From an Oregon State University Media Release (h/t to Leif Svalgaard)
Long debate ended over cause, demise of ice ages – may also help predict future
)
The above image shows how much the Earth’s orbit can vary in shape.
This process in a slow one, taking roughly 100,000 to cycle.
(Credit: Texas A&M University note: illustration is not to scale)
CORVALLIS, Ore. – A team of researchers says it has largely put to rest a long debate on the underlying mechanism that has caused periodic ice ages on Earth for the past 2.5 million years – they are ultimately linked to slight shifts in solar radiation caused by predictable changes in Earth’s rotation and axis.
In a publication to be released Friday in the journal Science, researchers from Oregon State University and other institutions conclude that the known wobbles in Earth’s rotation caused global ice levels to reach their peak about 26,000 years ago, stabilize for 7,000 years and then begin melting 19,000 years ago, eventually bringing to an end the last ice age.
The melting was first caused by more solar radiation, not changes in carbon dioxide levels or ocean temperatures, as some scientists have suggested in recent years.
“Solar radiation was the trigger that started the ice melting, that’s now pretty certain,” said Peter Clark, a professor of geosciences at OSU. “There were also changes in atmospheric carbon dioxide levels and ocean circulation, but those happened later and amplified a process that had already begun.”
The findings are important, the scientists said, because they will give researchers a more precise understanding of how ice sheets melt in response to radiative forcing mechanisms. And even though the changes that occurred 19,000 years ago were due to increased solar radiation, that amount of heating can be translated into what is expected from current increases in greenhouse gas levels, and help scientists more accurately project how Earth’s existing ice sheets will react in the future.
“We now know with much more certainty how ancient ice sheets responded to solar radiation, and that will be very useful in better understanding what the future holds,” Clark said. “It’s good to get this pinned down.”
The researchers used an analysis of 6,000 dates and locations of ice sheets to define, with a high level of accuracy, when they started to melt. In doing this, they confirmed a theory that was first developed more than 50 years ago that pointed to small but definable changes in Earth’s rotation as the trigger for ice ages.
“We can calculate changes in the Earth’s axis and rotation that go back 50 million years,” Clark said. “These are caused primarily by the gravitational influences of the larger planets, such as Jupiter and Saturn, which pull and tug on the Earth in slightly different ways over periods of thousands of years.”
That, in turn, can change the Earth’s axis – the way it tilts towards the sun – about two degrees over long periods of time, which changes the way sunlight strikes the planet. And those small shifts in solar radiation were all it took to cause multiple ice ages during about the past 2.5 million years on Earth, which reach their extremes every 100,000 years or so.
Sometime around now, scientists say, the Earth should be changing from a long interglacial period that has lasted the past 10,000 years and shifting back towards conditions that will ultimately lead to another ice age – unless some other forces stop or slow it. But these are processes that literally move with glacial slowness, and due to greenhouse gas emissions the Earth has already warmed as much in about the past 200 years as it ordinarily might in several thousand years, Clark said.
“One of the biggest concerns right now is how the Greenland and Antarctic ice sheets will respond to global warming and contribute to sea level rise,” Clark said. “This study will help us better understand that process, and improve the validity of our models.”
The research was done in collaboration with scientists from the Geological Survey of Canada, University of Wisconsin, Stockholm University, Harvard University, the U.S. Geological Survey and University of Ulster. It was supported by the National Science Foundation and other agencies.
UPDATE: Science now has the paper online, which is behind a paywall. The abstract is open though and can be read below:
| Science 7 August 2009:
Vol. 325. no. 5941, pp. 710 – 714 DOI: 10.1126/science.1172873 |
Research Articles
The Last Glacial Maximum
Peter U. Clark,1,* Arthur S. Dyke,2 Jeremy D. Shakun,1 Anders E. Carlson,3 Jorie Clark,1 Barbara Wohlfarth,4 Jerry X. Mitrovica,5 Steven W. Hostetler,6 A. Marshall McCabe7
1 Department of Geosciences, Oregon State University, Corvallis, OR 97331, USA.
2 Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada.
3 Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706, USA.
4 Department of Geology and Geochemistry, Stockholm University, SE-10691, Stockholm, Sweden.
5 Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
6 U.S. Geological Survey, Department of Geosciences, Oregon State University, Corvallis, OR 97331, USA.
7 School of Environmental Science, University of Ulster, Coleraine, County Londonderry, BT52 1SA, UK.
Whoops. Delete the first one for bad spelling, please.
