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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In my opinion studying Arctic temperatures without understanding the tilt of the earth throughout history isn’t very helpful. For instance, without knowing the precise tilt at any given period of time leave me without accurate information to make any statement whether temperatures were or were not a result of more or less sun striking Arctic areas due to earth’s tilt and less about CO2 levels, not to mention possible ice ages or warm periods. Then throw in whether or not the sun was or was not as strong as today, specific actions of sun at that given time also leaves me with a completer lack of other known factors that affect earth other that CO2.
We do know for more than 55 million years, Ellesmere Island remained in one place while the world around it changed. Fifty-five million years ago, verdant forests grew at 75° North latitude. These wetland forests, comprised of species now primarily found in China, grew on an alluvial plain where channels meandered back and forth and periodic floods buried stumps, logs, and leaves intact. Today the forests are preserved as coal seams that outcrop on the edges …of modern Ellesmere Island, where there are no forests, and the tallest vegetation grows less than 15 cm high. Large parts of the area are polar desert, subject to intensely cold and dark winters and minimal precipitation.
Large parts of the area are polar desert, subject to intensely cold and dark winters and minimal precipitation. That there IS climate change!
“The scientists believe the multiple methods of analysis have yielded a more complete and accurate picture of ancient climate than previously possible.”
Wellllll…..at least they didn’t use a GIGO computer model.
Estimated continental positions here:
http://en.wikipedia.org/wiki/File:Paleogene-EoceneGlobal.jpg
—–Willis Eschenbach, take note:
“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 …. There were crocodiles above the Arctic Circle and palm trees in Alaska.”
“Eocene water temperature along the subtropical U.S. Gulf Coast hovered around 80 degrees Fahrenheit ….Modern temperatures in the study area average 75 degrees Fahrenheit”
———
Gee, its almost as though there was some type of thermostat keeping the tropics at nearly a constant temperature,
http://wattsupwiththat.com/2009/06/14/the-thermostat-hypothesis/
80 degrees with less seasonality? So the whole world was like Hawaii.
Sign me up.
So, did the level of CO2 cause the higher temperature or did the higher temperature cause the level of CO2? Discuss.
“The study does not mean elevated atmospheric CO2 levels did not produce a greenhouse effect…”
There’s that boilerplate text again. Translation: “Please don’t cut off our funding; we’re manufacturing evidence as fast as we can.”
Mike McMillan says:
July 5, 2011 at 4:06 pm
> 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.
None of the actual proxy temperature data for the Eocene (none that is again) shows the extreme numbers that some pro-AGW people have quoted before. Exaggeration is a big part of this science and anyone interested in the topic needs to check things out for themselves before believing the hype.
Every now and again, a climate scientist comes along and tries to correct the hype. This study appears to be one of those. The result, however, is that the researcher’s careers are usually slowed but, at least, other researchers start using the more accurate information and eventually the record gets corrected.
It was warmer in the Eocene – up to 6.0C warmer globally than today. Through polar amplification, the polar regions were probably up to 12.0C warmer. Equatorial regions would have been about 3.0C warmer just as this study says (the equatorial regions only change by about half of the global numbers in most studies). Through the 24 hours of sunlight in the summer, it probably got pretty warm in the polar regions in the summer but in the winter of 24 hours of darkness, it was still very cold. Some polar ice still formed in the winter.
This is, however, one of the few periods in Earth history where 3.0C per doubling of CO2 actually works. CO2 levels were around 1,000 ppm or 2 doublings at the time. But CO2 actually rose after this warm period, reaching 1,500 ppm just as the Earth started cooling off and CO2 didn’t drop again until about 30 million years ago, after Antarctica had glaciated over and temperatures had fallen close to today’s level 4 million years earlier. ie don’t blame CO2, something else happened.
There may have been crocs in the arctic, but at the N pole the sea is several km deep.
I am not dismissive of this study as others are, however I’d be careful about the claim that the globe was warmer 50mill yrs ago due to higher levels of CO2.
They have NO IDEA why the globe might have been warmer then and no idea if higher levels of CO2 drove the Ts or was the cause of higher Ts.
If the former, then the question must be answered, “What caused the higher levels of CO2 in the first place?”
“The question seems simple enough: What happens to the Earth’s temperature when atmospheric carbon dioxide levels increase?”
=================================================
Obviously not much………
According to this paper, CO2 forcing has been overestimated, and that CO2 does not create as much warming as assumed……
…and in spite of “50 million years ago when CO2 concentrations were higher than today.”
elevated levels of CO2 could not prevent the planet from going into another ice age
This paper is saying that CO2 is not driving the bus……………
What was the atmospheric CO2 concentration 50mil years ago? Interesting that the molluscs were not dissolved by the acidic oceans we have been warned about.
This seems like good science. It should impel more graduate students to sample similar Eocene fossils in (exotic) places both further north and south, and subject them to the same analyses, along with anything else that is useful. The Eocene, after all, represents the Earth’s not-so-distant future, according to the AGW crowd. Let’s get a good read on it. Wish I were still doing science. 😉
If they only could determine the angle and wobble of the earth towards the sun, the distance towards the sun, the distance to the moon, the state of the sun, in relevance to the land configuration and the configuration of the other planets, as well, maybe there will be some head way as to why our climate was as it was back when great grandpa walked the earth to school.
“Our results support predictions that increasing levels of atmospheric CO2 will result in a warmer climate with less seasonality across the globe.”
This association continues to allude me. How can CO2 increases be assigned as the driver of climate rather than the follower of temperature increases?
