Chance to rescue the world’s oceans from climate change is drifting away

Acehnese fishers are among the quarter of the world’s population who live on the coast, and for whom climate-driven changes to the oceans would make life much harder. Hotli Simanjuntak/EPA/AAP Image

by Ove Hoegh-Guldberg, Director, Global Change Institute, The University of Queensland, The Conversation, July 2, 2105

Until recently, you might be forgiven for thinking that the oceans were a trivial component of Earth’s climate system, and that the consequences of change were minimal. After all, only 5% of papers published on climate change involve ocean systems. The Intergovernmental Panel on Climate Change (IPCC), which evaluates the peer-reviewed scientific literature, did not devote a regional chapter to the ocean until its most recent major report.

Yet the ocean system could not be more important: it regulates the global temperature and atmosphere, feeds 3 billion people, and largely determines our weather. The ocean also has lots of “inertia” – which means that getting the ocean to change takes a lot of energy, but once it begins to change, slowing it down becomes more or less impossible.

A paper published today in Science (on which I am one of the authors) has issued a warning that our window of opportunity to save the oceans from major changes is in danger of slamming shut, bringing with it the risk that we will encounter planetary-scale tipping points in the behaviour of the climate. Building on the IPCC’s extensive assessment last year of the effects of climate change on the oceans, my co-authors and I have compiled the latest evidence and projections about the ocean under rapid human-driven climate change.

The news is not good. Failure to act on climate change will see warmer and more stagnant oceans, with declining oxygen levels and productivity in some regions, and the removal or modification of ecosystems in other areas. Fisheries and national economies are in the cross hairs in many regions. Rising seas and intensifying storms, plus a loss of critical coastal features, will make life on the shores of a rapidly changing ocean dangerously different to today.

The risks currently being experienced across the planet. Most, if not all, are set to increase. Gattuso et al.

Click to enlarge

A lot hinges on whether we can meet the globally agreed 2 C “warming guardrail,” but there are fears that this is impossible within current economic strategies, and that even this target is unsafe.

It would be fine to state this if we had a safe alternative, but we don’t. Consequently, the bar for the end-of-year Paris climate summit is set much higher than many understand. As I’ll explain below, we need a global deal that reduces global emissions to zero over the next 20 years, or else we will see momentous changes.

Calls to action

Thankfully, world leaders are beginning to wake up to the challenge facing our oceans. US Secretary of State John Kerry and Prince Albert II of Monaco, are among those who have spoken out against what many see as impending chaos.

The latest is Pope Francis, who became the first pontiff to warn of ocean warming, acidification and sea-level rise, pointing out in his recent encyclical that “a quarter of the world’s population lives on the coast or nearby, and … the majority of our megacities are situated in coastal areas.”

For the first time, the Vatican is fighting for the ocean. Ove Hoegh-Guldberg, Global Change Institute, University of Queensland

Our research adds to the already mounting evidence that these leaders are right when they say we need to act decisively on fossil fuel emissions and other drivers of climate change.

One of the most stunning conclusions from the IPCC’s report is the statement that “the current rate and magnitude of ocean acidification are at least 10 times faster than any event within the last 65 million years.” Given that periods of rapid acidification over tens of thousands of years – slow by our current human-driven standard – resulted in mass extinction and ecological collapse, this alone should be reason to act.

In a few regions, such as the North Sea, temporary increases in fisheries production are being reported, as the ice retreats, seas warm, and productivity increases. But these benefits are few and far between, and are likely to disappear over time as the ocean warms and acidifies further.

Coral reefs perhaps provide the perfect parable for the Pope’s encyclical. Everyone appreciates their beauty and value, but few may be aware of the crucial role that they play in terms of protecting coastlines, and supporting fisheries and other industries. They generate hundreds of billions of dollars each year and support some 500 million mostly poor people worldwide. Our report highlights the extreme sensitivity of these ecosystems to ocean warming and acidification.

Climate-driven changes in the oceans pose risks to organisms, ecosystems, people and industry. Gattuso et al.

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Work to do at the Paris summit

As we progress down the road to Paris, paved with skeletons of these important organisms, there is little doubt about the amount of work that needs to be done in Paris. Analysis of the world’s “carbon budget” (see here and here suggest that we can emit about another 500–800 billion tonnes (gigatonnes) of carbon dioxide before we push global temperatures beyond 2 C above the pre-industrial average. This gives us about 20 years before net global emissions have to fall to zero – a tall order indeed.

