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
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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.
I must be missing something here, but what exactly is new about this? It has long been the view of AGW advocates that the ice ages were terminated by orbital variations and then the increasing CO2 further amplifies the warming. In one paragraph the authors write:
“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.”
So their conclusion is, well, alarmist.
So… people with SUVs are making the planet wobble?
So, the ice ages are explained by changes in earth’s orbit caused by the outer gas giant planets, the ‘earth wobble’, but what about the ‘sun wobble’ also caused by the outer planets mentioned in the thread title. ?
Is Anthony finally taking a bit more of an interest in the ‘barycentric nonsense'(tm) that Geoff Sharp, myself, and Dr Nicola Scafetta keep going on about? 🙂
And,
Does the paper also explain the shift from 45,000 year cyclicity in ice ages to 100,000 years? I’m trying to get a copy to find out.
I can see I’m not the only one who’s having a problem with the title. At this stage, what it says is simply a lie. CO2 did not trigger the deglacations, but IS involved in it, it is actually the main conclusion of the paper. Maybe “CO2 not the primary cause” would fit better.
REPLY: I agree, I was working off the press release. In the paper (which wasn’t immediately available) the presentation is now clear that CO2 has a secondary role but is not the primary driver, so I’ve made a small change to the title. – A
Keep your eyes open for the next great AGW study that will explain the progression of the seasons…
Will someone please put me out of my misery in regard to the Milankovitvh Theory (MT)? Here are my problems. The MT seems to account for the present ~100 K year glaciation periods, but then also for the previous (before 900 K years ago, 45 K year glaciation cycles, and then before that 25 K year cycles. And before that there was a period of about I understand that there was a period of about 13 or 14 million years when there was no glaciation. Maybe this period might be explained by tectonic movement. But then why was there a prior glaciation? And what happens to the MT for those very long periods of time when glaiation is absent? There are hopefully some compresive answers to these questions, but, as in the recent article that is the subject of this series of comments, the MT is discussed as though it could be applied to conditions on the earth is a fairly simple and straightforward manner, and that certainly does not seem to be the case to me.
Its interesting that they used Isotopes generated by cosmic rays to determine the degree of solar radiation (e.g. C14 and Be10) The real effect of the Milankovich cycles may well be the direct effect of the shape of the orbit on sunspot activity as described by Rhodes Fairbridge and Theodore Landscheidt rather than changes in insolation from the changes in orbit as postulated by Milankovich.
agesilaus (19:32:47) :
The surprise is that Science is publishing it, they seem to have been in the same warmist group as Nature.
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I’d be willing to bet a small sum that, without the obligatory kowtow to AGW, the paper would not have been published and that the author made the statement for that purpose.
Dave (00:00:37) “…And werent wooly mammoths frozen suddenly as well? “
Here is one conjecture, Dave: “Preserved frozen remains of woolly mammoths have been found in the northern parts of Siberia. This is a rare occurrence, essentially requiring the animal to have been buried rapidly in liquid or semi-solids such as silt, mud and icy water which then froze.
“This may have occurred in a number of ways. Mammoths may have been trapped in bogs or quicksands and either died of starvation or exposure, or drowning if they sank under the surface.”
The BBC iPlayer edition of HARDtalk that was mentioned in this thread is available below.
http://www.bbc.co.uk/iplayer/episode/b00m01bl/HARDtalk_Dr_Gerd_Leipold_Executive_Director_of_Greenpeace_international/
It’s the outgoing Greenpeace Director Gerd Leipold being interviewd by Stephen Sackur, who gives a reasonable account of himself regarding Greenpeace’s over-optimistic appreciation of renewable energy versus their refusal to engage nuclear.
Allan M R MacRae (01:18:02): “I find it strange that so many people exhibit a Pavlovian hatred for energy companies. “
Ditto, Allan… in fact more than strange. I will read with great interest anything I can find on that. Mebbe, as I have ventured before, if we gave them all a government issue of stock they would begin to purr? How deep is conviction?
Dave vs Hal (01:52:13) :
“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?”
Nope it’s due to the northern hemisphere have much more land mass than the southern hemisphere. Land heats up far more quickly that the oceans. The total heat content of the oceans shows no such variations.