Bill Illis says:
July 5, 2011 at 6:25 pm
…
This is, however, one of the few periods in Earth history where 3.0C per doubling of CO2 actually works. CO2 levels were around 1,000 ppm or 2 doublings at the time. But CO2 actually rose after this warm period, reaching 1,500 ppm just as the Earth started cooling off and CO2 didn’t drop again until about 30 million years ago, after Antarctica had glaciated over and temperatures had fallen close to today’s level 4 million years earlier. ie don’t blame CO2, something else happened.
Not necessarily. It might just be appearances. The Eocene transition from the warm regime to a cold one is also a transition from a “greenhouse” state to an “icehouse” state in the extremely long term oscillations (ca. 50 – 100 my) that have marked planetary climate [see Gornitz, W. (ed.) Encylopedia of Paleoclimatology, entry on “Icehouse” (Cold) Climates]. It stands to reason that if the planet was warmer, atmospheric CO2 must have been higher simply because the oceans were warmer. It would be pretty much unavoidable. One of the points made in the encyclopedia is that “Icehouse” oceans such as at present are “well mixed.”
How they can mention CO2 as a factor in early Eocene climate without mentioning that the poles could be reached by currents from the tropics, I simply don’t know.
If polar oceans warmed to 10C, say, how much CO2 would that release (warm beer is flat)??
This seems to be a rather important point about the Eocene that the tropical temperatures were not that much warmer than the present. It is a situation noted in Lindzen’s “Climate Science: Is it currently designed to answer questions?”
“the original data analysis for the Eocene (Shackleton and Boersma, 1981) showed the polar regions to have been so much warmer than the present that a type of alligator existed on Spitzbergen as did florae and fauna in Minnesota that could not have survived frosts. At the same time, however, equatorial temperatures were found to be about 4K colder than at present. The first attempts to simulate the Eocene (Barron, 1987) assumed that the warming would be due to high levels of CO2, and using a climate GCM (General Circulation Model), he obtained relatively uniform warming at all latitudes, with the meridional gradients remaining much as they are today. This behavior continues to be the case with current GCMs (Huber, 2008). As a result, paleoclimatologists have devoted much effort to ‘correcting’ their data, but, until very recently, they were unable to bring temperatures at the equator higher than today’s (Schrag, 1999, Pearson et al, 2000). However, the latest paper (Huber, 2008) suggests that the equatorial data no longer constrains equatorial temperatures at all, and any values may have existed.”
While the wiki article on the Eocene does say initially that the Eocene tropics was similar in climate to today, but then contradicts itself by citing, I kid you not, a giant snake as proof that the data must be wrong. Mind boggling.
Anyway, as someone mentioned above, this is further evidence that the tropics have a tightly constrained climate.
I don’t get the comments of concern about the use of a single site to make all the data. The Church of Global Warming has already shown the way, where a single tree can be used to build worldwide reconstructions of warming and CO2, and just two geographically close sites can be used to determine the rise of the oceans.
Really, the science is settled!
/s
Baa,
Thank you, thank you, thank you! And thank you (belatedly) for the statement about reasoning; negotiating, whatever with the person that just robbed your house (no, there is no middle ground)
What drove the higher CO2 in the past?
If you want a classic example of pretzel logic, read the “Skeptical Science”? sections on CO2.
Cook says that that CO2 might not have been 4000 ppm in the Ordovician but if it was then the sun was weaker then to override (under ride?) the GHG effect. So…. does TSI (with CR or any other unknown) matter or not? Where will the funding go?
Where palm trees can survive is determined not so much by exceedingly warm temperatures as by lack of freezing temps. In other words, the less seasonality, the better. Which, as the paper states, was the name of the game in the Eocene.
Steve from rockwood says:
July 5, 2011 at 7:43 pm
Why do they keep assigning the transportation duty to a trace gas instead of the bus?
Oh, I suppose they keep the cart in front of the horse just in case. In case of emergency, they’re all ready to beat a hasty retreat. Another theory is that, after 80 years of assigning climate change to CO2 (it started in the 1930’s), the horse is quite dead, and is being carted about in the wagon. It must be an awkward arrangement to keep up the appearances. They’re Oh for Three.
Here is the salient quote: “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.”
These comments are based on fossil records, and so they show that the history of natural climate variability on Earth includes severe fluctuations. Trying to attribute this retrospectively (without clear evidence, I would add) to CO2 changes is horsefeathers. The truth is that this and other studies show clearly that whatever climate fluctuations we are currently experiencing are well within the bounds of natural variability and it is not necessary to invoke human causation to explain current observations. The truth is that the AGW crowd WANTS it to be true that there is an imminent, man-caused environmental disaster just waiting to destroy us all. They don’t care about rational assessment of evidence because the “narrative” is more important than the facts.
Bill Illis
Thanks. I always appreciate your comments.
timetochooseagain says:
July 5, 2011 at 8:09 pm “…Anyway, as someone mentioned above, this is further evidence that the tropics have a tightly constrained climate….”
I think Willis Eschenbach explained very well the daily tropical sequence of warming, thunderstorm activity, cooling, and repeat the sequence. A warmer climate would perhaps magnify this tropical tendency, to the point that some areas might be continuously cloud-covered and thus relatively cool (like King Kong’s island!).
I don’t know much about the Eocene, so I would be interested to know what is the sedimentary record of the period. In a system where the climate was (relatively) uniformly warm from tropics to poles, the thermohaline circulation may have ceased to operate. In which case there should be lots of black, pyritic shales in the sequence. Does anyone have any information on this?