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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radar (10:12:15) :
re: Richard Thorpe:
Thanks for the correction. CO2 would be a Positive feedback both into and out of the ice ages, [increasing the perturbation both ways].
I think it depends of the CO2 source, if from some grass species, it will undoubtedly provoke some peculiar perturbations, as to believe in global warming.
Indiana Bones (09:56:07) :
the article as it is still behind a paywall.
The ‘Supporting Online Material’ that tells what they really did can be accessed [deficiency in Science’s paywall system] and is here
Scientifically speaking, the case for a “forced” Milankovitch cycle as opposed to a continuum of unforced natural variability has not been convincingly evidenced.
In a chaotic system it is possible that cycles will synchronize with small external forcings.
A key to increased ice is lack of Summer melt in-between the Winter moisture and cold needed to build them some more. And the key to increased melting of ice is more and more Summer melt, by whatever means. My hunch is that Summer winds pick up to move the floating ice to parallels that promote melt and Summertime warm rainy days melt glaciers, more than they are restored during each Winter season. I just don’t see greenhouse gas variations being majorly involved. These weather-related long-term trends are ocean sourced that I believe occur with better results when the Earth is tilted to or away from the Sun in these extreme orbital wobbles.
Nogw (07:49:13) :
< Does some of you know why September (The Seventh month), October
< (The Eigth month), November (The Ninth month) and December (The
< Tenth moth), were called like that?
Those names were devised during the Roman empire. At that time, March was the first month of the year. Consequently, the seventh month was September. Those names were retained when later it was decided to start the calendar year with January.
**************************
GK (00:57:33) :
So this DEFINITIVELY proves that CO2 played no part in previous climate cycles.
There are 2 stunning conclusions from this :
1) The increase in CO2 that follows about 800 years after each interglacial starts has no (or very little) impact on earth`s climate.
2) It those massive increases in CO2 had no impact in earth`s climate back then, then CO2 can not possibily have an inpact now.
This finding proves there is no man made AGW.
*****************************
This is such a sweet moment and the authors of this paper either don’t get it or had to bow to the Team to get published. This result completes the process of making a complete fool of the Highest Idiot, Al Gore. He is a total clown and should be thrown in Jail for the harm to society he has done and the flim-flam he has promoted. Here is Al’s own infamous chart. You can see clearly that the temperature goes up first, THEN CO2 goes up. CO2 is the tail, not the dog.
http://tucsoncitizen.com/wryheat/2009/06/24/al-gores-favorite-graph/
Is it just possible that once in our lives; when somebody says; ‘this is how much the earth’s orbit can change.’ or words to that effect; that they actually make a real drawing that shows ‘how much the earth’s orbit can change’. Is that too much to expect ?
The drawing above shows two egg shaped orbits that are more pointy on the right (the Little Endians), and less pointy on the left (the Big Endians), and the sun is displaced upwards from the major axis, instead of being at one of the foci of the near elliptical orbits; both of which have vastly excessive eccentricities.
Oh I see it is an Aggie joke from the chicken farm; well that might explain it.
Reminds me of a high school Physics (Optics) exam, where a classmate, with fifteen seconds left to tackle one more 15 minute question on eye defects drew some eggs like that and added lenses to show how short sightednesss etc worked; took him five seconds to scribble the eyes, and a couple of rays. Well better than missing an entire question.
The teacher; on marking his paper wrote in equally scribly red ink; “Anyone with eyes like this would be blind anyway !”
This is suppoed to be the Premier Science Blog; I’ll not blame you though Anthony; nor Chasmod.
George
“”” Smokey (19:58:33) :
This article completely disregards Occam’s Razor: “Never increase, beyond what is necessary, the number of entities required to explain anything.”
~William of Ockham, 1285-1349 “””
And I believe it was Albert Einstein who said; “Science theories should be as simple as possible ; but no simpler !”
George
“And the key to increased melting of ice is more and more Summer melt, by whatever means.”
And that is what I believe not enough people concentrate on. They look only at temperature when considering melt and do not consider changes in precipitation patterns. An area that might have had a dry summer season could see a change in jet stream patterns that brings in more summer rain. A torrential rain can melt a very large amount of ice, particularly if followed by a few sunny days.
Also, as the ice melts, its surface will become “dirtier” as accumulated dust builds up on the surface. This would reduce the overall albedo and increase heating from sunlight even more.
There is evidence that the jet stream over North America brought Pacific storms in at a much more Southerly location than it currently does. This has been hypothesized to be the source of such lakes as Bonneville (current Great Salt Lake, UT) and Lahontan (current Pyramid Lake, NV) in the Great Basin region. As this jet stream migrated farther North, it would have brought rains to the upper Midwest and would be expected to greatly impact any ice sheets under these storms.
“…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, serious greenhouse gas emissions occurred 200 years ago? That’s 41 years earler than even “We must return to the Garden of Eden” James Hansen claims anthropogenic greenhouse gas emissions were starting to be a problem. U.S. climate “research” is a trainwreck.
Huh.
Dumb question from the the less well-schooled on this topic:
What happens when the cooling portion of the Milankovitch cycle combines with an extended solar minimum like the one we seem to be seeing now? Does it amplify the cooling even more?
