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.
J. Bob (07:58:57) :
Bill – 06:40:49 – Would you put on a reference where you got the graphs, thanks
The plots are mine
The data is from various sources:
but mainly
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/
The basic story is, we have been living in an ice age for the last 2 million years -the pleistocene – and this had been punctuated for brief periods of so called interglacials. Yet there is no Milankovitch cycle that endures for 2 million years so the pleistocene must have been caused by something else.
The real question is how come we emerge into interglacials for periods of 10 or 11 thousand years? This period is closest to the period of precession. So maybe it is the precession that takes us out, when the NH summer is closest to the sun. Now we are at the exact opposite and are maybe ready to go back in the fridge. Just a thought.
Now if they could only explain–from first principles–how the power of insolation can be amplified by CO2, they’d really have something.
Have a good weekend everybody, that’s not going to happen today.
crosspatch (12:23:46) :
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 bears on the posting I just made. I have no information regarding rapidity of falling into an ice age. Is it as rapid as the climb out appears to be? The paths in and out could involve different geographical areas, but still one needs a large feedback (my term) or trigger (your term) to accomplish this. And CO2 has a long delay–perhaps H2O works better. Coming as it did at the tail end of the LIA, even Tambora was not a large enough perturbation to do the job. It did produce a year without summer. But one of the narratives about initiating an ice age, that it occurs with a summer carry-over of snow cover in northern Quebec, is not actually right. Otherwise 1815 should have done the job, right?
Earth is not isolated in the cold, 3D, unbounded and infinite space:
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1978ApJ…223..589V&db_key=AST&page_ind=0&data_type=GIF&type=SCREEN_VIEW&classic=YES
Anthony, July and August were originally named Quintilis and Sextilis as the 5th and 6th months of the roman calendar. They did use a 10 month calendar at one time but that was a long, long time before Julius Ceasar, who had July named after himself after he was assassinated.
Which is one way to get your name immortalised, but not one I’d pick if I was given the choice…
The significance of this paper as other’s have mentioned is way overhyped.
The idea that the malinkovich cycles have triggered ice ages has been generally accepted for years.
However the axial tilt change is only a trigger. It causes the summer ice and snow cover to decrease, reducing the earths albedo. This is a positive feedback, causes further melting and an increase in atmospheric CO2 and methaen. The greenhouse effect causes a feedback cycle which further warms the earth and deglaciation proceeds. When the axial tilt change is reversed, the feedbacks amplify a temperature decrease, and glaciation proceeds completing the cycle.
This is explained in the following article:
http://pubs.giss.nasa.gov/docs/2003/2003_Hansen.pdf
“Can we Defuse the Global Warming Time Bomb?”
“…The natural millennial climate changes are associated with slow variations of the Earth’s
orbit induced by gravitational torque by other planets, mainly Jupiter and Saturn (because they
are so heavy) and Venus (because it comes so close). These torques cause the Earth’s spin axis,
now tilted 23 degrees from perpendicular to the plane of the Earth’s orbit, to wobble more than
one degree (about 40,000 year periodicity), the season at which the Earth is closest to the sun to
move slowly through the year (about 20,000 year periodicity), and the Earth’s orbit to vary from
near circular to elliptical with as much as 7 percent elongation (no regular periodicity, but large
changes on 100,000 year and longer time scales).
These perturbations hardly affect the annual mean solar energy striking the Earth, but
they alter the geographical and seasonal distribution of insolation as much as 10-20 percent. The
insolation changes, over long periods, affect the building and melting of ice sheets. Today, for
example, the Earth is nearest the sun in January and farthest away in July. This orbital
configuration increases winter atmospheric moisture and snowfall and slows summer melting in
the Northern Hemisphere, thus, other things being equal, favoring buildup of glaciers. Insolation
and climate changes also affect uptake and release of CO2 and CH4 by plants, soil and the ocean,
as shown by changes of atmospheric CO2 and CH4 that are nearly synchronous with the climate
changes (Figure 2)….”
“
In other news, water wet.
Seriously, this is in the IPCC report guys.
@Mike Abott
Surely this report totally debunks AGW no matter how you spin it and it is what will always debunk AGW. We’ve had severe temperature swings without man made CO2 which would suggest that AGW has had nothing significant to do with the swings?
Note the safe harbor 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, Clark said.”
Which was neither suppported nor referenced. Nor true.
Bah Goom, clever fellow that J Caeser fellow to get July named after him only after he had been murdered.
Still probably no problem to a lad used to throwing legions across rivers.
