Report: Climate change drove bleaching of reefs
A recently completed aerial survey of the Great Barrier Reef found that 93 percent of the smaller reefs that comprise it showed at least some bleaching, and in the northern sector of the reef, a large majority of reefs saw bleaching that was severe — meaning many of these corals could die.
There was already considerable murmuring that this event, which damages a famous World Heritage site and could deal a blow to a highly valuable tourism industry, did not simply happen by chance. And now, a nearly real-time analysis by a group of Australian climate and coral reef researchers has affirmed that the extremely warm March sea temperatures in the Coral Sea, which are responsible for the event, were hardly “natural.”
“Human-caused climate change made the extreme ocean temperatures that led to the massive bleaching events along the Great Barrier Reef this year at least 175 times more likely,” finds the analysis, which was led by Andrew King, a researcher studying climate extremes at the University of Melbourne.
King and his four colleagues freely confess that their analysis has not yet been peer-reviewed — science doesn’t move that fast — and admit to adopting the “unusual approach of releasing the results before publication.” But they defend the move in light of the situation.
“Because we have confidence in the methods, the methods have been peer reviewed, and because the results are so strong, we decided we needed to release them almost immediately. It’s important for the public to know that climate change is making these bleaching events far more likely,” King said in an interview.
The researchers have also posted their data and methods online. King said in an interview that the researchers were sure to include a coral-reef expert, Ove Hoegh-Guldberg, who directs the Global Change Institute at the University of Queensland, in the analysis.
At the heart of the new analysis is the warm March sea temperatures of the Coral Sea region, which the researchers say set a new record for that month, at more than 1 degree Celsius above the long-term average. The scientists then proceeded to conduct what is called an “attribution” study, which involves running large numbers of climate model iterations, with and without the human global warming influence included, to determine how likely such a warm de- parture is to occur in each set of model runs.
The result was that the warm Coral Sea extremes were far more likely in the runs that included humaninduced climate change than in those that did not. This is where the statement that the event is 175 times more likely to occur due to climate change comes from.
“The likelihood of bleaching in the normal climate is just under 0.1 percent, a one in a thousand year event, roughly,” King said. “But in the modern world, it’s much more likely.”
The scientists also wrote about the analysis at the website The Conversation, where they made a similar point: “Surface temperatures like those in March 2016 would be extremely unlikely to occur in a world without humans.”
Reacting to the research in an interview with Climate Central, David Kline, a researcher who studies corals at the Scripps Institution of Oceanography but was not involved with the study, commented, “This is the smoking gun.”