How hot did Earth get in the past?
By Judy Holmes, Syracuse University (press release)
The question seems simple enough: What happens to the Earth’s temperature when atmospheric carbon dioxide levels increase? The answer is elusive. However, clues are hidden in the fossil record. A new study by researchers from Syracuse and Yale universities provides a much clearer picture of the Earth’s temperature approximately 50 million years ago when CO2 concentrations were higher than today. The results may shed light on what to expect in the future if CO2 levels keep rising.
The study, which for the first time compared multiple geochemical and temperature proxies to determine mean annual and seasonal temperatures, is published online in the journal Geology, the premier publication of the Geological Society of America, and is forthcoming in print Aug. 1.
SU Alumnus Caitlin Keating-Bitonti ’09 is the corresponding author of the study. She conducted the research as an undergraduate student under the guidance of Linda Ivany, associate professor of earth sciences, and Scott Samson, professor of earth sciences, both in Syracuse University’s College of Arts and Sciences. Early results led the team to bring in Hagit Affek, assistant professor of geology and geophysics at Yale University, and Yale Ph.D. candidate Peter Douglas for collaborative study. The National Science Foundation and the American Chemical Society funded the research.
“The early Eocene Epoch (50 million years ago) was about as warm as the Earth has been over the past 65 million years, since the extinction of the dinosaurs,” Ivany says. “There were crocodiles above the Arctic Circle and palm trees in Alaska. The questions we are trying to answer are how much warmer was it at different latitudes and how can that information be used to project future temperatures based on what we know about CO2 levels?”
Previous studies have suggested that the polar regions (high-latitude areas) during the Eocene were very hot—greater than 30 degrees centigrade (86 degrees Fahrenheit). However, because the sun’s rays are strongest at the Earth’s equator, tropical and subtropical areas (lower latitude) will always be at least as warm as polar areas, if not hotter. Until now, temperature data for subtropical regions were limited.
The SU and Yale research team found that average Eocene water temperature along the subtropical U.S. Gulf Coast hovered around 27 degrees centigrade (80 degrees Fahrenheit), slightly cooler than earlier studies predicted. Modern temperatures in the study area average 75 degrees Fahrenheit. Additionally, the scientists discovered that, during the Eocene, temperatures in the study area did not change more than 3 to 5 degrees centigrade across seasons, whereas today, the area’s seasonal temperatures fluctuate by 12 degrees centigrade.
The new results indicate that the polar and sub-polar regions, while still very warm, could not have been quite as hot as previously suggested.
The findings are based on a chemical analysis of the growth rings of the shells of fossilized bivalve mollusks and on the organic materials trapped in the sediment packed inside the shells, which was conducted by Keating-Bitonti and her colleagues. Ivany collected the fossils from sediment layers exposed along the Tombigbee River in Alabama. The mollusks lived in a near-shore marine environment during a time when the sea level was higher and the ocean flooded much of southern Alabama. The sediments that accumulated there contain one of the richest and best-preserved fossil records in the country.
“Our study shows that previous estimates of temperatures during the early Eocene were likely overestimated, especially at higher latitudes near the poles,” Keating-Bitonti says. “The study does not mean elevated atmospheric CO2 levels did not produce a greenhouse effect—the Earth was clearly hotter during the early Eocene. Our results support predictions that increasing levels of atmospheric CO2 will result in a warmer climate with less seasonality across the globe.”
To determine the average seasonal temperatures in the study area, Keating-Bitonti sampled the mollusk shells for high-resolution oxygen and strontium isotope analyses, which were done at SU. The Yale team analyzed shells and sediments for clumped-isotope and tetraether-lipid analysis. The results were consistent across all of the independent analytic methods. The scientists believe the multiple methods of analysis have yielded a more complete and accurate picture of ancient climate than previously possible.
The study also marks the first time clumped-isotope analysis has been used alongside traditional oxygen isotope and organic geochemical analyses in paleoclimate work. The research team is currently using the same analytical process to determine Eocene Epoch mean annual and seasonal temperatures in polar-regions.
“Clumped isotopes is a new way to measure past temperatures that offers a distinct advantage over other approaches because the technique requires fewer assumptions; it’s based on well understood physics,” Affek says. “The agreement among different methods gives us confidence in the results and enables us to use these methods in other locations, such as Antarctica.”
