Australia’s Record Heat Means Another Blow to Great Barrier Reef

For the third time in five years, abnormally warm water has caused a “mass bleaching” of coral, and some of it will not survive. Scientists say global warming is killing reefs worldwide. Record-breaking warm waters have bleached large parts of Australia’s Great Barrier Reef this year, as they did in 2016 and 2017, scientists reported on Thursday — the latest sign that global warming threatens the health of one of the world’s most important marine ecosystems. “We can confirm that the Great Barrier Reef is experiencing its third mass bleaching event in five years,” David Wachenfeld, chief scientist of the Great Barrier Reef Marine Park Authority, said in a video posted on its website.

Water that is warmer than normal stresses the corals that create a reef, causing them to lose color and even become white. Corals that experience minor or moderate bleaching usually recover, but those that are severely bleached often die. Scientists say reefs around the world have been dying at an alarming rate for several years because of global warming. Reef corals grow very slowly, and while most of them can live only in warm water, they are highly sensitive to above-normal temperatures.

The Great Barrier Reef is estimated to support thousands of marine species, and it is essential to the lives of some aboriginal groups and the natives of the Torres Strait Islands, between the Australian mainland and New Guinea. It also drives significant economic activities like tourism and fishing; scientists said important areas for reef tourism, particularly in the north, have not been hit badly this year. The Great Barrier Reef Authority, an Australian government agency, based its announcement of mass bleaching on observations, still underway, made in the water and from the air. The data is new.

But the same weather patterns that generated record-breaking heat and catastrophic fires in Australia during the Southern Hemisphere’s spring and summer have also heated the oceans. In terms of water temperatures around the reef, February was the warmest month on record, with readings in some places more than 5 degrees Fahrenheit above average for the time of year, the authority recently reported. “The Great Barrier Reef remains under pressure from heat stress that accumulated over the 2019/20 summer, particularly in February and early March 2020, and resultant bleaching that is occurring,” the authority said in a statement released on Thursday. The reef — really a network of hundreds of reefs — is the world’s largest, running for more than 1,100 miles in the Pacific Ocean, off Australia’s tropical northeastern coast.