There is hope. The recent US–China climate deal is one reason to be optimistic that negotiations in Paris will be smoother than at the Copenhagen climate talks in 2009. But I wonder whether leaders are aware of the true scale of the work that needs to be done to avoid catastrophe. Perhaps the fact that China this week made clear the strength of its new climate commitments is evidence of this.

Yet here is a sobering calculation: imagine that the rest of the world falls into line with the US and Chinese climate targets. How much of the world’s budget would we burn?

The answer would be that the world had emitted 1,400 gigatonnes of CO₂, or 175–280% of our remaining budget, dragging average global warming to 3C and beyond (see the orange line on the graph below). This would be disastrous for us and our children, and many of the benefits of our oceans (coral reefs, fisheries, coastal living) would be transformed beyond recognition.

The relationship between cumulative carbon dioxide emissions and future average global temperatures. IPCC

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An ethical response

Mention of “us and our children” brings us back to Pope Francis and the importance of not reducing everything to a dollar value. Yet even in pure economic terms, given that the IPCC calculates that keeping atmospheric CO₂ below about 450 parts per million (which would give us a good chance of staying within the 2 C guardrail) would cost just 0.06% of global consumption growth per year, one is left wondering why we are not jumping right in and solving this problem.

Pope Francis made an important observation:

In a word, businesses profit by calculating and paying only a fraction of the costs involved. Yet only when “the economic and social costs of using up shared environmental resources are recognized with transparency and fully borne by those who incur them, not by other peoples or future generations,” can those actions be considered ethical.

Once can only hope the leaders heading to Paris will heed his words and drive their efforts in a new direction.

https://theconversation.com/new-report-the-chance-to-rescue-the-worlds-oceans-from-climate-change-is-drifting-away-43257

The One-Two Punch of Climate Change on the Great Barrier Reef

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Graham Readfearn: The Slippery Slope to Slime -- Australia's Great Barrier Reef

by Graham Readfearn, ABC (Australia) Environment, April 15, 2013

Australia's Great Barrier Reef is unparalleled in its beauty. But now a new scientific experiment is revealing the future for the reef if climate change continues, and it doesn't look good.

Heron Island is a hub of marine research in the Great Barrier Reef.Credit: University of Queensland (supplied)

ON A LARGE WOODEN deck on a coral cay island in the middle of the Great Barrier Reef, research assistant Aaron Chai removes the lid from one of 12 circular white water tanks.

"This is the 'do nothing' tank," he says, peering inside at a careful arrangement of dead, slimy, algae-covered and bleached-white corals.

In July last year, this small reef ecosystem looked very different - corals of vivid purples and blues beside the bright greens of turtle weeds. Since then the levels of carbon dioxide and temperature in the bowl-shaped tank have been changed to the kind of conditions expected by the end of this century if the world 'does nothing' about climate change and its fossil fuel use.

"It's the slippery slope to slime," says the University of Queensland's Associate Professor Sophie Dove, who is running this experiment on the university's research station on Heron Island, about 80 kilometres off Gladstone in central Queensland.

The World Heritage-listed Great Barrier Reef is already under stress from natural and man-made hazards. There's climate change and ocean acidification, both driven by burning fossil fuels; run-off from farmland; attacks by crown-of-thorns starfish; cyclones; fishing; and shipping.

A study led by the Australian Institute for Marine Sciences found that since 1985 the reef has lost more than half its coral cover, with two thirds of that loss occurring since 1998.

Tanks of tests

Dove's experiment aims to find out what the future may hold for the reef. All the tanks have inside a near-identical mini-ecosystem with specimens taken from a reef slope next to Heron Island. Each tank is filled with sediments, rocks, 11 different types of coral, two types of snails and various other species such as sea cucumbers, small crabs and blenny fish.

There are three 'control' tanks where temperature and carbon dioxide (CO₂) levels change every two hours in line with measurements taken by a sensor on the reef slope.

Conditions in three 'pre-industrial' tanks are treated to temperatures about 1°C less than today and CO₂ levels at 100 parts per million below current levels in the atmosphere, a reduction of around 25 per cent.

