Field of Science

Geology and Cyclicity: Milankovitch´s idea

"I do not think that's my duty to teach to the ignorant the most basic things, and I have never forced anyone to accept my theory, on so far nobody could expose something."
Milutin Milankovitch in 1950

Milutin Milankovitch (1879 - 1958) was born in a relatively wealthy Serbian family, so it was almost a kind of obligation for him to archive a higher education degree and later take over the family business. So he studied agriculture, but following a passion for natural sciences he went to Vienna, where he in 1904 concluded his studies as an engineer.
Five years later he returned to Belgrad where he found employment as professor for mathematical studies at the University.
Like Croll he was in search of a scientific problem worth his efforts, and in 1911, sharing some presumably good wine with a friend, he decided to develop a mathematical theory to explain climate changes on the planets of the solar system.

He studied the work of Croll, recognized his previous achievements but also noted his insufficient data. Milankovitch also consulted the work of the German mathematician Ludwig Pilgrim, who in 1904 published exact calculations of the orbital eccentricity, earth's obliquity and the rotation of the axis of earth (change of the perihelion). Pilgrim also tried to correlate the eccentricity with the occurrence of ice ages.
Between 1912 and the beginning of World War I Milankovitch published some preliminary abstracts of his developing theory, concluding that all three factors, in contrast to previous authors, are important to explain earth's climate. At the beginning of the War, Milankovitch was arrested as Serbian officer and imprisoned in his hometown Daly, but fortunately he was carrying with him his work, and so even in the first night as prisoner he continued to work. "When after midnight I looked around in the room, I needed some time to realize where I was. The small room seemed to me like an accommodation for one night during my voyage in the Universe."Soon after he was released and travelled back to Belgrad, where he continued his work during the entire War and published some ideas about the climate of Mars and Venus.


Finally he published his theory in 1920 "Mathematische Theorie der durch Sonneneinstrahlung ausgelösten Wärmephänomene" (Mathematical theory of thermal phenomena caused by solar radiation).

Fig.1. Variations in the Earth's orbital parameters:
1. Eccentricity: the shape of the orbit around the sun.

2. Changes in obliquity: changes in the angle that Earth's axis makes with the plane of Earth's orbit.

3. Precession: the change in the direction of the Earth's axis of rotation, i.e., the axis of rotation behaves like the spin axis of a top that is winding down; hence it traces a circle on the celestial sphere over a period of time.
Together, the periods of these orbital motions have become known as Milankovitch cycles. These parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N).


In his theory he postulated:
- Glaciations are caused by variations of astronomical parameters

- The parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N)

- It is possible to calculate these changes, and so calculate the climate in the past.


The German meteorologists Wladimir Köppen and Alfred Wegener supported the new theory, and noted the apparent coincidence of the calculated curve with the by Penck and Brückner postulated four European glaciations.


Fig. 2. Figure from KÖPPEN & WEGENER 1924, where they correlated the calculated cycles to the know ice ages at that time.

Fig.3. Outcrop of the Trubi-Formation at Capo Spartivento (South-Italy), a succession of Globigerina-marls from the Pliocene-Pleistocene transition. The regular stripes are caused by organic rich layers, thought to be caused by changes in the biological productivity in response of changes in solar insolation - and so of the astronomical parameters - the Milankovitch cycles.

References:

CHORLTON, W. (ed) (1985): Ice Ages (Planet Earth). Time-Life Books: 176
KÖPPEN, W. & WEGENER, A. (1924): Die Klimate der geologischen Vorzeit. Borntraeger, Berlin: 256


Resources:

NASA Earth Observatory: Milutin Milankovitch (1879 - 1958). Accessed 26.06.2010

1 comment:

  1. .
    I think the (or one) missing element in the models of climate change has to do with Gravity.
    -
    The Milankovitch Cycles are always looked at [on both sides of the debate] only in the perspective of Light intensity.
    I've seen no analysis of the fluctuations in Earths gravity due to the Sun, other planets or periodic comets and so forth.
    -
    We know gravity has a HUGE effect on Earths environment by the simple fact that the tides follow our relatively small moon.
    We also know that Sea Level and Ocean Current behavior vary slightly due to the density of the nearby land masses.
    -
    Stands to reason that the Sun's Gravity as felt by the Earth [both in intensity and location] is going to vary in sync with the Milankovitch Cycles just as the Sun Light intensity does.
    -
    That could have a huge affect Ocean Currents and it's accepted that those are driving factors in our weather.
    -
    At the vary least changes in Gravity will affect the quantity of gasses [all gasses, not just Green House gasses] that the Earth loses into Space.
    .
    We only -really- began looking at Earths Gravity fluctuations in 2002 with the GRACE satellite.
    .
    .
    .
    Additionally the "Radiative Forcing Components" charts I see are devoid of any mention of water vapor.
    Water vapor reportedly has a Radiative Forcing of 2 W/m³ which is GREATER than CO2's effect.
    The few reports than mention water vapor say the water vapor has been increasing at nearly the same rate as CO2.
    - That means that a 1-to-1 comparison between CO2 change and Temperature change is based on defective equations.
    .
    .

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