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.
TallDave (04:26:49) :
“So… people with SUVs are making the planet wobble?”
I worked in a very green oil industry service company for a while. Just about everyone there drove to work and a lot of them had SUVs. I was one of the very few sceptics there and about the only one who always got the bus to and from work. (Mind you I was usually hung over in the mornings…)
CheshireRed:-)
Well done that man, roast the litte so ‘n so. He really looked terribly uncomfortable as if he was desparate for a underwear adjustment period! I just loved that repsonse to the Greenpeace claim that the Greenland ice sheet would be gone by 2020/30 or whatever, “I didn’t check that press release I can’t do all of them”. He’s a CEO for crying out loud, he employs people to employ people to do that for him, just shows what calibre of employee they really do have at Redwar! Just like good old Von-Daniken? of UFO/Aliens fame claiming thay he never took most of the photos in his books but relied on others, when challenged on the scale of them in a “good old” BBC doc years ago. Well done Stephen Sackur! He won’t last.
Jeremy (19:08:36) :
How the world of science has changed – now we COMPLETELY Ignore observations!
Yes. Which leads one to suspect virtually the entire creation you call the “world of science.” Only the use of mind altering drugs would explain the collective dyspepsia that has kidnapped good scientific minds and locked them behind a wall of political hysteria.
Unless the computer models are a spectacular failure. And their supremely arrogant creators are unwilling to acknowledge it.
Interesting paper, which CONFIRMS the overwhelming importance of CO2. Take the last lines:
“subsequent increases in atmospheric CO2 and tropical Pacific SSTs (Fig. 5, C and D) demonstrate the importance of carbon cycle and ocean feedbacks in amplifying the deglacial response and causing global warming. Whether these changes in CO2 and SSTs were induced by deglaciation of Northern Hemisphere ice sheets (12) or high southern latitude insolation (40, 41), however, remains an open question.”
That’s right– this paper note the carbon cycle (CO2) has a huge role in amplifying global warming.
Did any of you read the paper?
edcon,
The most common explanation for the cause of the Younger Dryas is the shutdown of the North Atlantic thermohaline circulation in response to a sudden influx of fresh water from Lake Agassiz (a massive freshwater lake covering a chunk of North America that spilled into the Atlantic as temperatures warmed). See http://www.ldeo.columbia.edu/res/div/ocp/gs/pubs/broecker_science.pdf for more on this.
The paper here doesn’t really address these sort of abrupt paleo changes, but rather deals with conventional glacial cycles.
I still don’t think that greenhouse gasses are the main feedback, and certainly not the driver. The melting of the ice seems to have the ability to affect oceanic oscillations. This oscillation disturbance from the ice age to the warmer period more than likely set up oscillations that continued the warming trend, regardless of greenhouse variation. That greenhouse gasses became more abundant seems less of a driver than the disturbed oceanic oscillations and their ability to create weather pattern variations across the land. As the oscillating oceans warmed the land, CO2 became more abundant, but was not the major source of more warming. It was the oceans that done it.
The Sun melts ice – who would have thought!
A guess: Are oscillations always harmonic or regular?, what if sudden changes?
References to months names (above) are from (if I remember well) from Inmanuel Velikovki’s “Worlds in collision”
From the Wikipedia article on Milankovitch cycles:
This is an extremely interesting topic for me. But I am utterly unimpressed by the abstract. The evidence is essentially based on one number, between 14,000 and 15,000 years (ago, a timing of some change), and doesn’t seem to say anything about the true problems with the Milankovitch-like theories which is the apparent absence of the 100,000-year timescale in the theory and their excessive presence in the data – even though the latter are heavily discussed in the press releases.
So in some sense, I remain an agnostic on the question whether the ice age curves are predominantly described by orbital and/or radiation changes of the Earth vs the Sun. They can be due to some new internal solar dynamics, random fluctuations in surrounding galactic cosmic rays, or internal chaotic “weather” on the Earth, too.
evanmjones (20:42:35) : lacking end of your poem:
“….return to the right”
Causality and politics? How can the researchers, or the peson being interviewed go from orbital oscillations (which have been known for quite some time) and it’s effects on global weather patterns to short term theorized CO2 induced warming ? To make the leap from a 50 million year time scale to 200 years is simply remarkable.
Mixing hypothesises is not just irresponsible but irrational.
I keep reading about the recent rapid temp increase! What increase? When I look at the station temps for the well placed stations, most show a decrease since 1934… the few that show an increase can be justified by changing ocean currents, or conditions! The only increase I see is from human manipulation of the data, and or heat island effect! Ice, (like glaciers etc.), will have a rapid melt at the end of its’ life, but that is the result of a natural process, even with a steady temp… set an ice cube out in a warm room and watch it melt slowly and then suddenly vanish at the end. When conditions are warm enough for humans to live comfortably on earth, the ice is going to melt, as it has been doing for the last 19,000 years!
Stephen
OSU, huh?
The report (I blogged about earlier this week) that said Americans should quit having children to save the planet from AGW came out of OSU.
They are obviously awash in Kool Aid.
Interesting article.
.
