Study: Ancient Fish Thrived During PETM Extreme Global Warming

Guest essay by Eric Worrall

The Paleocene-Eocene Thermal Maximum (PETM), a period of extremely rapid global warming which occurred 10 million years after the demise of the dinosaurs, was supposed to have been an ocean catastrophe. Instead, even temperate climate fish treated the warmth like a tropical food buffet.

Ancient Fish Thrived During a Period of Rapid Global Warming

Teeth and scales preserved in marine sediments suggest that fish thrived during one of Earth’s fastest-warming periods.

By Elyse DeFranco 14 December 2021

About 55 million years ago, Earth’s climate underwent a rapid and intense period of warming, both on land and at sea. Temperatures soared more than 5°C, and even Arctic seas turned tropical. Reconstructing this warm era, the Paleocene-Eocene Thermal Maximum (PETM), provides a glimpse into Earth’s possible future. “One of the best tools we have to understand how the [ocean] system responds is to look at past instances of global change,” said Elizabeth Sibert, a paleoceanographer and paleoecologist at the Yale Institute for Biospheric Studies.

By examining fossil evidence from the PETM preserved in marine sediment cores, Sibert and her colleagues sought to understand how fish might respond to warming oceans. Contrary to the predictions of many models, they found that fish actually grew more abundant as temperatures soared. Sibert and her team will present their research on 14 December at AGU’s Fall Meeting 2021.

Sibert and her team examined sediment records in three different cores collected by the Ocean Drilling Program. The drill sites spanned tropical reaches of the north central Pacific, eastern equatorial Pacific, and Atlantic Oceans. The researchers filtered microscopic fish scales and teeth from varying depths of the sediment core, counting and sorting them for a window into past ocean life during the PETM.

“This is the first time we have an idea of what mid to upper trophic level groups were doing during this warming event,” said team member Richard Norris, a paleobiologist at the Scripps Institution of Oceanography. “Previously, almost all studies of the PETM have been based upon unicellular plankton or microzooplankton.”

The results paint a consistent picture of the past across all three samples: Fish became more abundant as temperatures climbed, then gradually decreased again as the warming waned. Plus, the various fish types didn’t change much during this temperature flux. “It’s really surprising,” said Norris. “You’d think that as things warm up that you might get a really different community of fishes.”

Still, Sibert urges caution when comparing fish outcomes during the PETM and what might happen this century—and beyond. “The rate of warming…can have dramatic and differential impacts on marine ecosystems,” she noted.

Read more:

The abstract of the study;

PP23A-02 – Enhanced open-ocean fish production and community resilience across the Paleocene-Eocene thermal maximum


Elizabeth C Sibert  Yale University
Douglas W Tomczik  Scripps Institution of Oceanography
Daniel Gaskell  Yale University
Gregory L. Britten  Massachusetts Institute of Technology
Richard D Norris  Scripps Institution of Oceanography

Marine ecosystem models predict that anthropogenic warming will likely result in decreased marine fish production in the coming centuries, although the magnitude of this effect is poorly constrained. By contrast, preliminary work on the early Paleogene (62-48 Ma) has suggested that warmer climate periods were associated with long-term increases in open-ocean fish production. The historical response of fish communities to rapid-scale warming events closer in rate to anthropogenic warming remains unknown. The Paleocene-Eocene Thermal Maximum (PETM) was a transient and rapid interval of global warming approximately 56 million years ago (Ma) and is a partial analog to modern climate change. To test how fish populations responded to past rapid ocean warming, we compiled records of fish abundance and diversity across the PETM, using isolated microfossil fish teeth and shark scales (ichthyoliths) preserved in three deep-sea sediment cores: Ocean Drilling Program (ODP) Site 1209 in the North Pacific Ocean, ODP Site 1220 in the Equatorial Pacific, and ODP Site 1260 in the Equatorial North Atlantic Ocean. We find that, in contrast to future projections, ichthyolith accumulation rates (IARs) from all sites show significant increases in fish production coincident with early stages of the PETM, before returning to pre-PETM levels as the hyperthermal conditions waned. Furthermore, the morphological diversity and composition of PETM ichthyolith assemblages remain largely constant across the event, with no evidence of excursion or disaster biotas. These findings suggest that on millennial timescales fishes may be more resilient to rapid global climate change than previously thought. Further, the temperature sensitivity of fish production across the rapid warming of the PETM can be quantitatively compared to the temperature sensitivity of fish production throughout the Early Paleogene, providing a means to interrogate the sensitivity of fish populations to changes in ocean temperature throughout Earth’s past and across different time scales.