Then there are the future tanks. One future scenario presumes the world will do something on emissions so that as we approach the end of this century temperatures are about 2°C warmer and CO₂ levels rise a further 220 ppm.

The ecosystems in three 'do nothing' tanks undergo temperatures about 4.5°C above today with CO₂ levels raised 600ppm.

All of the different scenario tanks move in tandem with the control tanks, meaning they undergo the normal daily and seasonal changes that happen on the reef.

Coral in Tank 4 in July 2012. This tank imitated contemporary conditions on the reef.


Coral in Tank 4 in March 2013. The coral has developed as expected.

Slime

In the 'do nothing' tanks all but one of the corals has died and is being slowly covered in algae. Some of the coral skeletons have actually started to dissolve in the increased acidity of the water.

"If you look at those reefs in those future tanks now, they are really not all that attractive to tourists," says Dove. "It's not something that people would want to go and see. It is becoming more of a mono-culture and that stuff probably isn't that palatable to the fish. That slippery slope to slime looks to be coming true."

As humans have pumped more carbon dioxide into the atmosphere from burning fossil fuels, oceans have absorbed about a third of this extra CO₂. This makes the water slightly more acidic and in theory makes it harder for corals to maintain their skeletons.

Coral in Tank 3 in July 2012. Conditions in this tank mimicked those expected in around 100 years if the world does nothing to kerb its fossil fuel use, with higher temperatures and acidity.


Coral in Tank 3 in March 2013. The coral has not survived and algae has taken over.

Warmer and cloudier water can also slow down the growth of corals and some studies have found corals are already growing more slowly in parts of the reef.

When increased temperatures put stress on corals their relationship with their colour-giving algae can break down, leaving behind a "bleached" coral.

"There's always life and death on the reef," says Dove. "We want to see if those corals that are bleached can spring back and go again.

"But we do need to look at what happens to dead coral because most of our live coral sits on a bed of dead stuff underneath. You don't want to be standing on a ladder that's full of woodworm.

"We want to keep the experiment running because we want to see how quickly some things disappear altogether."

Scientific studies published in recent weeks have used projections and computer models to predict the kind of effects on coral reefs that Dove can see in the tanks on Heron Island.

One study published in the journal Nature Climate Change looked at how often coral reefs might bleach in the future. The study found that under all but the most optimistic scenarios for cutting CO₂ emissions, bleaching would be an annual event for 95 per cent of the world's coral reefs by the year 2075

Some reefs in northwestern Australia were even more susceptible to bleaching, the study predicted, with annual bleaching taking place in less than 14 years from now if emissions go unchecked.

A recent study from Western Australia found that a severely disturbed reef may take as long as 12 years to recover from a bleaching.

Meanwhile a study led by the University of New South Wales Climate Change Research Centre found that reefs in shallow waters could be subjected to even higher levels of acidification than was previously thought.

Yet far from climate change being a problem for the future, Dove says the healthy coral in her 'pre-industrial' tanks suggests "the world's already been running a big experiment on the reef over the last 100 years".

She plans to keep her own experiment running to get at least a full year of observations and will soon start to write up results to submit to scientific journals.

When she moves off the subjects of statistics, measurement, "calcification rates" and "symbionts" and onto reefs as amazing places to visit, a whimsical smile breaks.

She has spent the last 30 years or so exploring the wonders of coral reefs. If she's not studying them, she's holidaying on them.

"Some places are just magic," she says. "It's beautiful. There is still some hope but we have to put in a bit of effort. I would hate for it not to be there for people to see."

http://www.abc.net.au/environment/articles/2013/04/15/3730941.htm

In depth article on coral reefs at Skeptical Science

Figure 6. Example of a French Polynesian reef devastated by a COTS outbreak. A, healthy reef with cover in excess of 40%; B, algae have colonized the reef after attack by COTS; C, weakened or dead coral are swept away by a cyclone leaving less than 5% living coral cover. From Kayal (2012). 