Keating-Bitonti recently completed a master’s degree in geology at the University of Wisconsin and will be continuing her studies at Stanford University as a Ph.D. student in the Department of Geological and Environmental Sciences, School of Earth Sciences.
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h/t to Dr. Leif Svalgaard
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rbateman;
Forget ‘transportation duty’, wait ’til they calculate the CO2 on the production of cement and asphalt, power generation pales! And they have already expressed violent disapproval of dirt roads here in the Rockies so the ‘logical’ end is no roads…. period.
I should temper the statement ‘power generation pales’ it has provided us with the standard of living we have but…… so has concrete and asphalt and refrigerated trucks and………
Clearly a fraudulent study.. We are told that increasing CO2 will make the oceans acid, so that there will be no shellfish. How can there have been any shellfish 50 million years ago when CO2 levels were much higher? The oceans would have been pure acid, unable to support any shellfish. Everyone knows shellfish have been extinct for 350 million years, since the last time CO2 levels were as low as they are today. The earth has been too hot and the oceans to acid to support life except for 350 million years ago when CO2 levels were low, and today when CO2 levels are also low. Life is only a recent development on earth, made possible by the low CO2 levels over the past few million years. [trimmed. Robt]
All I know is that if the equator to pole temperature difference was much smaller it requires that latitudinal heat transfer have been much more efficient. No Thermohaline operating strikes me as the opposite. Unless the boost was entirely from atmospheric circulation. Hm, interesting…
timetochooseagain says:
July 5, 2011 at 9:38 pm
I posted this in “tips & notes”: http://www.nature.com/ngeo/journal/v4/n7/full/ngeo1179.html#/model-data-comparison
an article about the carbon isotope excursion related to the PETM. Interestingly, the Spitsbergen sequence discussed (a marine profile that hasn’t moved more than miles since the its formation in the Eocene) is a black, TOC-rich, pyritic mudstone that shows evidence of “anoxia” developing in the depositional basin.
The thermohaline circulation works by having water in the tropics become dense due to evaporation: water leaves, salt stays. This denser material is transported pole-ward by the Coriolis effect; in due course it cools, becomes even denser and plunges back into the briny depths. However, it is oxygenated and therefor oxidizes the seafloor. Result: no TOC-rich, pyritic black shales (and, no oil generation potential).
Spitzbergen is now (and in the Eocene) near the northern terminus of the thermohaline surficial flow. In the Eocene, the thermohaline sinking zone either moved south of Spitzbergen, or simply ceased to operate for a considerable length of time. If you remove temperature differentials, some phenomena don’t happen (like cooling-related density changes).
Peter says: “Centigrade”? These days, it’s “Celsius.”
Early Eocene was still using Centigrade.
Ric Werme says: July 5, 2011 at 6:18 pm
>Mike McMillan says: “Crocodiles at the North Pole.
>Give the polar bears something to worry about.”
The certainly didn’t bother the polar bears back then, as PBs evolved only 150,000 – 130,000 years ago and crocodiles were in the arctic around 50,000,000 years earlier.
Thank you Ric. I often get the Eemian and Eocene confused.
Not unless they have very deep genetic phobias. PBs didn’t evolve until much less than 1 mya. Even Cephalogale, ancestor of all modern bears, is only half that old or less!
😉
By the time new crocs make the NP home, PBs will have evolved into something else altogether. Except for the ones conservationists hoard in breeding zoos somewhere.
No, couldn’t happen. Needs the hot sun till afternoon to generate the rising air to make clouds. It would have to be fewer storms, less circulation, etc. because of smaller “sinks” for the heat to flow into. Much more boring altogether.
Willem de Lange says:
July 5, 2011 at 4:32 pm
Due to plate tectonics, the configuration of land masses and ocean basins was not the same in the Eocene as now. This means that ocean heat transport was quite different, particularly the movement of heat from the equatorial Pacific Ocean to the northern Atlantic Ocean.
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You’d think so, but here’s conventional wisdom re where things were in the Eocene http://www.scotese.com/newpage9.htm. Other than a narrower Atlantic, a larger and better connected Mediterranean and Antarctica being shifted North a bit, it’s not THAT different from today. The Arctic was apparently still a poorly connected sea centered on the North Pole. Maybe circulation wasn’t that different.
