66 Million Years of Earth’s Climate History Uncovered – Puts Current Changes in Context

Past and Future Global Temperature Trends

Past and future trends in global mean temperature spanning the last 67 million years. Oxygen isotope values in deep-sea benthic foraminifera from sediment cores are a measure of global temperature and ice volume. Temperature is relative to the 1961-1990 global mean. Data from ice core records of the last 25,000 years illustrate the transition from the last glacial to the current warmer period, the Holocene. Historic data from 1850 to today show the distinct increase after 1950 marking the onset of the Anthropocene. Future projections for global temperature for three Representative Concentration Pathways (RCP) scenarios in relation to the benthic deep-sea record suggest that by 2100 the climate state will be comparable to the Miocene Climate Optimum (~16 million years ago), well beyond the threshold for nucleating continental ice sheets. If emissions are constant after 2100 and are not stabilized before 2250, global climate by 2300 might enter the hothouse world of the early Eocene (~50 million years ago) with its multiple global warming events and no large ice sheets at the poles. Credit: Westerhold et al., CENOGRID

A continuous record of the past 66 million years shows natural climate variability due to changes in Earth’s orbit around the sun is much smaller than projected future warming due to greenhouse gas emissions.

For the first time, climate scientists have compiled a continuous, high-fidelity record of variations in Earth’s climate extending 66 million years into the past. The record reveals four distinctive climate states, which the researchers dubbed Hothouse, Warmhouse, Coolhouse, and Icehouse.

These major climate states persisted for millions and sometimes tens of millions of years, and within each one, the climate shows rhythmic variations corresponding to changes in Earth’s orbit around the sun. But each climate state has a distinctive response to orbital variations, which drive relatively small changes in global temperatures compared with the dramatic shifts between different climate states.

The new findings, published today (September 10, 2020 in the journal Science, are the result of decades of work and a large international collaboration. The challenge was to determine past climate variations on a time scale fine enough to see the variability attributable to orbital variations (in the eccentricity of Earth’s orbit around the sun and the precession and tilt of its rotational axis).

“We’ve known for a long time that the glacial-interglacial cycles are paced by changes in Earth’s orbit, which alter the amount of solar energy reaching Earth’s surface, and astronomers have been computing these orbital variations back in time,” explained coauthor James Zachos, distinguished professor of Earth and planetary sciences and Ida Benson Lynn Professor of Ocean Health at UC Santa Cruz.

“As we reconstructed past climates, we could see long-term coarse changes quite well. We also knew there should be finer-scale rhythmic variability due to orbital variations, but for a long time it was considered impossible to recover that signal,” Zachos said. “Now that we have succeeded in capturing the natural climate variability, we can see that the projected anthropogenic warming will be much greater than that.”

For the past 3 million years, Earth’s climate has been in an Icehouse state characterized by alternating glacial and interglacial periods. Modern humans evolved during this time, but greenhouse gas emissions and other human activities are now driving the planet toward the Warmhouse and Hothouse climate states not seen since the Eocene epoch, which ended about 34 million years ago. During the early Eocene, there were no polar ice caps, and average global temperatures were 9 to 14 degrees Celsius (16 to  25 degrees Fahrenheit) higher than today.

“The IPCC projections for 2300 in the ‘business-as-usual’ scenario will potentially bring the global temperature to a level the planet has not seen in 50 million years,” Zachos said.


The new global climate record CENOGRID (lower panel) is the first to continually and accurately trace how Earth’s climate has changed since the great extinction of the dinosaurs 66 million years ago. The record was generated using the oxygen (shown) and carbon isotopes from tiny microfossils found in deep-sea sediments collected by the IODP ship R/V JOIDES Resolution (shown in the photo) and shows the natural range of climate change and variability over the last 66 million years. Credit: Thomas Westerhold / Adam Kutz

Critical to compiling the new climate record was getting high-quality sediment cores from deep ocean basins through the international Ocean Drilling Program (ODP, later the Integrated Ocean Drilling Program, IODP, succeeded in 2013 by the International Ocean Discovery Program). Signatures of past climates are recorded in the shells of microscopic plankton (called foraminifera) preserved in the seafloor sediments. After analyzing the sediment cores, researchers then had to develop an “astrochronology” by matching the climate variations recorded in sediment layers with variations in Earth’s orbit (known as Milankovitch cycles).

