Researchers have applied a temperature proxy to exceptionally well-preserved fossil phytoplankton for the first time. The results suggest that conditions in the North Atlantic have been cooler than previously believed since the Miocene epoch.
Accurate forecasts of how Earth’s climate will respond to rising atmospheric carbon dioxide depend on climate models. To test and refine these models, scientists look to past geological periods when CO2 levels shifted in ways similar to those observed today and projected for the near future. They reconstruct these ancient conditions using measurable indicators known as proxies.
In a new study published in Nature Communications, researchers present a detailed temperature record from the North Atlantic spanning the past 16 million years—offering an important window into one such period. By applying clumped-isotope geochemistry to exceptionally pure fossil calcareous algae (coccoliths), they found that the region was significantly cooler than earlier estimates had suggested. This revised temperature record aligns more closely with climate model simulations and challenges the long-standing view of extreme warmth in high northern latitudes during the Miocene.
To better understand this discrepancy, Dr. Luz María Mejía, now at MARUM – Center for Marine Environmental Sciences at the University of Bremen, and her colleagues focused on the last 16 million years, with particular attention to the Miocene. During this interval, atmospheric CO2 levels, estimated at 400 to 600 ppm (parts per million) based on the latest IPCC report, were comparable to those projected under current emission scenarios.
“Understanding the Miocene climate, between 5 and 23 million years ago, could help us better predict the climate response to anthropogenic CO2 emissions of the near future,” says Mejía.
Fossil algae preserve climate signals
To estimate past temperatures, the team studied clumped isotopes in fossil coccoliths, which are bonds between heavier oxygen and carbon isotopes. These coccoliths are calcite plates produced by marine plankton that serve as an external structure. The organisms, called coccolithophores, live in the sunlit surface ocean and carry out photosynthesis.
Their calcite plates preserve a chemical signature that reflects the temperature of the surrounding water during their lifetime, allowing scientists to reconstruct past ocean conditions independently of seawater chemistry. After these organisms die, their plates sink and become part of seafloor sediments, where they remain preserved over millions of years.
Scientists collect these sediments by drilling into the ocean floor and extracting cores. Like tree rings, these layers contain markers that make it possible to determine their age and link them to specific geological periods. Temperature affects how frequently heavy oxygen and carbon isotopes bond within the calcite. More clustering occurs at lower temperatures and less at higher temperatures. By measuring this clustering, researchers can estimate the temperature of the water when the coccolithophores were alive.
Before analyzing the fossils, Dr. Mejía developed a method to isolate large amounts of coccoliths without contamination from other materials. The team designed a semi-automatic filtering system and combined it with centrifugation at the Eidgenössischen Technische Hochschule (ETH) Zurich (Switzerland) to produce samples of exceptional purity.
Results challenge warm Miocene paradigm
The findings differed from widely accepted expectations.
“Perhaps the most widely used and accepted temperature indicator, especially for the Miocene, is the alkenone unsaturation index, which is based on organic fossil molecules that are also produced by coccolithophores. Sea surface temperature estimates using alkenones have contributed to the widely accepted paradigm amongst the proxy and climate-model communities – that during past warm periods such as the Miocene, high latitudes were extremely warm, and the meridional temperature gradient was greatly reduced,” explains Mejía.
This idea suggests that higher CO2 levels lead to warmer oceans and smaller temperature differences between the tropics and the poles.
“This paradigm always seemed odd to me, because in the Caribbean, where I studied marine biology, I could see with my own eyes how most life struggles terribly during the warm season. How is it possible that life in general could survive and thrive at higher temperatures, including in non-tropical regions, over millions of years?” she wondered.
New analyses using coccolith clumped isotopes offer a different conclusion. The results indicate that the North Atlantic was about 9 degrees Celsius cooler than earlier estimates suggested. The researchers emphasize that this challenges the long-standing view of extreme warmth in northern high latitudes and brings observational evidence into closer agreement with climate model simulations for the Miocene.
Implications for future climate projections
The study suggests that temperatures in high northern latitudes during the Miocene may not have been as extreme as previously believed, and may not reach such levels in the future. The team also stresses that climate proxies must be continually re-evaluated to ensure both long-term trends and absolute temperature values are interpreted accurately.