Jay (11:51:20) :
What happens when the cooling portion of the Milankovitch cycle combines with an extended solar minimum like the one we seem to be seeing now? Does it amplify the cooling even more?
The Milankovich variations are 50 times larger than solar cycle effects, so the latter are drowned in the noise.
Only one thing left to do now, cut off all funding to Oregon State University, send out an army of reporters to dig through the trash of Peter Clark, Arthur Dyke, and Jeremy D. Shakun and use all material to attack personally. Heck make a youtube video, picket there places of work and home, link them to the oil companies, compare them to the third reich, etc, etc etc
Does anybody have a link to the actual paper itself (rather than the summary)? Would love to read it…
Ed
So? They re-observed Milankovitch’s 100,000 year natural cycle?
There is a 11,500 year cycle between ice ages. We are nearing the end of an interglacial warm period. We are only a few short summers away from an ice age in geological terms. If the sun spots do not ramp up I think we are in for a mini ice age anyway.
How does the theory correlate with other ice ages? During the Pliocene 33 ice ages occurred—every 47,000 years. Then during the present age–the Pleistocene–we have had 16 ice ages which are 100,000 years duration, when seal levels fluctuated 120 meters. How does the time-change affect the above theory?
See William McClenney’s article for the above data:
http://icecap.us/images/uploads/McClenneyPart_I.pdf
By the way, for those who are interested, McClenney divided his article into five parts. To access those simply change the number after Part_ .
Oh great funded research from tree cutter Oregon State, and Oilers Texas A&M.
http://fiestamovement.com/agents/view/58
Jay,
Considering that over the past couple of million years we are 90% of the time in glaciation and 10% of the time in warm interglacial, we would expect to see glaciation continuing over the entire spectrum of solar activity profiles. So glacial periods would continue even during extremely active solar cycles.
But having said that … there certainly is some “trigger” that very rapidly causes a state change from glaciation to interglacial and back. This change is apparently not gradual at all and happens very quickly … over the span of a human lifetime. Also, climate tends to be very unstable during glacial periods with extreme changes in climate happening very quickly. Areas can change from forest or grassland to tundra and back again in only a couple of human generations.
This “trigger” could be any number of things … a major volcanic eruption at just the right moment … a change in jet stream location … who knows? We will be finding out “soon”.
Dave:
And werent wooly mammoths frozen suddenly as well? Didnt they live in temperate lands, as shown by the grass in their stomachs? And then were frozen solid in some cases, almost overnight?
Chances are that if this happens again….grass will be found in “their” stomachs. 🙂
Considering what has been happening at the NSIDC this makes a whole lot of sense to me.
The melt in the spring has been accelerating over the past couple of years. But the freeze has also been accelerating in the fall. I was wondering what was going on. If the earth’s orbit is slipping into a greater elliptical path this makes complete sense. As it gets closer to the sun the rate accelerates but then when it slips farther away the opposite could be expected.
Does anybody else see this trend?
Nogw (09:43:26) :
Interesting you should note Democritus whose atomist theory was developed alongside his euthymia view of cheerfulness. It requires a certain philosophical cheer not to be discouraged by warmist’s need to discard the foundations of science.
Agreed it takes an open mind to read the books that contain that foundation. But with the vituperous attacks on those critical of AGW “consensus” – it’s hard to find encouragement to do so(this site an exception.) Pythagorus, and Keppler would suffocate on the paucity of intellectual curiosity today. Democritus would likely collapse in a fit of laughter.
Some time ago Danish researchers, looking at Greenland ice cores, noted that we come out of “ice ages” very abruptly–perhaps in a decade air temperature goes from that typical of the ice age to that typical of interstadial. I never recall any data showing a correspondingly rapid descent into the ice age.
Now a sufficiently large positive feedback can take a slow orbital forcing input and produce a large rate of change in the output. What/where is this feedback? It cannot be CO2, which as someone else on this thread pointed out is positive in both directions. This feedback must be asymmetric.
George E. Smith (11:00:41) :
The drawing above shows two egg shaped orbits that are more pointy on the right (the Little Endians), and less pointy on the left (the Big Endians), and the sun is displaced upwards from the major axis, instead of being at one of the foci of the near elliptical orbits; both of which have vastly excessive eccentricities.
I don’t understand those who have so much trouble accepting with this simple sketch. It isn’t perfect, but too bad either. Just consider the oblique viewpoint.
If you want a slightly more realistic view, I have a simulator with a similar diagram at http://arnholm.org/astro/software/ssg/ (Sun/planet sizes not to scale in web page diagram, but it is an option on the software).
Actually, the eccentricity of the earth’s orbit is so modest that it is not immediately obvious in such a diagram where the long and the short axes are oriented, especially if you select an arbitrary viewpoint relatively close to the ecliptic.
When talking about ellipses, precessions and other variations we need to bear in mind that there are many bronze age (and later) artefacts designed to let the sun into a specific point at a specific hour on a specific day. The one I saw yesterday still fulfils this function exactly so presumably post ice age ellipses and variations have been minimal for the last ten thousand years and have no impact on climate during this time.
Tonyb