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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Jimmy Haigh (18:47:46) :
“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.”
I’ve worked it out now – it’s the money shot.
What he is saying is: “Can I have some more funding please?”
So they are now informing us that Milankovitch was always right, after all? Did anyone ever actually doubt that? Well, I hardly think that they have rendered the “debate over”-it still is difficult to understand how exactly those orbital changes influence climate-in particular why changes in solar insolation in the North Hemisphere summer would be connected to climate all the way down in Antarctica. Of course we may some day understand these variations and how the work more precisely, but I doubt these guys have it figured.
Nasif Nahle (18:44:07) :
That’s precisely what I said in my article on Continents Flooded… (red to purple angry face).
Well, not exactly; I didn’t say this…
“…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.”
…because it’s not true. However, they had to twist their conclusions for their paper was “peer reviewed” and published.
“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 appears to have been a clipping fallen out of another paper. I’ve noticed the odd fact recently with the tide turning on AGW that papers presenting new evidence for alternative mechanisms to CO2 causing significant climate change have a token, respectful, non sequitur or half-step back or genuflection to the Holy Synod of Gaia. Perhaps this is what one must do these days in academia to get published, to get by the peerage on the subject of Climate Change. Look for these awkward implants or scholarly tumors in future timorous papers that go against AGW alchemy. Maybe we can make a collection for the Smithsonian or some such keeper of artifacts.
Science pretty much settled this 30+ years ago with http://osec.rutgers.edu/ebme/HistoryEarthSystems/HistEarthSystems_Fall2008/Week12a/Hays_et_al_Science_1976.pdf
Perhaps the detour along the scenic route is almost back to the main road.
Fundamental geometry and physics equations relate a temperature change to distance from the sun. That is obvious. It is not so obvious how to calculate the irregular orbit of the earth around the sun.
Here’s a small competition. How far into the future can we calculate earth’s solar orbit with adequate accuracy to chart future “global temperature changes” of +/- one tenth of a deg C accuracy? I’ll start the ball rolling with a guesstimate of 500 years.
Now hindcast that.
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. The headline should be, if you believe that GHG has contributed primarily to the warming observed: MAN-MADE GLOBAL WARMING WILL DELAY START OF NEXT ICE AGE!!!
It is clear, the equilibrium condition for our world in the last several million years is iceage conditions. We won’t truly know what will tip us into a new ice age until it happens. However, once we do see another ice age start, I bet we can create a computer model that will predict it in hindsight.
Mick (19:21:24) :
The 0.1% TSI variation is bugger all to explain 0.5C referenced @20deg.C
The 0.1% TSI explains only about 0.05-0.1C.
The 50 times larger Milankovich effect explains 2.5-5 degrees, which applied in the right regions [Land, Northern Hemisphere] is enough to explain the glaciations.
Geoff Sherrington (19:48:29) :
It is not so obvious how to calculate the irregular orbit of the earth around the sun.
That is actually even more obvious. I think the consensus is that we can do this accurately [enough for this purpose] for some millions of years.
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
Gratuitously throwing in an unnecessary entity — carbon dioxide — is simple rent-seeking behavior by these researchers, who will no doubt attempt to leverage their paper into a financial grant. [Mentioning CO2 certainly got them published in Science, didn’t it?]
In place of CO2 they could have just as well have mentioned undersea volcanic eruptions, or varying albedo. All three are equally rank speculation.
Had they not added an unnecessary entity — the cause du jour [the ee-e-vil minor trace gas CO2] — their paper would have come to exactly the same conclusions, and it would have the added benefit of credibility.
[Cathy (18:34:39),
You might have been knocked over by Mr Higgs’ boson. But so far, they haven’t apprehended the culprit.]
I see nothing in this research that contradicts AGW theory. The researchers propose a mechanism for the cause of 100,000-year ice age cycles. AGW theory predicts catastrophe within 100 years. If the alarmists are right, the Greenland and Antarctic ice sheets will have melted and flooded much of the world before the next ice age gets out of the starting gate. There is much evidence against AGW theory, but none is provided by this new research.
