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Researchers Find that CO2 Forcing Alone Doesn’t Explain Magnitude of Ancient Global Warming Episode

By analyzing data from deep-sea sediment cores to study an ancient global warming episode (the Paleocene-Eocene Thermal Maximum, PETM), researchers found a less-than two-fold increase (70%) in atmospheric carbon dioxide levels corresponding to the 5–9 °C (9-16 °F) warming of the PETM. Based on current knowledge and models of the Earth’s climate system, they had expected to find a three- to eight-fold increase in atmospheric carbon dioxide levels to drive that amount of warming.

In a paper published online in the journal Nature Geoscience, the team, led by Richard Zeebe of the University of Hawai‘i at Manoa’s School of Ocean and Earth Science and Technology, suggests that in addition to direct CO2 forcing, other processes and/or feedbacks that are hitherto unknown must have caused a substantial portion of the warming during the Paleocene–Eocene Thermal Maximum.

We were pretty surprised that the increase in atmospheric carbon dioxide turned out to be so small. To explain the entire warming, you would need a whole lot more carbon.

—Richard Zeebe

The Paleocene-Eocene Thermal Maximum warming event occurred about 55 million years ago, and was marked by an increase in global temperature of 5-9 °C over about 10,000 years. A key feature of the event was the release of a large mass of 13C-depleted carbon into the atmosphere, possibly from the dissociation of oceanic methane hydrates, although the source remains an open issue.

Zeebe and his colleagues used data from the sediment cores and a carbon cycle model to calculate that the initial carbon pulse in the PETM was some 3,000 Pg C or less.

As a result, atmospheric carbon dioxide concentrations increased during the main event by less than about 70% compared with pre-event levels. At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration, this rise in CO2 can explain only between 1 and 3.5 °C of the warming inferred from proxy records.

—Zeebe et al. (2009)

[From the pre-industrial value of 280 ppm (parts per million), the current atmospheric concentration of CO2 is more than 380 ppm—about a 36% increase. (Earlier post.)]

Once these other processes have been identified, the authors wrote, their potential effect on future climate change needs to be taken into account.

In a nutshell, theoretical models cannot explain what we observe in the geological record. There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models...Some feedback loop or other processes that aren’t accounted for in these models—the same ones used by the IPCC for current best estimates of 21st Century warming—caused a substantial portion of the warming that occurred during the PETM.

—Gerald Dickens, co-author and professor of Earth science at Rice University

There are a few ideas what may have contributed to the additional warming. But I don’t think we fully understand these events of intense and rapid global warming. By continuing to put these huge amounts of carbon dioxide in the atmosphere, we’re gambling with climate and the outcome is still uncertain.

—Richard Zeebe


  • Zeebe, R. E., Zachos, J. C., and Dickens, G. R. (2009) Carbon dioxide forcing alone insufficient to explain Paleocene-Eocene Thermal Maximum warming. Nature Geoscience, Advance Online Publication, doi: 10.1038/ngeo578



"At the start of the PETM, the ocean circulation patterns changed radically in the course of under 5,000 years. Global-scale current directions reversed; for example, deep water in the Atlantic flowed from north to south instead of the usual south to north. This "backwards" flow persisted for 40,000 years. Such a change would transport warm water to the deep oceans, enhancing further warming." Not only would this warm water have released methane hydrates from the sea bed but it would have been anoxia too. As a result the "PETM is accompanied by a mass extinction of 35-50% of benthic foraminifera (especially in deeper waters) over the course of ~1000 years - the group suffering more than during the dinosaur-slaying K-T extinction. Contrarily, planktonic foraminifera diversified, and dinoflagellates bloomed. Success was also enjoyed by the mammals, who radiated profusely around this time."

More important for Global Warming anoxia means a lot of the released methane would not have quickly dissociated: Methane is a much more powerful greenhouse gas.

What's more I think the rise in mammals, with their different digestion system, may have cause even more methane. [Don't quote me; this last part is pure speculation.]


