New Scientist: Bleaching Protects Coral – But Only Up to 2C of Global Warming

Guest essay by Eric Worrall

New Scientist has discovered that bleaching is a mechanism by which coral protects itself from abrupt warming (or cooling). But if global warming hits 2C, somehow all the coral will know it is time to die.

Corals swap in heat-resistant algae to better cope with global warming


By  Karina Shah

Some corals can swap out the algae that live inside their tissues for different strains that are more heat tolerant – and these coral species have a better chance of surviving global climate change in the coming decades.

When sea temperatures are too high, corals expel the microscopic algae living in their tissues. This is what occurs during coral bleaching. Losing algae in this way is harmful for the corals because the algae normally provide oxygen for them and remove their waste products. However, marine biologists have previously discovered that when some corals are exposed to warmer temperatures, they can swap the algae inside their tissues for strains that have a higher thermal tolerance.

The researchers found that the coral species that are able to swap their algae for more heat-resistant strains are more likely to survive until 2100 by resisting bleaching. But this was only the case in scenarios in which greenhouse gas emissions are kept low and ocean warming is restricted to below 2°C.

Read more:

The abstract of the study;

Quantifying global potential for coral evolutionary response to climate change

Cheryl A. LoganJohn P. DunneJames S. RyanMarissa L. Baskett & Simon D. Donner 


Incorporating species’ ability to adaptively respond to climate change is critical for robustly predicting persistence. One such example could be the adaptive role of algal symbionts in setting coral thermal tolerance under global warming and ocean acidification. Using a global ecological and evolutionary model of competing branching and mounding coral morphotypes, we show symbiont shuffling (towards taxa with increased heat tolerance) was more effective than symbiont evolution in delaying coral-cover declines, but stronger warming rates (high emissions scenarios) outpace the ability of these adaptive processes and limit coral persistence. Acidification has a small impact on reef degradation rates relative to warming. Global patterns in coral reef vulnerability to climate are sensitive to the interaction of warming rate and adaptive capacity and cannot be predicted by either factor alone. Overall, our results show how models of spatially resolved adaptive mechanisms can inform conservation decisions.

Read more:

One thing I’m curious about, how do all the corals know its time to die, when average global temperature reaches 2C above pre-industrial? With large contiguous reefs like the Great Barrier Reef in Australia, there is a substantial difference between the average sea temperature of the cool southern end of the reef, and water temperatures in the tropical far North. Yet somehow a death signal manages to propagate across all these hugely varied biomes, like a kind of coral telepathy.

Do I need the /sarc tag?

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Fred Hubler
May 18, 2021 10:06 am

It seems that everything is going to go to hell with 2C of warming.

Bryan A
Reply to  Fred Hubler
May 18, 2021 10:14 am

Well of course. It’s not like it has EVER been 2C warmer in the entire history of Coral. Tis a brave new world…

Reply to  Fred Hubler
May 18, 2021 11:00 am

And when one goes to hell, everything gets 2000C warmer!

Reply to  IanE
May 18, 2021 11:16 am

Apparently hell froze over back in November of last year. It’s still pretty frosty last I heard. 😉

Walter Sobchak
Reply to  IanE
May 18, 2021 12:16 pm

There is a long running dispute as whether hell is hot or cold. Some thoughts about this can be found at:

Now Dante is the only person who toured hell and wrote a description of it. And he said there were hot spots on top, but the bottom pit was frozen solid.

We should also consult with Robert frost who wrote in Fire and Ice:

Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.

And it is Dante and Frost we should attend to because as Shelly wrote in his Defense of Poetry:

Poets are the hierophants of an unapprehended inspiration; the mirrors of the gigantic shadows which futurity casts upon the present; the words which express what they understand not; the trumpets which sing to battle, and feel not what they inspire; the influence which is moved not, but moves. Poets are the unacknowledged legislators of the world.

Reply to  Walter Sobchak
May 18, 2021 12:50 pm

Thanks for that Walter.

Reply to  Walter Sobchak
May 18, 2021 11:27 pm

NICE!! – Plus 100!

Reply to  Walter Sobchak
May 19, 2021 2:20 pm

In these times it looks like judges are the “unacknowledged legislators of the world,” not poets.