For article go to this link:  http://www.skepticalscience.com/Australias-Great-Barrier-Reef-Last-Chance-to-See.html

"Limiting global warming to 2 °C is unlikely to save most coral reefs," by K. Frieler et al., Nature Climate Change, 3 (2013); doi: doi:10.1038/nclimate1674

Nature Climate Change, 3 (2013) 165-170; doi: doi:10.1038/nclimate1674

Limiting global warming to 2 °C is unlikely to save most coral reefs

• K. Frieler,
• M. Meinshausen,
• A. Golly,
• M. Mengel,
• K. Lebek,
• S. D. Donner and
•  O. Hoegh-Guldberg

Abstract

Mass coral bleaching events have become a widespread phenomenon causing serious concerns with regard to the survival of corals. Triggered by high ocean temperatures, bleaching events are projected to increase in frequency and intensity. Here, we provide a comprehensive global study of coral bleaching in terms of global mean temperature change, based on an extended set of emissions scenarios and models. We show that preserving >10% of coral reefs worldwide would require limiting warming to below 1.5 °C (atmosphere–ocean general circulation models (AOGCMs) range: 1.3–1.8 °C) relative to pre-industrial levels. Even under optimistic assumptions regarding corals’ thermal adaptation, one-third (9–60%, 68% uncertainty range) of the world’s coral reefs are projected to be subject to long-term degradation under the most optimistic new IPCC emissions scenario, RCP3-PD. Under RCP4.5 this fraction increases to two-thirds (30–88%, 68% uncertainty range). Possible effects of ocean acidification reducing thermal tolerance are assessed within a sensitivity experiment.

At a glance

• Figures

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Link: http://www.nature.com/nclimate/journal/v3/n2/full/nclimate1674.html

Queensland floodwater threatens overwhelming damage to Great Barrier Reef

Floodwater threatens overwhelming damage to Great Barrier Reef

The great deluge is pumping contaminated water into the ocean, with potentially disastrous results

by Michael McCarthy, The Independent, U.K., January 13, 2011

JAMES COOK UNIVERSITY/ AFP/ GETTY IMAGES

Previous floods have hit the reef's biodiversity but this event is in a different league

Australia's great Barrier Reef, one of the ecological wonders of the world, may also be severely affected by the Queensland floods.

The pristine waters of the vast 1,400-mile reef system, home to thousands of exotic and often endangered marine species, from whales and dolphins, seabirds and tropical fish to tiny coral polyps, are threatened by huge volumes of polluted floodwater flowing out from the coast.

Already the brown flood "plume" has been detected offshore over a huge expanse of sea, stretching more than 1,000 miles from Cooktown in northern Queensland to Grafton, south of Brisbane in northern New South Wales. But it is in the centre of this area – the Barrier Reef's southern sector – that the threat is greatest.

Here, three big rivers are pouring their swollen and filthy waters out constantly – from north to south the Burdekin, which flows into the sea at Upstart Bay south of Townsville, the Fitzroy which enters the sea at Keppel Bay near Rockhampton, and the Burnett River, which empties into the Pacific at Burnett Heads near Bundaberg.

In all of these, top soil, sediment, rubbish, pesticides and fertilisers from farmland are being washed through the river systems out to sea, as well, potentially, as trace metals from flooded mines. All of these contaminants will be dumped on the reef and affect its salinity and water quality, besides directly threatening much of the fragile life in what is the world's largest living organism and the only one which can be seen from space.

The sediment in particular can silt up the coral reefs, the foundation for the whole ecosystem, and other habitats such as the extensive sea grass beds, which are used for grazing by those exotic sea mammals, dugongs. And there can be other, stranger impacts.

In the past, large floods of the Burdekin River have led to outbreaks of coral-eating crown-of-thorns starfish, and there is concern that a new wave could soon form on the reef.

"The timing and location of the three observed outbreaks of crown-of-thorns starfish in the past have all coincided with the times and place where the largest Burdekin floods have impinged on the reef," said Dr Katharina Fabricius, principal research scientist at the Australian Institute of Marine Science. "These outbreaks are still the greatest source of coral mortality on the Great Barrier Reef."

Off the Fitzroy River delta, where hydrologists estimate that the equivalent of three Sydney Harbours of floodwater is flowing out to sea through nearby Rockhampton and into the Great Barrier Reef lagoon every day, the Keppel Island group is in the firing line. Floods in 1991 wiped out vast swathes of coral in the islands.

Laureth Craggs, who runs the tourist resort of Pumpkin Island, said that water visibility was already down to one metre. "It is normally 25-30m under water, but the usually crystal-clear turquoise water is a murky mud brown," she said. "You can't see a thing."

