Milankovitch Cycles: Astronomical Theory of Climate Change and Ice Ages

Milankovitch Cycles: Astronomical Theory of Climate Change and Ice Ages


The following is an interview of George Kukla.

From An Unrepentant Prognosticator

GK: Well, I think that neither the “bad boys” nor the “good guys” know what is going on, and even worse, would be able to comprehend it. (This is not to claim that I am absolutely sure about it).

However, this is how I see it:

Yes, the globe is warming, so we do have “global warming” indeed! It proceeds in up and down cycles, but the general trend is up, no doubt about it.

What is happening is very similar to the time 115,000 years ago, when the last glaciation started. It is difficult to comprehend, but it is really so: The last glacial was accompanied by the increase of a really averaged global mean surface temperature, alias global warming.

What happened then was that the shifting sun warmed the tropics and cooled the Arctic and Antarctic. Because the tropics are so much larger than the poles, the area-weighted global mean temperature was increasing. But also increasing was the temperature difference between the oceans and the poles, the basic condition of polar ice growth. Believe it or not, the last glacial started with “global warming”!

The shifts of solar orbit today are about two to three times weaker than in the last glacial, or by the way, in the last 400,000 years. So, on that basis, we have little to worry. However, to expect today a possible complete melting of the Antarctic and Greenland ice sheets is entirely out of place.

So my advice: wait and see what happens! In no more than 50 years we’ll see who’s right.

GM: You said that “neither the “bad boys” nor the “good guys” know what is going on, and even worse, would be able to comprehend it.” Does that mean we shouldn’t worry about it? Why are all of these other scientists worried?

GK: The only thing to worry about is the damage that can be done by worrying. Why are some scientists worried? Perhaps because they feel that to stop worrying may mean to stop being paid.

GM: I’m afraid to ask this question: What do you think of the way the media has covered both “global cooling” and “global warming”?

GK: I just think that they need to make money and they seem to know best how to do it. You can’t blame them for that.

GM: In most cases, it seems like global warming and global cooling are separated by political lines. Are you surprised that the issue is so politicized?

GK: Am I surprised that global warming and cooling are separated by political lines? NOT at all. Especially if media seem to be helping a lot.

GM: What effects do carbon-dioxide emissions have on the cooling and warming cycles? Could they throw it out of balance, and what would that look like?

GK: Good question! The CO2 certainly has an influence. For instance, it appears that already now, with still relatively low concentrations, it may have a significant warming impact on the night [temperature] minima. And because the usual way to determine the daily mean is as the average of the daily minimum and maximum, here we go! But it is difficult to be sure: more clouds can do the same.

GM: In 2000, you told the Columbia University News that you believed that global warming was merely a blip before a coming ice age. Do you still agree with that?

GK: That article is principally still OK. Only then I didn’t know that the glacials, all glacials by the way, started by global warming. (Understood as area-weighted average global mean temperature, that is.) So the title of that Columbia article today would have been: “Evidence of approaching ice age is in accelerated global warming.” [Editor’s note: The current subtitle of the piece reads, “Sees Evidence of Approaching Ice Age Despite Global Warming”] Also, I didn’t stress the exceptional weakness of currently ongoing astronomic changes as compared to the last three glacial cycles. No doubt that we have about 10,000 or even possibly 20,000 years still ahead before the major ice advance can start. What we should watch now is the El Niño and La Niña. They can tell.

GM: There’s a general consensus among scientists (or at least scientific representation in the media) that man is responsible for global warming. What do you think about that? Do you agree?

GK: What I think is this: Man is responsible for a PART of global warming. MOST of it is still natural.


From Orbital forcing timescales: an introduction

A brief review is given of orbital patterns affecting the Earth which may be of use in establishing, for long or short periods, orbital forcing timescales (OFT). The metronomic variations of the Earth-Moon system and of the Earth-Sun orbital patterns produce gravitational and temperature effects which alter the physical environment on the Earth’s surface. These give an interpenetrating effect of forcing cycles ranging from twice daily tides, day-night alternations, various tidal patterns and the annual solar pattern. All of these have been used palaeontologically to give precision to short-term age determination in the past.

It is cycles of the Milankovitch band which are showing promise of enabling new practical timescales to be established for parts of geological time. These depend on changes in the Earth-Sun distance (perihelion and precession cycles of 19 and 23 ka at the present time), changes in the tilt of the Earth’s axis with respect to the Earth’s orbit round the Sun (the obliquity cycles of 41 and 54 ka), and changes in the geometry of the Earth’s orbit around the Sun (eccentricity cycles of 106 and 414 ka). Since the number of days in the year have changed through time; so have the periods of the perihelion and precession cycles. There is increasing evidence that small-scale sedimentary rhythmic couplets, often grouped into bundles, may represent the effect of some of these; often the precessional couplets are grouped into bundles of five or so with in the lower eccentricity period. The disentangling of the interpenetrating cycles to produce an OFT is an exciting problem and challenge for palaeobiology and sedimentology. These should enable numerical dates to be given to biostratigraphic and chronostratigraphic timescales and eventually enable many earth processes to be analysed in real time.

26 Ma oscillations related to the Cosmic Year (c. 260 Ma) have been invoked to explain periodic mass extinctions in the fossil record. But evidence is presented to suggest such extinctions are not, in fact, periodic.



