(Re)Confirmed: Earth’s Wobble, Plus CO2, Ended Last Ice Age

April 5, 2012

As the Earth’s orbital and axial characteristics changed over thousands of years, increases in corresponding solar incidence at key northern latitudes gradually brought the planet out of the last ice age. This is the picture that has long been the best fit for the observations, and has now been further confirmed by a team from Oregon State.

The prevailing view over the last decade has been that the change in insolation gradually brought about a rise in greenhouse gases, which took a long time to begin percolating out of ocean and soils, and were a critical component of the forcing that brought the planet into the current interglacial.  This lag has often been deviously used by denialists in arguing that greenhouse gases have no effect on global temps.  The video above tells that story.

One of the difficulties in telling this story, is that climate scientists have been putting together a puzzle using only one piece – the ice core data from a single location in Antarctica. The “lag” issue emerged as an artifact of the paucity of data.

The new research, drawing on 80 proxy records from diverse locations around the planet to show that “temperature is correlated with and generally lags CO2 during the last (that is, the most recent) deglaciation”.

UPDATE: Seth Borenstein probably has the best summary I’ve seen, here.

TG Daily:

Rising levels of carbon dioxide have for the first time been definitively linked to the global warming that led to the last Ice Age.

A team at Oregon State University reconstructed globally averaged temperature changes during the end of the last Ice Age, in contrast to previous studies, which only compared CO2 levels with local temperatures.

They found that average temperature around the Earth correlated with – and generally lagged behind – rising levels of CO2.

Carbon dioxide has been suspected as an important factor in ending the last Ice Age, but its exact role has always been unclear because rising temperatures reflected in Antarctic ice cores came before rising levels of CO2, says Jeremy Shakun, a former doctoral student at OSU and now a post-doctoral fellow at Harvard and Columbia.

“But if you reconstruct temperatures on a global scale – and not just examine Antarctic temperatures – it becomes apparent that the CO2 change slightly preceded much of the global warming, and this means the global greenhouse effect had an important role in driving up global temperatures and bringing the planet out of the last Ice Age.”

The theory is that the Earth’s natural wobble affected the amount of sunlight striking the northern hemisphere, melting ice sheets that covered Canada and Europe. Fresh water flowed into the Atlantic Ocean, where it formed a lid over the sinking end of the Atlantic Meridional Overturning Circulation.

This put an end to the movement of warm water up from the tropics which had delivered heat to the northern latitudes.

The discovery has implications, of course, for how human-generated carbon dioxide will affect the planet in future.

“CO2 was a big part of bringing the world out of the last Ice Age, and it took about 10,000 years to do it. Now CO2 levels are rising again, but this time an equivalent increase in CO2 has occurred in only about 200 years, and there are clear signs that the planet is already beginning to respond,” says Shakun.

Red Orbit:

The team believes that small changes in the Earth’s orbit around the sun affected the amount of sunlight striking the northern hemisphere, which caused the ice to melt in Canada and Europe.

This ice turned into fresh water, which flowed off of the continent and into the Atlantic Ocean, where it formed a lid cover the sinking end of the Atlantic Meridional Overturning Circulation.  This area is part of a global network of currents that brings warm water up from the tropics and keeps Europe temperate despite its high latitudes.

The researchers said when the fresh water draining off the continent at the end of the Ice Age entered the North Atlantic, it essentially put the brakes on the current and disrupted the delivery of heat to the northern latitudes.

“When the heat transport stops, it cools the north and heat builds up in the Southern Hemisphere,” Shakun said in the press release. “The Antarctic would have warmed rapidly, much faster than the time it takes to get CO2 out of the deep sea, where it was likely stored.

“The warming of the Southern Ocean may have shifted the winds as well as melted sea ice, and eventually drawn the CO2 out of the deep water, and released it into the atmosphere,” Shakun said. “That, in turn, would have amplified warming on a global scale.”

The team found that the average temperature around the Earth at the end of the Ice Age correlated with rising levels of carbon dioxide.

Below, Richard Alley tries to explain the concept to an intellectually challenged congress critter.

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14 Responses to “(Re)Confirmed: Earth’s Wobble, Plus CO2, Ended Last Ice Age”

  1. Peter Mizla Says:

    Not surprising News- at least for those who understand climate change, C02 amounts and the Milankovitch cycles.

  2. Bruce Miller Says:

    Is earth’s “wobble” affected by the weight losses as Arctic ice melts flows away from the pole and spreads across the oceans? Also: Were any of the nuclear explosion since 1946 big enough to alter the “wobble”?
    Does the large amount of unprecedented heat, generated by reactors concentrated in U.S.A. and France in particular, have any Geological, Geophysical,Environmental, Ecological or climate consequences? Can this unprecedented and uneven heating affect the “wobble” of the earth? Do higher CO2 concentrations in the atmosphere change the mass and therefore the inertia of weather formations? Can these mass changes alter the “wobble”?
    Watch as even in one man’s lifetime, the magnetic north pole moves very noticeably. Can this cause changes in the “wobble”, or is the result of a change in the ‘wobble’?
    Can the collective forces of the thrust of so many jet planes, totalled and combined into one factor explain differing wind patterns experienced recently?one relative to the other, wind to jet turbulence, is there a factor?