Back in the bad old days of the Soviet evil Empire scientists in most disciplines had to bend the knee to Marxism. It was often qutie amusing. They would spend the first few paragraphs declaring their allegiance to Karl and Vlad (and the Great Teacher of Humanity Joseph Stalin) and then go on to describe their research in paleontology, math, archaeology, etc., which had absoluteoy nothing to do with Marxism. Some fields suffered more than most: archaeologists had to create a new “culture” in 4th century Ukraine to replace the Ostrogothic state, and Russian SF was denied Einstinian time dilation because Lenin didn’t like it. Something similar seems to be happening here, in as much as Science or Nature will not publish “deniers” and yoiu can’t get NSF funding (and thus tenure) if you are on the outs with the Goracle.
Am I crazy? I thought I learned this years ago.
Say it isn’t so, a wobble, a shift? But we were told it was CO2 by the Goracle and other high priests….
sarc off…
it shows that actually many factors influence climate, and why we get hung up on co2 blows me away…
“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.”
Loosely translated from climatespeak this means the equivalent of “Dad – I am working hard at university – please send more money”
But seriously, this sounds like a throw away line from a media release that may come back to haunt him or may have been an attempt to avoid antagonising the believers and/or holders of the purse strings.
Careful, alarmists wanting to cool the planet are going to be looking for a way to jolt the earth’s wobble back…
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.”
CO2 levels 200 years ago were about 280 ppm which is around the levels they’ve been since at least 1000 AD.
And “ordinarily might’ gives a lot of wiggle room.
Richard Muller outlines several problems in the first chapter of his book “Ice Ages and Astronomical Causes. http://muller.lbl.gov/pages/IceAgeBook/IceAgeTheories.html
Has this paper addressed these problems sufficiently? He also places the date of the end of the last ice age at 10-14,000 years ago. I have a problem with placing the date at 10,000. The GISP2 Ice Core records show 14,548 and 10,276 at approximately the same temperature. Younger Dryas period was most likely caused by a comet impact. The duration of this interglacial period is closer to 14,000 BP than 10,000 BP. Was 10,000 adopted to make global warming a more imamate danger?
Some say the world will end in Eccentricity
Some say in Obliquity
But many of my generation
Tend to favor Inclination
So we are left to wonder when
Until our earth returns through dust
And will again
As so it must
Jimmy Haigh (19:36:39) :
You may be right Jimmy, I was only going by what I saw on the animated blurb prior to the program coming on. The name Roger Harrabin was repeated many times but as I was scrabbling for the remote I could well have been mistaken as to the messenger!
But not the message- that was the old BBC – the one we both grew up with AND loved!
Whoever he was, I respect him.
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.
Well, mr. Clark, as others already observed recorded warming that might be attributed to CO2 took place only in the last part of those 200 years. In addition, CO2 influence is so puny, it cannot even push against the PDO, as the measured global temperatures are decreasing the past ten years.
I wonder what trust can one have on the rest of your scientific conclusions, when you are so wrong on the obvious recent conclusions from recent measurements.
Zero?
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.
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.
In the HS Earth Science classes I teach, I am constantly having to counter these poor graphics that are in every astronomy/ES textbook or website. They just reinforce the common misconceptions that people have about astronomy. Please either fix the graphic or at least reword the caption to something along the lines of: “The Earth’s orbit can vary in ellipticallity in a cycle of approximately 100,000 years. (The ellipses shown above are both highly exaggerated.)” TAMU should be ashamed for having that graphic up at all.
What about the precession of the equinox’s? I was taught back in the ’70s about ice ages and the THREE things that caused them…1) Orbit 2) Tilt 3) Precession
page48 (20:16:26) :
Am I crazy? I thought I learned this years ago.
You’re not, and you did.
Milankovitch cycles plus positive feedbacks (albedo, CO2, and some others) have been the prevailing theory on the causes of ice ages (at least those during the pleistocene) for some time now:
http://ipcc-wg1.ucar.edu/wg1/FAQ/wg1_faq-6.1.html
It looks like this latest research has provided additional evidence for that.
OK assuming there argument is correct and when the planet gets warmer the CO2 content increases and that in turn makes it warmer yet and that releases more CO2 witch increases the temperatures even more.
But where than is the mechanism witch made it all stop and prevented the planet from exceeding temperatures that don’t support live anymore as it did billions of years?
Could it be water vapor that limits this runaway effect perhaps?