A Death of Beauty — Climate Change is Bleaching the Great Barrier Reef Out of Existence


It’s a hard, tough thing to consider. One of those possibilities people justifiably do not want to talk about. This notion that a creature we’re fond of and familiar with — a glorious living being along with all its near and distant relatives — could be entirely removed from the web of existence here on Earth.

Our aversion to the topic likely stems from our own fear of death. Or worse — the notion that the entire human race might eventually be faced with such an end. But extinction is a threat that we’ll see arising more and more as we force the world to rapidly warm. For species of the world now face existential crisis with increasing frequency as atmospheric and ocean temperatures have risen so fast that a growing number of them have simply become unable to cope with the heat.

The Great Barrier Reef of Australia — the world’s largest single structure made up of living organisms — is no exception. For this 1,440 mile long expanse of corals composed of more than 2,900 individual reefs that has existed in one form or another for 600,000 years has suffered a severe blow — one from which it may never be able to recover. One that appears likely to kill up to 90 percent of its corals along previously pristine regions in its northern half.

(Governments failed to listen to the warnings of scientists like Terry Hughes. Now, it appears that the Great Barrier Reef has been hit by a blow from coral bleaching from which it may never be able to recover. Video source: Australian Broadcasting on the Great Barrier Reef’s Worst Coral Bleaching Event on Record.)

The damage comes in the form of extreme ocean heat. Heat resulting from global temperatures that are now well in excess of 1 degree C above preindustrial times. Heat that has forced ocean temperature variability into a range that is now lethal for certain forms of sea life. Particularly for the world’s corals which are now suffering and dying through the worst global bleaching event ever experienced.

The Worst Global Coral Bleaching Event Ever Experienced

During 2014 the oceans began to heat up into never-before seen temperature ranges. This warming initiated a global coral bleaching event that worsened throughout 2015. By early 2016 global surface temperatures rocketed to about 1.5 C above 1880s averages for the months of February and March. These new record high temperatures came on the back of annual carbon emissions now in the range of 13 billion tons each year and at the hotter end of the global natural variability cycle called El Nino. Both the atmosphere near the land surface and the upper levels of the ocean experienced this extreme warming.

In the ocean, corals rely on symbiotic microbes to aid in the production of energy for their cellular bodies. These microbes are what give the corals their wild arrays of varied and brilliant colors. But if water temperatures rise high enough, the symbiotic microbes that the corals rely on begin to produce substances that are toxic to the corals. At this point, the corals expel the microbes and lose their brilliant coloration — reverting to a stark white.

Worst coral bleaching event on record

(A vast region of the world’s ocean system continues to experience coral bleaching. In area, extent, height of extreme temperature, and duration, the current global coral bleaching event is the worst ever experienced by a good margin. As global temperatures continue to warm due to ongoing fossil fuel burning and related carbon emissions, widespread coral bleaching is likely to become an annual occurrence. Temperatures have risen far enough and will continue to rise for long enough to set about ocean conditions that will result in mass coral die-offs around the world. Image source: NOAA.)

Bleaching isn’t necessarily lethal to corals. However, once the microbes are gone, the corals have lost a key energy source and will eventually die without them. If ocean temperatures return to normal soon enough, the corals can begin to accept the symbiotic microbes back, return to a healthy cellular energy production, and survive — albeit in a weakened and more vulnerable state for some time to come. But if ocean temperatures remain too warm for an extended period, then the corals will be deprived of energy and nutrients for too long and they will inevitably perish.

The kind of coral bleaching event that we’re experiencing now is a mass killer of corals. Not simply due to the heat itself, but due to the long duration of the extreme temperature spike. By late February, many ocean scientists were very concerned about the already severe damage reports that were starting to come in. At that time, NOAA issued this warning:

“We are currently experiencing the longest global coral bleaching event ever observed. We may be looking at a 2- to 2½-year-long event. Some areas have already seen bleaching two years in a row.”

93 Percent of Great Barrier Reef Affected by Bleaching

By late February, the level of concern for the Great Barrier Reef was palpable. Stark reports were starting to come in from places like Fiji — which had experienced two years of severe bleaching — and Christmas Atoll about 1,300 miles south of Hawaii — whose reported losses were best described as staggering. So far, the worst of the hot water had stayed away from Australia’s great reef.