Read more:

Good on the authors for having the courage to report and present their findings.

I would have loved to be at the AGU meeting where Elizabeth and the other authors presented their study, her evidence that all their carefully crafted alarmist ocean biome global warming models could be totally wrong.

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December 15, 2021 6:11 pm

The alarmists will say it’s fishy.

Michael S. Kelly
Reply to  Scissor
December 16, 2021 1:44 am

Yet the fish were this big (I’m holding my hands at least 18 inches apart, just like the one that got away).

December 15, 2021 6:16 pm

But you don’t understand. Modern fish can’t handle heat stress the way ancient fish did.
We have models that prove it. /sarc

Reply to  MarkW
December 15, 2021 6:50 pm

If you had included a link it would be click bait.

Reply to  Scissor
December 16, 2021 7:03 am

How about a link to my PayPal site?

Joao Martins
Reply to  MarkW
December 16, 2021 5:55 am

Yes! Modern fish die of climate anxiety and become extinct!

John Tillman
December 15, 2021 6:19 pm

PETM balminess was soon exceeded during peak Eocene warmth. Result, extreme happiness among species then enjoying life on Earth. That includes our primate ancestors in the subtropical forests of Wyoming.

Life was good. Then came dreadful, destructive, disastrous, deadly global cooling.

Last edited 1 year ago by John Tillman
Reply to  John Tillman
December 15, 2021 7:08 pm

Earth has been slowly dying after the KT extinction. Antarctica going South Pole putting us into an icehouse, and CO2 levels collapsing to near death levels for C3 plants just 15kyo. Fifteen million years(?) from now and the complexity of Life would all be back to pre-Cambrian times…

John Tillman
Reply to  Ruleo
December 16, 2021 7:28 am

I don’t think that multicellular life on land will disappear within 15 million years, nor sealife be based upon cyanobacterial slime mats. Even should CO2 drop below the level needed for C3 photosynthesis, that would still leave C4 and CAM land plants to form the basis of animal food chains. And more C3 plants might evolve versions of the C4 process.

Mike Dubrasich
Reply to  John Tillman
December 15, 2021 8:38 pm

Shout it out loud with all that you’re worth: Warmer Is Better for our Planet Earth.

Joseph Zorzin
Reply to  Mike Dubrasich
December 16, 2021 3:55 am

going to be in the sixties F here in MA today- NOBODY is complaining

Ron Long
Reply to  John Tillman
December 16, 2021 2:09 am

Right on, John. The early Eocene Willwood fm, located in the Bighorn Basin of Wyoming, showed that land mammal response to either warming or cooling needed at least 5 deg C, and maybe 8 deg C, to show significant change. So add land-based fauna and flora to the good-to-go list.

Reply to  John Tillman
December 16, 2021 5:27 am

comment image

Cenozoic biodiversity of Amazonia (Hoorn et al., 2010). Rain forests must like “ocean acidification.”

December 15, 2021 6:29 pm

It is a sad time when anthropogenic global warming is cited as if fact.

Joseph Zorzin
Reply to  Rob_Dawg
December 16, 2021 3:57 am

exactly as bible thumpers start all their debating with non believers with the premise that the bible is 100% fact

Reply to  Joseph Zorzin
December 16, 2021 5:30 pm

Somewhat similar to all of the “adjustments” throughout time when biblical texts were being “composed” by many different people, prior to the advent of the printing press.