  3. Jean Mcmahon Says:

    TG Daily:

    Rising levels of carbon dioxide have for the first time been definitively linked to the global warming that led to the last Ice Age. ???

    • greenman3610 Says:

      there’s a little confusion on this point. the study, it seems, is more of a clarification than a new conclusion.

      • climatehawk1 Says:

        Jean is noting the contradiction in global warming leading TO an Ice Age, clearly not what the writer intended to say.

        • greenman3610 Says:

          oh, right

          • pendantry Says:

            Confusing.

            Since the title of the TG article is “Earth’s wobble led to CO2 release that ended last Ice Age“, and it ends with

            “our study bolsters the consensus view that rising CO2 will lead to more global warming

            , it follows that

            “Rising levels of carbon dioxide have for the first time been definitively linked to the global warming that led to the last Ice Age”

            is a simple typo that should read

            “Rising levels of carbon dioxide have for the first time been definitively linked to the global warming that led to the end of the last Ice Age.”

            (my bold).

            Yes/ No?

          • climatehawk1 Says:

            Yes, that is consistent with the rest of the information contained in the articles.


  4. […] Shakun is lead author of the new study in Nature this week, confirming from multiple proxy records that “temperature is correlated with and generally […]

  5. Daniel LaLiberte Says:

    Regarding the 800 year lag in the rise in CO2 following temperature rise, a couple things need to be explained (in a simple way) that would help neutralize the confusion on this point.

    1. Explain how positive (or reinforcing) feedback works, such that an increase in temperature does cause an increase in CO2, and that CO2 increase *also* further increases temperature which further increases the CO2, etc. It might be helpful to show how much less the temperature would have been without the CO2 increase causing further temperature increase.

    2. Despite the positive feedback between temperature and CO2, explain why the temperature does *not continue* to increase indefinitely along with increasing CO2. There must be a stronger negative (or stabilizing) forcing effect that reduces the temperature even while the CO2 is still increasing (with its 800 year lag) and still contributing to a warming effect. Without understanding this stronger negative force on the temperature, people will tend to believe that CO2 had nothing to do with the rise in temperature in the first place.

    At this point I don’t know what that stronger negative force is. If it was explained, I missed it. This negative force might be caused by the increase in temperature itself, and if so, it would be a negative feedback effect. Or it might be caused by something completely independent.

    • Daniel LaLiberte Says:

      Here is, I hope, an easy to understand analogy to the reinforcing feedback between temperature and CO2. The viral video phenomena happens when someone first posts a video and enough people watch it who like it enough to post a link to the video to their friends, resulting in more people watching it and a few posting more links, etc.

      The posting of a link to a viral video causing an increase in the number of watchers is analogous to CO2 causing an increase in temperature.

      The increasing number of watchers of the video causing some to post their own links to the video is analogous to the increase in temperature causing an increase in CO2.

      Now to push this analogy further, there is a lag between when a person watches the viral video and when (or if) they post a link to it. This is analogous to the increase in temperature causing an increase in CO2 but with an 800 year lag. (Just to be clear, there is also a longer lag between when someone posts a link to the video and when other people watch it. So the analogy is not perfect.)

      The number of watchers of a viral video can’t increase indefinitely, however because the number of people who have not yet watched the video decreases as more people watch it. This is a negative or stabilizing feedback force. So at some point, the viral video effect will reach a limit and may tend to crash quickly as it runs out of people to spread the video further. Does the same kind of thing happen with an upper bound on the temperature?

      • Daniel LaLiberte Says:

        Forgot to mention another parallel: The human caused increase in CO2 is analogous to artificially spamming the video to a larger audience, or paying people to repost the video link even if they would not do it naturally themselves. This will result in more viewers, some of whom might post their own links, etc.

        What we need to do is block the spam, and remove counter-productive incentives to do the wrong thing, just as we need to stop producing more CO2 than nature can absorb.

        OK someone suggest a better analogy. :)


  6. What’s interesting (and I still dont have clarity in) is by how much the Milankovich cycles themselves act as a direct forcing compared to the CO2 one which we get from less ice cover. As we know the earth moves rather fast out of an ice age (but way slower than the warming we have today). Still it seems that the cycle, lower albedo (more energy absorbed) as well as 100ppm more CO2 actually brings the temperature up +5C from the ice ages.

    So considering we now have 100ppm more on top of this, the interesting thing is how much the Milankovich cycles now moving towards cooling will actually affect the warming of 40% additional CO2. If the cycles themselves dont directly affect energy income by much it seems its basically the CO2 that is the main warming driver and the cycles just makes the planet have more or less albedo based on its ability to regain ice on the poles.

    But since it seems to be a slower haul to drag it down into an ice age, but rather fast to get out of it, it feels some additional forcing is at play here, like a lot more methane emissions. And that really is my biggest worry about AGW, as its clearly a lot of methane still in the Arctic that could be unstable in the very near future with much more warming. Hope is of course that this will be a slow venting over hundreds of years and not over decades.


    • Your video and James Hansen’s original research really explains this orbital forcing as being fairly small so that’s basically what I thought as well. (Somehow I ended up viewing a different video than the one you had posted here). Thanks for explaining it plainly in the video.


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