The Great Barrier Reef in Australia has long been one of the world’s most elegant natural wonders, so enormous it can be seen from space, so beautiful that it can move visitors to tears. But the profusion of sea creatures living near it and the reef, are in profound trouble. Huge sections of the Great Barrier Reef, stretching across hundreds of miles of its most pristine northern sector, were recently found to be killed, dead last year by overheated seawater. More southerly sections around the middle of the reef that scarcely escaped then are bleaching now, a possible precursor to another die-off that could rob some of the reef’s most visited areas of life and color.
The damage to the Great Barrier Reef, one of the world’s largest living structures, is part of a global disaster that has been unfolding intermittently for nearly two decades and seems to be aggravating. Dozens of scientists described in a paper, the recent disaster as the third worldwide mass bleaching of coral reefs since 1998, but by far the most damaging and widespread. The state of coral reefs is a telling sign of the health of the seas. Their death and distress are yet another marker of the ravages of global climate change.
If most of the world’s coral reefs die, as scientists fear is increasingly likely, some of the most colorful and richest life in the ocean could be lost, along with huge sums from reef tourism. In poorer countries, lives are at stake: Hundreds of millions of people get their protein primarily from reef fish, and the decrease of that food supply could become a humanitarian crisis. With this latest global bleaching in its third year, reef scientists say they have no doubt as to the responsible party.
Decades ago, they warned that the coral reefs would be at risk if human society kept burning fossil fuels at a runaway pace, releasing greenhouse gases that warm the ocean. Emissions were rising continuously, and now the background ocean temperature is high enough that any temporary spike poses a critical risk to reefs.
Corals require warm water to bloom, but they are attractively sensitive to extra heat. Just two or three degrees Fahrenheit of excess warming can sometimes kill the tiny creatures. It was obvious last year that the corals on many reefs were likely to die, but now formal scientific appraisal is coming in. The paper in Nature documents vast coral bleaching in 2016 along with a 500-mile section of the reef north of Cairns, a city on Australia’s eastern coast. Bleaching indicates that corals are under heat stress, but they do not always die and cooler water can help them recover. Subsequent surveys of the Great Barrier Reef, organized late last year after the deadline for inclusion in the Nature paper, documented that extensive patches of the reef had in fact died, and would not be likely to recover soon, if at all.