Reply to  IanE
May 18, 2021 2:56 pm

Hell is in Michigan, and at the moment 24degrees C. IMO, + 2C more probably wouldn’t hurt.

Reply to  dk_
May 19, 2021 1:55 am

I thought Hell was in Sweden (or perhaps Norway, I can’t remember).

Reply to  Disputin
May 19, 2021 2:16 am

I’m pretty sure that it is in D.C., but going by the map…

Tom Johnson
Reply to  dk_
May 19, 2021 3:15 am

No, DC has the mid-point temperature. It’s where you insert the (rectal) thermometer.

john harmsworth
Reply to  Fred Hubler
May 20, 2021 10:07 am

I believe the IPCC stated in an earlier assessment that up to 1.8C was beneficial for the planet. 0.2C is a pretty fine window of survivability for a species that survived the last glaciation and lives everywhere from the heart of the world’s deserts to the high Arctic and has without modern technology for thousands of years. Maybe only climate scientists are not smart enough to survive a nice, hot day or two.

May 18, 2021 10:07 am

I do believe that the waters off Indonesia are more than 2 degrees warmer than Northern Australia, so of course there is no coral there?

Bryan A
Reply to  Tom Halla
May 18, 2021 10:15 am

Likely those corals haven’t read the journals or viewed the modeling scenarios

Reply to  Bryan A
May 18, 2021 12:04 pm

Those corals don’t understand English, only Indonesian, and some of the older ones speak Dutch.

Reply to  Tom Halla
May 18, 2021 10:53 am

Other places with lots of coral are also warmer than in the Great Barrier Reef which averages up to 29 deg C in summer .. such as the Arabian Sea (30 deg C in summer) … Celebes Sea (31+ deg C) .. Andaman sea (30 deg C) …. etc etc

Rich Davis
Reply to  Duane
May 18, 2021 11:46 am

That’s fine in practice, but does it work in theory?

Joel O'Bryan
Reply to  Rich Davis
May 18, 2021 1:38 pm

All one needs to know is that scary theory pays better than ho-hum reality.

Reply to  Tom Halla
May 18, 2021 10:31 pm

Different corals. Transplant corals from off the south Island of New Zealand to Queensland and see how they go.

Reply to  Gee Aye
May 18, 2021 10:50 pm

Or leave them where they are and let them all just follow the natural life cycle. The con here is that the corals were once in a steady state instead of following cyclic patterns like all other species on the planet. Marohasy has shown that the same colonies called dead are in fact alive and healthy. Human action to “save” them would be a fool’s errand, but snake oil performance art claiming a magical cure on behalf of a nonsentient victim that isn’t even slightly ill is bound to get cash donations from silly people with more time and money than sense.

Reply to  dk_
May 18, 2021 11:40 pm

No doubt that is true but is nothing to do with my comment or the one I responded to.

Reply to  Gee Aye
May 19, 2021 12:00 am

You suggested transplanting corals. I suggested that it unnecessary, since there is nothing really there to fix. Please do as you suggest, I’ve no right to stop you. I maintain my characterization. I shall applaud your success, why were you doing it, again?

Reply to  dk_
May 20, 2021 9:57 pm

I was making the point that corals in 2 different biomes will die if their conditions are swapped (note this is an example and not a suggestion- why do I need to point this out?). Tom made this false comparison

I do believe that the waters off Indonesia are more than 2 degrees warmer than Northern Australia, so of course there is no coral there?

The Indonesian coral are different coral. The GBR coral that live in 2 degree, on average cooler waters, would not survive. The proposition of them not surviving in warmer water is not debunked by the existence of Indonesian coral.

My transplant anaolgy was more elegant and brief but I hope you get it now?

Rich Davis
Reply to  Gee Aye
May 19, 2021 3:40 am

I suspect that the cold water corals may do better in warmer waters than the warm water corals would do in colder waters. Either way they both depend on symbiont species adapted to the environment in order to survive. If they are floating around then the transplanted coral stands a chance.

Has anyone actually done the experiment? I don’t mean cooking coral in the lab. I mean literally transplanting living coral from southern New Zealand to northern Australia.