Dr. Mejía clarifies, however, that this study is just the beginning: “We need to test more,” she says.
The next step will be to analyze fossil coccoliths from different regions and across a wider range of latitudes to develop a more complete picture of past climate conditions.
Reference: “Coccolith clumped isotopes reveal modest rather than extreme northern high latitude amplification during the Miocene” by Luz María Mejía, Stefano M. Bernasconi, Alvaro Fernandez, Hongrui Zhang, José Guitián, Madalina Jaggi, Victoria E. Taylor, Alberto Perez-Huerta and Heather Stoll, 9 December 2025, Nature Communications.
DOI: 10.1038/s41467-025-65954-y
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22 Comments
“… the last 16 million years, with particular attention to the Miocene. During this interval, atmospheric CO2 levels, estimated at 400 to 600 ppm (parts per million) …”
[The above is a partial quote from the actual published article, not this press release.]
The authors state that the impetus for their research is to validate the Miocene temperature estimates used in climate models that are trying to forecast future high-latitude Sea Surface Temperatures as the CO2 concentration increases, with the unstated assumption that the CO2 is responsible for increasing temperatures.
Figure 2 shows estimates for the modern calcification temperature: 6.7 °C (AVHRR-derived temperature at modern sediment trap at Purple Star) and a single-event coccolith bloom of an estimated delta-47 temperature of 7.4 °C; ± 59% @ 95% CI. Modern Sea Surface Temperature for the region appears to be approximately 9 °C (red line). That is, modern Sea Surface Temperatures appear to be in the range of 3-12 °C.
The authors state “pure and well preserved coccolith separations … show mid-Miocene peak temperatures of 18.3 ± 5.0 °C, and a gradual cooling of ~9.0 °C from the Miocene to the Quaternary …” Albeit, the authors are a little cavalier with the uncertainties, which appear to be about ± 4-5 °C (95% CI) for all the temperatures.
In summary, the authors are making the case that the current IPCC model predictions, tuned to a warmer Miocene, are probably not correct, particularly for the high latitudes where the concern is about Arctic Amplification.
Well, the summary is perhaps a bit cavalier (I don’t have the knowledge base to test that). Have you read the original text and is the issue in the study itself or in the press release-like summary seen here?
I suggest you re-read what I wrote. I specifically quoted from the original published article.
The science is settled! SETTLED. Or can I use the people who ridiculed me and called me a climate denier and wanted to imprison me for thinking otherwise?
This doesn’t change that fact Dave. We have known about this since the 1940’s.
I’m sorry if you don’t want to believe it but unfortunately reality is unaffected by your decision to to acknowledge it or not.
Nor is reality affected by your unsupported assertions.
You leave it unclear as to just what you think we knew in the 1940s. In the early-1940s we still didn’t know if an A-bomb was possible, and if it was, whether or not it might ignite the atmosphere. We didn’t know about the Van Allen radiation belts in the 1940s. And as I recollect, the first quantitative evidence for Milankovitch periodicity — a Fourier Transform of available data — wasn’t published until the late-1970s. While it is commonly claimed that “Exxon knew” in the 1970s, they were little more than speculations illustrating an upward slope of temperature with increasing CO2, some of which were absurd. They didn’t take into account the numerous feedback loops. Indeed, the first quality measurements of CO2 weren’t taken until 1958, and it was a few years before there was enough data to establish the Keeling Curve. In the ’60s, there was some concern about whether the climate was cooling. There weren’t actual models (versus hand-drawn ‘cartoons’) until James Hansen’s 1988 presentation to Congress, which had numerous failings ( https://wattsupwiththat.com/2018/06/30/analysis-of-james-hansens-1988-prediction-of-global-temperatures-for-the-last-30-years/ )
If you are going to make broad brush claims, be prepared to back them up with more than just your personal opinions.
Thanks for the common denier slogan. This does NOT change the fact that the planet is warming 10 times faster than the warming that ends ice ages. Nor does it change indisputable fact that the cause is increased atmospheric CO2 from human activities. There is nothing natural about this climate change. There are several lines of evidence supporting that most of the CO2 increase is from burning fossil fuels, especially that the CO2 from fossil fuels emissions have different isotopes of carbon than the CO2 from other sources – directly observed.
