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Climate At A Glance Factchecks–Coral Reefs

March 21, 2020

By Paul Homewood




The Heartland Institute have introduced an important new website, Climate at a Glance, which present short one or two page factchecks about many of the topics involving both climate and energy issues.

I will try and publish one topic each day, but it is well worth bookmarking their site for future reference. I will tag each post as “Factcheck”, and there is also a Factcheck tag at the top of my website.

Today, I’ll start with the subject of coral reefs:


A thriving coral reef. Photo by Francesco Ungaro. Licensed from

View this page in a printable PDF here:



Bullet Point Summary:

  • Coral thrive in warm water, not cold water.
  • Recent warming has allowed coral to expand their range poleward, while still thriving near the equator.
  • Coral has existed continuously for the past 40 million years, surviving temperatures and carbon dioxide levels significantly higher than what is occurring today.
  • The primary causes of coral bleaching include oxybenzone (a chemical found in sunscreen), sediment runoff from nearby coastal lands, and cold temperatures like those recorded in 2010 off the Florida coast.

Short Summary: Coral require warm water, not cold water, to live. Coral cannot live outside of tropical or subtropical waters. (See Figure 1.) As Earth continues to modestly warm, coral are extending their range toward the poles while still thriving at and near the equator. The primary reasons for bleaching events include sediment pollution from nearby coastal lands, chemicals found in sunscreen, and cold temperature events. Coral have existed continuously for the past 40 million years. Coral survived and thrived when temperatures were significantly warmer than they are today.


Temperature Swings: Short-term strong heatwaves or cold snaps can cause bleaching events, but such events have occurred long before recent warming. Moreover, studies show coral can and do adapt to the gradual long-term pace of global warming. History shows that cold snaps can harm coral much worse than warm spells. In 2010, colder ocean temperatures off the coast of Florida killed more coral than any warm-water event, killing more than 40 percent of reef-building corals.

A poster child for coral alarmism is the Great Barrier Reef. The Great Barrier Reef is 20 million years old, and it has survived significantly warmer temperatures than today. Although the Australian Institute of Marine Science documented that approximately 22 percent of the reef experienced recent bleaching (not 93 percent, as reported in alarmist media stories), 75 percent of the bleached portion of the Reef is expected to make a full recovery. Poor water quality resulting from nearby coastal development is the main culprit for bleached reef areas that do not recover. Evidence shows much of the bleached coral in the Great Barrier Reef are recovering.

Figure 1: Coral Reef Locations

Coral continue to require warm water and thrive in the warmest of Earth’s waters.
Source: NOAA Ocean Service Education, 

Quote from the source:

The majority of reef building corals are found within tropical and subtropical waters. These typically occur between 300 north and 300 south latitudes. The red dots on this map show the location of major stony coral reefs of the world.”

Climate At A Glance is a Project of The Heartland Institute

© Copyright – The Heartland Institute

  1. Broadlands permalink
    March 21, 2020 1:39 pm

    “Temperature Swings: Short-term strong heatwaves or cold snaps can cause bleaching events…”

    It seems important to distinguish between air temperature swings and surface water temperatures when evaluating coral reef bleaching events. There has been no evidence that any ‘heatwaves’ or ‘cold snaps’ have been involved on the Great Barrier Reef…

    The other causes mentioned are involved along with solar UV under clear water conditions.

    Gleason, D.F. and Wellington, G.M. 1993. Ultraviolet radiation and coral bleaching. Nature 365: 836-838.

    • A C Osborn permalink
      March 21, 2020 5:52 pm

      Yes, one they missed is low water levels allowing UV to bleach them.
      ie the opposite of Rising Sea Levels.

      • Mack permalink
        March 21, 2020 8:18 pm

        Might have missed this too, but I’m sure Crown of Thorn Starfish are known to have periodically wreaked havoc on healthy coral reefs. The destruction caused is quite significant and, unbelievably, not a single starfish has fossil fuelled engines. Quite remarkable really.

      • Bloke no longer down the pub permalink
        March 22, 2020 1:48 pm

        Yep, combination of El Niño and king tides can drop sea level sufficiently to expose reefs to more sunlight than’s good for them. Another vital element to reef health is the Parrot fish. Over-fishing reduces numbers of these creatures and puts the reef out of balance.

  2. tom0mason permalink
    March 21, 2020 3:42 pm

    Also of note is that ‘corals’ are not just one species or thing. They are many species that take advantage of the local resources (including the climatic conditions).

    Also of note is that there are such things as cold water corals .

    “The habitat of deep-water corals, also known as cold-water corals, extends to deeper, darker parts of the oceans than tropical corals, ranging from near the surface to the abyss, beyond 2,000 metres (6,600 ft) where water temperatures may be as cold as 4 °C (39 °F). Deep-water corals belong to the Phylum Cnidaria and are most often stony corals, but also include black and horny corals and soft corals including the Gorgonians (sea fans).[1] Like tropical corals, they provide habitat to other species, but deep-water corals do not require zooxanthellae to survive.”

    Also see the freely available ‘Corals of the Aleutian Islands’ at ( ) to see some of the very colorful corals off the Canadian coast.

    Warm water or cold water the corals can survive!

    • March 21, 2020 5:53 pm

      To put that in context;

      Mammals facing inordinate pressure towards extinction. Since the 1500, somewhere between 80 – 130 mammals species have gone extinct, while the IUCN lists only 34 reptiles and 58 insects and 190 birds species of birds as well.

