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Encyclopedia > Milankovitch cycles

Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. The eccentricity, axial tilt, and precession of the Earth's orbit vary in several patterns, resulting in 100,000 year ice age cycles of the Quaternary glaciation over the last few million years. The Earth's axis completes one full cycle of precession approximately every 26,000 years. At the same time, the elliptical orbit rotates, more slowly, leading to a 21,000 year cycle between the seasons and the orbit. In addition, the angle between Earth's rotational axis and the normal to the plane of its orbit changes from 21.5 degrees to 24.5 degrees and back again on a 41,000 year cycle. Presently, this angle is 23.44 degrees. Image File history File links Milankovitch_Variations. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... Anthem Serbia() on the European continent() Capital (and largest city) Belgrade Official languages Serbian language 1 Recognised regional languages Hungarian, Croatian, Slovak, Romanian, Rusyn 2 Albanian, English 3 Government Parliamentary republic  -  President Boris Tadić  -  Prime Minister Vojislav KoÅ¡tunica Establishment  -  Formation 8th century   -  First unified state c. ... The Falkirk Wheel in Scotland. ... Leonhard Euler, one of the greatest mathematicians of all time A mathematician is a person whose primary area of study and research is the field of mathematics. ... Milutin Milanković (1879–1958) Milutin Milanković (Serbian Cyrillic: Милутин Миланковић) (also known as Milankovitch) (May 28, 1879, Dalj near Osijek, (Austria-Hungary) – December 12, 1958, Belgrade) was a Serbian geophysicist, best known for his theory of ice ages, relating variations of the Earths orbit and long-term climate change, now known... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... In astronomy, Axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... Precession of a gyroscope Precession refers to a change in the direction of the axis of a rotating object. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... The Quaternary Period is the geologic time period from the end of the Pliocene Epoch roughly 1. ...


The Milankovitch theory of climate change is not perfectly worked out; in particular, the largest observed response is at the 100,000 year timescale, but the forcing is apparently small at this scale, in regard to the ice ages. Various feedbacks (from carbon dioxide, or from ice sheet dynamics) are invoked to explain this discrepancy. Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ...


Milankovitch-like theories were advanced by Joseph Adhemar, James Croll, Milutin Milanković and others, but verification was difficult due to the absence of reliably dated evidence and doubts as to exactly which periods were important. Not until the advent of deep-ocean cores and the seminal paper by Hays, Imbrie and Shackleton "Variations in the earths orbit: pacemaker of the ice ages" in Science, 1976, did the theory attain its present state. Joseph Alphonse Adhemar (1797 — 1862) was a French mathematician. ... James Croll (2 January 1821 – 15 December 1890) was a 19th century Scottish scientist who developed a theory of climate change based on changes in the earths orbit. ... Milutin Milanković (1879–1958) Milutin Milanković (Serbian Cyrillic: Милутин Миланковић) (also known as Milankovitch) (May 28, 1879, Dalj near Osijek, (Austria-Hungary) – December 12, 1958, Belgrade) was a Serbian geophysicist, best known for his theory of ice ages, relating variations of the Earths orbit and long-term climate change, now known... John Imbrie (born July 4, 1925) is an American climatologist. ... Sir Nicholas John Shackleton (23 June 1937—24 January 2006) was a British geologist and climatologist who specialised in the Quaternary Period. ... Science, the journal of the American Association for the Advancement of Science (AAAS), is one of the worlds most prestigious scientific publications. ...

Contents

Earth’s movements

As the Earth spins around its axis and orbits around the Sun, several quasi-periodic variations occur. Although the curves have a large number of sinusoidal components, a few components are dominant. Milankovitch studied changes in the eccentricity, obliquity, and precession of Earth's movements. Such changes in movement and orientation change the amount and location of solar radiation reaching the Earth. This is known as solar forcing (an example of radiative forcing). Changes near the north polar area are considered important due to the large amount of land, which reacts to such changes more quickly than the oceans do. The generalised concept of radiative forcing in climate science is any change in the radiation (heat) entering the climate system or changes in radiatively active gases. ...




