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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When you’re hot, you’re hot.
When you’re not, you’re not.
Reed, et al (1971)
Nasif Nahle (20:40:04) :
“Ah, but according to Nasif, there is no heat stored in the oceans :-)”
It’s not my opinion… Would you like I start again quoting those authors who scientifically define heat?
Yet another example of how modern science has progressed in usage of the concept of stored heat:
Geophysical Research Abstracts, Vol. 11, EGU2009-7488-2, 2009 EGU General Assembly 2009
Accuracy of ARGO-derived global ocean heat content trends, interannual and seasonal variabilities. M. Juza et al.,
“One of the primary objectives of the ARGO array is to monitor the evolution of the global ocean heat content over a wide range of timescales.[…]”
“The most obvious benefit from Argo has been a marked reduction in the uncertainty of ocean heat storage calculations. […]”
it is rather impossible to say with a straight face that CO2 and other greenhouse gases are responsible for stored heat in the oceans.
I don’t remember saying that. I don’t know the facts either way, and I’m not sure what it has to do with the topic of this thread. One thing I do know is that the purported global warming signal is stronger over land surface than sea surface.
If you want to know what is warming or cooling the Earth, check out what the trade winds do to SST’s.
Aren’t you talkling about weather phenomena here? Or are you suggesting that the trade winds create a long-term, climatic signal, rather than vary within an equilibrium?
For those who think that SST’s have no real ability to warm or cool land surfaces, all I can say is that you don’t live near an ocean.
I live near the beach. Are you actually attributing these ideas to me, or are you playing to a wider audience? Please, if you discuss with me, attend to what I actually say.
As for GHG’s, those are about as steady state as the Sun in their ability to warm the planet.
I don’t understand what this means. The sun oscillates. CO2 is rising. Are you seriously contending that rising CO2 emissions have no affect on global temperatures? That’s an unphysical proposition.
Removing CO2 will not cool us down.
I completely disagree. In any case, I’m not interested in cooling us down but rather slowing down the rate of warming caused by us.
Preventing Sunlight reaching the surface has a better chance.
Well, it’s a very expensive option, I suppose, but I am leery of geoengineering (or space-based sun-occluding programs).
Why choose CO2 when it is such a bit player?
Clearly we disagree on the contribution of CO2 to post-industrial warming, but I would say that without reducing emissions, other options are stop-gaps. We may slow thing down, but the radiative properties of GHGs will continue to push the envelope. Better to turn down the spigot than build more and more dams.
So tell me Adam, are you a rubber necker in terms of understanding the scene or have you studied this issue for years?
I have spent most of my spare time reading blogs, studies, books and etc on the general subject of climate change for the past 2.5 years. Some subjects I’m pretty well informed about, and I never forget that there are people who have been studying these subjects in detail for years, who are astronomically more qualified than me.
I’m no physicist – not even a good mathematician. The subjects I grasp fairly well conceptually are: Ice age dynamics, the ‘greenhouse’ effect and its changing status, the carbon cycle, and am conversant with numerous sub-topics in the general debate. On ice age dynamics, for example, I’ve read about 50 scientific papers, skimmed 50 more, and have read numerous blogs on the matter. I’m not an expert, just an interested observer. I usually spend my time untangling misconceptions on the science – the ones I know something about. As I said, my drift into advocacy was a rare event. I try to be reasonable and hardly ever speculate about the capacity of others to contribute to the discussion (believing it a waste of time). How about you?
Oh, and I’ve learned quite a bit about the cryosphere over the last couple of years.
Nasif Nahle (21:19:23) :
I’m all thermodynamics and know that a photon has not mass.
But apparently not that heat is not photons.
You’re comparing photons with trains, planets and its orbits, stars, and other lumps of matter’s motions.
No just giving examples of energy that is not heat, contrary to your claim “Heat is energy, so heat is photons”
the_butcher (21:20:29) :
I can’t believe Leif is using other ‘bloggers’ here as references…
These are respectable people [don’t you think] and their sensible usage of terminology matches that of contemporary professional climate scientists and physicists, which is my whole point.
