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.
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This is (at least) the second time the “ice age mystery” has been solved in recent years. In 2005, Ohio State scientists made headlines when they published a paper claiming ice ages were caused by the CO2 greenhouse gas effect. See STUDY BOLSTERS GREENHOUSE EFFECT THEORY, SOLVES ICE AGE MYSTERY at:
http://researchnews.osu.edu/archive/earlyice.htm
Well, this still posses an interesting conundrum. So co2 has never been higher in (take yer pick, but ill go for ) 400thousand years. But the previous four interglacial s peaked warmer than this one has…. And we didnt hit that magical tipping point that prevented re glaciation… Were the wobbles from this interglacial less pronounced than previous interglacial s? Or have we had an ocean circulation change that has moderated the shifts more? (im thinking berring strait)
And if re glaciation is caused by this effect also, are we that confident that GHG’s trump albedo changes… i know there are instances when the earth has gone into ice ages with higher co2 levels, which would suggest, maybe not? (am aware of resolution problems with far distant record)
Oh so many questions. 🙂
I’m sure I’ve read elsewhere that evidence of glaciations, and interglacials suggest they begin and end suddenly, and NOT over thousands of years.
I still like the idea that our climate experiences a variety of cyclical effects of independent period, driven by the various heavenly bodies in our solar system or perhaps beyond it.
Sometimes their amplitudes converge, sometimes diverge. Rogue wave effect.
I first learned about the Milankovitch cycles (about 1972 or so) in the context of hydrology. The topic under discussion was the stationarity of long term precipitation time series and how that impacted the stationarity of long term flood series.
The take home message was that estimating the x thousand year flood or the Probable Maximum Precipitation at a location were impossible given the Milankovitch cycles making the above mentioned time series non-stationary. Although the Milankovitch cycles could be predicted, their impacts on precipitation and runoff were well beyond our scientific understanding in hydrology. I suspect this is still true in hydrology and climate science.
Mike Abbott (20:54:31) :
This is (at least) the second time the “ice age mystery” has been solved in recent years. In 2005, Ohio State scientists made headlines when they published a paper claiming ice ages were caused by the CO2 greenhouse gas effect.
You need to read your link again! That’s not what it says.
I am a little puzzled. If this has conclusively settled the matter, where are the calculations that decisively predict the planet’s future temperatures?
Or is this simply a rough correlation of cycles with ice ages?
This is so ironic considering OSU is stressing green energy everything. In my field, all we ever talk about is how to generate renewable sources of power. Even the city of Corvallis is rated as one of the “Greenest” of cities under 100,000. The city does everything green here. If you throw a rock into traffic 6 out of 10 times you will hit a Prius. Even the mayor has an electric “mayor-mobile”. I just cannot believe that my university actually produced research that didn’t tell us how horrible CO2 is.
If you actually read the literature written by so-called “alarmists” you’ll see this is nothing shocking. I’d recommend “The Long Thaw” by David Archer as a good readable book with some nice graphs of correlations between northern hemisphere insolation reaching a trigger value and glacial growth. Archer’s book points out that the next potential trigger point would have been in about 3000 years, but that insolation wasn’t predicted to drop quite enough to trigger a new ice age… probably. On the other hand, with long-lived CO2 in the atmosphere, not only will we sail right past the 3000 year trigger, but probably the next potential trigger at 50,000 years.
I find it amusing that all of you like this paper so much, when the guy who wrote it is probably a proponent of CO2 control because he understands the climate Much Better Than You (TM).
Roy Spencer discussed problems with Milankovitch theory June 17th. http://www.drroyspencer.com/2009/06/ice-ages-or-20th-century-warming-it-all-comes-down-to-causation/
Leif Svalgaard (19:54:27) :
“The 0.1% TSI explains only about 0.05-0.1C.”
I reckon the black lines on my mercury thermometer are at least 0.1C thick.
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. My University. I lost a LOT of stuff at that college (and gained a bit too). But back then we were firmly steeped in cow &^%$ and completely believed the cheerleader yell. Something about saving a beaver but I forget the exact words. We coulda cared less about nitrogen seeping into rivers along the Willamette Valley. And the cookbook I still have from the Home Ec department makes you gain weight just by readin it. But I guess as time goes by, you will pay the pied piper for a bit o’ grant money to study Earth’s temperature.
This article reads as if this is some new theory – hardly. See links:
http://en.wikipedia.org/wiki/Milankovitch_cycles
http://en.wikipedia.org/wiki/Milutin_Milanković
He 1st proposed analogous ideas nearly 100 years ago!
Anyone have a link to the paper and the data.
It seems reasonable to me that as long as Milankovitch cycles result in the snow not melting completely in the summer on Ellesmere Island, Baffin Island and the Torngat mountain range in northern Labrado (still snow on the ground in the Torngats even at this time of the year), that the ice-albedo feedback would put us into an ice age.