Alexy Scherbakoff
December 15, 2021 7:03 pm

Boomer fish had it easy. Millenial fish have it tough.

Reply to  Alexy Scherbakoff
December 16, 2021 12:19 am

And as for Doomer fish…

December 15, 2021 7:06 pm

I don’t know any class of animals or plants that doesn’t thrive on hot weather. Insects, most flowering plants, reptiles, amphibians, most mammals, etc, etc. We worry about losing polar bears to +1.5C wamer weather. Give me a break.

Reply to  Pauleta
December 15, 2021 8:20 pm

Yeah, go visit the polar bears at the San Diego Zoo sometime. They don’t look distressed to me.

Neil Jordan
Reply to  Taylor Pohlman
December 15, 2021 9:12 pm

Been there, done that, but didn’t get the t-shirt. Daughter got a sarong instead.
“At first thought, a polar bear in sunny San Diego seems curiously out of place. But at the Zoo, you’ll discover that polar bears are right at home, and every day is an Arctic summer day. The focal point of the Conrad Prebys Polar Bear Plunge is, naturally, the pool. From the underwater viewing room, you can see how agile and playful these Arctic bruins really are. In fact, they’re known to swim right up to the glass to check out all the humans on display. Other interactive elements at the Plunge include life-size polar bear statues and a polar bear den to crawl through.”

I noted that the polar bears are positively svelte, unlike those Arctic bears that are morbidly obese with high BMIs (Bear Mass Indices).

Reply to  Neil Jordan
December 16, 2021 5:32 pm

Cute.. thanks.

Reply to  Taylor Pohlman
December 15, 2021 11:04 pm

The first live poley barr I ever saw was at Singapore Zoo.

That saved me lotsa air miles and those nasty CO2 emissions by not having to go all the way from Sydney to Canada.

Just doing my bit to save the planet 😇

John Shotsky
December 15, 2021 7:09 pm

Fish, like birds, don’t have houses. They simply migrate to where conditions are more to their liking. And usually, later, they migrate back as conditions change back. My dear departed friend, Gary Sharp, worked with the marine fisheries and monitored their migrations – away and back. Everything is cyclical. He has several publications on the subject.

Vlad the Impaler
December 15, 2021 7:44 pm

Second sentence, of the first paragraph:

“Temperatures soared more than 5 (degrees) Celsius, … ”

OK, no problem there. My reading of the Geological Time Scale 2020, page 1089 of Volume II tells me that the ‘baseline’ temperature at the time of the PETM was about five Celsius degrees WARMER that it is right now, in our part of the Holocene. The baseline might have been even warmer than that, the conversion from delta-O-eighteen to temperature being something of an approximation.

And for those who think I might not understand it, yes, I do understand the reference of the Pee Dee Belemnite as the standard when measure paleotemperature through the oxygen proxy.

Regards to all,


December 15, 2021 10:05 pm

The paper contradicts itself. “About 55 million years ago, Earth’s climate underwent a rapid and intense period of warming, [] Fish became more abundant as temperatures climbed”. Then “Sibert urges caution [] The rate of warming…can have dramatic and differential impacts”.

I suspect that the paper could not have got published without the final sop to political correctness.

Reply to  Mike Jonas
December 15, 2021 11:13 pm

Notice that its not the warming itself, its the rate of warming that’s mentioned as having impact. Since we haven’t warmed at all for over 5 years, no worries.

Janice Moore
Reply to  Doonman
December 16, 2021 3:53 pm

Hi, Doonman,

Hakuna Matata, indeed! 😃 For over 5 years … Rather,

essentially, we haven’t warmed meaningfully since 1998 (super El Niño year).

