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Climate change guardrail too hot for coral reefs?

One of the ambitions of the United Nations Framework Convention on Climate Change (UNFCCC) is galvanising the international community to avoid dangerous interference with Earth’s climate. To do this, it…

We thought we’d set a safe limit on climate change - 450ppm CO2 - but it may be too high for most of the world’s reefs. Paul Toogood

One of the ambitions of the United Nations Framework Convention on Climate Change (UNFCCC) is galvanising the international community to avoid dangerous interference with Earth’s climate. To do this, it sets limits to the amount of change we can afford. But new research on reefs suggests the limits are too high.

The UNFCCC tries to reduce climate change to a point where humans have a chance to tolerate or adapt to any changes. The currently accepted point is 450 ppm of CO₂ in the atmosphere. But there is growing evidence that 450 ppm (which is likely to result in an average global temperature around 2 degrees warmer than the pre-industrial period) may result in unacceptable change and risks to natural and human systems.

In the case of the world’s ocean, 450 ppm will see us reach key thresholds such as under-saturation in the Southern Ocean. This is the concentration at which calcium carbonate crystals, in many shells and skeletons, no longer form naturally. This is also the point at which the resulting sea temperatures will begin to irreversibly impact ecosystems from coral reefs to kelp forests. These changes in the ocean are matched by similar points within terrestrial systems as the 450 ppm threshold is reached and exceeded.

Most importantly, 450 ppm appears to be the lowest emission scenario to deliver a climate that somewhat stabilises by the end of the century. At higher temperatures, the climate increasingly continues to change for many decades and centuries.

The “burning embers” diagrams from the Intergovernmental Panel on Climate Change in 2001 (see Figure 1) provide a convincing case for adopting a 450 ppm or 2°C climate change “guardrail” to avoid dangerous climate change. This sentiment was central to the synthesis report published by the Climate Change Congress held in Copenhagen in March 2009. Since then, it has become central plank of climate policy, driving discussions at the 15th Conference of the Parties (COP 15) and the United Nations Framework Convention on Climate Change later that year in Copenhagen.

Figure 1: ‘Burning embers’ Intergovernmental Panel on Climate Change

But recent evidence suggests that the 450 ppm guardrail may not be as safe as at first thought. Our modelling study published in international journal Nature Climate Change this week reveals that increasing global temperatures to 2°C above pre-industrial global temperatures will be too hot for two-thirds of the world’s corals and reefs.

The study involved scientists from Potsdam, the University of British Columbia in Canada and the Universities of Melbourne and Queensland in Australia. To project the cumulative heat stress at 2160 reef locations worldwide, they used 19 global climate models that represent the combined work of the Coupled Model Intercomparison Project. By applying different emission scenarios covering the 21st century and multiple climate model simulations, a total of more than 32,000 simulation years was diagnosed. This allows for a more robust representation of the implications of the current set of climate projections, and consequently the inherent uncertainties, than any previous study.

The news from the study published today is not encouraging. Corals might be okay if they were able to adapt to the changes through rapid evolution. However, this is extremely optimistic and has little scientific evidence to support it.

Corals also have long generation times that may range from five to several hundred years, and often relatively low levels of genetic diversity. All of these features of their life cycle militate against the rapid evolution of corals to keep pace with rising sea temperatures.

In a nutshell, corals are not like fruit flies or bacteria, which have much shorter generation times (hours to weeks) and consequently can evolve relatively rapidly.

Per Edin

The paper also investigates what would happen if the susceptibility of corals to thermal stress increased as a result of other factors such as ocean acidification and pollution.

Ocean acidification is a consequence of the increasing amount of carbon dioxide entering the world oceans. Recent studies have indicated that the sensitivity of corals to thermal stress increases when they are exposed to acidified conditions. This situation has serious implications: current estimates of thermal sensitivity might underestimate, not overestimate, the future impact of climate change on corals.

On the basis of this information, the authors conclude that the thermal threshold required to protect at least half of the coral reefs worldwide lies at or below a 1.5°C mean increase in global average temperature.

The key question in all of this is how general the analysis and conclusions are for other systems. Recent observations of the behaviour of Arctic summer sea ice (which is plummeting and may disappear as early as the end of this decade) suggest that like corals, sea ice dynamics are much more sensitive to changes in greenhouse gases and hence average global temperature than at first thought.

We may have to revise our understanding of the vulnerability of Earth’s natural and physical systems. If so, we may need to rethink the past 2°C climate change guardrail and readjust it to 1.5°C or even lower. While this may seem like an ever-shifting guardrail, getting an accurate picture on where it lies is absolutely crucial to the international policy on climate change that the world is so desperately needs.