Orbital shape

Circular orbit, no eccentricity.
Orbit with 0.5 eccentricity.

The Earth's orbit is an ellipse. The eccentricity is a measure of the departure of this ellipse from circularity. The shape of the Earth's orbit varies from being nearly circular (low eccentricity of 0.005) to being mildly elliptical (high eccentricity of 0.058) and has a mean eccentricity of 0.028. The major component of these variations occurs on a period of 413,000 years (eccentricity variation of ±0.012). A number of other terms vary between 95,000 and 136,000 years, and loosely combine into a 100,000 year cycle (variation of -0.03 to +0.02). The present eccentricity is 0.017. Circular orbit: Ellipse with zero eccentricity. ... Circular orbit: Ellipse with zero eccentricity. ... Eccentric orbit. ... Eccentric orbit. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ...


If the Earth were the only planet orbiting our Sun, the eccentricity of its orbit would not vary in time. The Earth's eccentricity varies primarily due to interactions with the gravitational fields of Jupiter and Saturn. As the eccentricity of the orbit evolves, the semi-major axis of the orbital ellipse remains unchanged. From the perspective of the perturbation theory used in celestial mechanics to compute the evolution of the orbit, the semi-major axis is an adiabatic invariant. Following the Third of Kepler's Laws of Planetary Motion, the period of the orbit is determined by the semi-major axis. It follows that the Earth's orbital period, the length of a sidereal year, also remains unchanged as the orbit evolves. The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... An adiabatic invariant in general is a property of motion which is conserved to exponential accuracy in the small parameter representing the typical rate of change of the gross properties of the body. ... Johannes Keplers primary contributions to astronomy/astrophysics were his three laws of planetary motion. ... The sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. ...


Currently the difference between closest approach to the Sun (perihelion) and furthest distance (aphelion) is only 3.4% (5.1 million km). This difference amounts to about a 6.8% increase in incoming solar radiation. Perihelion presently occurs around January 3, while aphelion is around July 4. When the orbit is at its most highly elliptical, the amount of solar radiation at perihelion is about 23% greater than at aphelion. This difference is roughly 4 times the value of the eccentricity. This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...

Season (Northern Hemisphere) Durations
data from United States Naval Observatory
Year Date: GMT Season Duration
2005 Winter Solstice 12/21/2005 18:35 88.99 days
2006 Spring Equinox 3/20/2006 18:26 92.75 days
2006 Summer Solstice 6/21/2006 12:26 93.65 days
2006 Fall Equinox 9/23/2006 4:03 89.85 days
2006 Winter Solstice 12/22/2006 0:22 88.99 days
2007 Spring Equinox 3/21/2007 0:07  

Orbital mechanics require that the length of the seasons be proportional to the areas of the seasonal quadrants, so when the eccentricity is extreme, the seasons on the far side of the orbit can be substantially longer in duration. When autumn and winter occur at closest approach, as is the case currently in the northern hemisphere, the earth is moving at its maximum velocity and therefore autumn and winter are slightly shorter than spring and summer. Thus, summer in the northern hemisphere is 4.66 days longer than winter and spring is 2.9 days longer than fall. Source


Axial tilt

Main article: Axial tilt
22.1-24.5° range of Earth's obliquity.
22.1-24.5° range of Earth's obliquity.

The Earth's rotation axis wobbles, causing a slow 2.4° change in the tilt of the axis (obliquity) with respect to the plane of the Earth's orbit. The obliquity variations are roughly periodic, with a period of approximately 41,000 years. When the obliquity increases, the amplitude of the seasonal cycle in insolation increases, with summers in both hemispheres receiving more radiative flux from the Sun, and the winters less radiative flux. As a result, it is assumed that the winters become colder and summers warmer. In astronomy, Axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... 22. ... 22. ... Axial tilt is an astronomical term regarding the inclination angle of a planets rotational axis in relation to its orbital plane. ...


