Dating an ancient episode of severe global warming

Jun 15, 2011
The image shows a location in Longyearbyen, Spisbergen, where the researchers carried out field work. Credit: Ian Harding

Using sophisticated methods of dating rocks, a team including University of Southampton researchers based at the National Oceanography Centre, Southampton, have pinned down the timing of the start of an episode of an ancient global warming known as the Paleocene-Eocene thermal maximum (PETM), with implications for the triggering mechanism.

The early part of the Cenozoic era, which started around 65.5 million years ago witnessed a series of transient global warming events called hyperthermals. The most severe of these was the PETM at the Paleocene–Eocene boundary, around 56 million years ago. Over a period of around 20,000 years, a mere blink of the eye in geological terms, ocean temperatures rose globally by approximately 5 C. There is evidence that the concentration of atmospheric carbon oxide increased, but the phenomena that triggered the event remain controversial.

One possibility is that these hyperthermals were driven by cyclic variations in the eccentricity of the Earth's orbit around the sun. At the cycle peaks, increased temperatures could have caused methane hydrate deposits in the deep sea to release large amounts of methane. Some of this potent greenhouse gas would have entered the atmosphere resulting in further intensification of the climatic warming, which would have continued as the methane was fairly rapidly converted into carbon dioxide in the atmosphere.

Alternatively, it may have been geological processes, unrelated to variation in the Earth's orbit, which could have been the culprit for the warming associated with the PETM. In this scenario, magmatism would have caused the baking of marine organic sediments, leading to the massive release of methane and/or carbon dioxide, possibly through hydrothermal vents, thus initiating the which led to the methane release.

"Determining exactly what triggered the PETM requires very accurate dating of the event itself, to determine whether it occurred during a known maximum in the Earth's orbital eccentricity" explains Adam Charles, a University of Southampton PhD student supervised by Dr Ian Harding, and first author of the newly published report.

To getter a better grip on the numerical age of the Paleocene–Eocene boundary, the researchers measured radio-isotopes of uranium and lead in the mineral zircon, found as crystals in two volcanic ash horizons deposited during the PETM. These rocks were collected from two locations in Spitsbergen, the largest island of the Svalbard Archipelago in the Arctic.

Based on their data, the researchers dated the Paleocene–Eocene boundary at between 55.728 and 55.964 ago, which they believe to be the most accurate estimate to date. Their analyses indicated that the onset of the PETM, unlike those of other Eocene hyperthermals, did not occur at the peak of a 400 thousand year cycle in the Earth's orbital eccentricity. Instead, it occurred on the falling limb of a cycle when warming by the sun would not have been at a maximum.

"Compared to other early Eocene hyperthermals, it appears that the PETM was triggered by a different mechanism, and thus may have involved volcanism. However, a thorough test of this hypothesis will require further detailed dating studies," Adam concluded.

Explore further: Erosion may trigger earthquakes

More information: Charles, A. J., Condon, D. J., Harding, I. C., Pälike, H., Marshall, J. E. A., Cui, Y. & Kump, L. Constraints on the numerical age of the Paleocene–Eocene boundary. Geochemistry Geophysics Geosystems 12, Q0AA17, doi:10.1029/2010GC003426

Provided by National Oceanography Centre, Southampton

4.3 /5 (12 votes)

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NotParker
1.4 / 5 (11) Jun 15, 2011
"ancient global warming"

The logic of the above phrase is amazing.

They are assuming glaciation is normal and warming up is abnormal.

In the last few million years glaciation is normal and warming is abnormal. 90% of the time there are massive ice sheets covering a large part of the earth.

Aren't we lucky to be living in a warm time?

emsquared
5 / 5 (5) Jun 15, 2011
Aren't we lucky to be living in a warm time?

I don't know that luck has much to do with it.

I think it could be argued that, at least in significant part, it is precisely because of the "warm time" that we've flourished.
wiyosaya
5 / 5 (6) Jun 15, 2011
"ancient global warming"

The logic of the above phrase is amazing.

They are assuming glaciation is normal and warming up is abnormal.

In the last few million years glaciation is normal and warming is abnormal. 90% of the time there are massive ice sheets covering a large part of the earth.

Aren't we lucky to be living in a warm time?


Personally, I do not see any hint of determination of what is normal or abnormal in this article regarding the phrase you quoted, i.e., "ancient global warming."

Perhaps it is your own interpretation of "what they are assuming" that is the problem?
frenchie
5 / 5 (5) Jun 15, 2011
NotParker. Maybe you should read the article instead of taking 3 words out of context to fit your "OMG this must be a AGW article."

This article is all about finding the date of the start of a warming period. Has the debate over current global climate issues degenerated so much that we can't even speak of previous cold and warm periods?

Chill out. Even the authors aknowledge the still unknown triggers of this warming, clearly stating that it could be due to the earth eccentric rotation around the sun at the time or due be driven by a more biological reason.

Are you simply bothered (due to bias) that both of their potential causes induce a similar increase of methane and/or CO2 in the atmosphere? Are you trying to debate the existence of the Greenhouse effect?

emsquared. I would strongly agree with you that the rise of "civilizations" as we know them now is largely due to having a warm period.
NotParker
1 / 5 (11) Jun 15, 2011
The term "global warming" is all about conning people that cold is normal and warm is abnormal. Glaciers are a perfect example where the AGW cult members insist that the point at which glaciers advanced to their maximum size is "normal" and any retreat from that point is abnormal.

We should be very, very grateful glaciers are no longer advancing. That means agriculture gets to flourish, and we can feed ourselves and we get to live instead of starving to death in the cold.

Remember the article does say: "There is evidence that the concentration of atmospheric carbon oxide increased"

Yet they are only talking about 5C of warming in 20,000 years.

The Eemian (previous interglacial) warmed up 12C in 7500 years ... with CO2 lagging temperature.

http://www.ferdin...ian.html
Howhot
4 / 5 (4) Jun 15, 2011
NotP, you could not be farther from the truth. Global warming is not about "Conning" people, but simply is reporting on trends in climate over the past 60 years or so. If you want to believe science is all about pulling the wool over your eyes, then we as humans have not achieve much.

Historically yes, glaciers have advanced and retreated. What GW has done is to make glacier retreat amazingly fast, like decades verse centuries.

It is pretty foolish to shrug off 5degrees C, I mean occasionally there are unusual days, but the 5C (~9F) is an average for the year to GW. And that is global. See the problem with Agriculture is not that the pants don't like the extra CO2, but the other things that go with 5C increases, like droughts, evaporation of water supplies, etc.

I think you are minimizing the consequences of GW.
rubberman
1 / 5 (2) Jun 16, 2011
So instead of calling it "Global warming", let's call it "Global warming POLICY". Which at this point appears to be to exploit the majority by playing on their fears of an unstable future. Not saying were not sucking the life out of the planet, were just sucking the life out of each other faster.
GSwift7
5 / 5 (2) Jun 17, 2011
emsquared. I would strongly agree with you that the rise of "civilizations" as we know them now is largely due to having a warm period


Perhaps just a small technical point here, but I think it's fair to say that the ice ages played a huge part in our current success too. There were vast human migrations during the ice ages. Who knows what would have happened if we hadn't spread out like we did?
NotParker
1 / 5 (1) Jun 17, 2011
but simply is reporting on trends in climate over the past 60 years or so.


There were two periods before 1950 where it warmed just fast as it has recently. Natural variability.

1910 to 1940
1860 to 1880

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