Ms Craggs, who owns the five-cottage eco-island with her partner Wayne Rumble, said: "It is frightening to think that if 90 per cent of the coral dies, then all the sea life and tropical fish will also die with it or disappear."

"These are extraordinary events," said Jon Brodie, principle researcher for the James Cook University's Australian Centre for Tropical Freshwater Research. "The whole of the inner-shore reef lagoon is filled with river water."

Mr Brodie describes the threat to many coral reefs closest to the flooding rivers as "quite high" but expects the flood waters to affect in some way the reefs stretching from Frazer Island, 125 miles north of Brisbane, all the way to Cairns, 930 miles further north, as the prevailing tides and south-easterly winds mean the flood waters will probably continue to head in a northerly direction.

"It's quite remarkable to see," he said. "If you were to snorkel where the flood water meets the seawater and look to one side, the sea water will be clear with visibility to 50 metres, while the other side is fresh, dirty brown water where visibility is down to a metre."

The mix of nutrients, sediment and pesticides from agricultural run-off, plus unknown amounts of trace metals from flooded mines, will be likely to have an immediately devastating impact on corals and sea grasses, Mr Brodie said, with salinity possibly dropping to 10 parts per thousand or less, and remaining like that for weeks. "Nothing can live in those conditions," he said.

The reef is one of the world's most biodiverse, or species-rich, habitats in the world. Besides its 1,500 species of tropical fish, 30 species of whales, dolphins and porpoises have been recorded in its waters, along with six out of the seven sea turtle species, 15 species of seagrass, 215 species of birds and 17 species of sea snake.

Link:  http://www.independent.co.uk/environment/nature/floodwater-threatens-overwhelming-damage-to-great-barrier-reef-2183250.html

J. E. N. Veron: The end is in sight for the world’s coral reefs

Veron: The end is in sight for the world’s coral reefs

Climate Progress, December 7, 2010

Reefs are the ocean’s canaries and we must hear their call. This call is not just for themselves, for the other great ecosystems of the ocean stand behind reefs like a row of dominoes. If coral reefs fail, the rest will follow in rapid succession, and the Sixth Mass Extinction will be upon us — and will be of our making.

J.R.: When J.E.N. Veron speaks, we all should listen.  Veron is the former chief scientist of the Australian Institute of Marine Science.  He is principal author of 8 monographs and more than 70 scientific articles on the taxonomy, systematics, biogeography, and the fossil record of corals.  His books include the three-volume Corals of the World and A Reef in Time: The Great Barrier Reef from Beginning to End (2008).  His research has taken him to all the major coral reef regions of the world during 66 expeditions.
In a Yale e360 piece reprinted below, Veron explains that, “the science is clear: Unless we change the way we live, the Earth’s coral reefs will be utterly destroyed within our children’s lifetimes.”



Over the past decades, there have dozens of articles in the media describing dire futures for coral reefs. In the 1960s and 1970s, we were informed that many reefs were being consumed by a voracious coral predator, the crown-of-thorns starfish. In the 1980s and 1990s, although these starfish still reared their thorny heads from time to time, the principal threats had moved on — to sediment runoff, nutrients, overfishing, and general habitat destruction.

For me, an Australian marine scientist who has spent the past 40 years working on reefs the world over, these threats were of real concern, but their implications were limited in time or in space or both. Although crown-of-thorns starfish can certainly devastate reefs, the impacts of sediments, nutrients and habitat loss have usually been of greater concern, and I have been repeatedly shocked by the destruction I have witnessed. However, nothing comes close to the devastation waiting in the wings at the moment.

You may well feel that dire predictions about anything almost always turn out to be exaggerations. You may think there may be something in it to worry about, but it won’t be as bad as doomsayers like me are predicting. This view is understandable given that only a few decades ago I, myself, would have thought it ridiculous to imagine that reefs might have a limited lifespan on Earth as a consequence of human actions. It would have seemed preposterous that, for example, the Great Barrier Reef — the biggest structure ever made by life on Earth — could be mortally threatened by any present or foreseeable environmental change.  Yet here I am today, humbled to have spent the most productive scientific years of my life around the rich wonders of the underwater world, and utterly convinced that they will not be there for our children’s children to enjoy unless we drastically change our priorities and the way we live.  A decade ago, my increasing concern for the plight of reefs in the face of global temperature changes led me to start researching the effects of climate change on reefs, drawing on my experience in reef science, evolution, biodiversity, genetics, and conservation, as well as my profound interests in geology, palaeontology, and oceanography, not to mention the challenging task of understanding the climate science, geochemical processes, and ocean chemistry.

