleaching Task Force has surveyed 911 coral reefs by air, and found at least some bleaching of the vast majority of them. The bleaching was the worst in the reef’s northern sector — where virtually no reefs escaped it.

“Between 60 and 100 per cent of coral are severely bleached on 316 reefs, nearly all in the northern half of the Reef,” Prof. Terry Hughes, the lead researcher, said in a statement to the news media.

Severe bleaching means that coral could die, depending on how long they are subject to these conditions. The scientists also reported that based on diving surveys of the northern reef, they already are seeing nearly 50 per cent coral death.

“The fact that the most severely affected regions are those that are remote and hence otherwise in good shape, means that a lot of prime reef is being devastated,” said Nancy Knowlton, Sant Chair for Marine Science at the Smithsonian Institution, in an email in response to the bleaching announcement. “One has to hope that these protected reefs are more resilient and better able to (recover), but it will be a lengthy process even so.”

Knowlton added that Hughes, who led the research, is “NOT an alarmist.”

Coral bleaching occurs when coral are stressed by unusually high water temperatures, or from other causes. When this happens, symbiotic algae, called zooxanthellae, leave the coral’ bodies. This changes their colour to white and can also in effect starve them of nutrients. If bleaching continues for too long, coral die.

There already have been reports of mass coral death around the Pacific atoll of Kiribati this year — and widespread coral bleaching worldwide, a phenomenon that scientists attribute to a strong El Niño event surfing atop a general climate warming trend.

Tourism involving the Great Barrier Reef is worth about $6.5 billion annually, and accounts for close to 70,000 jobs, according to the news release from the Australian National Coral Bleaching Taskforce.

Recently, journalist Chelsea Harvey reported that some scientists think coral bleaching this extensive could be a sign of “dangerous” climate change caused by humans.

The 1992 United Nations Framework Convention on Climate Change, just after saying that countries should avoid such dangerous interference with the climate, adds that atmospheric greenhouse gas levels should be stabilized “within a time frame sufficient to allow ecosystems to adapt naturally to climate change.”

Indeed, recent research suggests that although Great Barrier Reef coral have a mechanism to protect them if waters warm up beyond normal, but then cool down again before a second warming that crosses the bleaching threshold. However, as oceans continue to warm, it found, that pattern will be less prevalent, meaning that coral will be less able to cope.

Past global coral bleaching events have occurred in 1998 and 2010. In 1998, scientists ultimately documented through much followup research that 16 per cent of the world’s coral died in that event. The full toll of the current global bleaching event has not been determined.

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