If memory serves, the scotese site has paleoclimate estimates somewhere although it isn’t immediately obvious how to get to them.
General comment: I don’t really have any problem with studies like this as long as we remember that they are indicative, not definitive. We do know that lifeforms that look to be subtropical were probably thriving in the Eocene Arctic. We don’t really know for sure what the temperatures were in the Arctic, Alabama, or the tropics although we can make some somewhat educated guesses. We don’t even really know for absolutely certain where the poles were. Neither do we know what the CO2 levels were although we have some rough estimates that might be correct … or not.
A great deal of the science I learned in high school and college in the 1950s is no longer operative. The physics has stood up well. And chemistry. Geology, on the other hand is virtually unrecognizable. And medicine … sigh … It has changed dramatically. And it is still an incoherent shambles. Frankly I’ve gotten really, really tired of people telling me what science ‘proves’. Based on past experience, my guess is that half of what science has ‘proved’ today will be unproven over the next half century. And none of us knows which half it will be.
This is a nice little study that uses a relatively new isotope palaeothermometer. It is not the first study of it’s kind. For example Came et al, 2007, Nature, Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era, v449, p198-202. There will be many more such studies published over the coming years as the ‘clumped isotope palaeothermometer’ becomes more widely used as a method for determining growth temperatures for once living fossils.
The standard 18-O isotope thermometer relies on measuring the partitioning of 18-O between calcium carbonate and the water in which the carbonate was deposited. Unfortunately such a system is usually under determined in the sense that we cannot measure the isotope composition of the water in which a particular fossil once lived. Using marine fossils we can make some assumptions about the isotopic composition of ancient oceans but these are hard to validate. The clumped isotope method relies on measuring the distribution of 18-O and 13-C in the carbonate lattice. At low temperatures the 18-O and 13-C show a slight tendency to clump together. The degree of clustering is temperature dependent and independent of the water composition in which the organism lived. The mixing thermodynamics of 18-O and 13-C are now becoming well understood theoretically and experimentally with good coherence between the 2 approaches.
I will add a caveat. The clumped isotope method is new and has already thrown up some interesting and controversial data. The Came paper referred to above is a good example. One hypothesis for global climate evolution is that temperatures have been relatively stable, oscillating between a maxima and minima that are broadly within +/- 5 degrees or so of present day conditions (c.f. Shaviv and Veizer, 2003) and that temperatures are decoupled from atmospheric CO2 compositions. This hypothesis is supported by many thousands of 18-O analyses of Phanerozoic marine fossils. However, the Came et al study using clumped isotopes shows different temperatures to those previously estimated using just 18-O. We still don’t fully understand the origin of this discrepancy. For those interested see the online discussion of the Came et al paper at the Nature website.
In my lab at UEA we’re carrying out similar studies to try to help understand the evolution of Earth surface temperatures throughout geologic time. It’s understandable that the early studies such as that just published focus on either hot or cold periods in Earth history. They alone however can tell us relatively little about the overall picture until a much wider range of data are available that encompass a broad palaeo-geographic and palaeo-environmental range and better temporal resolution. At the moment I’m looking for new graduate students to carry out some of this research.
So basically the Sahara was no worse than it is today, Britain had a climate like Spain and Greenland was a rich and fertile place.
All hands to the CO2 pump now!
According to Prof. emerit. Jan Veizer universty of Ottwa 300 000000 years ago the CO2 content of atmosphere was at least 10 times higher as today and the earth climate was dominated by a glacial period
“The question seems simple enough: What happens to the Earth’s temperature when atmospheric carbon dioxide levels increase?”
The question is simple but wrong. The right question:
The question seems simple enough: What’s happened to the Earth’s temperature when atmospheric carbon dioxide levels increase?
The answer:
The Earth’s temperature has increased.
Ross, yes palm trees can survive today on the West Coast of Scotland, but only grow there because we planted them. There is no natural “reproductive route” in place today.
The situation 50 million years ago was quite different, here there was a natural reproductive route, coupled with the fact that freezing events in the Arctic must have been very rare/non existent.
So in these past eras with higher atmospheric CO2, were there corals and shellfish and arthropods? I ask because there was this National Geographic story that strongly implied the whole ocean would be as acid and fizzy as a bottle of Coke, and everything would die.