(But good luck getting those past the Oz customs, mate! Much less work to speculate and issue an armchair conclusion.)

Bryan A
May 18, 2021 10:12 am

It’s obvious Eric,
Corals read and follow the Pseudo-Scientific Journals and pattern their behavior according to published Modeling. Once the models indicate the temperature at which they should succumb, they oblige the PseudoSceintists when the seas reach that temperature

Tom in Toronto
May 18, 2021 10:18 am

So we’ll have more coral along Canadian beaches? Awesome! Can’t wait for all our white sand and terrific snorkeling!

Reply to  Tom in Toronto
May 18, 2021 10:44 am

Yeah, instead of traveling to the Caribbean just head for Newfoundland!

Reply to  Duane
May 18, 2021 10:45 am

The dive boat operators in Victoria and in Nome will love the new business!

Reply to  Tom in Toronto
May 18, 2021 10:45 am

I’ve seen a lot of beachgoers in Canada who look like they’ve been bleached, (mainly in early Summer), but not sure how the corals fare there. 🙂

Reply to  Eric Worrall
May 19, 2021 9:19 am

Isn’t it funny how people who purport to believe in evolution can’t even consider something as simple as adaptation? They want it both ways.

Rud Istvan
May 18, 2021 10:20 am

She even has the biology wrong. The algal symbionts primarily provide food for the corals, not oxygen, since the corals are otherwise only filter feeding in nutrient poor water. Jim Steele has explained this and bleaching here many times.

Richard Page
Reply to  Rud Istvan
May 19, 2021 2:51 am

Yup. These educated idiots are re-inventing the wheel with a little spin of their own re climate change. Some further grant money and modelling will correct the mistakes made in this paper and it will be hailed as a breakthrough.
I’m rapidly coming to the conclusion that none of these climate enthusiasts have ever read books in their own fields or just disbelieve that any proper science was ever done before the invention of computer modelling.

May 18, 2021 10:29 am

I remember to have read something comparable some few years ago.

May 18, 2021 10:31 am

When? It’s when the NGOs tell them “time to die”.

May 18, 2021 10:39 am

and ocean warming is restricted to below 2°C”

If the idiot was quoted correctly, she actually said ocean warming of 2C.

Reply to  philincalifornia
May 18, 2021 6:27 pm

One of the nice things about “global warming” is that it isn’t really very global. It disproportionately warms frigid winter nights at chilly high latitudes, and slightly lengthens their short growing seasons, which is certainly a Good Thing, and obviously of no concern to corals.

“Global warming” also warms the land more than the oceans.

So 2°C of “global warming” would be much less than 2°C in the tropics, and even less than that in tropical oceans.

What’s more, when activists say we must limit global warming to “1.5°C” or “2°C,” they don’t actually mean that. They don’t really mean what “1.5°C of warming” and “2°C of warming” mean in plain English.

They define their 1.5 or 2°C of warming relative to the 1700s, i.e., the chilly “pre-industrial” Little Ice Age, instead of the plain English meaning, which is relative to present temperatures.

The 1700s are generally guessed to have been very roughly 1°C colder, on average, than our present climate, with a greater difference at high latitudes, and a smaller difference in the tropics. But nobody really knows what the Earth’s average temperature was to a fraction of a degree in the 1700s, because there were hardly any systematic temperature measurements then. James Six didn’t invent his min-max thermometer until 1780.

When activists define their temperature goals relative to an uncertain baseline, they thereby make their goals ill-defined, as well.

Because of that, whenever somebody comes up with a new estimate of “pre-industrial” temperatures, that creates a completely meaningless change in IPCC target temperatures. Here’s an example of that, in a headline from New Scientist in December: “Earth may be even closer to 1.5°C of global warming than we thought.”

Translation: the beneficial warming since the Little Ice Age is now estimated by one research group to have been 1.07°C instead of the previous estimate of 0.91°C. (Preposterously, you’re supposed to think that means It’s Worse Than We Thought.™)

So, why would they intentionally define their temperature goals imprecisely? Why do such a thing? My guess is that it is to reduce the sniggering that would result if they said what they really mean, which is they they contend pretend that it would be disastrous if globally averaged temperatures were to rise by more than 0.5°C (or, 0.59°C, or now 0.43°C), even though the 0.91°C or 1.07°C or whatever warming we’ve experienced since the LIA was undeniably beneficial.