Nature caused CO2 increases over the last 450,000 years, from ice core data
80ppm increase — took 50,000 years
110ppm increase — 25,000 years
120ppm increase — 20,000 years
60ppm increase — 20,000 years
90ppm increase — 15,000 years
100ppm increase — 24,800 years
the fastest natural CO2 increase was 90ppm taking 15,000 years.
WE have done that in about the last 65 years.
—————
Humans increased CO2 by 25ppm in the last 10 years
Humans increased CO2 by 45ppm in the last 20 years.
Humans increased CO2 by over 80ppm in the last 60 years
Humans increased CO2 by 100ppm in the last 70 years
Humans increased CO2 by 146ppm in the last 144 years
———————————————–
“As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years.
In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly TEN TIMES FASTER than the average rate of ice-age-recovery warming.”
NASA Earth Observatory
—————————
That is from 2010. The warming since 1880 is now about double the 0.7C warming NASA was referring to.
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Also, there could be other factors affecting North Atlantic temperatures, other than CO2 levels, like changes in ocean currents millions of years ago. For example, was the AMOC just the same as it is now? Are Milankovitch cycles the same now as during the Miocene?
I have seen your dogmatic boiler plate before. It appears that you learned nothing from this particular research.
CO² increases in atmosphere arrive after the warming, not before.
Therefore cannot be Causal to climate “change”.
Plus, nobody can explain PRECISELY how we measure THE ocean temperature. Because it just isn’t as simple as the models would lead you to believe.
Correlation alone does NOT establish causation. Look up “spurious correlation.”
thank you for this
At least you have to accept the studies and findings are fair an unbiased considering there is zero scoence coming from the deniars as a group. The only science is coming from the same source of academics organizations. If you think this study means we shouldn’t even consider reducing co2 output at least you have something climate scientist decided to publish even though it goes against some predictions within the mainstream.
“… there is zero scoence [sic] coming from the deniars [sic] as a group.”
That statement is demonstrably false. You are obviously unaware of the Nobel Laureate physicists who have gone on record questioning the ‘settled science.’ That is probably because the mainstream media rarely publishes anything that goes against the consensus paradigm, regardless of the credentials of the person(s) making the claim.
The “academics organizations” are more like a Home Owners Association that enforces uniform behavior than they are actual research organizations. The ‘leadership’ positions are unpaid volunteers who are obviously getting something emotionally from the small amount of power they wield. I would guess that in most cases they are mediocre researchers that get validation from their political influence. They are anything but unbiased and objective. They are the ‘Karens’ of academia.
So science seems to score an own goal, or that the doom laden green eco warriors like millibrain are just a load of scare mongering gravy train wannabees..
NOPE. This disproves nothing about the FACT that humans are causing global warming.
EVERY association of professional scientists on the planet, EVERY major university science dept. on the planet, and with now the ONE exception of Trump’s EPA, EVERY govt. science agency that’s relevant to earth sciences on the planet – ALL agree on AGW.
It takes a lot of absurdity to believe that they’re all involved in a hoax, or are wrong, but the fossil fuels industry funded so called think tanks that dispense disinformation for them, have the truth.
I have heard/read the claim that climate scientists are in it for the money, probably 5,000 times, and NEVER a speck of evidence to support the claim.
Meanwhile, what you believe comes from Here. Unlike the ridiculous conspiracy theories religiously believed by deniers, without a speck of skepticism, this is an extremely well documented and indisputable FACT.
The disinformation is spread by these proxies, that they fund.
These 32 conservative organizations have all been funded by and involved in the Tobacco industry’s campaign to deny the science showing the dangers of tobacco.
They are all now funded by fossil fuels, to do the same in the campaign to deny the science of climate change.