In other words, the geological record shows, for this event 55 million years ago at least, a relatively small increase of CO2 triggers a secondary effect that gives you much greater warming than the CO2 can on its own. (This tripping point has been repeatedly postulated and methane is a good call)
If true this time around then hardly good news. Firstly because we are already half way there, and we dont know at what point it really starts to take off, secondly the skeptics will sieze on this to prove conclusively that all existing computer models meaningless.


It is not because CO2 can generates warming that all warmings on planet earth have been caused by CO2. It could be a increase in solar activity or something linked to the drift of the continents. The problem is that the CO2 value 55 millions years ago are not very precise as well, because ice records goes at best to 500 000 years, other tracking methods exist but they are not very precise


It is gratifying to see the appearance of sober science here. Of course the study shows there is a great lapse of understanding about what warms the planet. Here is the part fo the study not quoted by GCC and alarmist tracts:

"In a nutshell, theoretical models cannot explain what we observe in the geological record,” said oceanographer Gerald Dickens, a co-author of the study and professor of Earth science at Rice University. “There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models.

The time to put down the CO2 alarm bell is here. Let's pick up the Energy Independence flag (which does all the same machinations except with believable science and lower cost) and break our addiction to fossil fuel.


And SVW calls it!



Roger Pham

Let's remember that CO2 is not the only GHG, but water vapor and methane are even stronger GHG's.

Increase in CO2 level causes a modest increase in GW, which, acting like a switch, causes higher increase in water vapor concentration in the atmosphere, causing a positive feedback effect. For example, a mere 1.6% increase in temperature from 303 K to 308 K (30 C to 35 C) will cause vapor pressure to increase from 32 mmHg to 42 mmHg, or a 31 % increase in the amount of water vapor in the atmosphere!

Drastic rise in Global temp will cause melting of methane hydrate releasing vast quantity of methane in the atmosphere.

Melting of surface snow and ice, which reflects most of solar energy, even from modest amount of initial warming, will greatly accelerate the subsequent rate of global warming due to increase solar energy absorption. Warming atmospheric temperatures will reduce cloud formation, further increase the rate of solar energy absorption. An increase in water vapor concentration alone cannot cause global warming because this will cause more cloud formation and subsequent condensation into precipitation.

Look at Venus, a planet that is far hotter at its surface (800 degrees) than can be explained merely by its distance from the Sun. Perhaps a better GHG warming model can be formulated by extrapolating combined data from the Earth, Venus and Mars, than from Earth alone.

The effect of CO2 on GW is therefore, far from linear, but acting like an amplifier's circuitry. Increasing level of CO2 will cause disproportionally high temperature rise. With many unknown or unquantifiable variables, it would be difficult to model the direct numerical relationship between CO2 level and degree of global warming.

But, most important of all, the lack of a precise model does not disprove the effect of AGW, but this data shows even much more serious concern about RUN-AWAY GLOBAL WARMING, with devastating consequences yet to be predicted from much higher rise in global temperatures yet to come. The Titanic is taking on more and more water, folks, this is not time to argue about how big the gash in the hull and the rate of water intake...Time to take drastic actions in curbing all anthropomorphic CO2 release by full steam ahead investment in solar, wind, geothermal energy...banning all livestocks that can release methane in the atmosphere...etc...

Roger Pham

I should further add that the role of methane is but transient in the atmosphere in geologic time frame, as this methane will be oxidized into CO2 and H2O from UV radiation and other factors. CO2, however, is a very stable compound that can only be removed by photosynthesis...provided that we don't release any further geologically-sequestered fossil-fuel-origin CO2 into the atmosphere. Our human's rate of release of CO2 of recent time frame is far too rapid for the ecosystem to absorb in geological time frame.


In geologic past we have had Earth atmospheres with 1800ppm CO2 give rise to the entire plant kingdom. No catastrophic warming. No catastrophic destruction of land mass. No 800C temperatures like Venus. Earth, is nothing like Venus, or Mars for that matter.

