question: How do events on Earth’s surface shift Earth’s axis?
comment: Very slightly. You know how a diver do certain tricks during a high dive where she spins faster or slower by straightening her body or tightening it in? Or a figure skater pulling her arms in to do a really fast spin? It's like that. The general rule is that if a change leads to more mass being held farther out from the center of rotation, the overall rotation is slower, and if mass gets pulled in toward the axis, it spins faster.
passages: Using numerical methods to simulate Solar System behavior, long-term changes in Earth's orbit, and hence its obliquity, have been investigated over a period of several million years. For the past 5 million years, Earth's obliquity has varied between and , with a mean period of 41,040 years. This cycle is a combination of precession and the largest term in the motion of the ecliptic. For the next 1 million years, the cycle will carry the obliquity between and .
   The magnetic field of the Earth, and of other planets that have magnetic fields, is generated by dynamo action in which convection of molten iron in the planetary core generates electric currents which in turn give rise to magnetic fields. In simulations of planetary dynamos, reversals often emerge spontaneously from the underlying dynamics. For example, Gary Glatzmaier and collaborator Paul Roberts of UCLA ran a numerical model of the coupling between electromagnetism and fluid dynamics in the Earth's interior. Their simulation reproduced key features of the magnetic field over more than 40,000 years of simulated time and the computer-generated field reversed itself. Global field reversals at irregular intervals have also been observed in the laboratory liquid metal experiment "VKS2".
   Section::::Temporal change.
  
  In geodesy, temporal change can be studied by a variety of techniques. Points on Earth's surface change their location due to a variety of mechanisms:
  
  BULLET::::- Continental plate motion, plate tectonics
  
  BULLET::::- Episodic motion of tectonic origin, especially close to fault lines
  
  BULLET::::- Periodic effects due to tides
  
  BULLET::::- Postglacial land uplift due to isostatic adjustment
  
  BULLET::::- Mass variations due to hydrological changes
  
  BULLET::::- Anthropogenic movements such as reservoir construction or petroleum or water extraction
   Artifacts taken from the Earth have been studied to infer the cycles of past climate. A study of the chronology of Antarctic ice cores using oxygen-nitrogen ratios in air bubbles trapped in the ice, which appear to respond directly to the local insolation, concluded that the climatic response documented in the ice cores was driven by northern hemisphere insolation as proposed by the Milankovitch hypothesis. Analysis of deep-ocean cores, analysis of lake depths, and a seminal paper by Hays, Imbrie, and Shackleton provide additional validation through physical artifacts. Climate records contained in a core of rock drilled in Arizona show a pattern synchronized with Earth's eccentricity, and cores drilled in New England match it, going back 215 million years.
   Slight variations in the Earth's motion lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged, annually-averaged sunshine; but there can be strong changes in the geographical and seasonal distribution. The three types of kinematic change are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis. Combined together, these produce Milankovitch cycles which affect climate and are notable for their correlation to glacial and interglacial periods.
   Slight variations in Earth's motion lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged annually averaged sunshine; but there can be strong changes in the geographical and seasonal distribution. The three types of kinematic change are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis. Combined together, these produce Milankovitch cycles which affect climate and are notable for their correlation to glacial and interglacial periods, their correlation with the advance and retreat of the Sahara, and for their appearance in the stratigraphic record.
   Crustal movements (such as continental drift) or polar cap melting are slow secular events. The characteristic coupling time between core and mantle has been estimated to be on the order of ten years, and the so-called 'decade fluctuations' of Earth's rotation rate are thought to result from fluctuations within the core, transferred to the mantle. The length of day (LOD) varies significantly even for time scales from a few years down to weeks (Figure), and the observed fluctuations in the LOD - after eliminating the effects of external torques - are a direct consequence of the action of internal torques. These short term fluctuations are very probably generated by the interaction between the solid Earth and the atmosphere.
   Because the dynamic motions of the planets are so well known, their nutations can be calculated to within arcseconds over periods of many decades. There is another disturbance of the Earth's rotation called polar motion that can be estimated for only a few months into the future because it is influenced by rapidly and unpredictably varying things such as ocean currents, wind systems, and hypothesised motions in the liquid nickel-iron outer core of the Earth.
  
  Section::::Nutation of the Earth's axis.
  
  Section::::Nutation of the Earth's axis.:Causes.
   This interaction between the anomalistic and tropical cycle is important in the long-term climate variations on Earth, called the Milankovitch cycles. An equivalent is also known on Mars.
   In the case of Earth, the principal sources of tidal force are the Sun and Moon, which continuously change location relative to each other and thus cause nutation in Earth's axis. The largest component of Earth's nutation has a period of 18.6 years, the same as that of the precession of the Moon's orbital nodes. However, there are other significant periodic terms that must be accounted for depending upon the desired accuracy of the result. A mathematical description (set of equations) that represents nutation is called a "theory of nutation". In the theory, parameters are adjusted in a more or less "ad hoc" method to obtain the best fit to data. Simple rigid body dynamics do not give the best theory; one has to account for deformations of the Earth, including mantle inelasticity and changes in the core–mantle boundary.
   Polarity reversals in the Earth's magnetic field have also been used to determine geologic time. Periodically, the magnetic field of the earth reverses leaving a magnetic signal in volcanic and sedimentary rocks. This signal can be detected and sequences recorded, and in the case of volcanic rocks, tied to radiometric dates.
   There are various solar/celestial effects that exist which have an effect on Earth's climate. These effects usually occur in cycles, and primarily include how Earth's obliquity, the eccentricity of Earth's orbit, and the precession of the equinoxes and solstices affect Earth's climate. In addition to these effects, there are also other factors that have an effect on Earth's climate. These other factors include how sun activity affects climate and how celestial phenomena, such as meteors, affect Earth's climate. Some of these factors aren't yet well understood, for instance the ice ages occur on 100,000 year cycles, and it's not completely understood why the various effects with this periodicity have such a strong effect on glaciation (see the 100,000-year problem).
   In addition to the vertical movement of the land and sea, isostatic adjustment of the Earth also involves horizontal movements. It can cause changes in Earth's gravitational field and rotation rate, polar wander, and earthquakes.
  