But by early March a plume of very extreme ocean heat began to appear over The Great Barrier Reef’s northern sections. Sea surface temperatures spiked to well above, a dangerous to corals, 30 degrees Celsius for days and weeks. This 30 C or greater heat extended deep — hitting as far as 50 meters below the ocean surface over the reef. And it rippled southward — hitting section after section until few parts of the reef were spared.

Terry Hughes, one of the world’s foremost experts on the Great Barrier Reef, on March 18th tweeted his fear and anguish over the situation:

Terry Hughes tweet

At this point, there was no stopping the tragedy. Fossil fuel emissions had already warmed the airs and waters to levels deadly to the living reef. It was all researchers could do to work frantically to assess the damage. Teams of the world’s top reef scientists swept out — performing an extensive survey of the losses. More than 911 reef systems were assessed and, in total, the teams found that fully 93 percent of the Great Barrier Reef system had experienced some level of bleaching.

Final Death Toll for Some Sections Likely to Exceed 90 Percent

In extent, this was the worst bleaching event for the Great Barrier Reef by a long shot. Back during the previous most severe bleaching events of 1998 and 2002, 42 percent and 54 percent of the reef was affected. By any measure, the greatly expanded 2016 damage was catastrophic. “We’ve never seen anything like this scale of bleaching before. In the northern Great Barrier Reef, it’s like 10 cyclones have come ashore all at once,”said Professor Terry Hughes in the ARC coral bleaching report.

Out of all the reefs surveyed in the report, just 7% escaped bleaching. Most of these reefs occupied the southern section — a region that was spared the worst of the current bleaching event due to cooler water upwelling provided by the powerful winds of Hurricane Winston. But impacts to the Northern section of the reef could best be described as stark. There, a section composing almost the entire northern half of the reef saw between 60 and 100% of corals experiencing severe bleaching. In the reports, Hughes notes that many of these corals are not likely to survive. In the hardest hit reefs — which were in the most remote sections least affected by Australia’s industrial run-off — algae has been observed growing over 50 percent of the corals affected — an indication that these corals are already dead:

“Tragically, this is the most remote part of the Reef, and its remoteness has protected it from most human pressures: but not climate change. North of Port Douglas, we’re already measuring an average of close to 50% mortality of bleached corals. At some reefs, the final death toll is likely to exceed 90%. When bleaching is this severe it affects almost all coral species, including old, slow-growing corals that once lost will take decades or longer to return (Emphasis added).”

But with the oceans still warming, and with more and still worse coral bleaching events almost certainly on the way, the question has to be asked — will these corals ever be afforded the opportunity to recover?

A Context of Catastrophe with Worse Still to Come

As ocean surface temperatures are now entering a range of 1 C or more above 1880s levels, corals are expected to experience bleaching with greater and greater frequency. The Intergovernmental Panel on Climate Change in 2007 identified the time-frame of 2012 to 2040 as a period of rising and extreme risk to corals due to bleaching. IPCC also identified bleaching as the greatest threat to corals and related reef-dependent sea life.

When ocean surface temperatures warm into a range of 2 C above 1880s levels — the kind of severe global heating that could arise under worst-case fossil fuel emissions and related warming scenarios by the mid 2030s — corals in the Great Barrier Reef are expected to experience bleaching on an annual basis. Every year, in other words, would be a mass coral bleaching and die-off year.


(Sea surface temperatures and temperatures withing the top 50 meters of water over the Great Barrier Reef of Australia rose to 3-4 C above average during the austral Summer and Fall of 2016. These record temperatures lasted for weeks in some regions setting off the worst coral bleaching event the Great Barrier Reef has ever seen. By mid-Century, coral bleaching and mass die-offs are likely to occur on an annual basis as global temperatures surpass the 1.5 C and 2 C thresholds. Image source: Earth Nullschool.)