1. Acton Institute
2. American Legislative Exchange Council (ALEC)
3. Alexis de Tocqueville Institute
4. American Enterprise Institute (AEI)
5. Americans for Prosperity
6. Atlas Economic Research Foundation
7. Burson-Marsteller (PR firm)
8. Citizens Against Government Waste (CAGW)
9. Cato Institute
10. Competitive Enterprise Institute (CEI
11. Consumer Alert
12. DCI Group (PR firm)
13. European Science and Environment Forum
14. Fraser Institute
15. Frontiers of Freedom
16. George C. Marshall Institute
17. Harvard Center for Risk Analysis
18. Heartland Institute
19. Heritage Foundation
20. Independent Institute
21. International Center for a Scientific Ecology
22. International Policy Network
23. John Locke Foundation
24. Junk Science
25. National Center for Public Policy Research
26. National Journalism Center
27. National Legal Center for the Public Interest (NLCPI)
28. Pacific Research Institute
29. Reason Foundation
30. Small Business Survival Committee
31. The Advancement of Sound Science Coalition (TASSC)
32. Washington Legal Foundation
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#5, #9 and #10 were created by the billionaire oil and lumber tycoon Koch brothers, who fund all kinds of anti-environmental PR.
#24 Junk Science, which is aptly named, is run by Steve Milloy, who Fox News likes to feature as an “expert” on climate change. Milloy is NOT a scientist. He’s a paid lobbyist for fossil fuel interests and a professional PR man. Did Fox ever divulge that? I doubt it. And Milloy gets funding from, guess who? – the Koch brothers.
Never let real facts get in the way of what you believe the facts to be.
Yo Richard, by your FACTS,
would we have less Global Warming if you had no children? Is this what you are proposing, or do you just want to tell OTHER PEOPLE how they are supposed to live?
If you really want to help out, you could.
Funny that you should denigrate the Koch brothers. I know them for funding the PBS TV NOVA series for years.
I challenged Microsoft’s Copilot LLM to provide the amounts, dates, and sources of the alleged contributions from fossil fuel companies to sow disinformation. It was unable to provide any of the details. I would say that the claims made by others, that you have parroted, fall into the category of Urban Legends.
So, science deniers love repeating slogans like yours. That is not science.
And, as I said to another science denier here, there are many other factors that may have affected CO2 levels and global average temperature during the Miocene, that are much different from now. Changes in ocean currents, differences in the AMOC ocean current system, for example, possible differences in the Milankovitch cycles, etc.
Things that happened over 10s of !,000s, 100s of 1,000s even millions of years, are now happening in a couple of human lifetimes, 170 years. 170 years is also how long the greenhouse effect of CO2 has been know. And it is FAR better understood now.
Even if we were to accept your claim that the undesirable changes in climate are valid, the implication is that only anthropogenic changes accelerate and natural changes only increase linearly, if at all. Thus, by your way of thinking, the claimed increases have to be anthropogenic. Unfortunately, that is unsupported, circular reasoning.
“170 years is also how long the greenhouse effect of CO2 has been know. And it is FAR better understood now.”
What is your source for the claim of 170 years?
Yes, it is “FAR better understood now.” We now have evidence that during the Eemian, with similar CO2 concentrations to today, the Greenland Ice Sheet melted back to allow Greenland to be vegetated. Antarctic ice cores (Law Dome) for the last 800,000-years strongly suggest that warming took place before the increases in CO2. NASA has documented significant increases in the Leaf Area Index around the globe, what they refer to as “greening.” That means the annual detritus is increasing and it is the annual decomposition during Winter and Spring that drives the seasonal increase in atmospheric CO2, which is not compensated by the shorter draw-down by photosynthesis.
Isotopic fractionation (particularly for CO2) is often cited as proof of CO2’s anthropogenic origins. Unfortunately, that is based on the unstated assumption that the increased C12 is exclusively from fossil fuel burning. It ignores the fact that the light C12 CO2 more easily escapes from sea water than C13. Actually, one can anticipate isotopic fractionation anytime one has two or more isotopes involved in phase changes or chemical reactions. Isotopic fractionation is not as well studied as a lot of environmental factors that you say we now know “FAR better.”
One can prove anything if they Cherry Pick the data, as you do.
Will still need to act proactively to lower CO2 emissions but not like the activists like millibrain are doing , he is a total loose cannon.