Check a map of the earth 50 mya. A shallow sea where central america is now, the Med Sea connected the Atlantic and Indian Ocean (and an ocean currnet running from the Indian in the east, through the Med to the Carribean to the Pacific in the West), a massive inland sea in Asia, and no cirucm-polar current in the Antarctic as South America and Australia were practically connected to Antarctica. India still an island. No possibility this drastically different geography could have influenced the weather, er, climate?
Can anyone recommend a simple ‘foundation primer’ into paleoclimate? I often see maps of Pangea and how the continents break up and move around, but it would be interesting to see that happening diagramatically, together with the likely oceanic circulations. Surely sliding all that mass around the place (not to mention ice accumulating around mountains and at poles), has to affect precession, length of day etc? How does one deconvolve all these signals to end up with consistent and reliable chronologies that allow one to reconstruct what is essentially paleogeography? There seems the real risk of building circular arguments here and so I’d assume there are reviewable foundations to the science. Where can I find them at an accessible multi-disciplinary level?
“and palm trees in Alaska”
Not all palms are tropical, there are a lot of cold hardy palms.
Chamaerops, Trachycarpus, etc would grow in some areas of Alaska today.
Trachycarpus is also known as the Himalayan Palm, because of where it’s from.
Well, this is a Syracuse University press release. The study might or might not be a good one, but the first sentence, “…What happens to the Earth’s temperature when atmospheric carbon dioxide levels increase?” indicates that this is Syracuse U’s extreme focus. I did not find any statement about the effects of atmospheric CO2 in the abstract.
I would be interested in studies that emerge from those universities that do not contribute heavily to political campaigns — largely these days Democratic — and that do not receive government grants with the vast majority of the funding paid to the general operating budget of the university. Are there any? I think this qualification omits Syracuse, Yale, and Stanford — oh, and probably U of Wisconsin. I would be glad for comenters here to show me where I am wrong about the funding “ethics” of our universities.
I would also be interested, very interested, in further discussion of the proxies for temperature used, specifically delta-O-18, tetraether lipid analyses (I assume BIT – Branched and Isoprenoid Tetraether index), clumped isotope geochemistry “the study of naturally occurring, multiply-substituted isotopologues”. I had to do some research, but don’t know the science. Have they been as carefully vetted as tree rings?
One further question — without having read the study — if these methods prove quite valuable scientifically, are younger scientists behaving honorably according to the scientific method in spite of the behaviors of many of their middle-aged priofessors? (As we can see, those educated in the time of real science, an older generation, know natural variations of “climate” and do not give in to nonsense for the purposes of keeping an elite “well funded”).
Bystander says:
July 5, 2011 at 4:41 pm
Why bother to repeat the AGW mantra from the paper? Most people here can read. Most people here also understand it is placed there to ensure future grant funding.
Repeating it adds nothing. Don’t waste screen space – it’s not sustainable.
How did the coral reefs survive such high levels of CO2
This would have been an interesting study if the obvious ‘CO2 causes global warming’ blah blah blah wasn’t included in the middle and the end of the article. (I paraphrased). Credibility falls when there is an obvious desire to support a particular slant through extrapolation. The mystery still stands as to whether warming (through the sun’s activities and earth’s rotation, tilt, etc) produces more CO2, or does CO2 add to warming? The evidence of the cool period during and after the onset of the industrial revolution paints evidence of the former.
Dixon says:
July 6, 2011 at 7:03 am
Can anyone recommend a simple ‘foundation primer’ into paleoclimate? I often see maps of Pangea and how the continents break up and move around, but it would be interesting to see that happening diagramatically, together with the likely oceanic circulations. …
====
Try here http://www.scotese.com/climate.htm If you find that helpful, move up to the home page for the site and prowl around. There’s quite a lot of stuff there and no particular agenda that I’m aware of.
Dixon says:
July 6, 2011 at 7:03 am
“…Can anyone recommend a simple ‘foundation primer’ into paleoclimate?…”
Your question veered into plate tectonics and other things (probably because its necessary). These two textbooks are about as good as it gets for the general discussion. After that, you have to read many, various papers.
Origin and Evolution of Earth: Principles of Historical Geology
Kent C. Condie (Author), Robert E. Sloan (Author)
Plate Tectonics, Fourth Edition
Kent C. Condie (Author)
Check these out at Amazon and other booksellers. I’m not sure what the latest revision dates are.