Globally, bleaching events under even moderate fossil fuel emissions scenarios would tend to take up much of the Equatorial region on an annual basis by mid-Century. Events that can, during single years, wipe out between 90 and 95 percent of corals at any given location. A handful of corals will likely survive these events — representing a remote and far-flung remnant who were simply a bit hardier, or lucky, or who had developed an ability to accept microbes that are tolerant to warmer temperatures. But these hardy or fortunate few would take hundreds to thousands of years to re-establish previous coral reef vitality even if other harmful ocean conditions did not arrive to provide still more damage.

As coral bleaching expands at the Equator due to increasing rates of ocean warming, increasing levels of carbon dioxide in the atmosphere causes oceans to become more acidic. Cooler waters at the poles are better able to transfer gasses into the ocean’s waters. And higher levels of carbon dioxide in the world ocean results in a growing acidity that is harmful to corals. Increasing levels of ocean acidity thus creep down from the poles at the same time that bleaching events move up from the Equator.

If fossil fuel emissions continue, by mid-Century atmospheric carbon dioxide levels in the range of 450 to 500 parts per million will have provided a never-before seen spike to ocean acidity. Such high ocean acidity would then provide a second severe blow to corals already devastated by bleaching events. It’s a 1-2 punch that represents a mass extinction threat for corals this Century. And we’re starting to see the severe impacts ramp up now.


(Coral bleaching is a severe threat to tropical coral reefs now. But CO2 potentially hitting above 500 parts per million, according to a 2014 study, risks a complete loss of equatorial coral reefs by 2050 to 2100. Between bleaching and acidification, there’s no way out for corals so long as fossil fuel burning continues. Image source: Threat to Coral Reefs From Ocean Acidification.)

The only hope for stopping this ever-expanding harm is a rapid cessation of fossil fuel emissions. And we owe it to the corals of the world, the millions of species that depend on them, and the hundreds of millions of people whose food sources and economic well being come from the corals.

“And Then We Wept”

When researchers told students of the extent of harm to corals upon the Great Barrier Reef, the students were reported to have wept. And with good reason. For our Earth had just experienced a profound death of beauty. A death of a vital and wondrous living treasure of our world. A priceless liquid gem of our Earth. A wonder that gives life to millions of species and one that grants both food and vitality to Australia herself. For if the reef goes, so does a huge portion of the living wealth of that Nation and our world.

Sadly, the tears will just keep coming and coming as these kinds of events are bound to worsen without the most dramatic and urgent global actions. The current and most recent catastrophe is thus yet one more in a litany of wake up calls to the world. But will we hear it loud and clear enough to act in ways that are necessary to ensure the corals survival? And what of the billions of creatures and of the millions of humans too that depend on the corals? Do we care about them enough to act?


Only Seven Percent of the Great Barrier Reef Has Avoided Coral Bleaching

And Then We Wept: 93 Percent of the Great Barrier Reef Now Bleached

NOAA’s Coral Reef Watch

Earth Nullschool

Coral Reefs Hit by Worst Coral Bleaching Event

Terry Hughes Twitter Feed

Coral Bleaching

Threat to Coral Reefs From Ocean Acidification

Ocean Acidification: We are Looking at the Complete Loss of Tropical Coral Reefs by 2050 to 2100

Australian Broadcasting on the Great Barrier Reef’s Worst Coral Bleaching Event on Record

Hat tip to Caroline

Hat tip to Spike

Hat tip to Colorado Bob

Hat tip to Ryan in New England

Hat tip to Griffon

(Please support public, non-special interest based science like the essential work that has been provided by Terry Hughes over so many years and decades. Scientists like Terry provide a vital public service. For years, they have given us a clear warning of a very real and ever more present danger. A warning that gives us a fleeting opportunity to respond to events before we lose the richest living treasures of our world. Before we are bereft of our ability to continue to make livelihoods as environmental abundance and the related regional and global life support systems are irreparably damaged.)


Human Hothouse Spurs Longest Coral Die-Off on Record

The big coral die-off began in the Western Pacific as a massive ocean temperature spike built up during 2014. Back then, ocean heat accumulation had hit a very high ramp. A vicious, century-and-a-half long increase in atmospheric greenhouse gasses re-radiated greater and greater portions of the sun’s energy hitting the Earth — transferring the bulk (about 90 percent) to the world ocean system.

Major Coral Bleaching Event

(A report out today from AGU finds that the world is now experiencing its longest coral die-off event on record. Image source: AGU.)

