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.
Marcus,
“On the other hand, with long-lived CO2 in the atmosphere,”
At odds with this
http://pubs.acs.org/doi/full/10.1021/ef800581r
John F. Hultquist (21:46:13) :
I’ll just read the paper before passing judgment. These issues are complicated. Meanwhile…
Here the article is:
http://www.sciencemag.org/cgi/content/full/325/5941/710
Fire and Iceby Robert Frost
evanmjones (20:42:35) :
I like it! I Googled the first line and found the poem by Robert Frost called ‘Fire and Ice’.
Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.
Perhaps “Frost” will have the last word…
From the article at http://www.sciencemag.org/cgi/content/full/325/5941/710:
“The responses of the Northern and Southern Hemispheres differed significantly, which reveals how the evolution of specific ice sheets affected sea level and provides insight into how insolation controlled the deglaciation.”
Wow, now maybe they’ll discover the pressure on Venus,
at the surface, is 90 atmospheres.
Nasif Nahle (21:34:56) :
they are trying to convince their readers that the solar activity was the culprit of all changes in the geological past,
Solar insolation changes and Milankovich mechanisms are NOT solar activity.
John F. Hultquist (21:46:13) :
Many believe it is because Earth is nearer the Sun in Summer.
It is, if you live in Australia…
Leif Svalgaard (22:36:44) :
Nasif Nahle (21:34:56) :
they are trying to convince their readers that the solar activity was the culprit of all changes in the geological past,
Solar insolation changes and Milankovich mechanisms are NOT solar activity.
John F. Hultquist (21:46:13) :
Many believe it is because Earth is nearer the Sun in Summer.
It is, if you live in Australia…
I stand corrected.
Without the obligatory nod to AGW, you can bet Science wouldn’t have touched it with a ten meter bunsen burner.
To Invent Armageddon
When software supposes the world ends in flame,
And Hansen and Gore paint brushstrokes of blame,
And other false prophets scream, “GREEN” in their name,
I wonder a bit, just a tiny amount,
How many people know what it’s about,
And how many good folk can see past the shame
While driving around in their carbon-mobiles,
immersed in the guilt of spinning their wheels,
Intent on respecting the earth just the same,
They play the victim while playing the game!
Warming and cooling are twins of the world,
But one twin is cruel and one twin is good.
You’d know the cruel one if you saw his work,
When fog freezes flesh and wolves howl in the murk,
When glaciers come calling and icy winds blow,
And summer is absent and death stalks the snow.
And millions and millions are slain by the cold,
Crops failed and we died while rats swarmed, we are told,
When the Vikings were booted from Greenland’s embrace,
And the so-called “little ice-age” tried it’s best to erase
All that we made that the warm winds delivered,
As the darkness descended, we froze and we shivered,
Awaiting the warming that came far too late,
A third of humanity slaughtered by fate,
Four hundred years of freezing and drought,
And pestilence, plague – that “twin” goes all out!
The globe still recovers and glaciers still melt,
And though a chill in the air can almost be felt,
There’s nothing more normal than warming that’s global,
Despite Chicken Littles droning on about weather
And whether or not science daring to question
Their dogma is legal, and should even be mentioned,
Their hockey-stick lies tilt mad at the skies,
To invent armageddon, true science DIES…
© Dave Stephens 2009
Yes, this is what we learned in high school in the late 60’s.
There is something left from the last 20,000 yrs to explain, however, and that is the Younger Dryas period. Halfway out of the melting of the Laurentide Ice Sheet and you get a 1,000 yr reversal. For 19,000 of those years, the Pacific Northwest was always either a forest or a woodland. During the Younger Dryas it was supposedly a desert. Go figure. In the 1840’s the Columbia River Basin had a 10 year drought.
Why would the climate in N. America do a reversal if the only factor was orbital shape?
This is still not totally solved, but the orbit surely gives a longer and bigger picture.
I have to make two corrections to my previous post Nasif Nahle (21:34:56):
1. “They are trying to convince their readers that the solar radiation striking on the Earth’s surface was the culprit of all changes in the geological past…”
2. Clark et al did not mention that the CO2 was the culprit, but that the northern latitude insolation was the main trigger of the initial deglaciation of the northern ice sheets and glaciers, which finally headed to increases of atmospheric CO2.
Nonetheless, the authors of the paper point to CO2 and oceans as feedbacks which amplified the deglaciation event. From my knowledge, it is true for oceans, not for carbon dioxide.
People here seem to miss the most important argument that this acknowledgement of natural factors gives us.
The warmists always repeat the mantra “The extra heat from GHG:s will still make the earth warmer than it would be, disregarding natural factors.”
BUT: This study acknowledges what we all already knew; that the natural process is; increased heat comes first, increased GHG:s comes second.