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39 Comments sorted by

  1. Mike Swinbourne

    logged in via Facebook

    Dr Hoegh-Guldberg,

    I have read many of your papers on the likely impact of climate change on coral, and your warnings could not be clearer or more stark.

    Unfortunately, your warnings about 450ppm CO2 would appear to be coming too late. We already appear to be on track to surpass that in the next decade or so, with little to no prospect of remaining on the 'safe' side. Everything I have read indicates that there is already enough energy in the system to surpass your 1.5 degree limit, and we are committed to burning enough fossil fuels to take us well past the 2 degree limit.

    What then for corals, for the oceans, and for human civilisation? For there is little doubt, that if your predictions about coral decline are to come to pass, then it is more than the loss of some nice holiday destinations, it is about a total collapse of the ocean ecosystem.

    Of all the warnings about climate change, this one would have to be the most dire.

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    1. John Coochey

      Mr

      In reply to Mike Swinbourne

      And what would be the cost of reaching this goal given Lomborg's recent statements?

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    2. Mike Swinbourne

      logged in via Facebook

      In reply to John Coochey

      I think that's the point John.

      How much would you be prepared to pay to ensure the health of the oceans on which we rely for survival? Because rest assured, if these predictions about coral decline and the ocean ecosystem are valid, then the costs of inaction would be far greater.

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    3. John Coochey

      Mr

      In reply to Mike Swinbourne

      IF you are not aware of it Lomborg's statement was that Europe would spend $250 billion every year to the end of the century for a result of one twentieth of a a degree. Are you aware of the economic concept of Budget Constraint?

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    4. Mike Swinbourne

      logged in via Facebook

      In reply to John Coochey

      I am aware of Lomborg's statements - what of them? What makes you think they are accurate?

      And I ask again John - what do you think would be the cost of a total collapse of the ocean ecosystem? How much would you be willing to pay to stop that from happening? Because if it does, it will be much more than a few dollars (or euros) that we have to worry about

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    5. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to Mike Swinbourne

      Mike,
      In your estimation what do you consider the odds are of a "a total collapse of the ocean ecosystem?"

      Do you think this opinion has a touch of hyperbole to it?

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    6. David Arthur

      resistance gnome

      In reply to John Coochey

      Err, Mr Lomborg is pretty clueless about climate change, as evidenced by his blithe discounting of the costs of sea level rise and of forced large-scale polewards emigration over the next couple of centuries.

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    7. David Arthur

      resistance gnome

      In reply to John Coochey

      Don't forget, every one of those $250 billion dollars is a saving on the fossil fuel bill.

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    8. John Coochey

      Mr

      In reply to Mike Swinbourne

      This is typical of the Student Association mentality, you are not one of the club so we will ignore you. If Lomborg is incorrect explain why and give alternative figures. The most humanity can do is disappear when the senior Climate Change Commissioner was asked how long it would take for the world to cool he said a thousand years. When Andy Pitman of the ANU was asked the same question he said no cooling for twenty to thirty. I have asked three eminent Climate Scientists (please note capitalization) who was correct and non could give a coherent answer, Ian Chubb the Chief Scientist answering he did not have a clue. So what is the answer if the science is settled? Obviously any action less than total cessation would have a lesser effect.

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    9. John Coochey

      Mr

      In reply to David Arthur

      Well actually no. There is the issue of capital expenditure and spinning reserve for when the sun goes behind a cloud.

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    10. John Coochey

      Mr

      In reply to David Arthur

      So the real figures are?

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    11. Mike Swinbourne

      logged in via Facebook

      In reply to Marc Hendrickx

      Marc

      "....In your estimation what do you consider the odds are of a "a total collapse of the ocean ecosystem?...."

      High

      "...Do you think this opinion has a touch of hyperbole to it?..."

      No.

      But don't take my opinion on the issue Marc - I am not an oceanographer. But Dr Hoegh-Guldberg is - in fact he is one of the world's pre-eminent experts on corals. As you claim to be a geologist, that must mean that you studied some science at university once upon a time. Why don't you go away and read some of his work, and see what he has to say on the issue.

      Then, if you think he is wrong - because it is his work we are discussing here - then you can come back and tell us what you have found and why you believe it is wrong. With evidence of course.

      So how about it Marc? What is wrong with Dr Hoegh-Guldberg's work? What is your evidence for that view?