But these changes of opposite sign in the summer and winter are not of the same magnitude. The annual mean insolation increases in high latitudes with increasing obliquity, while lower latitudes experience a reduction in insolation. Cooler summers are suspected of encouraging the start of an ice age by melting less of the previous winter's ice and snow. So it can be argued that lower obliquity favors ice ages both because of the mean insolation reduction in high latitudes as well as the additional reduction in summer insolation.


Presently the Earth is tilted at 23.44 degrees from its orbital plane, roughly half way between its extreme values.




Precession

Precessional movement.
Precessional movement.

Precession is the change in the direction of the Earth's axis of rotation relative to the fixed stars, with a period of roughly 26,000 years. This gyroscopic motion is due to the tidal forces exerted by the sun and the moon on the solid Earth, associated with the fact that the Earth is not a perfect sphere but has an equatorial bulge. The sun and moon contribute roughly equally to this effect. In addition, the orbital ellipse itself precesses in space (anomalistic precession), primarily as a result of interactions with Jupiter and Saturn. This orbital precession is in the opposite sense to the gyroscopic motion of the axis of rotation, shortening the period of the precession of the equinoxes with respect to the perihelion from 26,000 to 21,000 years. The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Precession of rotational axis relative to the direction to the Sun at perihelion and aphelion. ... Precession of rotational axis relative to the direction to the Sun at perihelion and aphelion. ...


When the axis is aligned so it points toward the Sun during perihelion, one polar hemisphere will have a greater difference between the seasons while the other hemisphere will have milder seasons. The hemisphere which is in summer at perihelion will receive much of the corresponding increase in solar radiation, but that same hemisphere will be in winter at aphelion and have a colder winter. The other hemisphere will have a relatively warmer winter and cooler summer.


When the Earth's axis is aligned such that aphelion and perihelion occur near the equinoxes, the Northern and Southern Hemispheres will have similar contrasts in the seasons.


At present perihelion occurs during the Southern Hemisphere's summer, and aphelion is reached during the southern winter. Thus the Southern Hemisphere seasons are somewhat more extreme than the Northern Hemisphere seasons, when other factors are equal.


Orbital inclination

The inclination of Earth's orbit drifts up and down relative to its present orbit with a cycle having a period of about 70,000 years. Milankovitch did not study this three-dimensional movement. Inclination in general is the angle between a reference plane and another plane or axis of direction. ...


More recent researchers noted this drift and that the orbit also moves relative to the orbits of the other planets. The invariable plane, the plane that represents the angular momentum of the solar system, is approximately the orbital plane of Jupiter. The inclination of the Earth's orbit has a 100,000 year cycle relative to the invariable plane. This 100,000 year cycle closely matches the 100,000 year pattern of ice ages. The invariable plane of the solar system is the plane passing through its barycenter (center of mass) which is perpendicular to its angular momentum vector, about 98% of which is contributed by the orbital angular momenta of the four jovian planets (Jupiter, Saturn, Uranus, and Neptune). ... This gyroscope remains upright while spinning due to its angular momentum. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ...


It has been proposed that a disk of dust and other debris is in the invariable plane, and this affects the Earth's climate through several possible means. The Earth presently moves through this plane around January 9 and July 9, when there is an increase in radar-detected meteors and meteor-related noctilucent clouds.[1][2] Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... Noctilucent clouds (also known as polar mesospheric clouds) are rare bright cloudlike atmospheric phenomena visible in a deep twilight (the name means roughly night shining). They are most commonly observed in the summer months at latitudes between 50° and 60° (north and south). ...


Problems

Because the observed periodicities of climate fit so well with the orbital periods, the orbital theory has overwhelming support. Nonetheless, there are several difficulties in reconciling theory with observations.


