With ocean temperatures off the northeastern Australia coast once again having reached record highs, marine biologists fear the Great Barrier Reef may soon be exposed to another mass bleaching event by March 2023.
Australia's Great Barrier Reef continues to see regular rapid bleaching and die-off of its majestic coral reefs, as the climate crisis has brought unprecedented heat to the ocean surrounding them. (Image courtesy Pixabay)
In the late southern Pacific summer last year, the Great Barrier Reef went through its sixth ever mass bleaching event in history. Bleaching means that the coral dies and with it most of the reefs other inhabitants.
That die-off and all previous mass bleaching events, which happened in 1998, 2002, 2016, 2017, and 2020, were caused by super-heated ocean waters off the coast of Queensland. Over time, as global heating due to the climate crisis has grown more intense, the average temperatures in these waters by late summer have grown hotter. Along with that increase has come even more serious coral reef die-off in the region over time, as the coral could not survive the high temperatures.
Temperatures in the region begin to rise starting in October and November every year as the Australian summer approaches. Last year at this time, temperature increases set off alarm bells in part because this was a La Niña year, one in which ocean currents would typically have kept the reef area cooler than normal. As was noted then, for the period between mid-November and mid-December 2021 minimum temperatures for some 80% of the 2,500 kilometer (1,400 miles) extent of the reef off the coast were higher than normal.
As NOAA’s Coral Reef Watch scientist Dr. William Skirving said then, “There’s never been heat stress like that in our records.” He was comparing to records dating back to 1985.
As the summer progressed, by March the temperatures warmed even further, with most running between 1°- 2° C over the averages typically measured in the area. That eventually resulted in the single biggest die-off of the most important coral reef in the southern Pacific. Over 91% of the coral reef mass was affected by it.
It was also the first ever such die-off during a La Niña year.
The deaths of the coral reefs are considered one of the most serious early warning signs of what the climate crisis is bringing to the planet. Since an estimated 25% of all marine life, including some 4,000 species of fish, directly depends on the presence of healthy coral reef ecosystems, and more than half of all marine life depends on them indirectly as part of the food chain, the death of such a major reef can have far-reaching impacts over time. Further, as can be seen by the impact of last year’s rise of “just” up to 1°- 2° Celsius in this area, what may seem like a minor temperature increase can indeed be devastating.
Based on recent data gathered from multiple sources, it looks like this summer, lasting roughly from now until March, could create even worse havoc on the reef.
The bad news began with information collected by the United States’ National Oceanic and Atmospheric Administration’s (NOAA) satellites, which revealed the surface temperatures over the reef were the hottest they have ever been, again going back to 1985 when records were first measured.
A map of sea surface temperatures in the Great Barrier Reef, marked over time this year and with indicators warning of a mass bleaching event. Photo: NOAA
The combined impact of ocean surface and atmospheric heat takes some months to accumulate in the waters. And based on forecasts currently being analyzed, this could make the coral death event in March 2023 the worst ever.
A map of the sea surface temperature variations from the norm over the Great Barrier Reef as of November 24, 2022. Photo: Australia Bureau of Meteorology
Although it is possible, as Professor Terry Hughes, a coral reef bleaching expert at Australia’s James Cook University, said, that a “well-timed cyclone” before 2022 could cool the waters quite a bit, until that happens the region is watching the situation carefully.
“It is certainly the case that temperature records are tumbling,” he told the press recently in an interview. “The warning signs are clear.”
If it does happen, not only could this be the first time in history that back-to-back bleaching events will happen, it also could move up the mass bleaching event from March to as early as January. That could allow a multiple month “cooking” of the ocean waters even longer after the bleaching event begins, resulting in a longer die-off period than ever before.
Experts at the Great Barrier Reef Marine Park Authority (GBRMPA) have been monitoring the situation closely.
Dr. David Wachenfeld, chief scientist fo the GBRMPA, expressed concern but did still hope for easing of heat conditions as the La Niña conditions continue for a second year.
“The current La Niña event is expected to increase rainfall along the east and northeastern coast” before temperatures peak this year. That could be good news, but it did not come through last year and equally might not this year.
Despite that, other coral reef experts, such as Professor Ove Hoegh-Guldberg of the University of Queensland, warned things could get worse.
“This is very worrying,” the professor explained. “This [heat stress] is happening many weeks earlier than usual – in the past it has been in January. “The fact it’s probably the warmest November on record [over the reef] and given what we know about heat stress on corals, this does not bode well.”
Coral Reefs are essential to many marine species and ocean food chains. With most coral reefs around the globe suffering stress and die-offs from more acidic waters and higher temperatures, marine life will continue to collapse. For humans, this means they will no longer be able to consume seafood. And that means more consumption of land animals — most all of which are fed grain to fatten them up more quickly. That means more deforestation and more rapid mass extinction of land animals and more ocean dead zones from the chemical and manure runoff.
More humans could choose to adopt a healthy plant-based diet which has far less negative impact on the planet and human health, but most won't until there is no other option and by then their options will be severely limited.