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    12. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to Mike Swinbourne

      While I understand from reading quite a few of his papers that Dr Hoegh-Guldberg considers there is a problem, I don't think I have ever heard him or any other experts state that there is a high likelihood of a (quote) "total collapse of the ocean ecosystem" (unquote). It seems you have misunderstood the evidence in regard to this. The statement is pure exaggeration, and hyperbole.

      Perhaps you (or indeed perhaps Ove) can point out where a (quote) "total collapse of the ocean ecosystem" (unquote) is indicated in the peer reviewed literature for CO2>450ppm..

      Geological evidence indicates a (quote) "total collapse of the ocean ecosystem" (unquote) is highly unlikely.

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    13. David Arthur

      resistance gnome

      In reply to John Coochey

      Much much much higher - incalculably high.

      1) Abandonment of most Pacific Islands, including Nauru and Manaus Is.

      2) Abandonment of (in no particular order) Florida and Louisiana, much of London, Denmark and the Netherlands, most of Bangladesh, the Nile delta, Shanghai, even Gold Coast canal estates, much of Brisbane and Sydney.

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    14. David Arthur

      resistance gnome

      In reply to John Coochey

      The spinning reserve furphy is blown out of the water by the recent experience of South Australia.

      I strongly recommend you to start Business Spectator's site specialising in business developments in addressing climate change - Climate Spectator (http://www.climatespectator.com.au). It's free.

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    15. John Coochey

      Mr

      In reply to David Arthur

      And when? I remember being told many Pacific Island would disappear whereas they are getting larger, as is Bangladesh.

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    16. Grendelus Malleolus

      Senior Nerd

      In reply to John Coochey

      As far as Bangladesh is concerned John, you are correct. At present it is growing at around 20 square kilometres each year - almost entirely as a result of deposits of sediment from the Ganges, the Brahmaputra and other rivers. This is nothing new however as the land area of Bangladesh has been growing in this manner for quite some time. The problem is that sea levels in that area are indeed rising and it is becoming a race between the rate of deposit, and the rate of sea level rise. As you can imagine…

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    17. David Arthur

      resistance gnome

      In reply to John Coochey

      Mr Coochey asks when we can expect big sea level rises.

      At least 1m mean sea level rise, possibly 2m, by 2100, requiring retreat of several hundred metres in many coastal locations. That's a big infrastructure bill, and a huge hike in insurance premiums, assuming you can find an insurer willing to take on your risk. It's also a major loss in propoerty value for affected land (but possibly good for real estate values in the slightly elevated hinterland).

      There is a significant likelihood that Greenland's ice-cap will be irreversibly collapsing by 2500. That's 8m sea level rise on its own; further rises depends on Antarctic processes.

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  2. Marc Hendrickx

    Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

    Perhaps it's time to experiment with transplanting corals from the Persian Gulf into systems considered susceptible to predicted temperature extremes. The Gulf corals are presently thriving in a thermal regime the IPCC have predicted for tropical oceans for 2090-2099.

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    1. David Arthur

      resistance gnome

      In reply to Marc Hendrickx

      We know that corals can adapt to changing temperatures, provided the rate of change is slow enough. Translocating corals implies translocating substantial chunks of alien ecosystem, with their supporting algae and microbiota.

      Just as introduced species may play havoc with the natives, varying water chemistry (eg salinity) may not be good for the transplanted community.

      Both native and alien species must also cope with rapidly altering water chemistry due to elevated acidity. To get you started on your journey of learning, try these:
      http://research.nmsu.edu/molbio/bioinfo/tutorials/env-engr/carbonate/carbonate.html
      http://www.chem1.com/acad/webtext/pdf/c3carb.pdf
      http://envsci.rutgers.edu/~reinfelder/cpesnotes/carb.pdf
      http://www.reefresilience.org/Toolkit_Coral/COAa2_CarbonateSystem.html
      http://www.scopenvironment.org/downloadpubs/scope13/chapter09.html

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    2. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to David Arthur

      David, You seem to be at odds with Prof. Hoegh-Guldberg on this. To get your learning journey on the right track see the following paper in which he and other authors write the following; (link below-open access):

      "We argue here that Gulf corals should be considered for assisted migration to the tropical Indo-Pacific. This would have the double benefit of avoiding local extinction of the world's most heat-adapted holobionts while at the same time introducing their genetic information to populations…

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    3. David Arthur

      resistance gnome

      In reply to Marc Hendrickx

      Thanks Marc. If you re-read what I wrote, you'll realise that I'm not saying that the proposal is without merit.

      What I'm doing is pointing out some of the ecological difficulties that may be encountered. Thanks for the reference, I expect that Reigl et al are aware of the issues I raise.