(Copied from my December 2, 2021 comment here: )

  1. [S]ince 1998, the Earth has basically seen no temperature trend. …

2. We had a warming episode in 1978-1998, probably comparable to several tenths of a degree. I am using the word “probably” because when the measurement error is plus minus 0.2 °C, you may always modify your results to match a trend you find convenient.
To deduce trends from changes comparable to tenths of a degree is nonsense from a statistical perspective.

It is almost impossible to say with certainty that the warming has taken place. The international panel of the U.N. known as the IPCC acronym is claiming: The warming between 1919 and 1940 wasn’t caused by humans but the warming between 1978 and 1998 was. But their magnitude and shape was basically identical. It’s propaganda. You may always focus on small changes and scale the graph so that it looks dramatic to the naked eye.

Source: Richard Lindzen, May, 2017,

Last edited 1 year ago by Janice Moore
Joao Martins
Reply to  Mike Jonas
December 16, 2021 6:35 am

Well, that is the simplified story line; the real world was more complex.

Temperature rose, so fishes, which cannot control their inner temperature, started to feel better and as a consequence enjoyed reproductive practices and increased in numbers.

Then, some more illustrated fishes (known as the “fishyelite”) started to think that having so many (and counting!) happy fishes was bad, because with their living activities (reproductive and otherwise) they would increase temprature still further, which would end up with a lot more happy fishes (not to mention those hypochondriac extremists who designed some models that predicted a lot of boiled fishes).

Then, those fished who where unhappyconcerned with the happiness of the other fishes started to preach in novels, radio stations, TV channels and other fishy mass media that being warm was bad, would lead to the end of the fish world and that there could have a lot of boiled fishes by their fault.

Some other fishes, which were rather happy with the welfare created by the warming of the waters, started to have doubts and to question if their well-being was a real well-being that could shortly after end in a catastrophe. And started to talk about their doubts in the fishy networks through which fishes communicate in their fishish language.

Because of that, many other fishes who lived rather well in their warming waters also sarted to have doubts. And, as their numbers increased, a few experts called psycofishologists discovered that this was an umprecedented psycofishic diseased and called it “climate anxiety”.

Meanwhile, the warming of the waters stopped (a phenomenon that the other experts called climatefishologists called “the pause”). But the disease, climate anxiety, had been panfishy and already became enfishy with a rather high incidence. So when, some time afterwards, the warming of the waters restarted, it grew and infected many, many more fishes, to the point that the majority of fished were unhappy with their lives and frightened by the warming of the waters.

Those fears and anxiety led to the fishes become less interested in reproductive activities and, contrasting to what had happened in the past, their numbers went reducing as the temperature of the water rose. To a certain moment when the population reduced so much that it became extinct.

Sorry to have been so long, but I felt that a more detailed explanations was needed.

To bed B
December 15, 2021 11:37 pm

Temperatures soared more than 5°C, and even Arctic seas turned tropical.”

What’s the warmest arctic seas get to in August? Its 5.9°C for Svalbard (Longyearbyen). Minimum SST of tropical waters, 22°C?

Estimates seem to be a maximum rise of 12 degrees of polar seas, so turned tropical is an exaggeration. Still obvious that its not about CO2 acting as a blanket. The mean can rise without the total T^4 going up if more heat accumulating in the tropics is conveyed to the temperate and polar regions. Not saying that it hadn’t warmed to address an energy imbalance, its just that warmer polar temperatures doesn’t necessarily mean the global average went up to address an imbalance because CO2 was higher.

John Tillman
Reply to  To bed B
December 16, 2021 7:34 am

You’re right. “Turned temperate” would be more accurate.

Julian Flood
December 15, 2021 11:42 pm

I have a Feynman guess about what caused the PETM.


December 15, 2021 11:47 pm

55 million years ago ambient CO2 was over 1,000 ppm. I keep reading how oceans now are supposed to be getting more “acidic” as CO2 is rising & that will mess fish up.