By 2015, as one of the strongest El Ninos on record began to extend its influence across the globe, a broad region stretching from the Western Pacific, through the Central Pacific and on into the Eastern Pacific and Caribbean were all experiencing mass coral die-offs. Into early 2016, die-off events again expanded taking in Australian waters and sections of the Indian Ocean off East Africa and Western India.

After 20 months of ongoing coral mortality, we are now in the midst of the longest coral die-off event on record — one of only four such events that the world has ever experienced.

The Fourth Major Coral Die-Off

Researchers have long known that corals are sensitive to changes in ocean temperature. A rise in ocean water readings by as little as 1 degree Celsius above average peaks over the period of a month can be enough to set off a life-threatening condition called a coral bleaching event. According to a recent report in AGU:

The bleaching, or whitening, occurs when the corals expel the symbiotic algae that live in their tissues. Without the algae, corals lose a significant source of food and are more vulnerable to disease. In a severe bleaching event, large swaths of reef-building corals die. This causes reefs to erode, destroying fish habitat and exposing previously protected shorelines to the destructive force of ocean waves.

The typical bleaching threshold for most corals tends to be in the range of 29-30 degrees Celsius or about 84-86 degrees Fahrenheit over an extended period. And with the world ocean surface approaching a range near 1 C above 1880s averages, this threshold is hit more and more frequently — putting corals at greater and greater risk.

(World Resources Institute Published the above video in 2012 as a survey of, then current, threats to global coral reef systems. By 2030, heating of the world ocean system, ocean acidification and global warming related dead zones will provide an extreme existential challenge to the world’s beautiful and diverse coral reef systems.)

Prior to the 1980s, widespread coral bleaching events were unheard of. Though isolated events occurred, the world ocean system had not yet warmed enough to put corals at major risk. However, by the 1980s global ocean temperatures had begun to rise into ranges at which peak ocean warming periods could put corals in the firing line for major, globe-spanning die offs.

The first such major, global coral die-off occurred during the, then record, 1982-1983 El Nino. At the time this event was unprecedented. And it held the dubious standing as the only such event until the 1997-1998 Super El Nino set off a similar, though longer-lasting mass die off. By the late 2000s, global ocean temperatures had again risen — hitting marks high enough to enable a weak 2010 El Nino to set off the third mass coral die-off.

The fourth mass die off began in 2014 prior to the most recent super El Nino — which has only exaggerated and lengthened its impact. It is now the longest lasting coral die-off ever recorded. And researchers expect it to continue on through at least much of 2016 and possibly into 2017.

Corals Entering a Period of Killing Heat

As the oceans are predicted to continue warming over the next few decades, corals are expected to come under ever-worsening stress. A recent report by the World Resources Institute (WRI) found that regions experiencing the current mass die-off were 70-90 percent likely to experience similar events at a frequency of once every two years by 2030. And a much larger region was expected to have a 50 to 70 percent risk of experiencing a bleaching event over a two year time-frame.


(World Resources Institute in 2012 found that mass coral bleaching and related die-off would occur with extraordinary frequency post 2030. Image source: The World Resources Institute.)

By the 2050s, under business as usual fossil fuel burning, WRI expects that much of the world’s temperate and tropical oceans would experience coral bleaching events bi-annually.

Taking this stark prediction into account we find that the threat to corals over the coming decades will eventually exceed El Nino periodicity and become common during most ocean climate states. The current, likely two year to 30 month, coral die off should serve as a warning for the worse and more frequent hits to corals that will, sadly, be stacking up over the coming decades. Eventually, mass coral die-offs in the continually warming world ocean will become continuous and ubiquitous unless the current trend somehow draws swiftly to a halt.

In addition, given an expanding ocean acidification proceeding southward from the poles and more and more widespread zones of ocean anoxia (areas of water containing very little oxygen), what we are seeing is that threats to coral health are rapidly multiplying due to influences directly related to human-forced climate change.


El Nino Prolongs Longest Coral Bleaching Event

NOAA: Coral Bleaching Background

World Resources Institute Shows Widespread Coral Bleaching by 2030

The World Resources Institute

Hat Tip to TodaysGuestIs

Hat Tip to DT Lange


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