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    4. Grendelus Malleolus

      Senior Nerd

      In reply to Marc Hendrickx

      Perhaps it's time to experiment with transplanting corals from the Persian Gulf into systems considered susceptible to predicted temperature extremes. The Gulf corals are presently thriving in a thermal regime the IPCC have predicted for tropical oceans for 2090-2099..

      Sort-of true Marc. The rationale for migrating some corals is two-fold. The first issue is that in situ the water temperature in the Gulf is predicted to increase to beyond a survivable threshold for many colonies witnin the next 30-50 years. Moving some species to the Indian Ocean will preserve them till at least the end of the century - which is when Indian Ocean temperatures are expected to approach those of the Gulf. Unfortunatly it appears that the Great Barrier Reef will reach that point somewhat earlier around 2050.

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    5. John Nicol

      logged in via email @bigpond.com

      In reply to Grendelus Malleolus

      These would be good experiments for people such as Ove Hoegh-Guldberg to work on.

      Rather than simply worrying about what may be an inevitable warming of the planet, this would unboubtedly prove to be a relaxing and useful exercise.

      Remember that the planet may well start warming again as between 1979 and 1998 and also we should accept that since it has been recovering from the Little Ice Age since about 1850, it is likely to keep warming for a little while longer, just as it has warmed steadily…

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    6. David Arthur

      resistance gnome

      In reply to John Nicol

      "Since the planet has entered all major Ice Ages and the Little Ice Age in much earlier times without any help from mankind ..."
      Correct, John: in fact, since the onset of the Pleistocene, the glaciated state known as "Ice Age" has been the planet's most common climatic mode. This is because the dispositions of continents and oceans have favoured CO2 dissolution in the Southern Ocean, which has cooled the atmosphere and thence the oceans leading to expansion of Northern Hemisphere ice-sheets…

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  3. Comment removed by moderator.

  4. David Nutzuki

    logged in via Twitter

    You amateur arm chair wanna be climatologists are too too funny!

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    1. John Coochey

      Mr

      In reply to David Nutzuki

      I understand Flannery's first degree was in English Literature and Pitman's was in geography. I studied both so does that make me one of the club?

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  5. Comment removed by moderator.

  6. Tim Scanlon

    Debunker

    Cutting emissions and reducing the impacts, this seems to be a standard call that has come from climate science since before I was born. All I have to say is that it is about time it started happening.

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  7. Toby James

    retired physicist

    The data show that the upper 700 metres of the oceans have not warmed for 10 years, despite the continued rise of atmospheric CO2. And by no means all the experts believe that corals are doomed - even if the oceans begin to warm in the future.

    This seems to be rather an alarmist prognostication, given the facts.

    Perhaps a little more balance would give an article like this a little more interest for an uncommitted reader.

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    1. trevor prowse

      retired farmer

      In reply to Toby James

      Could someone comment on the following----the nearest temperature measurements to the GBR are the BOM`s 70 years records at Willis Island which show no extreme temperature rise. Also does the variation in sea temperatures between the north and south of the GBR equal the projected sea temperature rise for the next 100 years. Why has not the scientific people who study the reef brought these statistics to the notice of the public ?

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    2. Toby James

      retired physicist

      In reply to trevor prowse

      Trevor, the answer to your question relates to the nature of climate science. Facts are not generally part of the equation - they're a nuisance.

      Its all about models and keeping as many people awake at night with fear as possible.

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    3. David Arthur

      resistance gnome

      In reply to Toby James

      Oceans not warmed over the last 10 years? They're transferring heat to polar ice sheets, which melt taking up the heat.

      It's kind of like putting your party beers in a bathtub with ice: so long as there's still some unmelted ice, the beers stay cold.

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    4. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to David Arthur

      David the heat seems to be heading north only, SH sea ice is near record levels.

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    5. David Arthur

      resistance gnome

      In reply to Marc Hendrickx

      Quite correct Marc, largely because, despite increases in both West and East Antarctica snowfall (increased evaporation off the Southern Ocean), terrestrial ice mass over both parts of Antarctica are in net decline. Ergo, Antarctic glaciers must be speeding up, by more than that forced by the increased snow mass.

      Hence, more pack ice around Antarctica.

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    6. David Arthur

      resistance gnome

      In reply to Marc Hendrickx

      For more information, try Golledge et al. Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing. Proceedings of the National Academy of Sciences, 2012; DOI: 10.1073/pnas.1205385109

      There's a news release about it at Science Daily: "Warming Ocean Could Start Big Shift of Antarctic Ice", http://www.sciencedaily.com/releases/2012/09/120919103610.htm

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