Will S

Sulleny, the existing agriculture base relies on continuing rainfall patterns (amount AND timing). As this shifts due to climate change, winter snow reduction in mountain ranges means less spring run-off. Less rain during summer means crop withering drought (California grows 1/4 of the crops for the US and is losing ag capacity rapidly). Less frequent but more intense storms mean more runoff and drier soils.


Sorry Will... Fundamentally wrong is fundamentally wrong.

Acceptance is hard.


Will - also please note that precipitation in the Crown of the Continent Ecosystem (Rockies, BC, Alberta) has increased about 10% during the past century. Even with snowpack shrinkage - we have no definitive causality between CO2 and temperature other than natural variation.

Put the politics aside and let's get on with ending reliance on fossil fuel.

Roger Pham

The warming effect of Green House Gases is an established FACT, not subjected to any further debate. It follows logically that the higher the concentration of GHG's, the more warming will follow. The extent of the warming is debatable, since so many variables are involved...But the evidences so far does not bode well for the future of humanity!


“There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models."

Yes Roger... I should say AGW so as to identify the .0003 percent of the atmosphere representing man-made CO2. When are the Warmists going to face facts? The global warming campaign has failed. Do you get that? It's a failure. No big deal. Everyone fails sometime. Forget the marxist agitprop and FOCUS. All the purported "climate" goals (except the ludicrous socialist ones) can be easily met through a realistic campaign based on Global Energy Independence. No voodoo or apocalyptic religion required.

In fact goals are all being met now via electrification and biofuels and improved technology of all sorts. Just because this transition did not need the help of a climate catastrophe does not make it any less admirable. All have made a fine contribution and now realize that old fashioned "scare campaigns" don't work anymore. That's part of growing up. Admirable in itself.

In geologic past we have had Earth atmospheres with 1800ppm CO2 give rise to the entire plant kingdom.
And the sun was much dimmer back then. That would tend to support the demonstrated fact that CO2 warms the atmosphere wouldn't it?

I guess Sulleny's right; we should throw away all legitimate climate science due to a healthy scientific method which points out problems in the existing hypotheses and corrects them, interestingly making the possible consequences of AGW even worse than previously believed.... and rather, we should just accept that God did it, end of story.....


"we should just accept that God did it, end of story....."

religious fruitcake or...???


"we should just accept that God did it, end of story....."

religious fruitcake or...???

Nat Pearre

"The global warming campaign has failed. Do you get that?"

Um... could explain the purpose of Waxman-Markey? In my mind it seems like the triumph of good science (and adequate environmental economics) over corporate interest lobbying, but you must see it as something else, something unrelated to curbing CO2 emissions. I'm intrigued to learn what that something is.


Let it slide Nat he's not worth it. And besides, you can't talk "good science" to someone who's looking down their nose at it. Haven't you noticed how thousands of climate scientists can write a report on AGW and the denialists will invalidate the whole thing if it has so much as a typo but if a retired metallurgist or an electrical engineer [with a history of disputing medical research for the benefit of the cigarette companies] writes against AGW on the oil company's dime they take it as the word of GOD. And then there's their most recent hero - an economist, a 'real' expert on the climate. One denialist here actually tried to pass off a piece from a right wing religious site- http://discerningtoday.org/ -as peer review. I don't know if that makes him a "religious fruitcake" or just a damn poor googler but either way he has "little credibility left."

Now sulleny here seems all fired up by the quote “There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models." Well I got another quote; "according to aerodynamic theory bumble bees can't fly."

This is an old joke told since the 1930s. The story goes that an aerodynamist and a biologist were having lunch when the aerodynamist got out his note pad and proved bumble bees couldn't fly. Ever since then those people who hate science have used it to 'prove' scientists are a silly lot who don't know anything. But to a more thoughtful person it's obvious: Of course the aerodynamist knew bees can fly and, being an aerodynamist, he knew his theories worked(his airplanes flew). The point he was making was when you drastically change the scale of things even the best theory fails. It doesn't stop you from using it to build large things like airplanes, you just need more to understand small things like bees. In the same light we still teach Newtonian laws in school and even the astronauts landed on the moon using them but Einstein prove Newton was "fundamentally wrong" by drastically change the scale, even einstein was proven wrong by Hawkins when he went even deeper. None of this stops you from using Newton's laws in every day life.