      The raw numbers don’t tell the real story: as a percentage of diversity within each kingdom,
      Mammalian approx 2%
      Reptilian approx .3%
      Avian approx 1.9%
      Insect approx .002%
      Protozoian approx .000001%

      It is the mammals we must worry about. It is mostly rodents that are perishing in the mammalian world, with a few Australian varieties.

      That is if you feel we must worry about this. I am not sure that Dodo’s in the wild were a great evolutionary path. Nor do I believe we should save smallpox. The fact that they now regularly talk about ‘local extinction’ and ‘ocean acidification’ when it is ‘change of range’ and ‘ocean nuetralization’ .

      Creating spin by connotative mechanism just exposes their activism.

  3. Joel Heinrich permalink
    March 21, 2020 4:53 pm

    there are corals even at a temperature of -1.5°C.

  4. OldFogey permalink
    March 22, 2020 12:26 am

    Paul, Are you going to send these comments to the Heartland Institute, to give them the opportunity to improve their sheets?

  5. March 22, 2020 6:01 am

    Yes sir, thank you very much for this much needed clarification of a persistent climate science lie. Corals do bleach when it gets too hot but that doesn’t mean the end of coral. Coral bleaching and recovery cycles have been a natural cyclical event for time immemorial. Yet another good source in this area of research is Professor Paul Kench

  6. paul weldon permalink
    March 22, 2020 7:50 am

    I am surprised that the lowering of sea-water pH has not got a mention – many websites still put forward the lie that shells (and corals) are struggling because of a lack of carbonate in the water. Whereas in fact, it is bicarbonate that is used to make the shells. Shell dissolution is supposedly increasing, but no mention is given to the fact that most shells have a protective coating..
    Described as the ‘evil twin’ of climate change, total blame is given to the demon CO2. This subject has a strong influence on alarmists, so it might be prudent for the theme to be covered.
    On the same subject, I find it tragic that marine biologists do nothing to counter-act the false information given out by many websites.

    • March 22, 2020 1:25 pm

      This is a real good tweet from paul weldon. as for melting shells and all, what they haven’t explained is why benthic shelled critters like to hang out around hydrothermal vents.

    • Broadlands permalink
      March 22, 2020 1:44 pm

      The problem of current views on marine pH changes and “demon CO2” could be put to rest by reading and citing this comprehensive paper published in 1919…

      A.G. Mayor, On detecting ocean currents by observing their hydrogen ion concentration.

      Proceedings of the American Philosophical Society, Vol. 58, No. 2 (1919), pp. 150- 160

      Click to access 984531.pdf

  7. edwardrodolph1891 permalink
    March 22, 2020 10:16 am

    Even in totally non-polluted waters near remote Indian Ocean islands one can find dead bleached coral, – it HAS been dying off naturally for millions of years, -and re-growing nearby. Crown of thorns starfish eat it, parrot fish endlessly gnaw at it it. ALL natural and NOTHING to do with sea warming or level increasing. Not greta ‘tear-jerker’ thunberg either. ‘

  8. Harry Davidson permalink
    March 22, 2020 10:36 pm

    ‘Climate at a glance’ will not remain credible as it stands. The irritating style with every article on the home page having a title starting “Climate at a glance: …..”. No BTL verification for people to point out where they have got it wrong. No ‘Contact Us’ address to tell them where they have got it wrong (they will sometimes).

    It’s a bit hectoring and “we know best”. Not a stance that Climate Sceptics warm to.

    I would tell them this directly, but no ‘Contact Us’, which underlines the problem.

    • paul weldon permalink
      March 23, 2020 8:04 am

      I would agree with you, Harry. Reminds me of a Punch and Judy show. Not for those that wish to go deeper into a subject to discover what is truth, what is propaganda. I was most disappointed about the reference to corals needing warm water. That mat be true in most cases, but no reference to how close the sea-water temperature is to the edge of the range in which they are found. Not a site I would look to for enlightenment.

      • March 23, 2020 10:32 am

        The trouble is that most people have no interest in delving into the details – they merely believe the propaganda fed to them by the media.

        To address this we need short, punchy factsheets

  9. March 23, 2020 3:47 am

    May I add another fact check here? Climate at a glance. Fact checks. Antarctica.

  10. March 23, 2020 4:52 am

    Bleaching in the Great Barrier Reef is caused by elevated temperatures during el Ninos and is something the reef has been coping with for millions of years; elevated temperatures mean that the surrounding Ocean give off CO2 – ie increasing pH – not decreasing it, which is what is implied by the unscientific term ‘acidisation’ Run off is not a serious contender in the Great Barrier Reef, most of which lies some 200km out to see where searches for land based pollutants has failed to find anything. Even close inshore human pollution has not affected reef growth. Much of this is covered by IPA at

    • paul weldon permalink
      March 23, 2020 8:18 am

      I find it difficult to believe that pollution has no effect on coral growth. Of course it depends on what the pollution is. Increase in nutrients would mean a change in the coral ecosystem. Any change in water clarity is gong to have a marked effect. Any change in the functioning of the coral ecosystem will have knock-on effects on CO2 content and thus pH. The situation is much more complex than both sides of the climate argument state. As far as I can gather, that was the main thrust of Peter Ridd’s argument. I fully support him in this, let’s take an holistic view of the situation and not just get into a rut with our pre-conceived beliefs.

  11. Tim Spence permalink
    March 23, 2020 9:43 am

    Never mind the corals, stock up on candles. We all know what’s going to happen to the grid with increased home demand and especially if there’s a shortage of workers and supplies for generation.

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