100K Year Problem

Main article: 100,000 year problem

The 100,000 year problem is that the eccentricity variations have a significantly smaller impact on solar forcing than precession or obliquity and hence might be expected to produce the weakest effects. However, observations show that during the last 1 million years, the strongest climate signal is the 100,000 year cycle. In addition, despite the relatively large 100,000 year cycle, some have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.[3] Some models can however reproduce the 100,000 year cycles as a result of non-linear interactions between small changes in the Earth's orbit and internal oscillations of the climate system.[4][5] A record of δ18O, a proxy for temperature, the past 1,200,000 years The 100,000 year problem is a discrepancy between the actual extent of glaciations and that expected when considering the amount of incoming solar radiation, or insolation, which changes little on a 100,000 year (100...


400K Year Problem

The 400,000 year problem is that the eccentricity variations have a strong 400,000 year cycle. That cycle is only clearly present in climate records older than the last million years. If the 100ky variations are having such a strong effect, the 400ky variations might also be expected to be apparent. This is also known as the stage 11 problem, after the interglacial in marine isotopic stage 11 which would be unexpected if the 400,000 year cycle has an impact on climate. The relative absence of this periodicity in the marine isotopic record may be due, at least in part, to the response times of the climate system components involved - in particular, the carbon cycle. Marine isotopic stages (MIS) are alternating warm and cool periods in the Earths palaeoclimate, deduced from oxygen isotope data reflecting temperature curves derived from data from deep sea core samples. ... The carbon cycle is the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere,and atmosphere of the Earth (other astronomical objects may have similar carbon cycles, but nothing is yet known about them). ...


Stage 5 problem

The stage 5 problem refers to the timing of the penultimate interglacial (in marine isotopic stage 5) which appears to have begun 10 thousand years in advance of the solar forcing hypothesized to have been causing it. This is also referred to as the causality problem. Marine isotopic stages (MIS) are alternating warm and cool periods in the Earths palaeoclimate, deduced from oxygen isotope data reflecting temperature curves derived from data from deep sea core samples. ...


Effect exceeds cause

420,000 years of ice core data from Vostok, Antarctica research station.

The effects of these variations are primarily believed to be due to variations in the intensity of solar radiation upon various parts of the globe. Observations show climate behaviour is much more intense than the calculated variations. Various internal characteristics of climate systems are believed to be sensitive to the insolation changes, causing amplification (positive feedback) and damping responses (negative feedback). Download high resolution version (1600x1092, 188 KB)420,000 years of ice core data from Vostok, Antarctica research station. ... Download high resolution version (1600x1092, 188 KB)420,000 years of ice core data from Vostok, Antarctica research station. ... Ice Core sample taken from drill. ... Vostok, Antarctica is a Russian research station located near the Geomagnetic South Pole (see South Pole), at the center of the East Antarctic Ice Sheet. ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ... This article or section does not cite any references or sources. ...


The unsplit peak problem

The unsplit peak problem refers to the fact that eccentricity has cleanly resolved variations at both 95 and 125 ky frequencies. A sufficiently long, well-dated record of climate change should be able to resolve both frequencies, but some researchers interpret climate records of the last million years as showing only a single spectral peak at 100 kyr periodicity. It is debatable whether the quality of existing data ought to be sufficient to resolve both frequencies over the last million years.


The transition problem

The transition problem refers to the change in the frequency of climate variations 1 million years ago. From 1-3 million years, climate had a dominant mode matching the 41 ky cycle in obliquity. After 1 million years ago, this changed to a 100 ky variation matching eccentricity. No reason for this change has been established.


Present conditions

The amount of solar radiation (insolation) in the Northern Hemisphere at 65°N seems to be related to occurrence of an ice age. Astronomical calculations show that 65°N summer insolation should increase gradually over the next 25,000 years, and that no declines in 65°N summer insolation sufficient to cause an ice age are expected in the next 50,000 - 100,000 years. Variation in summer insolation (solar radiation) at 65°N due to orbital variations. ... TOA and surface insolation, annual mean Insolation is the incoming solar radiation that reaches a planet and its atmosphere or, by extension, any object exposed to solar rays, such as watts per square meter of Sun-facing cross section, across the entire electromagnetic spectrum; most of that power is in...