“The community figured out how to extend this strategy to older time intervals in the mid-1990s,” said Zachos, who led a study published in 2001 in Science that showed the climate response to orbital variations for a 5-million-year period covering the transition from the Oligocene epoch to the Miocene, about 25 million years ago.

“That changed everything, because if we could do that, we knew we could go all the way back to maybe 66 million years ago and put these transient events and major transitions in Earth’s climate in the context of orbital-scale variations,” he said.

Zachos has collaborated for years with lead author Thomas Westerhold at the University of Bremen Center for Marine Environmental Sciences (MARUM) in Germany, which houses a vast repository of sediment cores. The Bremen lab along with Zachos’s group at UCSC generated much of the new data for the older part of the record.

Westerhold oversaw a critical step, splicing together overlapping segments of the climate record obtained from sediment cores from different parts of the world. “It’s a tedious process to assemble this long mega splice of climate records, and we also wanted to replicate the records with separate sediment cores to verify the signals, so this was a big effort of the international community working together,” Zachos said.

Now that they have compiled a continuous, astronomically dated climate record of the past 66 million years, the researchers can see that the climate’s response to orbital variations depends on factors such as greenhouse gas levels and the extent of polar ice sheets.

“In an extreme greenhouse world with no ice, there won’t be any feedback involving the ice sheets, and that changes the dynamics of the climate,” Zachos explained.

Most of the major climate transitions in the past 66 million years have been associated with changes in greenhouse gas levels. Zachos has done extensive research on the Paleocene-Eocene Thermal Maximum (PETM), for example, showing that this episode of rapid global warming, which drove the climate into a Hothouse state, was associated with a massive release of carbon into the atmosphere. Similarly, in the late Eocene, as atmospheric carbon dioxide levels were dropping, ice sheets began to form in Antarctica and the climate transitioned to a Coolhouse state.

“The climate can become unstable when it’s nearing one of these transitions, and we see more deterministic responses to orbital forcing, so that’s something we would like to better understand,” Zachos said.

The new climate record provides a valuable framework for many areas of research, he added. It is not only useful for testing climate models, but also for geophysicists studying different aspects of Earth dynamics and paleontologists studying how changing environments drive the evolution of species.

“It’s a significant advance in Earth science, and a major legacy of the international Ocean Drilling Program,” Zachos said.

Reference: “An astronomically dated record of Earth’s climate and its predictability over the last 66 million years” by Thomas Westerhold, Norbert Marwan, Anna Joy Drury, Diederik Liebrand, Claudia Agnini, Eleni Anagnostou, James S. K. Barnet, Steven M. Bohaty, David De Vleeschouwer, Fabio Florindo, Thomas Frederichs, David A. Hodell, Ann E. Holbourn, Dick Kroon, Vittoria Lauretano, Kate Littler, Lucas J. Lourens, Mitchell Lyle, Heiko Pälike, Ursula Röhl, Jun Tian, Roy H. Wilkens, Paul A. Wilson and James C. Zachos, 10 September 2020, Science.
DOI: 10.1126/science.aba6853

Coauthors Steven Bohaty, now at the University of Southampton, and Kate Littler, now at the University of Exeter, both worked with Zachos at UC Santa Cruz. The paper’s coauthors also include researchers at more than a dozen institutions around the world. This work was funded by the German Research Foundation (DFG), Natural Environmental Research Council (NERC), European Union’s Horizon 2020 program, National Science Foundation of China, Netherlands Earth System Science Centre, and the U.S. National Science Foundation.

21 Comments on "66 Million Years of Earth’s Climate History Uncovered – Puts Current Changes in Context"

  1. It is great that there is now a higher resolution temperature history for Earth. The problem is that appending the unvalidated GCM predictions makes it appear that the future is known with the same assurance as the empirical data. Many believe that the RCP8.5 scenario is improbable, and even the less extreme scenarios appear to be running warm based on recent historical records. Conflating actual data with model predictions is not good science.

    • Yes, 100% agree. Thank you.
      To me, it seems like they’re trying to pack excessive information and terminology in here so they can sprinkle in their predictions and ideological slant unnoticed by someone who isn’t so well versed in these things.

  2. Graph’s left side label needs to say “Surface”, not “Suface”.

  3. This is not science.

  4. This has attracted some attention from others with the skill to ‘peer review’ the research. People with an open mind might find the following to be interesting:

    • That is a really well done article/review in terms of this study/article..
      In terms of his theory of Emergent Climate Phenomenon theory is very interesting and I’ve not heard anything like it before. It sounds like a plausible theory on it’s face, I’ll have to look more into it later.
      Thank you for the link.