So, if all the basics in GHG theory is correct, and this study also is correct it will also mean that:
Any decrease in heat will also lead to a decrease in GHG:s.
A process which in turn will amplify any climatic cooling process that starts.
I write GHG:s here, because it’s 100% logical to assume that for instance H2O gas will decrease.
So it matters very little if we have 1-200 extra ppm:s of anthropogenic CO2 if such a cooling process starts, since H2O and “natural” CO2 will drastically decrease and over time things will even out.
And the most important thing is that this is of course the case regardless of what natural climate factors we are talking about:
The amplified cooling effect must be true if the amplified warming effect is true.
Elizabeth (20:29:31) “Careful, alarmists wanting to cool the planet are going to be looking for a way to jolt the earth’s wobble back…”
Very Interesting. If they move that far, there will be splintering for sure – and maybe even a split right down the middle.
–
Mark (20:35:24) “I’ve got a problem with this statement:
“the Earth has already warmed as much in about the past 200 years as it ordinarily might in several thousand years, Clark said.””
Recognize the funding hook. Venality is just as sickening in academia as it is elsewhere.
anna v (20:44:15) “To all: we have to be hard on these people that add those warming mantras to get their grants. They should be made aware they are prostituting themselves and their science.”
Researchers will change funding hooks with the wind. The needles should be directed strategically into the weaknesses of the funding agencies, which Anna has correctly identified.
I recall that there was some research that showed that ice sheets melted very quickly at the end of the last ice age.
If my memory is correct, this would be at odd with these latest findings.
Does anyone know if there is evidence of sudden melting? If so, then this would cast doubt on this paper, as it expects changes to be slow.
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?
I would like to know if this fact I remember is actually true, anyone out there able to confirm or deny it?
Well knock me over with a hv. It wil be very interesting how this is factored into some of the current theories on CO2 vs solar vs GCM’s etc.
David P:
“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?”
Where would you have got a notion like that from? CO2 concentrations started rising when the Industrial Revolution started, and if you know your history you’ll know that was actually a little bit before the Second World War.
Jeremy:
“When I studied atmospheric physics in graduate school, thirty years ago… 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”
Wow, you must have been to a really bad university. Your statement does not correspond to a view ever held by any serious scientists. How can the greenhouse effect be “oversimplified”? That doesn’t even make sense.
Re: Steve (22:00:20)
See entry labeled “16 June. Australia” (posted by the authors of the study you mention) here:
http://nzclimatescience.net/index.php?option=com_content&task=view&id=80&Itemid=1
…That’s part of the story (…no further comment)…
Please, please! I have not read any of the comments yet but I do hope that no ‘well meaning person’ has provided the full article for us to read without paying the required coin. Ethics please people!
…OT but since it has surfaced on this thread, the BBC HARD TALK Stephen
Sackur interview, a little spanky…with outgoing Greenpeace boss{S Sackur’s word} Gert Leipold…
Can be seen for overseas and non-UK citizens in low quality RM MONO 35KBPS
making a small window you get a fairly good image too…At 13 min Sackur
manage to show GP simplified view of Arctic ice…A MUST BE SEEN…
I’m afraid that one statement
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,
totally negates the value of the rest of the paper. If they are that sloppy in thier work then it has no value whatsoever.
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.
Robert (19:15:52) :
For those of us with gray hair, is this not what we learned in earth science class in high school in the 70s?
Yes it is odd – I think the diagram is out of one of my old text books….
Are we going backwards…..?
“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 ”
They are right By looking at the past we should be getting an ice age about now.
Thing is… that you get about 90,000 years of glacial,10,000 years of interglacial (over very many cycles), We are now at the end of the typical interglacial length, in fact we are ‘overdue’….problem is you would look at a graph of these cycles and ‘know’ what will happen next because of the regularity of the cycles….
However the Earth is not currently in ‘position’ in a Milankovitch cycle to bring about an ice age anytime soon, Therefore I personally don’t think that Milankovitch cycles are the complete answer. unless there is something ‘special’ about the time we now live in and the next Ice age really is 50.000 years away, I will continue to believe the graph, and ponder about what the heck we will do/can do when it happens ‘soon’.
“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.”
Let us assume for the moment that the above paragraph is true.
So humanmade CO2 emissions are delaying the next Ice Age by several thousand years.
Can we now expect Gore LLC to advocate for ever-increasing CO2 emissions to keep delaying the Ice Age? What will Cap and Trade look like under this scenario?
Listen Big Oil, you will now have to meet or exceed your 1990 greenhouse gas emissions or pay hefty fines. And somehow, we will have to insert a further negative spin to make it all your fault.
I find it strange that so many people exhibit a Pavlovian hatred for energy companies. Since ~88% of global primary energy is generated from fossil fuels (the remainder is nuclear and hydro, with a trace of renewables), these “evil” energy companies keep our families from freezing and starving to death.