Back in the OriginalPost they declare fish thrived all those millions of years ago. I mean, what happened, did the fish hold music concerts like Woodstock and heed the advice: “Don’t take the brown acid” ?

H. D. Hoese
December 16, 2021 12:01 am

“The low rate of metabolic heat production, compared with mammals, and the high heat capacity of water result in continuous heat losses and cool bodies for most fish. ” Moyle and Cech, An Introduction to Ichthyology.

December 16, 2021 12:11 am

Are they seriously saying that climate change is caused by climate change?

What happened to the human race? How did we come to be ruled by imbeciles?

Reply to  Phil Salmon
December 16, 2021 12:21 am

Psychopaths. FTFY.

Reply to  Phil Salmon
December 16, 2021 12:22 am

What happened to the human race? How did we come to be ruled by imbeciles?

Too many people went to university

Joao Martins
Reply to  Phil Salmon
December 16, 2021 9:25 am

Lots of CACA.(/pt and es sarc)

Tom Abbott
Reply to  Phil Salmon
December 16, 2021 1:10 pm

“How did we come to be ruled by imbeciles?”

We really are ruled by imbeciles today.

We have one particular political party that is completely delusional, and wants the rest of us to take part in their delusion. No thanks, Democrats.

December 16, 2021 12:23 am

By examining fossil evidence from the PETM preserved in marine sediment cores, Sibert and her colleagues sought to understand how fish might respond to warming oceans. Contrary to the predictions of many models, they found that fish actually grew more abundant as temperatures soared.

But the fish that thrived during this catastrophic warming were denyer fish. They were deplorable, Trump-voting fish. The progressive right-on fish declined like dutiful citizens.

The weather-climate is a continual, never ending catastrophe. It’s a catastrophe without which there would be no life.

Joseph Zorzin
Reply to  Phil Salmon
December 16, 2021 4:00 am

“It’s a catastrophe without which there would be no life.”
And no evolution.

AGW is Not Science
Reply to  Phil Salmon
December 17, 2021 1:47 pm

Contrary to the predictions of many models, they found that fish actually grew more abundant as temperatures soared.

A nice summary of the value of “what the models say.” Garbage In, Garbage Out.

Jim Gorman
December 16, 2021 5:42 am

As a bass and crappie fisherman I can tell you this is hokum. I live in Kansas with good but not great largemouth bass and crappie. However, go south to Texas and WOW, what great sized largemouth bass. Here as temps cool the fish get lethargic and fishing goes away. Nice warm sunny days and the fish will hit any lure. Anyone with knowledge about bass tournaments know they are in the south.

Warm weather is the best thing for non-salt water fish. I don’t know about salt water fish.

December 16, 2021 7:12 am

Seriously, these climate cultists have utterly ignored the Earth’s history. Most of life came about and thrived during warm periods, ones that were mostly warmer than today. Complaining about rising seas taking out islands? A goodly chunk of those islands were created as coral atolls, meaning the seas were much higher when they were created. Just a bunch of doomsday cultists. This has nothing to do with science.

December 16, 2021 7:38 am

I always say, Warming is Good! Cooling is Bad!

It oughta be massively obvious that warming is good for humans as well as plant and animal species. Despite the wildly offensive and stupid claims that Earth is headed for the frying pan, all scientific knowledge to date clearly proves that warming periods are the most favorable for both biodiversity and for the total biomass of the planet. And for us people too!

December 16, 2021 9:35 am

The fishing would have been so good that you would have to hide behind a tree to bait the hook.

Wim Röst
December 16, 2021 12:55 pm

Does anyone know how many boreholes have been used to prove the existence of a PETM?

AGW is Not Science
December 17, 2021 1:03 pm

Only the logically impaired believe that warmer temperatures are “bad” for life of any variety. It is cold temperatures that endanger life, not warm temperatures. A glance at the quantity and diversity of life in the tropics vs. at the poles should illustrate for anyone capable of logic and reason.

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