You have to understand that sentences like this are an appeal for further funding from politicians, not statements of Scientific fact.
I was listening to a podcast from Sceptic Magazine the other day and they were interviewing a Geologist (actually a Palaeontologist). He started his remarks by saying how little funding there is in Palaeontology compared to many other (more politically interesting) endeavours. Of course, he spent most of his time tying advances in Palaeontology with what will happen in future due to Man Made Global Warming. I was a little surprised, given I was listening to Sceptic Magazine, that his bold assertions went unchallenged by the presenters.
Anyway, yes, as a Scientist it’s useful to add the above to your paper. It helps to pay the mortgage.
Given the links provided in the comment thread, the IPCC’s own literature, and the comments themselves, IMO, think the title of this post goes to far (too much flag waving).
It really just confirms Milankovitch cycles, with CO2 being a negative feedback going into the ice ages and a postive feedback coming out. Where’s the “debate” that was solved?
That title is no better than the worst of alarmist media reports. Ought to be fixed lest we look like Joe Romm.
REPLY: I agree. I was working off the press release, which was made available before the paper, the CO2 role is secondary, and I’ve made an adjustment to reflect that – Anthony
I’ve changed the last part of the title to be more reflective of the whole paper, now that it is available. While it is clear CO2 is not the trigger of the ice age recovery event, i.e. not the main driver, it is involved in a secondary way in the recovery.
Of course this is nothing new, nobody doubts the role of CO2 in providing a portion of the warming effect, so also does water vapor. But it is a lag effect of CO2 released in response to the change in earth’s wobble and thus not the main driver of the event.
tallbloke (04:13:43) :
Three factors to consider when trying to see how much difference the change from solar max to solar min has on temperature.
The sunspot number at solar max varies greatly [say a factor of three or more], therefore the TSI variation from min to max will also vary greatly, hence there will be a similar spread in dT. There is no “THE change”, as the change itself varies.
I think you have misunderstood my statement. In discussing the variation of temp with TSI, it is convenient to state that 0.1% dTSI results in 0.025% dT which is 0.07K. From cycle to cycle, dTSI will vary and hence dT. For the large cycles in the past dT would be more like 0.1K, and for the small cycles to come, more like 0.05K. The oceans with their large heat capacity will tend to dampen any changes, rather than magnify them.
“Dave vs Hal (01:52:13) :
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?
”
The peak to peak current variation in top of the atmosphere solar power is 90 w/m^2 out of 1363 w/m^2 with the maximum in jan and with the temperature peaks in july. On an annual basis there is a somewhat higher power – like about 30w/m^2 during jan which averages out to about 8 W/m^2 above the annual average. Yet, it’s warmer in july, when the power average is about 8 W/m^2 lower than the annual average.
Why the discrepancy? It’s because in jan. the Sun is in the southern hemisphere which is substantially ocean because most of the land mass is in the northern hemisphere. It would seem this ocean/land difference is responsible for more than overcoming quite a few W/m^2 difference in incoming power. THat difference is even more interesting considering that the surface albedo of ocean is about 1/3 to 1/5th that of land surface . What is happening is the ocean water is involved in a water vapor cycle creating clouds that reduce the albedo – something that can’t happen easily when there is little to no additional water available. The notion that ocean heatsink abilities are better than that of land surface may also play a part but it seems to be problematic for multiple reasons.
Leif Svalgaard (19:56:41) :
Geoff Sherrington (19:48:29) : “It is not so obvious how to calculate the irregular orbit of the earth around the sun.”
That is actually even more obvious. I think the consensus is that we can do this accurately [enough for this purpose] for some millions of years.
Really? I suppose that if the solar system was entirely determinate, and we had perfect knowledge, this would in principle be possible, using our most powerful computers (rather than my notebook PC) to model its behaviour.
But is it determinate?
How accurately, for example, do we know where the planets are, and what their masses and velocities are? Isn’t the accuracy of our forecasts or hindcasts dependent on the accuracy with which we know the initial conditions? And surely we need to know all these things with very great accuracy if we are going to make million year predictions? To what degree of accuracy do we know the mass of the Sun? To the nearest 10^6 kg? Or the nearest 10^12 kg? Or what? And isn’t it true that the mass of the Sun isn’t a constant, but is always changing as Coronal Mass Ejections hurl matter out into space, and comets and other bodies fall into it.