As mentioned above, at present perihelion occurs during the Southern Hemisphere's summer, and aphelion during the southern winter. Thus the Southern Hemisphere seasons should tend to be somewhat more extreme than the Northern Hemisphere seasons. The relatively low eccentricity of the present orbit results in a 6.8% difference in the amount of solar radiation during summer in the two hemispheres.


The future

Since orbital variations are predictable[6], if one has a model that relates orbital variations to climate, it is possible to run such a model forward to "predict" future climate. Two caveats are necessary: firstly, that anthropogenic effects (global warming) are likely to exert a larger influence, at least over the short term; and secondly that since the mechanism by which orbital forcing affects climate is not well understood, there is no very good model relating climate to orbital forcing. Look up anthropogenic in Wiktionary, the free dictionary. ... Global mean surface temperatures 1850 to 2006 Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980 Global warming is the observed increase in the average temperature of the Earths atmosphere and oceans in recent decades and the projected... Orbital forcing, or Milankovitch theory, describes the effect on climate of slow changes in the tilt of the Earths axis and shape of the orbit. ...


An often-cited 1980 study by Imbrie and Imbrie determined that "Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend which began some 6,000 years ago will continue for the next 23,000 years."[7]


More recent work by Berger and Loutre suggests that the current warm climate may last another 50,000 years.[8]


References

  1. ^ Richard A Muller, Gordon J MacDonald (1997). "Glacial Cycles and Astronomical Forcing". Science 277 (1997/07/11): 215-218. 
  2. ^ Origin of the 100 kyr Glacial Cycle: eccentricity or orbital inclination?. Richard A Muller. Retrieved on March 2, 2005.
  3. ^ Wunsch, Carl (2004). "Quantitative estimate of the Milankovitch-forced contribution to observed Quaternary climate change". Quaternary Science Reviews 23: 1001-1012.  DOI:10.1016/j.quascirev.2004.02.014
  4. ^ Ghil, Michael (1994). "Cryothermodynamics: the chaotic dynamics of paleoclimate". Physica D 77 (1-3): 130-159.  DOI:10.1016/0167-2789(94)90131-7
  5. ^ Gildor H, Tziperman E (2000). "Sea ice as the glacial cycles' climate switch: Role of seasonal and orbital forcing". Paleoceanography 15 (6): 605-615.  DOI:10.1029/1999PA000461
  6. ^ F. Varadi, B. Runnegar, M. Ghil (2003). "Successive Refinements in Long-Term Integrations of Planetary Orbits". The Astrophysical Journal 592: 620–630.  DOI:10.1086/375560
  7. ^ J Imbrie, J Z Imbrie (1980). "Modeling the Climatic Response to Orbital Variations". Science 207 (1980/02/29): 943-953. 
  8. ^ Berger A, Loutre MF (2002). "Climate: An exceptionally long interglacial ahead?". Science 297 (5585): 1287-1288. DOI:10.1126/science.1076120

March 2 is the 61st day of the year (62nd in leap years) in the Gregorian calendar. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

See also

Cyclostratigraphy is the study of astronomically forced climate cycles within sedimentary successions. ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ...

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NOAA Paleoclimatology Program - Orbital Variations and Milankovitch Theory (862 words)
The Milankovitch or astronomical theory of climate change is an explanation for changes in the seasons which result from changes in the earth's orbit around the sun.
The "roundness", or eccentricity, of the earth's orbit varies on cycles of 100,000 and 400,000 years, and this affects how important the timing of perihelion is to the strength of the seasons.
The combination of the 41,000 year tilt cycle and the 22,000 year precession cycles, plus the smaller eccentricity signal, affect the relative severity of summer and winter, and are thought to control the growth and retreat of ice sheets.
Milankovitch cycles - Wikipedia, the free encyclopedia (1896 words)
Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate, named after Serbian geophysicist Milutin Milanković.
In addition, despite the relatively large 100,000 year cycle, some have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.
That cycle is not being detected in climate.
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