  5. Opinion and ‘factual data’ are hard to separate from each other in this discipline called ‘climate science’. It is a fact that satellite data shows a 15%+ additional greening of the Earth in the past 30 years. It is a fact that CO2 is plant food encouraging plant growth, and more atmospheric CO2 confers drought resistance. It is a fact that the world ocean contains vastly more CO2 than is in the atmosphere. It is a fact that warmer temperatures release greater quantities of CO2 in the atmosphere from the world oceans. (in cold temperatures, the world oceans absorb CO2)

    According to proxy temperature data from various sources–including ocean core drilling–CO2 increases lag temperature increases.

    There is no doubt CO2 levels to some degree, affect the global climate–the question is to what degree? But is CO2 the primary global temperature knob? No, there is no scientific evidence to support this proposition.

    The climate always changes, but what is of concern is whether the climate changes catastrophically. Climate catastrophists claim the end is nigh, and evil humankind is the blame–but they have not presented a scientific case to justify their alarm.

    • Spot on! Well said.

      Also,the current (Holocene) Interglacial is the LEAST typical climate of climate regimes. Yet a smattering of the last 100 years of climate is used as if it were some departure from “normal climate” that, conveniently, is never described.

      Climate models are based on a specious theory that defies the evidence. Therefore, they are flawed from the outset and it is no wonder they always run “hot” (over-predict climate warming).

      No doubt, climate alarmists believe polar icecaps are “normal” yet they occur during less than 1% of the past 3.5 billion years of Earth’s climate history.

      “Climate change” funding is an immense waste of precious tax dollars.

  6. With or without human intervention the earth will warm. The polar ice caps will melt and the global temperature will rise creating mega storms flooding and turn lush forest into deserts. The seas will rise and envelope our costal cities and lowlands.As temperatures rise evaporation will increase the warmer it gets and we will have great flooding.Many species of animals will go extinct and humans will wage war over shrinking resources. But eventually the temperature will rise to a point we’re more water vapor will be suspended in the atmosphere longer and longer till eventually it will stop raining essentially becoming a green house. The oceans water will divide. The Earth will become an Eden again. Mist will start to rise covering the entire surface of our planet. The contents will grow in size and new lands revealed not seen since the time of Noah. The Firmament will be re established and take it’s permanent place in the heavens. We humans were all living in a garden of Eden until say 12500 years ago when the Earth was bombarded with meteors sending debris into the atmosphere blocking the sun. This created a rapid cooling over the entire globe. This has happen many times over the eons including 50,000 years ago.Mammoths and other creatures were rapidly frozen with grass and flowers in the stomachs.

    So who says global warming is a bad thing? Yes it will get much worse before it gets better but on the bright side eventually temperatures will become more stable and constant. Will will have an additional protective layer from the harmful uv and gama rays, solar flares and other hazards in the vacuum of space. This will enable humans and other survivors to live longer as there cells are no longer degrading rapidly from exposure and cancers.

    This is the natural coarse of life on this planet. The future ones who heed this warning and can adapt will reclaim the Garden of Eden. That if we humans in the present don’t f*** it up with a nuclear war. That will just reset the clock again say another 12500 years or so. PS start buying land in the Artics.

  7. 1. It’s astonishing the number of denialist and semi-denialist responses here.

    2. “RCP 8.5 isn’t known with the same precision as prehistoric or historical climate!” yes, no current climate model will happen exactly. It is neither possible to fully predict the behavior of the climate system nor, crucially, the behavior of human societies. However, by far the majority of uncertainty is human behavior. If one model says the planet warms on average 8 degrees by 2300 and the other says 10 under the same anthropogenic inputs, change the anthropogenic greenhouse warming and the first model might say 3 and the second model 4. Right, the ability to predict people is the biggest source of uncertainty here. Also RCP 8.5 isn’t the only model shown, so it’s not even claiming that it’s THE correct climate projection. Just that it’s one possible projection. Also note that in a world where all fossil fuels are consumed, all of these projections are wrong and you need to put the line going all the way to the top of the bar. Also true in any model where we start releasing some other extreme greenhouse gases that wouldn’t naturally exist in the atmosphere. Just as that model can overestimate the change, it can also underestimate it. End Permian-like weather forecasts are not completely impossible to cause anthropogenically.