Leif, as a side point, it is an interesting question which part of the energy content in the ocean you can clearly identify as “heat.” That seems to be the key objection to the use (or misuse) of the term “heat.”
Pamela Gray (19:19:33) :
The depth of SW penetration can be 150 m (!) in some places.
This idea keeps on coming up in discussions. In fact, the mixed layer is often 50-100 m deep, so I would feel quite comfortable saying that the atmosphere is capable of heating the ocean deeper than the few-mm “skin.” Keep in mind that water vapor is also condensing at the sea surface (the transfer of heat is not one-way). In all, the thermal skin idea is not a strong rebuttal of the GHG “heating” idea.
Such a quescient state is rather special. A well-mixed layer tens of meters deep is a more usual observation.
Cold water upwells when there is a divergence in the warm surface layer. On the other hand, where there is a convergence you can have downwelling instead.
Leif Svalgaard (21:50:56) :
But apparently not that heat is not photons.
Uh! Oh! Deeper and deeper you sink into waters of thermodynamics. Is heat electromagnetic energy? Yes, it is. What electromagnetic energy is? Waves and/or photons. Are there EM energy transferred by conduction, convection and radiation?
No just giving examples of energy that is not heat, contrary to your claim “Heat is energy, so heat is photons”
If heat is not energy, what is it? If heat from the Sun is not photons, what is it?
Heh!
the_butcher (21:20:29) :
I can’t believe Leif is using other ‘bloggers’ here as references…
These are respectable people [don’t you think] and their sensible usage of terminology matches that of contemporary professional climate scientists and physicists, which is my whole point.
Again, it’s not a matter of jargon, but of good unpolluted physics. Let’s take two professional climate scientists, Peixoto and Oort; from their book on Physics of Climate, PAGE 346, we read:
“…are the rates of energy storage in the atmosphere, oceans, land, and snow and ice.” (Emphasis is mine).
Why they didn’t write “heat storage…”?
From Modest’s book, Radiative Heat Transfer, we read on PAGE 1:
“All materials continuously emit and absorb electromagnetic waves, or photons, by lowering or raising their molecular energy levels.”
And on PAGE 3, we read:
“Thermal radiative energy may be viewed as consisting of electromagnetic waves (as predicted by…) or as consisting of massless energy parcels, called photons (as predicted by…)”
Only Leif in this world says that heat is not photons and that heat is kinetic energy.
oms (22:17:13) :
Leif, as a side point, it is an interesting question which part of the energy content in the ocean you can clearly identify as “heat.” That seems to be the key objection to the use (or misuse) of the term “heat.”
ARGO measures the temperature in the ocean and computes the thermal energy from that. What is important for this thread is that the professionals who designed and run the system refer to the thermal energy stored in the oceans as ‘heat storage’ [in Joules]. Changes in and relocation of the stored heat are referred to as ‘heat transfers’ [in Watts]. This terminology is consistent and does not leave room for any confusion [except for people that think energy cannot be stored]. One of the goals of the ARGO program is to reduce what they call the ‘heat storage errors’. By measuring the temperature, the ‘heat content’ becomes a measure of the random, disorganized kinetic energy we normally associate with heat. This is very different from the energy in the ocean currents which is not heat, but there is no ambiguity or problem keeping these things separate. So the ‘heat content’ of the oceans is not the total amount of energy, but only that part that comes from the random, disorganized kinetic energy of the molecules, and does not include the bulk kinetic energy of the ocean currents. All this is very sensible and straightforward.
Nasif Nahle (22:45:04) :
Is heat electromagnetic energy? Yes, it is.
You say that energy is measured in Joule, but heat is measured in Watt, so you were claiming they were not the same, but now they are, all the sudden, and so on.
Leif Svalgaard (22:55:28) :
Nasif Nahle (22:45:04) :
Is heat electromagnetic energy? Yes, it is.
You say that energy is measured in Joule, but heat is measured in Watt, so you were claiming they were not the same, but now they are, all the sudden, and so on.
