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.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Can we seek a rational energy and enviro policy yet?
No, didn’t think so.
If it is certain that the earths orbit causes ice ages, then it must stand to reason that the opposite is true that is when the orbit is near or around its least elipical path warming will occur. ie who cares what the co2 levels are!
So how do the changes in total solar radiation incident on earth as a result of these orbital shifts compare to the change in solar radiation caused by the observed waxing and waning of sunspot cycles (which I believe I’ve read here to be about 0.1% difference from sunspot cycle trough to crest)?
The commentary on the blogs suggests that the sunspot cycle effect (0.1% variation in solar radiation) is not large enough to cause major climate fluctuations without a secondary effect – such as the hypothesized increase in cosmic rays interacting with the atmosphere to increase cloudiness and cause cooling. So is the Milankovitch cycle effect (____%variation in solar radiation) much larger? Is that why it can cause ice ages? Does the size of that effect suggest that it is or is not enough to overcome the CO2 forcing thought to be central to AGW?
Well knock me over with a graviton.
C02. Our new best friend.
I’m glad that the Science is finally settled.
Cooling is of much more concern than any possible warming.
“…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.”
This is an odd statement, if I’m reading it correctly. What “greenhouse has emissions” from 200 yrs ago can he possibly be alluding to? Isn’t the consensus that there could be no AGW effect from GHGs until after WWII?
“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.”
They still have the blinkers on. [sigh]
That’s precisely what I said in my article on Continents Flooded… (red to purple angry face).
“…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 Clark is saying that, in spite of what has happened over geological time, what has happened over the last 200 years is our fault?
The natural cycle deniers are dead in the back seat…
Leave the gun, take the cannoli !
“There were also changes in atmospheric carbon dioxide levels and ocean circulation, but those happened later and amplified a process that had already begun.”
“They” will take that as complete and total victory….
So Milankovitch was right after all and all those years of labourious manual calculation were not in vain!
“Long debate ednded” seems pretty final. Somehow I doubt that we’ve seen the last word yet. But I would like to hear more about the details of this latest research in language a layman can understand.
Interesting that it wasn’t CO2 then, but it is now, and over the last 200 years, at that. Wasn’t it a bit chilly til about 1850 or so?
Cathy is right, another interpretation of what Clark is saying is that absent increased CO2, Canada would be uninhabitable right now. The LIA might have just become a BIA.
The IPCC is claiming that the current interglacial will last 50k more years, even without the CO2 increase. I wonder if this is the “consensus” of scientists who have studied Milankovich cylcles?
When I studied atmospheric physics in graduate school, thirty years ago, this theory about ice ages and planetary cycles was generally well accepted (based purely on OBSERVED MEASURED DATA rather than computer models). Despite the knowledge that CO2 was a “greenhouse gas”, CO2 greenhouse effect was generally regarded as an amusing neat idea that was only suited to high school physics because it was such an oversimplified way to describe such a complex system as the atmosphere – i.e. nobody back then was silly enough to believe computer models more than OBSERVED DATA.
How the world of science has changed – now we COMPLETELY Ignore observations!
For those of us with gray hair, is this not what we learned in earth science class in high school in the 70s?
Fish Man (18:34:37) :
So how do the changes in total solar radiation incident on earth as a result of these orbital shifts compare to the change in solar radiation caused by the observed waxing and waning of sunspot cycles
It is unfortunate that the article uses the word ‘radiation’ in a way that makes it ambiguous as to what it means. It means here the radiation we receive at the Earth [at the ‘top of the atmosphere’] which is not the same as what the Sun puts out [even measured at the same average distance from the Sun as the Earth has]. The Sun’s output varies only by about 1 W/m2 over the cycle, but because of the changing distance through the year [we are closest in January], what we receive varies by 90 W/m2 [almost a hundred times more].
Of course, the article ends with the mandatory statement that man is responsible for the recent [rapid] change.
The orbital cycles do not change the total amount of radiation hitting the earth just the time and locations of peak radiation. The peak effects are around 4 percent for a given location so much stronger than sunspots but localized. 4 percent was for the northern hemisphere summer minimum 115,000 years ago versus the 1950 value at a latitude of 60° N
Their conclusion is more along the lines of “yes, but”. Yes, if the several previously repeated pattern holds true we are about at the end of the warm part of the cycle, and yes that means we could start really getting cold, so cold that humanity would face a crisis that will perturb the world unlike any previous one, yes but, yes but global warming may have delayed it, although we really can’t say how much.
Please correct me, but are we obsessed to look temperature benchmark to suit us, humans? Hockey-stick is dramatic because it referenced to an arbitrary number to magnify the effect.
The 0.1% TSI variation is bugger all to explain 0.5C referenced @20deg.C
But if we reference to 300K the delta TSI 0.1% and the orbit variation can explain that.
Perhaps Leif can explain what is wrong with that?
OT but just had to share this. Just been watching BBC 24 – Hardtalk with Roger Harrabin interviewing the outgoing director of GreenPeace about Climate Change. I’d temporarily misplaced the remote control otherwise I’d have switched the TV off – so glad that I didn’t!
To my suprised delight the BBC interviewer took an entirely different approach from that which I’d expected and laid into “Mr Green” with aggressive gusto!
First he attacked the anti-democratic and over-alarmist stance taken by Greenpeace – he was particularl virulent with the Catastrophic Alarmism used by their propogandist wings!
He then made the claim that Greenpeace was itself tainted with the badge of “Denialism” just as much as the sceptics were. He poo-poohed the idea trumpeted in June by GP that the Greenland Ice Sheets would be gone by 2030 or so – this is unscientific and ridiculous he said- the GP director who by now seemed shell-shocked conceded that he thought it unlikely but was not responsible for all the press releases of his organisation.
Mr Harrabin finally brought up the subject of Nuclear Power and forced the confession from, by now, visibly sweating interviewee that – Nuclear was and in spite of 20 plus years of reassessment still not on the agenda of acceptability.
Roger Harrabin – Don’t agree with you all the time mate- but this was the BBC that I once respected. A glimpse of the future. God, I hope so!
You have to read until the last 3 paragreaphs. There, despite his own findings, Mr. Peter Clark kneels in front of the God of Manmade Global Warming.
The surprise is that Science is publishing it, they seem to have been in the same warmist group as Nature.
RoyFOMR (19:21:28) :
Are you sure it was Harrabin doing the interviewing? I’ve just watched Steven Sacur interviewing the outgoing Green peace guy on Hardtalk… He did give him a hard time though – I agree – is the BBC at last changing it’s tune? Like you – I hope so. The BBC used to make me proud to be British…