And no there is nothing new in this paper that you could not have read in papers written a hundred years ago.
Whih is why when was young the idea was so discredited, the cyles of the proposed mechanism don’t fit with the observation.
Talk about reinventing the wheel.
Kindest Regards.
Eric, what then causes the temp to correlate so highly, both in overall trend and ups and downs, historically as well as currently, with oceanic oscillations? Is there no place for oceanic circulation patterns (which have changed over the millions of years) and oscillations (which have also changed over the millions of years) in your model? How can that be when we see direct and obvious cause and affect, complete with data and well-known mechanisms? Just how and when do you jump from Earth bound natural variation ending as the driver to CO2 acting as the driver?
Two other quick questions/thoughts from someone way under-“edumacated” in this area:
1. Looking at Prof. Steven Dutch’s diagram (3rd down on the page http://www.uwgb.edu/dutchs/EarthSC202Notes/GLACgeog.HTM ) showing the retreat of the continental ice masses over North America, would it be logical to assume that this ‘retreat’ moved in the direction of the ‘birthing’ of those same glaciers? That ‘point of origin’ appears to be on Baffin Island, on the west side of the mountains. Other than general cooling of the planet, is there any other meteorological (jet stream variation/fixation, persistent storm zone, other), oceanic (current change) or geologic (volcanic or uplift?) mechanism that could have caused massive acceleration and persistence of the accumulation of snow on the west slope of Baffin Island? Or, could there have been a global accelerant (like a sudden doubling of global or hemispheric water vapor due to increased luminosity (driving evaporation) or an oceanic asteroid hit? (I know, reaching on that one–maybe the next Bruce Willis movie plot there)
2. (Per Nasif’s reference) What effect would the solar system’s passing through in interstellar cloud (for extended periods) have on GCR’s (thinking of the cloud ‘shielding’ the earth from the solar wind) and hence cloud formation? Any? Am I smoking dope here?
Thanks all–and have a great weekend!
To qualify carbon dioxide as a secondary amplifier of the Earth’s atmosphere warming, answer the following questions:
What’s the absorptivity-emissivity of carbon dioxide at its current partial pressure in the atmosphere?
What’s the total emittancy of carbon dioxide at its current partial pressure in the atmosphere?
What’s the real value for climate sensitivity to carbon dioxide?
What’s the heat capacity of carbon dioxide at its current density in the atmosphere?
What’s the specific heat capacity of carbon dioxide at its current density in the atmosphere?
What’s the thermal diffusivity of carbon dioxide at its current density in the atmosphere?
What’s the specific volume of carbon dioxide in the atmosphere at the present time?
What’s the real effect of carbon dioxide in the atmosphere?
After answering the previous questions tell me if the carbon dioxide is capable of warming up or cooling down the Earth.
The carbon dioxide more than being an amplifier of warming effects (which definitively it is not) it’s a distributor of heat and a drainer of heat into the outer space. A very different subject is water in anyone of its three phases. I have no doubt; Arrhenius inflicted a great damage to climate science with his assumptions.
If you accept the “secondary” role of carbon dioxide in warming, you’ll be accepting one more fallacious doctrine from AGW side and you’ll be approaching more and more to the fourth religion.
As a matter of sane thinking, why the carbon dioxide, during warmhouses does not heat up the Earth stopping the trend to the next icehouse? Evidently, the carbon dioxide is not the powerful “greenhouse” gas proclaimed by AGWers.
Thanks for reading…
Nasif Nahle
Just how and when do you jump from Earth bound natural variation ending as the driver to CO2 acting as the driver?
I can see CO2 content as having a small underlying effect, depending on overall conditions. I could see CO2 driving up surface or tropospheric temps by that much over a century. But I doubt it is a primary driver and I doubt the positive feedback assertions.
For the IPCC to be correct in its mailine predictions, temps would have to increase 5 times the NOAA-adjusted rate (and it’d have to be faster, after a decade or so of cooling). That seems to be well off the mark.
I saw a graph once showing ice ages correlated with volcanic activity.
Volcanic activity follows the sun
Like I say, hope for warming.
I haven’t read through all the comments, but I’m not buying this.
Unless the change in rotation is sudden, we don’t have a sudden triggering of, or out of, ice ages.
If it’s true, then we only have two sets of orbital parameters: one set which favors an ice age, and lasts a long time, and another set which favors interglacials and lasts a short time. A slow orbital change over 100,000 years doesn’t solve this problem.