    3. “moist greenhouse state Firmament and garden of Eden Noah blah blah blah” Who… asked? Seek help!

    4. “CO2 is plant food.” Yes it is. And animals live naked in the Arctic, so clearly nudity isn’t an issue in the cold, right? Sure. For a wolf or a bear or a caribou or muskoxen this is true. However, you or your pet iguana cannot live naked in the Arctic. Similarly, plants given adequate access to CO2 would not likely thrive under hotter or cooler climate conditions than they are adapted for. Additionally, modern plants are adapted for a range of climates. Ice age glacial periods and ice age interglacial periods. We are in an interglacial period. Ergo, it has never been much warmer than this in the last 2.5 million years and that neither plants nor animals nor fungi are adapted for a world that is not somewhere between the ice age minimums and our current climate. Every degree added is a degree further from the conditions that a particular plant is actually meant to survive in. Plants also can’t just slowly migrate with climate. All of the other conditions such as soil type, water, wind, etc will be simply incorrect for that to type of plant to thrive. Another thing plants are not adapted for is the things that can migrate with the climate. There are plenty of animals that currently share a land border with regions they would suddenly become invasive in should the temperature warm even a few degrees. This would further contribute to damage to plants. Increased CO2 is not likely to compensate an abrupt change in conditions.

  8. This article is a farce. The graphic is virtually ENTIRELY within an Ice Era that began about 65 million years ago. Yes, it was very warm then, the climate that is TYPICAL for Earth. Only seven Ice Eras have existed in Earth’s climate history, all occurring within the past 3.5 billion years since carbon-based life (cellular) first appeared. The average duration of an ice era has been 50 million years (seven totaling 350 million or 10% of the past 3.5 bn years). At 65 million years, the current Ice Era is one of the coldest. The chart does not show Ice Epochs, yet there have been five significant Ice Epochs, the most recent beginning 2.4 million years ago. During this Ice Epoch, only the past 800,000 years have been cold enough for year-round polar ice caps! This is also the length of time that long-period Ice Age/Interglacial cycles (~ 100,000 years each) brought the coldest climate of this Ice Epoch. Earth is currently in an Interglacial of an Ice Age cycle within an Ice Epoch of an Ice Era… which is hardly typical of Earth’s much hotter climate (about 13 to 14 deg. F hotter). These climate cycles have NOTHING whatsoever to do with carbon dioxide in the atmosphere. Indeed, the coldest Ice Era of the past 550 million years began when atmospheric CO2 was about 4100 ppm (nearly ten times current amount). That Ice Era lasted for about 30 million years. At the coldest point, atmospheric CO2 had RISEN to about 4500 ppm! Then, when climate recovered to it’s typical much hotter norm, atmospheric CO2 FELL to 3000 ppm! That’s 30 million years of proof that atmospheric CO2 is trivially inconsequential to global average surface temperature. “Climate change” hysteria is based on a specious claim that is invalidated by The Scientific Method (fails to agree with observation), whether observations be from geologic data, ice core data, or recorded observed temperatures since 1880. Finally, statistical analysis of real climate data clearly show there is no correlation between changing atmospheric CO2 and changing climate… no correlation, no causation. Q.E.D. The article is junk science designed to conform to the climate change narrative. No doubt funded by “climate change narrative” money.

  9. contemporary art movements | August 2, 2023 at 6:19 am | Reply

    The writing style in this article is engaging and eloquent. The author’s ability to convey ideas with clarity and finesse makes it a pleasure to read. I thoroughly enjoyed the flow and coherence of the content. Well done on such excellent writing!

  10. Love the misinformation gods who have commented here! The data that you say does not exist is definitive for 650K years. The level of C02 and Temp at current levels has never been experienced….for 650K years!

  11. so glad to see comments made with critical thinking skills, which of course may soon be declared “hate speech” and banned by the authoritarian Leftist Establishment.
    I challenge the woke cultists to show any previous global warming where biodiversity suffered a net loss.
    It was global COOLING which was deadly.

  12. Paul Higginson | March 27, 2024 at 4:57 am | Reply

    This graphic shows millions of years. The last section shows just 100yrs but a change of over 12oC! In relative terms to the millions of years shown before, this temperature change takes place in a split second and is unprecedented. It would be shown by a vertical line regardless of the model used. In this scenario the current echo system will fail to exist and us along with it.

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