Likewise sulleny is missing the most important point - the drastic change in scale. The climate models we use today are for the current time period; The Paleocene-Eocene Thermal Maximum warming event, which this report talks about, occurred about 55 million years ago. So of course there appears to be something fundamentally wrong with the way temperature and carbon are linked in the climate models, we don't have enough numbers to even make a good model for way back then. Temperature and CO2 ratios are not really known from that time period, they can only be inferred through indirect means. Nor do we know that else may have been in the air back then; more methane could have made things hotter with less CO2 and , in the case of a cool Earth even with 1800ppm CO2, a lot of particulate matter (like ash from the same volcanoes that might of put that extra CO2 in the air) could have made all the difference in keeping thing cool. Other factors we can't be sure of are the orbit of the Earth or the tilt of it's axis, the strength of the sun or even how thick the atmosphere was. Even the length of the day and the distance to the moon has changed.

None of this stops us from being able to use the climate models in the current period.

Roger Pham

Well said, ai vin!


Heck, I could write a chapter just on the effects of Paleogeography on the Earth's climate. The Paleocene-Eocene Thermal Maximum warming event marked the start of the Eocene epoch and wikipedia has this to say about the geography of that time:

"At the beginning of the period, Australia and Antarctica remained connected, and warm equatorial currents mixed with colder Antarctic waters, distributing the heat around the planet and keeping global temperatures high. But when Australia split from the southern continent around 45 mya, the warm equatorial currents were deflected away from Antarctica, and an isolated cold water channel developed between the two continents. The Antarctic region cooled down, and the ocean surrounding Antarctica began to freeze, sending cold water and icefloes north, reinforcing the cooling.

The northern supercontinent of Laurasia began to break up, as Europe, Greenland and North America drifted apart.

In western North America, mountain building started in the Eocene, and huge lakes formed in the high flat basins among uplifts, resulting in the deposition of the Green River Formation lagerstätte.

In Europe, the Tethys Sea finally vanished, while the uplift of the Alps isolated its final remnant, the Mediterranean, and created another shallow sea with island archipelagos to the north. Though the North Atlantic was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar.

India continued its journey away from Africa and began its collision with Asia, folding the Himalayas into existence."

[So you can see how ocean and air currents, which have to find their way around things like continents and mountains, would have been different.]

"It is hypothesized that the Eocene hothouse world was caused by runaway global warming from released methane clathrates deep in the oceans. The clathrates were buried beneath mud that was disturbed as the oceans warmed. Methane (CH4) has ten to twenty times the greenhouse gas effect of carbon dioxide (CO2)."


Actually, Waxman-Markey is about Congress handing out favors (exemptions from the cap and free allocations) to favored interests; the jockeying to get those favors will guarantee huge amounts of campaign cash for incumbents, and fat lobbying fees for their next careers.

If we had a pure AGW bill, it would be a straight carbon tax.


I agree E-P

The Goracle


...not subjected to any further debate.

LOL!!! The Globalwarmists REFUSE to allow dissent regarding their faith. Same with the Jews, Christians, and Muslims.

This article is EXACTLY about the "debate" having to continue. Should the researchers be jailed for blasphemy?


Roger Pham

Yes, Mr. Goracle, whoever you are (SP?), the warming effect of GHG is an established fact beyond debate, kinda like the warming effect of a glass greenhouse so that you can grow tomatoes in the winter, or solar thermal collector for hot water heating, or that you'll get warm if you put on a coat. Common sense!

The debate here is about to what extent CO2 can raise global temperature, and, for that the study is on-going. However, when the boat is sinking, one should not waste time arguing about how fast the water is entering the hull, but try to save the boat.

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