The problem is the estimates for the albedo changes are not enough to drop the average temperature by the -5.0C change of the ice ages. Earlier estimates from the late-1960s, the 1970s and early 1980s showed it could happen, but once climate models came on the scene, there was not enough ice-albedo feedback to meet the temp changes: hence the need for CO2 changes as well – not surprising since the early and modern climate models are based on greenhouse gas sensitivities that can only point in this direction.
Hopefully, someone (or this paper) has some albedo estimates that I can use for a project I’m working on.
RoyFOMR (20:43:13) :
Jimmy Haigh (19:36:39) :
“But not the message- that was the old BBC – the one we both grew up with AND loved!
Whoever he was, I respect him.”
Hear hear Sir!
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.
Chris V. (21:01:50) :
Mike Abbott (20:54:31) :
This is (at least) the second time the “ice age mystery” has been solved in recent years. In 2005, Ohio State scientists made headlines when they published a paper claiming ice ages were caused by the CO2 greenhouse gas effect.
You need to read your link again! That’s not what it says.
I guess you’re right. They merely say:
“Our results are consistent with the notion that CO2 concentrations drive climate.”
“Our results are consistent with the notion that CO2 concentrations drive climate.”
As Mike Abbott said above, I see nothing in this research that contradicts AGW theory. I think the significance of their study may be a better understanding of how earths ice reacts to forcings. Perhaps it will help climatologists gain a better understanding of why the ice is currently melting faster than they had predicted it would.
However maybe they were already on the right track. This NSIDC site discusses the correlation of cloud cover with rate-of-melt; “In 2007, unusually sunny skies throughout the summer melt season were one of the factors that helped lead to the record low ice extent.”
http://nsidc.org/arcticseaicenews/
Pete
Ooops.. didn’t mean to repeat myself.
Marcus (21:06:24) :
On the other hand, with long-lived CO2 in the atmosphere, not only will we sail right past the 3000 year trigger, but probably the next potential trigger at 50,000 years.
Your long lived CO2 cannot even push over a PDO shift from hot to cold. ( it was riding a hot PDO when the catastrophic heating was proposed)
What chance does it have against orbital changes in input energy? Zero.
Marcus (21:06:24):
I find it amusing that all of you like this paper so much, when the guy who wrote it is probably a proponent of CO2 control because he understands the climate Much Better Than You (TM).
I don’t think so:
http://www.biocab.org/Climate_Geologic_Timescale.html
My article was published on July 11th, 2009, while theirs will be published tomorrow. I win.
Anyway, I agree with you; they are trying to convince their readers that the solar activity was the culprit of all changes in the geological past, but not now because the climate change nowadays obeys to the emissions of carbon dioxide from human activities.
For your article to see the light in Science Magazine, you must to include something which blames to human beings of any change in nature, whether it is biological, geological or climatic.
evanmjones (20:42:35) :
Some say the world will end in Eccentricity
Some say in Obliquity
But many of my generation
Tend to favor Inclination
So we are left to wonder when
Until our earth returns through dust
And will again
As so it must
_______________________
Brilliant. I’m so glad that “greenhouse gas forcing from death trains with positive feedback and boiling oceans” does not scan well.
I shall try hard not to “steal” that “quote of the week” from you this time.
Marcus,
” On the other hand, with long-lived CO2 in the atmosphere,…”
Sorry, you are wrong again. No such animal as long-lived CO2.
Pete W (21:26:38) :
However maybe they were already on the right track. This NSIDC site discusses the correlation of cloud cover with rate-of-melt; “In 2007, unusually sunny skies throughout the summer melt season were one of the factors that helped lead to the record low ice extent.”
Interesting. That may be the first time they have acknowledged the importance of cloud cover. The other factor they increasingly cite is atmospheric circulation patterns, the effect of which have been dramatically demonstrated in animations posted on WUWT.
I’ll just read the paper before passing judgment. These issues are complicated. Meanwhile, . . .
Over the next few days, while you are engaged with folks about town, ask a dozen of them “What causes summer and winter?”
Many believe it is because Earth is nearer the Sun in Summer. The truth is difficult to explain without a globe. Think about this when you next enter your child’s classroom.
If there is fundamental misunderstanding about “the seasons” how much more troublesome are the issues in this paper? CO2 is so much easier.
Seems like the right time to float this comment. Not too long ago, I read an article where the authors noted that as the Sun rotates around the galactic center (pulling the planets along), it “meanders” in both X and Y (Z being the direction of rotation). I did not note the extremes of this “meandering” but it would cause the distance between Sun and Earth to increase and decrease slightly over time. Just wondering if anyone ever calculated the effect of this activity.
I shall try hard not to “steal” that “quote of the week” from you this time.
#B^1