You should know what I’m talking about. If heat is energy in transit between two systems, it propagates (flux) in electromagnetic waves and/or photons, as Modest says. That doesn’t mean the units for heat are Joules, but Joules/second, or Watts, because it is power, or total rate of energy transfer, like in an electrical current. If you write J for heat, you’re wrong. You can obtain the load of energy absorbed by the system and express it in Joules, but it would not be heat, but internal energy.
Leif Svalgaard (22:49:01) :
If heating results in a change to the general circulation, then a portion of the energy input has done work on the system and is stored in some other state. Thus it is still an interesting question re: the “heat balance” to ask where the energy has gone.
BTW, Nasif Nahle, why are you harping on this technicality? It’s obvious what’s being talked about.
oms (23:11:41) :
Thus it is still an interesting question re: the “heat balance” to ask where the energy has gone.
That is true and heating [the proper word to describe transfer of heat] can and does alter the bulk energy, but as that is different from the molecular motions, the separation between heat and other energy seems clear enough.
oms (23:11:41) : on 10.08
Quite so. It’s the same with the atmosphere near the surface. There is frictional drag of air over the solid surface and this tends to a lead to a rise in temperature; but this process cannot go on without limits and does not. Also, sunlight raises the air temperature, also with subsequent loss via heat flow. So the air has both a heat content and a kinetic energy. It is not strictly correct to say that the near-surface air contains heat and leave it at that.
“Nasif Nahle:Now you’ll come with the novelty that photons have mass.”
Einstein said that the photon has no rest mass Mo, but inertial mass M:
M = Mo / SQR(1-v^2/c^2)
For v=c one gets 0/0, so use hf=Mc^2
About units, the Bible (http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf) only says:
[amount of heat] = J
[heat flux density] = W/m^2
[heat capacity] = J/K
There seems to be no agreed definition of “heat”; some people use it only for dQ, others also for Q. So it is best not to use it.
to Leif & Nasif :
Thank you guys !!
Iv’e learnt quite a bit more about the semantics of heat and the science behind it : Its been an interesting debate and we all gain from it !!
oms (23:23:23) :
BTW, Nasif Nahle, why are you harping on this technicality? It’s obvious what’s being talked about.
It’s not just technicality; the way Leif offers is as saying that an elephant is a dog because both are formed by cells, which is plainly wrong.
Alexej Buergin (04:07:02) :
About units, the Bible (http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf) only says:
[amount of heat] = J
[heat flux density] = W/m^2
[heat capacity] = J/K
There seems to be no agreed definition of “heat”; some people use it only for dQ, others also for Q. So it is best not to use it.
From your Units Bible, PAGE 118:
Energy, work, joule: J–Nm–m^2 kg s^−2
Amount of heat, power, radiant flux; Watt W–J/s–m^2 kg s^−3
That’s the difference; energy is stored, heat is not stored.
Alexej Buergin (03:47:05) :
Einstein said that the photon has no rest mass Mo, but inertial mass M:
M = Mo / SQR(1-v^2/c^2)
For v=c one gets 0/0, so use hf=Mc^2
That’s precisely the novelty I was referring to. Momentum is not mass.
Lindsay H. (05:35:40) :
to Leif & Nasif :
Thank you guys !!
Iv’e learnt quite a bit more about the semantics of heat and the science behind it : Its been an interesting debate and we all gain from it !!
You are welcome!!! 🙂
It is odd that Co2 didn’t affect the climate back in the day until the industrial revolution isnt it?
http://helpcooltheearth.wordpress.com
Scikid
Once upon a time, Albert Einsten said:
“It’s easier to disintegrate an atom than a prejudice.”
“Es ist leichter, ein Atom zu zertrümmern, als ein Vorurteil.”
Nasif Nahle (07:04:07) :
From your Units Bible, PAGE 118:
Energy, work, amount of heat, joule: J–Nm–m^2 kg s^−2
power, radiant flux; Watt W–J/s–m^2 kg s^−3
You have put ‘amount of heat’ in the wrong box, probably because:
“Es ist leichter, ein Atom zu zertrümmern, als ein Vorurteil.”