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Unprecedented Harm to Great Barrier Reef From Back-to-Back Bleaching Confirmed

It’s becoming more and more clear that the Great Barrier Reef has been pushed onto the ropes by human-caused climate change. That its very future is now in serious jeopardy. That only swift action by a responsible populace will now be able to save it.

During 2016 to 2017, the Great Barrier Reef experienced an unprecedented back-to-back bleaching event. In 2016, more than 60 percent of the corals of the reef’s northern section experienced bleaching. Ultimately, roughly 2/3 of the shallow water corals along this section of the reef perished.

In 2017, warmer than normal waters shifted south. As a result, the central section of the Great Barrier Reef is presently experiencing 60 percent or higher bleaching rates. Now, mass mortality in regions unaffected or minimally affected by last year’s record bleaching is expected.

(New composite bleaching maps show the extent of the 2016-2017 coral mortality event which now heralds a near-term threat to the continued existence of the reef itself. Image source: ARC Centre of Excellence for Coral Reef Studies.)

In other words, back-to-back torrents of warm water are walking from north-to-south down the reef, taking out corals as they go from year-to-year, like some merciless ocean blow-torch. And what’s happening is that ocean temperatures are now entering a range where this kind of heat-caused mortality event is becoming more and more likely to occur at frequent intervals.

Terry Hughes, in an inteview with The Guardian on Sunday stated:

“The significance of bleaching this year is that it’s back to back, so there’s been zero time for recovery. It’s too early yet to tell what the full death toll will be from this year’s bleaching, but clearly it will extend 500km south of last year’s bleaching.”

The 2017 bleaching is also odd in that it occurred during a time of ENSO-nuetral conditions and during a year when only a weak-to-moderate El Nino is expected. In the past, mass coral bleaching and mortality along the Great Barrier Reef has only happened during very strong El Nino years (1998 and 2016). Meanwhile, this year’s cyclone Debbie appears to have done little to relieve the bleaching stress even as it has driven powerful waves across otherwise healthy sections of the reef — further adding to coral mortality.

Reefs require from 10 to 15 years to recover from the effects of severe bleaching and mortality. They can only bounce back if nearby live corals that survived can regrow into previously denuded sections. But the back-to-back waves of annual heat are ruining that needed connectivity even as the warming ocean is slamming the window shut on the required respite periods.

 

(The Great Barrier Reef is now experiencing the fastest rate of ocean warming since it began to form about 20 million years ago. Image source: Australia’s Bureau of Meteorology.)

David Sugget, University of Technology Sydney’s lead reef researcher, notes:

“It’s that connection ultimately that will drive the rate and extent of recovery. So if bleaching events are moving around the [Great Barrier Reef] system on an annual basis, it does really undermine any potential resilience through connectivity between neighbouring reefs.”

Since 1900, sea surface temperatures in the region of the Great Barrier Reef during times when the reef is most vulnerable to bleaching — late austral summer and early austral autumn — have risen by 1.5 to 2 degrees Celsius. And the rate of rise during recent years is accelerating. The result is that the risk of multiple severe bleaching events hitting the reef within decadal timescales is now high. And the reef is likely to continue to receive multiple blows as bad or worse than those experienced in the 2016-2017 timeframe.

Some Australian politicians are now promising new laws to help reduce runoff that also stresses the reef. But these policies do not address the root cause of what is now a threat to the reef’s very existence. The bleaching that is killing the reef is caused by ocean warming. And that warming, in its turn, is caused by fossil fuel burning which dumps billions of tons of heat-trapping gasses into the atmosphere each year. According to reports from NOAA, the rate of greenhouse gas accumulation is presently 100 to 200 times faster than at the end of the last ice age. And if this rate of greenhouse gas accumulation continues, there is no chance that the Great Barrier Reef, and most of the other reefs of the world, will survive.

(UPDATED)

Links:

ARC Centre of Excellence for Coral Reef Studies

Great Barrier Reef at Terminal Stage — Scientists Despair

Australia’s Bureau of Meteorology

Cyclone Debbie Strikes Healthiest Part of Great Barrier Reef

Great Barrier Reef Hit By Bleaching For a Second Year in a Row

Australia’s Politicians Have Betrayed the Great Barrier Reef and Only the People Can Save it

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World Resources Institute Shows Widespread Coral Bleaching by 2030

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The World Resources Institute recently issued a report on the health and future prospects for the world’s coral reefs. Entitled “Reefs at Risk Revisited,” the study tracks global warming impacts on coral reefs through 2050. The verdict? Not too hot for Earth’s reefs. Simply put, under business as usual fossil fuel emissions, it doesn’t seem likely there will be many, if any, reefs remaining by 2100.

http://www.wri.org/map/frequency-future-coral-reef-bleaching-events-2030s-and-2050s

The study shows warming will be highly damaging to coral reef systems by or before the 2030 and that such damage will become catastrophic by the 2050s. The above map only tracks damage due to coral bleaching, not damage due to reef stress from human activity, or damage due to ocean acidification.

Ocean acidification is caused by increasing levels of Carbon Dioxide (CO2) in the atmosphere. And since the dawn of the industrial revolution, CO2 levels have been creeping upward. Due to human emissions, world CO2 concentrations are now rising at the rate of 2.2 ppm each year. And a good amount of the CO2 that doesn’t end up in the air ends, instead, in the ocean. Scientists show that some corals and coral reef systems are under stress from acidification with current world CO2 levels at 393 ppm. Most studies show that coral reefs would be wiped out by the time concentrations reach 600-650 ppm. Under business as usual CO2 emissions, this level will likely be reached by the latter half of the 21rst century.

The WRI shows bleaching due to human-caused warming at critical levels during the same period.

The combined impacts of heat stress, human activity, and ocean acidification creates dangerous stresses to reef systems now. Over the coming decades, increasing damage from these sources will place the continued existence of coral reefs in doubt.

WRI also provides a compelling video investigating current stresses to coral reefs around the world:

 

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