Experts fear the fourth mass coral bleaching event in six years

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The odds that there are more than the average of four eastern Australian tropical cyclones this season are about two in three, according to the Bureau’s cyclone forecast.

The higher-than-usual number is linked to the La Nina event now underway in the Pacific, a phase that favors increased storms across northern Australia.

“While cyclones can be harmful to coral reefs and floods can wash pollutants in marine waters, increased rainfall and associated cloud cover can provide shading on the reef, cooling water temperatures,” said the Dr. Wachenfeld, pointing out the uncertainty of accurately capturing local weather conditions several months out.

However, with sea surface temperatures about 0.8 degrees warmer than a century ago, “the entire reef is warming,” increasing the chances of bleaching during what are relatively cold years in terms of swing El Nino-La Nina of climatic factors in the Pacific.

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Corals rely on algae known as zooxanthellae to provide most of their energy and much of their vibrant color. When exposed to prolonged abnormal heat, measured in so-called degree warming days, corals begin to excrete algae, leading to mass bleaching.

The Great Barrier Reef experienced unprecedented continuous coral bleaching in 2016 and 2017 and again in 2020. Dr Wachenfeld said researchers are still trying to determine how much coral cover was lost in this year’s event. and how corals in general are responding to unnatural heat stress attacks within a few years.

NOAA’s Dr Eakin said that regardless of whether there is a La Nina or El Nino event, “it appears that bleaching on the Great Barrier Reef is becoming more frequent and severe. This is most likely caused by global warming caused by ”. man”.

According to current projections, 2020 will end as one of the hottest years on record despite the Pacific having entered the La Nina phase in recent months and possibly even a strong phase.

During these times, the Pacific tends to absorb more heat than in the El Nino years, when the ocean releases more heat, causing global temperatures to rise.

Dr Eakin said the fact that another bleaching event is possible in a year in La Nina is an indicator of how vulnerable the reef is.

“This is a clear sign of what we can continue to expect if we don’t all work to keep climate change under control.”

The Office and CSIRO echoed these concerns in the recently released state of the climate report.

“Along with ocean acidification and nutrient runoff, the increased severity and frequency of marine heatwaves is likely to reduce reef resilience and hinder coral recovery from future bleaching events,” he said.

“The impacts on coral reefs of marine heatwaves are expected to worsen in the future with continued warming, but the intensification of marine heatwaves is much greater with greater global greenhouse gas emissions.”