The curent climate of the Earth is approx 90,000 years of glaciation and approx 10,000 years of interglacial warmth. The rest is just weather.
MarcusK (02:51:25) : If it’s just ‘local’ orbital mechanics (Saturn, Jupiter, etc) why does the earth stay completely out of the ice age cycles for dozens of millions of years? What causes the deeper phases of “ice age cycles” and “no ice ages cycles”?
C Colenaty (05:23:29) : Maybe this period might be explained by tectonic movement. But then why was there a prior glaciation? And what happens to the MT for those very long periods of time when glaciation is absent?
The most popular theory is that the presence of a continental landmass one or both of the Poles prevents oceanic circulation between polar and equatorial regions and causes ice to build up on the polar land mass(es). The tectonic drift of Antarctica brought it over the S. Pole 2.5 million years ago, triggering the current Ice Ages. Pangaea was the landmass over the South Pole during the Permian or Karoo Ice Age from 360–260 Mya. There are other theories, but that one seems most plausible to me.
On another issue, my understanding is that descent into glaciations is gradual, while the rise into interglacial periods is rapid (relatively). That implies some positive feedback tipping point is reached as Milankovitch insolation approaches maximum, but that such a tipping point is not present during the long neoglaciation descents.
BTW, we passed the maximum insolation point about 10,000 years ago and are in the gradual descent phase now. If CO2 can forestall neoglaciation (a big if), then it would be a GOOD THING, since warmer is better. So light up your cigars and gun the engines on your clunkers — you might be doing the entire planet a favor.
If I’m reading the abstract correctly, the main accomplishment of this paper is “to constrain the timing of the Last Glacial Maximum (LGM)” more precisely than before by using a large number of proxy measurements over the period in question, i.e. 10,000 to 50,000 years ago. As a result, these more precisely dated glacial events can now be better correlated (or de-correlated) with other geological events of the same period. Is that about right?
If so, then this would seem to be an example of the “improved measurement” type of paper so necessary to science, where the devil really is in the details. Though important to our scentific understanding, such fine tuning papers aren’t terribly sexy, which would explain the unjustified attempt at hype in the press release. While not terribly relevant to the CAGW question of our times, it’s certainly worth covering on a science blog like WUWT.
BTW, according to Wikipedia the Earth’s orbital eccentricity didn’t change a whole lot in the 40,000 years covered, so the orbital illustration at the top of the article seems a bit misleading. Maybe a better choice would have been one showing changes in axial tilt and precession.
Thanks for covering this, Anthony. I’ve always thought ice ages are really cool! (Sorry, couldn’t resist.)
“But the freeze has also been accelerating in the fall. I was wondering what was going on. ”
Changes in Earth’s orbit would not be fast enough to exhibit visible changes in a person’s lifetime. The changes are very slow. If it takes 100K years for a cycle, then it takes 1000 years for 1% of the cycle and a person’s lifetime (for the sake of round numbers) would be 10% of that so over the course of the life of a 100 year old person we see .1% of the total progression taking place.
There is some sort of a “tipping point” that takes place and flips the state.
Now that assumes the changes ARE gradual. Maybe they aren’t. Maybe alignment of things causes a sudden change in the shape of the orbit.
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.
Yes this is absolutely true. Think what fossil fuel energy has done for living standards and food production. Look around around your home or office or open the refridgerator – Imagine a world without plastic…
The sad fact is that “Greens” are completely delusional. Without all this energy and the ability of a few to produce so much stuff for the many, we all would have little time or energy to devote to being Green. We would all be either dead or living in abject poverty, diseased and totally exhausted from 14 hour days breaking our backs trying to scratch out a meagre existance.
Being “Green” is a luxury that only food and energy surplusses have recently allowed. It is jet aircraft and large diesel powered supply boats that allow some of us to study coral reefs around carribbean islands and worry about sea level rise. The very computers we all use are made from plastics and they are the very tools that help some of us write our Green research papers. Furthermore, the commercialization of these computers were actually pioneered by the massive funding of Oil Companies for seismic analysis long long before these computers found any application in business…without the funding these computers for climate modelling might not even exist.
I haven’t read through all the comments, but I’m not buying this.
Unless the change in rotation is sudden, we don’t have a sudden triggering of, or out of, ice ages.
There could be positive feedback that forces things more quickly than the orbital changes in and of themselves.
Peter Jones (19:52:20) :
Even though,
” 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 still say that,
“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 . . . ”
You can certainly tell where their funding is coming from.
Probably from the nuclear industry concerned about siting their power stations near the sea?