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According to the Marine Park’s chief scientist, a global weather phenomenon that typically keeps ocean temperatures lower in the Great Barrier Reef may not be enough to stop another massive coral bleaching this summer.
Global warming now meant that the risk of coral bleaching from heat stress was present even in the summer influenced by the La Niña weather phenomenon, said Dr David Wachenfeld of the Great Barrier Reef Marine Park Authority at Guardian Australia.
Authorities on Thursday revealed this summer’s outlook for the world’s largest coral reef system which has been hit by three mass bleaching events in the past five years.
Clouds, rain and cyclones could still combine to keep temperatures along the reef low enough to prevent another bleaching event.
But models from the US government’s National Oceanic and Atmospheric Administration (Noaa) and the Australian Bureau of Meteorology agreed that December and January would likely see ocean temperatures on the reef about 1 ° C warmer than the average.
“There is no prediction of a mass laundering event, but it is certainly possible and it all depends on that consideration of a typical La Niña,” Wachenfeld said.
“The whole world is a degree warmer, so we can’t just relax and say it’s La Niña and so there won’t be heat waves. The world is not that simple anymore. “
About 90% of the additional heat due to increased levels of greenhouse gases, caused primarily by fossil fuel combustion and deforestation, is absorbed by the oceans.
The authority announced the findings of a scientific workshop held Wednesday with more than 40 marine park managers, scientists, experts and representatives of the reef industry.
In September, the Bureau of Meteorology declared a La Niña and earlier this week it said it would likely last until at least January 2021.
Wachenfeld said La Niña will generally bring more clouds, more precipitation and more cyclones, all of which can help cool the waters of the Great Barrier Reef.
“The reef is about 0.8 ° C warmer than it was about 100 years ago and a lot of changes have taken place quite recently. Ten years ago I would have said in a La Niña that we cannot have a laundering event.
“It’s still cooler than average, but cooler than average today doesn’t mean what it meant 20 years ago.
“The problem with climate change is that the starting background conditions are warmer than [they] would have been otherwise.
“I think the reef is fundamentally in a precarious position because of climate change.
“We can turn around in April and say it was great and the weather wasn’t particularly bad for the reef.
“But the fact that the world is one degree warmer means that there is tremendously more thermal energy and this leads to a high risk of extreme weather conditions in many ecosystems around the world.
Urgent global action is needed to reduce greenhouse gas emissions, he said.
When asked if he was worried for the coming months, he said: “We are in a world with a changing climate, so there is always a background level of anxiety… we are in uncharted territory. .
Dr William Skirving, of Noaa’s Coral Reef Watch, presented the agency’s modeling of likely heat stress on the reef in the coming months during Wednesday’s briefing.
He told Guardian Australia that data from Noaa and the Bureau of Meteorology suggested there could be widespread heat stress across the reef that “would be enough to bleach the corals but probably not enough to kill”.
Skirving said: “It’s a long way to go, but everything indicates that the reef is going to have a stressful time this summer and it could take many forms. It could be heat stress if there are no cyclones, it could flow if there is more rain.
In past decades, Skirving has said that a La Niña event would have kept sea surface temperatures low enough to avoid widespread heat stress.
“But now we have bottom temperatures which are higher due to climate change. This essentially means that the sun has less work to do in raising temperatures to whitening levels.
But Skirving said the onset of cyclones and the timing of the tides relative to the local weather could keep the waters cooler, but it was not possible to predict the cyclones for months afterward.
The Bureau of Meteorology said there is a 67% chance there will be more than the average of four cyclones off eastern Australia this summer.
While a cyclone can help keep waters cool and protect corals from heat stress, it can also cause physical damage to reefs if it’s large enough.
The rains can cool the reef, but flooding on land can also cause additional pollution to flow into the reef waters.
The authority said outbreaks of thorn-crowned coral starfish are a permanent impact, especially in the central and southern parts of the reef.
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