That is it ~was~ interesting until the same old line of BS was shoveled in ‘liberally’ about so-called ‘greenhouse gases’ and the like, effectively killing every trace of the authors credibility.
.
Since it’s ALREADY been shown —numerous times— that CO2 is NOT a contributor to warming, and indeed when the Vostok core samples are factored in, CO2 lags and NOT leads whatever degree of warming had already started.
.
Allow me to rephrase my first remark: Interesting —yet deceitful— article. A connivance wrapped in a deceit, and proffered as the truth.
Pragmatic (08:50:57) Which remind us the words of our co-blogger Nasif Nahle:
“Scientia Redivivus” (Tr. Reconstruction of Science).
Insinuating we must revisit science from the beginning, going back to Pitagoras, Democritus, Johannes Kepler, etc., before changes intoduced by “cultural”, fanatics’, creed’s, or political revolutions.
Books, knowledge it is out there, waiting for open minded and free individuals.
First, I’ve not read the article as it is still behind a paywall. But from the abstract:
“Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. ”
Am I the only one that sees this language a study in waffling compromise? Hey, let’s tell everyone they’re right and that way no one has to be wrong! Wrong. IMO, the clan that has been force feeding AGW theory and disseminating it like a bad cold across the earth – is wrong. Nothing quoted from this paper so far provides evidence of the empirical correlation between temperature and atmospheric CO2. Geologists tell us CO2 changes follow temperature. The paper appears to tell us temperature changes because of earth’s orbital variability (high school physics.)
Can anyone who has read the paper, confirm the authors’ demonstration of atmospheric CO2 forcing temp change? And if so, what percentage of that change?
andy stoffers (09:00:43) :
“Interesting paper, which CONFIRMS the overwhelming importance of CO2. Take the last lines:
“subsequent increases in atmospheric…”
You lost the word “subsequent” and you’ve added “overwhelming”. Read the whole paper.
Nogw (09:43:26) :
“Pragmatic (08:50:57) Which remind us the words of our co-blogger Nasif Nahle:
“Scientia Redivivus” (Tr. Reconstruction of Science).
Insinuating we must revisit science from the beginning, going back to Pitagoras, Democritus, Johannes Kepler, etc., before changes intoduced by “cultural”, fanatics’, creed’s, or political revolutions.
Books, knowledge it is out there, waiting for open minded and free individuals.”
Indeed! Tealc said.
Highlander (09:39:27) : Interesting —yet deceitful—
Agree!, but, this time, instead of “pouring the empty into the void” they are “pouring the void into the empty”.
Better let us re-read Velikovsky’s “Worlds in Collision”, a beautiful book of the pre-global warming era.
I can accept increased insolation and elevated GHG levels as a catalyst for ENDING an ice age. However, decreased insolation, while perhaps resulting in a cooler planet, doesn’t on its own explain (in my mind) glacial genesis and sustained growth (of the extent in the last significant ice age).
We have glaciers in mountains where precipitation is the result of rising moist air dropping its moisture as it cools and air pressure drops. These glaciers can quickly grow or shrink, based on precipitation feeding them and other conditions. What really drove the continued accumulation of snow/ice in northern Canada? Do we have the zone of glacial genesis pinpointed? Shouldn’t a cooler world be drier? What was the condition of the Arctic Ocean during the last ice age–completely buried or possibly open with warm currents, feeding moisture to the glaciers?
The science of confirming changes in orbit may be settled, but I remain skeptical about our understanding of ice ages. There are too many other potential factors out there (the Earth has local climates within regional climates within a global climate; Earth is a planet in the ‘climate’ of the solar system, which is in the ‘climate’ of our galaxy, and so on).
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].
rickM (09:27:06) :
Causality and politics? How can the researchers, or the peson being interviewed go from orbital oscillations (which have been known for quite some time) and it’s effects on global weather patterns to short term theorized CO2 induced warming ? To make the leap from a 50 million year time scale to 200 years is simply remarkable.
Mixing hypothesises is not just irresponsible but irrational.
Had you actually bothered to read the paper (or even just the abstract) we would have been spared this irrelevant post!
The paper considered growth of the ice sheets in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Given that, it’s hardly surprising that the author when interviewed discusses two of the three forcings they studied!
Patrick K (20:44:40) :
None of this information is really new. However, I have to complain about the graphic and the caption attached to it. Both of the ellipses shown are extremely exaggerated and neither is anywhere close to the actual ellipticallity of the Earth’s actual orbit which ranges from an almost perfect circle to only slightly elliptical. Even at it’s most extreme elliptical orbit, the earth’s orbit is very close to a perfect circle (A perfect circle is e=1, the Earth’s most extreme orbit is e=0.97). In fact it is so close that a human cannot usually distinguish it from a circle.
Not only this, but the sun is also plotted at the center of the ellipes rather than at a focus. But the idea is what is important. I have another issue. Lief and other various posters are tossing around Delta insolation figures that are not clar to me. I can see that 0.1% TSI must be just a tad over 1w/m2, and I know that the annual variation is about 90 w/m2, but the only figure supplied for the variation in the orbital cycles is “50 times as much” which must mean about 50w/m2. This is the total, peak to peak, variation including all orbital parameters, and obliquity?