There are large numbers of other unknown bodies – such as comets – in orbit around the sun. These will be exerting a very small gravitational influence on planetary motion. This might have a very small effect over a single year, but over a million years it might accumulate into a very considerable effect.
Equally, the solar system might periodically pass through clouds of dust, the effect of which (I am guessing) would be to slow the planets slightly, and so change their orbits. If nothing else, there’s all those unpredictable mass ejections from the sun that are striking the planets.
And then we might ask how many large dark bodies there are floating around in the universe, one of which might pass through our solar system, and screw up the orbits completely.
In short, given what we know, we may be able to predict the motion of the planets for a million years (hey, why not 500 million years?). But the effects of what we don’t know about could entirely outweigh the effects that we do know about. How much do we think we know? 99%? 99.99%? 99.9999%?
Or, putting it another way, if we’re sure we can predict the next million years (or the previous million years) isn’t that just the same as saying that we pretty much know everything?
I think Geoff Sherrington has a point. Forecasting or hindcasting the motion of planets in the solar system may well be essentially as problematic as trying to forecast the behaviour of the Earth’s climate. There’s a’consensus’ about that too, after all.
Dave
Roger’s link is very good! If you would like to read an account of the finding of a wooly mammoth early in the 1900’s, google Fridtjof Nansen’s book “Through Siberia, the Land of the Future” and read beginning on page 119. He includes his ideas on how the preservation occurred.
Pamela Gray (21:22:00) :
I can’t believe that last statement was included in the submission without lots and lots of whiskey. This is my cow college you be talkin about. The only college that remained above and beyond the hippy generation of Oregon. The only college any respectable (cough cough) 16 year old from Wallowa County could go to back in 73
Small world, Pamela. I was also at OSU then. In ’73 I was an undergraduate, in the Economics department, finishing up my B.S. I stayed for two more years, for an M.S. in Agricultural and Resource Economics.
“TallDave wrote: “So… people with SUVs are making the planet wobble?”
That would be an even bigger ego boost, wouldn’t it? 😀
I agree with John Finn. In the title it says that CO2 is not involved. Yes, it isn’t involved in triggering the demise of an Ice Age, but as is stated later on amplifies the process. But I thought it is said CO2 cannot possibly amplify anything? What would happen without this amplification? And what happens when you reach CO2 levels that normally would amplify this process? Interesting questions, eh?
This is one of those articles, like the one about the PETM event, that really makes me wonder what it’s doing on WUWT. The comments make for entertaining reading, though. The power of subjective interpretation never ceases to amaze me.
I am with all of you who learned this 40-50 years ago. As far as CO2 goes, ie. being a magnifying, enhancing, exacerbating or whatever effect, let it go. The ice records from Greenland show a 15°C increase* in less than a decade. So much for some inexorable-thousands of years creeping up of temperatures. There is obviously a lot more than TSI, GHGs, and whatever else we think we know going on under our sun.
*Richard Alley, Alley et al, 1993
Are they serious with that figure showing how much the orbital eccentricity can change? It’s quite dramatic, isn’t it? Does anyone know what the extremes of the eccentricity are?
REPLY: It seems that other universities besides TAMU also exaggerate the eccentricity in diagrams, see:
http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm
– Anthony
Pierre Gosselin (03:41:10) :
This paper only confirms what the ice cores have shown time and again.
Using ice core data to see which came first (Temp rise/Co2 rise) is next to useless.
This plot shows the last ice age end. Co2 and temp rise as one. The dust is interesting however.
http://img11.imageshack.us/img11/6826/iceage040kkq1.jpg
note reverse timescale, and temperature plots from NH and SH sources.
zoomed in a bit:
http://img15.imageshack.us/img15/562/iceageco2ch450018500my5.jpg
or
http://img12.imageshack.us/img12/9952/iceage100200kbq5.jpg
http://img18.imageshack.us/img18/4103/iceageco2ch4360450lh8.jpg
etc
Most exits from ice ages CO2 and temp rise simultaneously. Entry to Ice ages CO2 lags fall in temperature. CH4 and temperature falls are nearly simultaneous
Thanks Anthony for the correction!