To the tune of Davy Crockett
Born in Austria-Hungary,
Schooled at the U of Technology
Thought about orbital eccentricity
Cause he thought insolation was the Ice Age key
Milutin, Milutin Milankovitch
King of the science frontier
Interned during the First World War
Had the time to take on the chore
Of calculating wobbles and tilts by the score
And made himself a legend forever more
Milutin, Milutin Milankovitch
King of the science frontier
Ninety years later at OSU
The geoscientists there had nothing to do
So they copied his work through and through
And presented it all as something new
Milutin, Milutin Milankovitch
King of the science frontier
due to greenhouse gas emissions the Earth has already warmed as much in about the past 200 years as it ordinarily might in several thousand years, Clark said.
Somebody point this d*mb*ss to Loehle reconstruction – http://www.co2science.org/articles/V11/N5/Loehle2007small.gif
“these are processes that literally move with glacial slowness, and due to greenhouse gas emissions the Earth has already warmed as much in about the past 200 years as it ordinarily might in several thousand years, Clark said.”
When will you scientific chaps stop all this double-speak, you have either nailed it or you haven’t. One cannot “nail” something more or less! How many times has a scientific discovery seemed so close to being made suddenly to be dashed against the rocks of reality, or a better theory?
This was taxpayer funded research one assumes, ergo they have to say this! How much did it cost the taxpayers of Oregon/USA to tell you something anybody over 40 with grey hairs should have already known? We did this in geograhy & history at senior school, it was assumed it was written in stone (more or less)!!!!!!
RoyFOMR/Jimmy Haigh:-)
It couldn’t have been Roger Harrabin, he has to many chubby grubby fingers in too many green pies! The leftist-greenie BBC won’t allow this to get out on to the mainstream tv, BBC 1 & 2, I’ll wager!
It always did make more sense for a phenomenon as obviously cyclical as the recent ice ages to be brought about by something else as obviously cyclical as the realtive motions of the sun and planets. Milankovitch recognised this intuitively. The erratic movements of the continents, the wavering of the ocean currents and the occassional outgassings of magma, sediments and regolith never really seemed to fit.
Question, am I seeing this graph right? I mean it looks like when the planet has warmed up it then stays warm for a very short period and then goes cold again. But the most recent warmth has been a sort of plateau. Doesn’t it look like we’re lucky to enjoy a long warm period? Isn’t the concern that we’ll go cold anytime now?
http://www.geo.arizona.edu/BGDL/images/Vostok_CO2_airt.gif
Leif said earlier that insolation varies by 90 W/m2 with a max in January. I note in Dr Spencer’s graph of atmospheric temps, the global max temperature peaks in July. Would this be because summer albedo is greater in the Antarctic than the arctic?
That well known Serb ‘cyclo-maniac’ Milutin Milankovic worked it out some 60 years ago.
GARY 19:47:19 The paper you cite does actually mention the (unknown ?) anthropogenic effects of burning fossil fuels- page 12 of the pdf-. I was surprised , the paper is 33 years old.
As I read it the article says this:
1. Exit from the last ice age was triggered by solar forcing.
2. We slip in the little kicker that the seeohtwo which was released due to warming caused an amplification (did this require the increased solar forcing to produce the amplification?)
3. Because we belched out lots of seeohtwo recently, we no longer need solar forcing to cause climate change.
I’m not an expert, so the two questions I would ask are:
i. Are detailed studies on the relationship between amplification by seeohtwo and solar radiation complete and what do they say?
ii. Can seeohtwo amplify responses if solar output drops?
The paper to me reads like the solar deniers now seeking to integrate solar influences into their theories whilst maintaining the moral high ground re seeohtwo.
It happens in politics all the time. Steal the opposition’s policies and repackage them as your own.
But I guess if the pure solar folks looked at seeohtwo and the seeohtwo folks looked at the sun, maybe we would reach truth sometime soon?
Ah well. They need new grants, I guess………
Nobody seems to have mentioned the shape of the temperature curve. For the last several glaciations it has been a sawtooth, temperatures rising rapidly (followed about 1000 years later by CO2) for about 20,000 years before cooling stepwise more slowly. So don’t panic, the full rigours of a new glaciation won’t be felt for at least 50,000 years.
Patrick K (20:44:40) :
None of this information is really new. However, I have to complain about the graphic and the caption attached to it. Both of the ellipses shown are extremely exaggerated and neither is anywhere close to the actual ellipticallity of the Earth’s actual orbit which ranges from an almost perfect circle to only slightly elliptical. Even at it’s most extreme elliptical orbit, the earth’s orbit is very close to a perfect circle (A perfect circle is e=1, the Earth’s most extreme orbit is e=0.97). In fact it is so close that a human cannot usually distinguish it from a circle.