We live in very unscientific times.

May 18, 2021 10:42 am

Acidification has a small impact on reef degradation rates relative to warming.

That’s because there is no ‘acidification’ going on in oceans.

(My statement above is the entire content of a paper I’m planning to submit to Nature.
What are my chances of publication?)

Reply to  Mr.
May 18, 2021 2:48 pm

Mr. Also, reef degradation isn’t shown and warming hasn’t been properly demonstrated. A small impact on nothing from nothing. Null sentence.

Can I co-author?

Reply to  dk_
May 18, 2021 3:41 pm

Yes dk_, but first we’d have to settle whose name would get top billing on our paper.

Because it would definitely become THE most-cited revelation in coralology (see, we’d even have a newly-minted field of scientific research to bolster our (self) nominations for Nobel prizes).

Reply to  Mr.
May 18, 2021 4:01 pm

Please, go first. You can even have the position as head of department. Make me professor emeritus.

Dave Fair
Reply to  dk_
May 18, 2021 4:43 pm

Yep, a paper by Mr. dk_.

Reply to  dk_
May 18, 2021 4:44 pm

An attractive offer.
But since this is climate research –
what’s my pay and junkets?

Reply to  Mr.
May 18, 2021 4:58 pm

Dear Mr. Bloomberg,…..

Bryan A
Reply to  Mr.
May 18, 2021 6:16 pm

You will need the buy in of a GastroEnterologist as a portion of the coral study will include the effects on Coral Polyps

May 18, 2021 10:42 am

So come again, how did all these corals we have today survive the hundreds of millions of years of pre-history when average temperatures were much more than 2 deg C higher than today?

And come again, what is so special about today’s temperatures?

And come again, since coral pretty much only grow in the shallower coastal areas, which are always the warmest seas we have, why warm is bad for coral? Seems like corals like it hot.

May 18, 2021 11:09 am

Most corals prefer warm water. Even the very warm southern Red Sea is dotted with healthy coral reefs (unlike the cooler Mediterranean). If you look at a map of coral reef locations, you’ll see that they’re clustered around the equator:
comment image

Some corals inhabit temperate zones, but most prefer the tropics. In fact, where there are seasons, corals grow fastest in summer.

At 7:20 in this BBC video you can hear how wonderfully healthy the coral are in warmest part of the very warm southern Red Sea, off Eritrea:

Australia’s Great Barrier Reef is not as warm, but it, too, is doing fine. It is about 20 million years old, and it has withstood CO2 levels both much higher and much lower, and temperatures both substantially warmer and much colder, and water levels both higher and much lower, than present. We needn’t worry that a degree or two of anthropogenic warming will destroy it. If you want to learn more about the GBR, the go-to experts are Australian Drs. Jennifer Marohasy and Peter Ridd.

Reply to  Dave Burton
May 18, 2021 2:39 pm

It’s very easy to understand that the inshore (ie Western) expanses of the GBR were not there during the last ice age (110k years ago?), because the sea level there up until 6k years ago was ~130m lower.

So the area was mostly dry coastal plains.

As can be seen by observing the now coral-fringed Whitsunday Group of islands off the central Queensland coast.
These were hill-tops in the last ice age.

The wonders of nature, eh?
(Real Nature that is, not the propaganda magazine masquerading as a science publication)

May 18, 2021 12:12 pm

You nailed it correctly in the end Eric. I don’t know how some of these things pass peer review… not to mention that in the Cretaceous, when temperatures were a lot higher, coral fossils were spread all over. They did not had climate models to warn them then.

Reply to  Eric Worrall
May 18, 2021 5:01 pm

Exactly. The whole present alarmist idea around corals does not match with anything in geological registry. If I want to take my students to see nothing less than exuberant coral fossil occurrences, I take them to cretaceous limestones (called coraliferous limestones for some reason!) . The poles where devoid of ice then and the average earth temperature could reach 35 Celsius!!!! Corals are a lot more resilient than some biologists tend to think.