When I started researching my book, A Reef in Time: The Great Barrier Reef from Beginning to End (Harvard, 2008), I knew that climate change was likely to have serious consequences for coral reefs. But the big picture that gradually emerged from my integration of these disparate disciplines left me shocked to the core.

In a long period of deep personal anguish, I turned to specialists in many different fields of science to findanything that might suggest a fault in my own conclusions. But in this quest I was depressingly unsuccessful. The bottom line remains: Science argues that coral reefs can indeed be utterly trashed in the lifetime of today’s children. That certainty is what motivates me to spread this message as clearly, and accurately, as I can.

So what are the issues? Most readers will know that there have been several major episodes of mass bleaching on major reef areas worldwide over the past 20 years. In the late-1980s when the first mass bleaching occurred, there was a great deal of concern among reef scientists and conservation organizations, but the phenomenon had no clear explanation. Since then, the number and frequency of mass bleachings have increased and sparked widespread research efforts.

Corals have an intimate symbiotic relationship with single-celled algae, zooxanthellae, which live in their cells and provide the photosynthetic fuel for them to grow and reefs to form. The research showed that this relationship can be surprisingly fragile if corals are exposed to high light conditions at the same time as above-normal water temperatures, because the algae produce toxic levels of oxygen, and excessive levels of oxygen are toxic to most animal life. Under these conditions, corals must expel the zooxanthellae, bleach, and probably die or succumb to the toxin and definitely die. A tough choice, one they have not had to make at any time in their long genetic history.

We tend to think of temperature in terms of our day-to-day comfort level. We don’t have to be told that atmospheric temperature shows huge swings and variations from day to night, among seasons, and cyclically on other scales. Early critics of global warming used this variability to argue that there was no evidence for overall thermal increases. This missed the point and delayed our recognition of the true problem because atmospheric temperature is only a minor part of the Earth’s thermal picture.

By far the most important mobile heat sinks on the planet are the oceans. As the greenhouse effect from elevated CO2 has increased, the oceans have absorbed more heat. The surface layers are affected most as mixing to the depths can take hundreds of years. Large ocean masses such as the Indo-Pacific Warm Pool do not continue to warm further, but rather they broaden and deepen. Now they commonly become so large that their outer edges are pulsed onto the continental margins, where waters are warmed further. This creates the mortal dilemma for corals — to expel or not to expel their oxygen-producing zooxanthellae.

Ecosystems can recover from all sorts of abuse, and coral reefs are no exception. Good recoveries from bleaching have been observed, provided that further events do not occur while the ecosystem is re-establishing. Unfortunately, there are no signs that greenhouse gas increases are moderating, and so we can assume that the frequency and severity of bleaching events will continue to increase — on our present course, the worst bleaching year we have had to date will be an average year by 2030, and a good year by 2050. Ocean and atmospheric rises in temperature are also predicted to increase the severity of cyclones, which will add an extra burden on the recovery process.

Scientists don’t need a pocket calculator to conclude that compressing the time periods between events in this way will prevent recovery: If we do not take action, the only corals not affected by mass bleaching by 2050 will be those hiding in refuges away from strong sunlight.

But there is more bad news. A decade or so ago, we thought that mass bleaching was the most serious threat to coral reefs. How wrong we were. It is clear now that there is a much more serious crisis on the horizon — that of ocean acidification. This will not only affect coral reefs (although reefs will be hit particularly hard), but will impact all marine ecosystems. The ultimate culprit is still CO2 but the mechanism is very different.

Normally there is a balance between CO2 in the atmosphere and its derivatives in surface waters of the ocean. As with temperature, the oceans act as a huge repository, absorbing and buffering any excess CO2 in the atmosphere. For this process to be efficient the oceans must have time for mixing to occur between its different layers, renewing the surface buffers from below. When CO2 increases too rapidly, these chemical reactions can falter, altering the balance of the buffers and gradually allowing the oceans to become less alkaline.