It is a simplified figure. Among other things, the relative sizes of the Sun & earth vs. orbit sizes are not to scale. And I don’t think the image plane is to be understood as the plane of the ecliptic, because you see the Earth’s rotation axis indicated as if viewed from some oblique angle.
We are looking towards the Sun from some point above the plane of the ecliptic, but we are not straight above the Sun. So even if the Earth orbit had been a perfect circle [it isn’t], this figure would still show ellipses for both orbits drawn.
One “extremely exaggerated” thing about the drawing is the large difference in shape of the two orbits ellipses. But I think that is just to make the point that the orbit is in fact changing its shape and orientation. Drawing the orbits to actual scale would be meaningless as they would overlap on the drawing.
Note: The extract from the article above only mention changes to the Earth’s axis of rotation causing Ic ages, nothing about orbital eccentricty, so the graphic is misleading the discussion, unless the Science article (which I cannot access) does refer to this as a cause of Ice ages.
So – why am I so sure I have known this for about 50 years?
I hope whoever wrote “debate ended” had their tongue firmly in their cheek.
The Milankovitch “forcings” are embedded in a noisy continuum of greater magnitude than the forcings themselves. The “forcings” are therefore inseparable from background noise. People who have their mindset firmly stuck in 17th century determinism insist there must be a simple cause / effect relationship when one may simply not exist.
I would encourage people to consider Carl Wunsch’s work on this (ref 1 below) but also take a quick look at the third example in section 2 of Demetris Koutsoyiannis’ work (ref 2 below). The former article shows that the Milankovitch cycles fit equally well with a stochastic model as a deterministic one, the latter notes that even with a leasts squares fit removal of the harmonic associated with the 100ky Milankovitch forcing, the energy even in that spectral band is essentially unchanged.
Scientifically speaking, the case for a “forced” Milankovitch cycle as opposed to a continuum of unforced natural variability has not been convincingly evidenced. Likewise the 20th century climate change also fits well with unforced natural variability (see ref. 2).
That is not to say the deterministic view is clearly wrong. But to argue there are no valid alternative hypotheses is also wrong. And I would argue that the stochastic model is a single model that fits all of the data; the deterministic modelling community seem to need a new explanation for every new data set we come across.
Ref 1. “Quantitative estimate of the Milankovitch-forcedcontribution to
observedQuaternary climate change”, Carl Wunsch, Quaternary Science Reviews Vol 23 2004 link
Ref 2. “A toy model of climatic variability with scaling behaviour”, Demetris Koutsoyiannis, Journal of Hydrology Vol 322 2006, link to preprint
From the title of this post:
Long debate ended over cause, demise of ice ages – solar and earth wobble – CO2 not involved
From the paper under discussion
Solar radiation was the trigger that started the ice melting, that’s now pretty certain,” said Peter Clark, a professor of geosciences at OSU. “There were also changes in atmospheric carbon dioxide levels and ocean circulation, but those happened later and amplified a process that had already begun.”
To be honest this is no different to a post I read on RealClimate about 3 or 4 years ago. The exact same argument was made, i.e. that an initial warming due to a change in insolation was amplified by an increase in carbon dioxide.
Pete W
Perhaps it will help climatologists gain a better understanding of why the ice is currently melting faster than they had predicted it would.
What ice? Total sea ice coverage appears to be pretty much steady. Sea level rise is currently miniscule to zero. Ice is accumulating in Greenland and Antartica.
“Jimmy Haigh: OT: I still listen to the Beeb’s Test Match Special though on the interweb thingy. Out here in Thailand we don’t get a good picture on the channel which shows the cricket on the telly. ‘T Headingley test starts today. Me Dad were a Yorkshireman – Huddersfield. And a big Boycott fan – like me. He calls a spade a spade.”
But when old Geoff beat up his girlfriend, I switched my allegiance (me luv ?) to the late Hansie Cronje; the way he could step on a ball reminds me of the antics of the AGW crowd.
The post is interesting and gives some evidence which gives the milancovitch theory more credibility.
But it dosn’t explain the multiplicity of glacial advances and retreats over the last 20k years, expecially the 10 to 12 advances and retreats recorded since the Younger Dryas. As outline by Rothlisberger 1986 : Jahre Gletschergeschichte der Erde, and others.
Glacier activity : BP 350-100, 850-600, 1150-1050, 1500-1300, 2700-2100, 3700-3000, 4900-4500, 5300 -5100, 5870-5700, 6400-6050, 7500-7300, 8600- 8200 etc. There is good evidence that these events occured worldwide.