May 18, 2021 12:15 pm

I’ve experience well over 2C temperature swings passing through thermoclines on the same bommies near Port Douglas! I think the corals can manage just fine.I’ve walked on corals exposed to direct sun in 33C air temperatures at low tide in Fiji with the locals harvesting seaweed. If the researchers were divers they’d intuitively know they’re spewing lies.

May 18, 2021 12:23 pm

“Do I need the /sarc tag?”

Eric (an exercise in recursion): NOW you ask?

addendum: Does it seem to you that perhaps the study, or New Scientist, is denying evolution?

Frankly, I got to the end of “ability to adaptively respond to climate change is critical for robustly predicting persistence.” and ran out of garbage collection space.

Reply to  Eric Worrall
May 18, 2021 3:09 pm

But when your sarcasm is the only sentence that actually makes sense, it is a little like nuking the mosquitoes. Seriously, I did not find a single line of the article that made sense, mostly concatenation of catch phrases, non-sequitur, and statements of facts not in evidence. Someone else here asked if peer review was even useful, I’ve got to ask did it ever exist?

Reply to  Eric Worrall
May 18, 2021 10:59 pm

Eric, you made me do it. I followed the link. These idiots didn’t identify species that migrate — they wrote gaming software computer models that used some fictional notion of a coral lifecycle. Then manipulated their cartoon with more fictional sea life and silly notions of global warming at a scale greater than the IPCC worst case. Much doodoo about nothing.

Reply to  dk_
May 19, 2021 9:31 am

“they wrote gaming software computer models”

This seems to be the new trend. Have you seen the Army recruiting commercial that basically is saying “Be a video game hero”?

We have an entire generation (at least one) with no concept of reality.

Charles Higley
May 18, 2021 12:54 pm

But this was only the case in scenarios in which greenhouse gas emissions are kept low and ocean warming is restricted to below 2°C.”

There is absolutely no basis for setting this limitation. They have no way of determining if corals have species of zooxanthelae for hot times. Such algal species exist in hotter areas, such as close inshore coral areas, so there is always a source that can service other areas in time of need.

Rich Davis
May 18, 2021 1:03 pm

There are not many species with a longer history of survival than our friends the coral. But yeah, I have no trouble believing that they are endangered. They had a good run. What is it, roughly a quarter billion years? Obviously they are balanced on a knife edge of survival. One tiny change…it’s doom. Doom I tells ya!

Carlo, Monte
May 18, 2021 1:07 pm

So the temperature in Newfoundland affects the Great Barrier Reef?

How stupid are these people?

Joao Martins
May 18, 2021 1:13 pm

“The researchers found that the coral species that are able to swap their algae for more heat-resistant strains are more likely to survive until 2100 by resisting bleaching. But this was only the case in scenarios in which greenhouse gas emissions are kept low and ocean warming is restricted to below 2°C.”

Until 2100???

Only 2ºC????

How do you spell BS in plain English?

Richard Page
Reply to  Joao Martins
May 19, 2021 2:43 am

It’s spelled; “modern scientific research”.

Stephen Skinner
May 18, 2021 1:37 pm

But this was only the case in scenarios in which greenhouse gas emissions are kept low and ocean warming is restricted to below 2°C.”
This is a science magazine? So what does ‘restricted to below 2°C’ mean? In relation to what and I guess from this that there is an ideal temperature that doesn’t change for ever?

May 18, 2021 3:17 pm

“> …and ocean warming is restricted to below 2°C”

Data from the US National Oceanic and Atmospheric Administration (NOAA) shows that the average global sea surface temperature – the temperature of the upper few metres of the oceanhas increased by approximately 0.13°C per decade over the past 100 years.

At that rate, it’s going to take quite a while to get to 2°C warming 🙂

Serge Wright
May 18, 2021 5:00 pm

The real issue is the warming causes coral to become white and therefore racist.

Pat from kerbob
Reply to  Serge Wright
May 18, 2021 8:12 pm

Wish I could upvote that 1,000,000 times

Reply to  Pat from kerbob
May 18, 2021 11:08 pm

wouldn’t that ability really be all about privileges?