All organisms that produce calcium carbonate skeletons (including shells, crabs, sea urchins, corals, coralline algae, calcareous phytoplankton, and many others) depend on their ability to deposit calcium carbonate, and this process is largely controlled by the prevailing water chemistry. As alkalinity decreases, precipitation of calcium carbonate becomes more and more difficult until eventually it is inhibited altogether. The potential consequences of such acidification are nothing less than catastrophic.

In my book, I examine the events that led up to each of the five mass extinctions in Earth’s history. Corals offer a unique insight into the past, both because they have been around for most of the history of life on Earth and also because they readily fossilize. I examine the theories offered to explain these global extinctions and find that ocean acidification is the only explanation which fits the evidence well. Ocean acidification has played a major part in the marine devastations which took place in those ancient times.

A particularly galling aspect of the past four mass extinction events (very little is known about the first) is that, following them, reefs disappeared — not just for a few tens of thousands of years, but for millions of years — long after adverse climatic conditions may have returned to benign levels. One of the characteristics of acidification is that while it can be initiated by high CO2 levels over relatively short periods, there are no short-term geochemical fixes to reverse the process. Reversal can take place only through the immensely slow weathering and dissolution processes of geological time, processes that take hundreds of thousands to millions of years.

Ocean physics dictates that we will observe the effects of acidification in colder and deeper waters before it spreads to shallower tropical climes. The early stages of acidification have now been detected in the Southern Ocean and, surprisingly perhaps, in tropical corals. On our current trajectory of increasing atmospheric CO2, we can expect that by 2030 to 2050 the acidification process will be affecting all the oceans of the world to some degree. At that point, the relatively cool, deep-water tropical regions that have offered refuges to corals from temperature stress will be those most affected by acidification.

No doubt different species of coral, coralline algae, plankton, and mollusks will show different tolerances, and their capacity to calcify will decline at different rates. But as acidification progresses, they will all suffer from some form of coralline osteoporosis. The result will be that corals will no longer be able to build reefs or maintain them against the forces of erosion. What were once thriving coral gardens that supported the greatest biodiversity of the marine realm will become red-black bacterial slime, and they will stay that way.

Another concept of great importance is that of commitment — a word climatologists use only too often. Many of the consequences of our current actions cannot yet be seen, and yet the Earth is already committed to their path. This delayed reaction is due to the inertia of the oceans, both thermal and chemical. The greenhouse gases we produce today will take a number of decades (and sometimes more) to unleash their full fury, but their effects are unavoidable and unstoppable. We cannot afford to wait until the predictions of science can be totally verified, because by that time it will be too late. How many of us wish to explain to our children and children’s children that the predictions were there but we wanted confirmation?

Coral reefs speak unambiguously about climate change. They survived Ice Age sea-level changes of 120 meters or more with impunity. They once survived in a world where CO2 from volcanoes and methane was much higher than anything predicted today. But that was over 40 million years ago, and the increase took place over millions of years, not just a few decades, time enough for ocean equilibration to take place and marine life to adapt.

This is not what is happening today. Ponder these facts: The atmospheric levels of CO2 we are already committed to reach, no matter what mitigation is now implemented, have no equal over the entire longevity of the Great Barrier Reef, perhaps 25 million years. And most significantly, the rate of CO2 increase we are now experiencing has no precedent in all known geological history.

Reefs are the ocean’s canaries and we must hear their call. This call is not just for themselves, for the other great ecosystems of the ocean stand behind reefs like a row of dominoes. If coral reefs fail, the rest will follow in rapid succession, and the Sixth Mass Extinction will be upon us — and will be of our making.

- J.E.N. Veron

Related posts:

• Scientists: Caribbean coral die-off may be worst ever, Southeast Asia and Indian Ocean bleaching “may prove to be the worst such event known to science.”
• Nature Geoscience study: Oceans are acidifying 10 times faster today than 55 million years ago when a mass extinction of marine species occurred
• Geological Society: Acidifying oceans spell marine biological meltdown “by end of century” — Co-author: “Unless we curb carbon emissions we risk mass extinctions, degrading coastal waters and encouraging outbreaks of toxic jellyfish and algae.”
• Nature Geoscience study concludes ocean dead zones “devoid of fish and seafood” are poised to expand and “remain for thousands of years”

Link:  http://climateprogress.org/2010/12/07/j-e-n-veron-coral-reefs-bleaching/#more-38111