A theory which will give us usefull explanations for these glaciation events would advance our knowledge and further undermine the position taken by the IPCC
Hi,
what I don’t get about this theory: If it’s just ‘local’ orbital mechanics (Saturn, Jupiter, etc) why does the earth stay completely out of the ice age cycles for dozens of millions of years? What causes the deeper phases of “ice age cycles” and “no ice ages cycles”? If causation is purely ‘local’, why do the planets in the solar system stop causing Milankowitch cycles for very long periods?
My feeling is that any theory of ice ages is fragile at best, without giving a possible explanation of these very long-lasting phases.
I personally like the Svensmark / Shaviv theory, that these cycles are caused by our position in the galaxy, which sometimes puts us much nearer to clusters of short-lived, hot, heavy blue stars, whose novas causes lot’s of cosmic rays, that will greatly increase cloud formation on earth and thereby cool it. Of course, this is still something of a long shot, but at least it gives a coherent explanation for 4 billion years of history and not just 2.5 millions.
Regards,
Marcus
Don’t you love it!
In a paper that largely destroys the CO2 argument, they still had to mention AGW in order to “get their funding” / “get the paper published” (delete as applicable).
.
Interesting. ALready 2-3 years ago on Climate Audit I mentioned the Earth tilting to be a factor in the Earth temperatures, but Steve McIntyre immediately chopped off that discussion with the remark “NO Earth tilting discussion on Climate Audit”! hmmm
REPLY: He probably didn’t want it to descend into Barycentrism arguments. – Anthony
[snip – unnecessarily accusatory Flanagan – if you want to talk about honesty, use your name and university affiliation – otherwise refrain]
“Our geochronology […] clearly demonstrates that only northern insolation led the termination and was thus the primary mechanism for triggering the onset of Northern Hemisphere deglaciation. ”
is a very important first conclusion, but is followed by
“Although the lead-lag relationships established here […] point to northern latitude insolation as the primary trigger of initial deglaciation of most Northern Hemisphere ice sheets and glaciers, subsequent increases in atmospheric CO2 and tropical Pacific SSTs (Fig. 5, C and D) demonstrate the importance of carbon cycle and ocean feedbacks in amplifying the deglacial response and causing global warming.”
So the conclusion is: changes in insolation IGNITED the deglaciation of the Northern hemisphere and CO2 and ocean feedbacks INDUCED A GLOBAL WARMING. This is actually proving CO2 can induce a warming at the global scale. Of course, a these time it was not anthropogenic :0)
This paper only confirms what the ice cores have shown time and again.
“…due to greenhouse gas emissions the Earth has already warmed as much in about the past 200 years as it ordinarily might in several thousand years…”
I was really enjoying a first class piece of science then they go and ruin the experience with a crass pile of BS warmistry (warmist sophistry). Maybe someone should introduce the authors to the temperature nuances of the Roman Warming Period and the Medieval Warming Period…
Leif Svalgaard (19:54:27) :
Mick (19:21:24) :
The 0.1% TSI variation is bugger all to explain 0.5C referenced @20deg.C
The 0.1% TSI explains only about 0.05-0.1C.
Depends whose figures you believe, but I’m glad to see Leif has moved on a bit from his previous 0.05C.
Three factors to consider when trying to see how much difference the change from solar max to solar min has on temperature.
1) El nino tends to occur at solar min, and is the manifestation of solar input to the oceans at solar max. This masks some of the true solar input to the climate system by ‘flattening’ the temperature curve.
2) Leif is using PMOD data, which uses a model to calculate TSI, based on the splicing together of records from several satellites used to measure irradiance over the last 30 years. PMOD and the IPCC prefer the use of ERBS data to calibrate the change during the ‘ACRIM gap’. The ACRIM team maintain this is not as good as the data from the other satellite, NEPTUNE which was working when the gap occurred and that consequently, TSI shows a little trend when it should show a rising trend at the end of the C20th.
3) Additionally, the Acrim data shows that cycle 21 had a difference of nearer 2W/m^2 between solar max and min than the 1W/m^2 Leif cites.
All this adds up to a spread of uncertainty about the effect of Solar max-solar min on temperatures.
Leif says 0.05 to 0.1C
I say it could be more like 0.35-0.4C depending how you account for heat storage in the oceans and heat energy release in el nino.
If correct, this means the temp change over the C20th can mostly be explained by the sun, as the lower, longer cycles with longer minima of the early part of the C20th averaged out means a lot less TSI recieved at earth.
It will be interesting to study this new paper and see if any of their figures are applicable to my model which estimates ocean heat accumulation from the sun.