Rick C
May 18, 2021 5:02 pm

These researchers should read more widely. Jim Steele described this process in a very good essay 6 years ago right here at WUWT.

Sorry about the first post with just the link.

May 18, 2021 6:00 pm

It is mind boggling that this is presented as “new science” when it was well known years ago. I suspect the main reason was “experts” like Terry Hughes and Hoegh-Guldberg were claiming coral only evolve very slowly and thus were endangered of extinction. Climate crises are good for funding and politicians to gain power

I published 4 years ago to the date how coral shift and shuffle their symbionts and rapidly evolve to changing climates on WUWT on May 18,2016

Loyd covered it in the Australian, but ABC & Media Watch did a hit piece on Loyd and me ignoring all the known science.

Reply to  Jim Steele
May 18, 2021 6:50 pm

Rick C wrote, Jim Steele described this process in a very good essay 6 years ago right here at WUWT.

Jim Steele wrote, I published 4 years ago to the date how coral shift and shuffle their symbionts and rapidly evolve to changing climates on WUWT on May 18,2016

How sweet it is when averaging cancels out errors. Too bad it’s not always so.

Reply to  Dave Burton
May 23, 2021 3:14 pm

That might have been too subtle.

(6 years + 4 years) / 2 = 5 years = (year 2021 – year 2016)

Reply to  Jim Steele
May 18, 2021 7:46 pm

I published 4 years ago to the date how coral shift and shuffle their symbionts and rapidly evolve to changing climates on WUWT on May 18,2016”

It seems that evolution, in the traditionally understood sense, is much faster than assumed. I’m sure I heard somewhere that the traditional understanding of the way evolution works is mathematically impossible. Therefore, something else is going on. Epigenetics?

May 18, 2021 8:24 pm

The real story here is that corals use human temperature measurement units. Who knew? SCIENCE!

May 18, 2021 8:26 pm

But haven’t the oceans warmed by 2C since 1900?
So all those reefs should be dead?

May 18, 2021 9:29 pm

Bleaching Protects Coral – But Only Up to 2C of Global Warming

And masks work, but only if you’re in a big box store where a thousand or so people go through every day. Masks don’t work in mom & pops stores, where maybe 50 or so people come through the doors each day.

Funny how that works, innit?
“Keep it below 2C or the coral gets it.”

robin townsend
May 19, 2021 1:00 am

because the algae normally provide oxygen for them

Can someone explain this please? the algae somehow process and concentrate the oxygen dissolved in seawater, which surrounds the coral anyhow, and what? fart it at the coral?

Reply to  robin townsend
May 19, 2021 1:06 am

“someone explain this”
That’s the deal. No one can. It is all nonsense.

May 19, 2021 3:53 am

This says it “this was only the case in scenarios in which greenhouse gas emissions are kept low and ocean warming is restricted to below 2°C.

They are talking about 2C of ocean warming. It has taken 100 years (plus some data adjustments) for the air to warm by 1C. Water needs about 4000x more energy to raise the temperature of 1kg by 1 degree. So before our ocean’s temperature has gone up by 2C, we need to wait several centuries. 🙂

May 19, 2021 7:01 am

So, the obvious.

Reply to  gush
May 19, 2021 7:05 am

Let me explain, if the temperature changes, the corals let the algae evolve as the polyps are more resistant than the algae.
If it heats more than it’s predicted to heat up (upper bound) in a hundred years, the coral will be pushed to evolve.

Who’d know, it’s almost like this happened time and again in the archeological record.

Coach Springer
May 19, 2021 9:35 am

2 degrees. From where? From now or rom the current (SCIENTIFIC) guesstimate made for 1740? And why? Explain your answer.

john harmsworth
May 20, 2021 10:03 am

I used to have a subscription to New Scientist. It’s Woke, Globalist anti-industry and Global Warming focus has turned it into a complete rag. wherein all scientific intimations are referenced against a list of politically acceptable topics and opinions before being published. It’s laughable now. Corals in the Red Sea are doing fine and thanks to the courage of Peter Ridd we now know that the Great Barrier reef suffers more from agricultural run-off than from any warming, which itself is a result of normal el Nino weather patterns. But, the lies continue ever more desperately as the world refuses to obey their simplistic hypothesis.

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