Key Concepts:

  • 23000 yrs cycle – Earth’s Precessional
  • 41000 yrs cycle – Earth’s Obliquity
  • 100000 yrs cycle – Earth’s Eccentricity
  • Glacial-Interglacial Cycles
  • Abrupt Climate Change
  • Paleo Climate
  • Glacial Inception
  • Interglacial Termination
  • Ice Age
  • End of Holocene
  • Anthropocene
  • Periodicity


Key People:

  • Andre Berger
  • George Kukla
  • J. Imbrie
  • N J Shackleton
  • WS Broecker
  • ME Raymo
  • J A Rial
  • David Archer
  • J D Hays
  • Michel Crucifix
  • Chronis Tzedakis



Key Sources of Research:


Challenges for ice age dynamics: a dynamical systems perspective

Michel Crucifix Guillaume Lenoir1, and Takahito Mitsui1

December 14, 2015


Click to access 1512.03557.pdf



J.Imbrie,• E.A.Boyle,2 S.C.Clemens,•
A. Duffy, • W.R. Howard,s G. Kukla,s
J. Kutzbach,4 D. G. Martinson,s A. Mcintyre?5, A. C. Mix, 6 B. Molfino, s J.J. Morley, s
L. C. Peterson,? N.G. Pisias,6 W.L. Prell, • M.E. Raytoo,2 N.J. Shackletons, and
J. R. Toggweiler


Click to access Imbrie_etal_1992_Paleoc_Milankovitch_Linear.pdf



2. THE 100,000-YEAR CYCLE

J.Imbrie,• A. Berger, E.A. Boyle, S.C. Clemens•, A.Duffy,• W.R. Howard, G.Kukla, J.Kutzbach, D.G.Martinson , A.Mcintyre A.C. Mix,  B. Molfino, J.J.Morley, L.C.Peterson, N.G.Pisias, W.L.Prell, M.E.Raymo,N.J.Shackleto9n,andJ.R. Toggweile



Click to access Imbrie_etal_1993_Paleoc_Milankovitch_100K.pdf


The 100,000-Year Ice-Age Cycle Identified and Found to Lag Temperature, Carbon Dioxide, and Orbital Eccentricity

Nicholas J. Shackleton


Click to access shackleton-2000.pdf



A. Berger


Ice Age Terminations

Hai Cheng,1 R. Lawrence Edwards,1* Wallace S. Broecker,2 George H. Denton,3 Xinggong Kong,4 Yongjin Wang,4 Rong Zhang,5 Xianfeng Wang1

Click to access Cheng%20et%20al.%202009_terminations.pdf


Variations in the Earth’s Orbit: Pacemaker of the IceAges

J.D.Hays,John Imbrie, N.J.Shackleton



Click to access 573cca0c08ae9ace840fe240.pdf


An outsider’s review of the astronomical theory of the climate: is the eccentricity-driven insolation the main driver of the ice ages?

Maya Elkibbi), Jose ́ A. Rial


Click to access ESRreviewpaper.pdf


The 41 kyr world: Milankovitch’s other unsolved mystery

Maureen E. Raymo

Kerim Nisancioglu


Click to access raymo-2003.pdf


Pacemaking the Ice Ages by Frequency Modulation of Earth’s Orbital Eccentricity

J. A. Rial

Click to access Pacemaking.pdf


Earth’s orbital eccentricity and the rhythm of the Pleistocene ice ages: the concealed pacemaker

J.A. Rial

Click to access GPCiceages.pdf



Unlocking the mysteries of the ice ages

Maureen E. Raymo & Peter Huybers

Click to access 2008_Raymo+Huybers.pdf


Orbital forcing timescales: an introduction


Click to access 1.full.pdf


Links between eccentricity forcing and the 100,000-year glacial cycle


Lorraine E. Lisiecki

Click to access ngeo828.pdf


Understanding nonlinear responses of the climate system to orbital forcing

J.A. Rial, C.A. Anaclerio

Click to access Nonlinear.pdf


The Earth’s Orbit and the Ice Ages

Curt Covey


Click to access SciAm1984.EarthsOrbitIceAges.pdf


A Paleoclimate Model of Ice-Albedo Feedback Forced by Variations in Earth’s Orbit

Richard McGehee∗ Clarence Lehman


Click to access 001fcdb7a08c2e20e7ab44fc0bd1f11f70ea.pdf


In defense of Milankovitch

Gerard Roe

Click to access roe06grl_54724.pdf


The End of Present Interglacial – How and When

Wallace S Broecker

Click to access broecker.pdf


Timing and duration of Last Interglacial conditions in Europe: a chronicle of a changing chronology

Chronis Tzedakis

Click to access tzedakis.pdf


Last Interglacial Climates

George J. Kukla  et all



Theories and Modeling of Glacial–Interglacial Cycles and Glacial Inception

Alexandra Jahn


Click to access TheoriesLGI_Jahn.pdf


An Unrepentant Prognosticator

Climatologist George Kukla still believes an ice age is likely.



Can we predict the duration of an interglacial?

P. C. Tzedakis1, E. W. Wolff2, L. C. Skinner3, V. Brovkin4, D. A. Hodell3, J. F. McManus5, and D. Raynaud

Click to access cp-8-1473-2012.pdf


Is Nature Warning Us of a New Ice Age?

by Laurence Hecht


Click to access warning_ice_age.pdf


CO2: The Greatest Scientific Scandal Of Our Time

by Zbigniew Jaworowski


Click to access 20_1-2_CO2_Scandal.pdf


Where the Global Warming Hoax Was Born


by Marjorie Mazel Hecht


Click to access GWHoaxBorn.pdf


The Coming (or Present) Ice Age

A long-term perspective on the current global warming fad

by Laurence Hecht


Click to access ComingPresentIceAge.pdf




Author: Mayank Chaturvedi

You can contact me using this email mchatur at the rate of AOL.COM. My professional profile is on

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