海水温度升高 大堡礁五年内出现第三次大规模珊瑚白化



A man snorkels in an area called the "Coral Gardens" near Lady Elliot Island, on the Great Barrier Reef, northeast of Bundaberg town in Queensland, Australia, June 11, 2015. [Photo/Agencies]

The government’s top Great Barrier Reef scientist says a third mass bleaching event in five years is a clear signal the marine wonder is “calling for urgent help” on climate change.


bleach [bliːtʃ]:v.漂白,晒白


One quarter of the Great Barrier Reef suffered severe bleaching this summer in the most widespread outbreak ever witnessed, according to analysis of aerial surveys of more than 1,000 individual reefs released on Tuesday.


Dr David Wachenfeld, chief scientist at the Great Barrier Reef Marine Park Authority, told Guardian Australia: “My greatest fear is that people will lose hope for the reef. Without hope there’s no action.


“People need to see these [bleaching] events. They are clear signals the Great Barrier Reef is calling for urgent help and for us to do everything we can.”


Great Barrier Reef's bleaching[Photo/China News Service]

Prof Terry Hughes, director of the Centre of Excellence for Coral Reef Studies at James Cook University, surveyed 1,036 reefs from a plane over nine days in late March. The marine park authority also had an observer on the flights.


Hughes has released maps showing severe levels of bleaching occurred in 2020 in all three sections of the reef – northern, central and southern – the first time this has happened since mass bleaching was first seen in 1998.


Some 25% of the reefs were severely bleached – meaning that more than 60% of the corals on each reef had bleached.


Great Barrier Reef's bleaching[Photo/China News Service]

Hughes said previous observations had shown that bleaching at that extent leads to “high levels of mortality” of corals.


The Great Barrier Reef has experienced five mass bleaching events – 1998, 2002, 2016, 2017 and 2020 – all caused by rising ocean temperatures driven by global heating.


Hughes said there probably would not be the same level of coral death in the north and central regions in 2020 as in previous years, but this was partly because previous bleaching outbreaks had killed off the less heat-tolerant species.


The 2020 bleaching was second only to 2016 for severity, Hughes said.


Great Barrier Reef's bleaching[Photo/China News Service]

Corals can recover from mild bleaching, but scientists say those corals are more susceptible to disease. Severe bleaching can kill corals.


“It’s not too late to turn this around with rapid action on emissions,” he said.


Australia's Great Barrier Reef[Photo/IC]

In February the reef was subjected to its hottest sea surface temperatures since records began in 1900.


Some scientists fear that rising levels of heat being taken up by the ocean have pushed tropical reefs to a tipping point at which many locations bleach almost annually.


tipping point:n.临界点;引爆点

Great Barrier Reef's bleaching[Photo/China News Service]

Wachenfeld said the reef’s sheer size – it comprises about 3,000 individual reefs – made it resilient, “but climate change brings a new scale of impact unlike anything we have seen before”.


“No one climate event will kill the Great Barrier Reef, but each successive event creates more damage. Its resilience is not limitless and we need the strongest possible action on climate change.”


The globe has already warmed by about 1C above pre-industrial levels, caused primarily by rising levels of greenhouse gases in the atmosphere from burning fossil fuels.


Measures to improve the resilience of the reef include improving water quality, controlling outbreaks of coral-eating starfish, and research and development to improve the heat tolerance of corals.


“None of that is a substitute for strong action on emissions,” Wachenfeld said. “Dealing with the climate problem is the underpinning for everything else to work.”




Queensland’s minister for environment and the Great Barrier Reef, Leeanne Enoch, said climate change, pollution from run-off and other threats “are testing the reef’s ability to recover from major disturbances like mass bleaching events, severe tropical cyclones and crown-of-thorns starfish.”


“The missing piece continues to be leadership and action from the federal government on climate change,” she said.





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