  Section::::Application of hypotheses of Isostasy.
  
  The hypothesis is used often to determine position of LAB (i.e., Lithosphere-Asthenosphere Boundary)
  
  Section::::Eustasy and relative sea level change.
   Similar astronomical hypotheses had been advanced in the 19th century by Joseph Adhemar, James Croll and others, but verification was difficult because there was no reliably dated evidence, and because it was unclear which periods were important.
  
  Now, materials on Earth that have been unchanged for millennia (obtained via ice, rock, and deep ocean cores) are being studied to indicate the history of Earth's climate. Though they are consistent with the Milankovitch hypothesis, there are still several observations that the hypothesis does not explain.
  
  Section::::Earth's movements.
   Section::::Definition and clarification.
  
  The geographic poles are defined by the points on the surface of the Earth that are intersected by the axis of rotation. The pole shift hypothesis describes a change in location of these poles with respect to the underlying surface – a phenomenon distinct from the changes in axial orientation with respect to the plane of the ecliptic that are caused by precession and nutation, and is an amplified event of a true polar wander.
   Over long time scales, ice sheet mass balance is governed by the amount of sunlight reaching the earth. This variation in sunlight reaching the earth, or insolation, over geologic time is in turn determined by the angle of the earth to the sun and shape of the Earth's orbit, as it is pulled on by neighboring planets; these variations occur in predictable patterns called Milankovitch cycles. Milankovitch cycles dominate climate on the glacial–interglacial timescale, but there exist variations in ice sheet extent that are not linked directly with insolation.
   The Earth's field is roughly like a tilted dipole, but it changes over time (a phenomenon called geomagnetic secular variation). Mostly the geomagnetic pole stays near the geographic pole, but at random intervals averaging 440,000 to a million years or so, the polarity of the Earth's field reverses. These geomagnetic reversals, analyzed within a Geomagnetic Polarity Time Scale, contain 184 polarity intervals in the last 83 million years, with change in frequency over time, with the most recent brief complete reversal of the Laschamp event occurring 41,000 years ago during the last glacial period. Geologists observed geomagnetic reversal recorded in volcanic rocks, through magnetostratigraphy correlation (see natural remanent magnetization) and their signature can be seen as parallel linear magnetic anomaly stripes on the seafloor. These stripes provide quantitative information on seafloor spreading, a part of plate tectonics. They are the basis of magnetostratigraphy, which correlates magnetic reversals with other stratigraphies to construct geologic time scales. In addition, the magnetization in rocks can be used to measure the motion of continents.
   Such a reorientation changes the latitudes of most points on the Earth by amounts that depend on how far they are from the axis near the equator that does not move.
  
  Section::::Examples.
  
  Cases of true polar wander have occurred several times in the course of the Earth's history. The speed of rotation (around the axis of lowest inertia) is thought to have been less than about 1° per million years. Mars, Europa, and Enceladus are also believed to have undergone true pole wander, in the case of Europa by 80°, flipping over almost completely.
   The Earth's rotation around its axis, and revolution around the Sun, evolve over time due to gravitational interactions with other bodies in the solar system. The variations are complex, but a few cycles are dominant.
   Observational evidence shows that there is no significant time delay between the change of AAM and its corresponding change of LOD for periods longer than about 10 days. This implies a strong coupling between atmosphere and solid Earth due to surface friction with a time constant of about 7 days, the spin-down time of the Ekman layer. This spin-down time is the characteristic time for the transfer of atmospheric axial angular momentum to Earth's surface and vice versa.
   The next major advance in understanding reversals came when techniques for radiometric dating were improved in the 1950s. Allan Cox and Richard Doell, at the United States Geological Survey, wanted to know whether reversals occurred at regular intervals, and invited the geochronologist Brent Dalrymple to join their group. They produced the first magnetic-polarity time scale in 1959. As they accumulated data, they continued to refine this scale in competition with Don Tarling and Ian McDougall at the Australian National University. A group led by Neil Opdyke at the Lamont-Doherty Geological Observatory showed that the same pattern of reversals was recorded in sediments from deep-sea cores.
   Section::::Precession of solstices and equinoxes.
  
  The precession of solstices and equinoxes is the third factor that plays a role in Earth climate change that deals directly with the earth itself. The basis of the precession of solstices and equinoxes is that it causes the seasons to occur at different times in Earth's revolution around the sun throughout a cycle recurring about every 23,000 years.
   Major earthquakes cause abrupt polar motion by altering the volume distribution of the Earth's solid mass. These shifts, however, are quite small in magnitude relative to the long-term core/mantle and isostatic rebound components of polar motion.
  
  Section::::Basic principles.
   The Earth's current orbital inclination is 1.57° (see above). Earth presently moves through the invariable plane around January 9 and July 9. At these times, there is an increase in meteors and noctilucent clouds. If this is because there is a disk of dust and debris in the invariable plane, then when the Earth's orbital inclination is near 0° and it is orbiting through this dust, materials could be accreted into the atmosphere. This process could explain the narrowness of the 100,000-year climate cycle.
  
  Section::::Present and future conditions.
   The axial tilt and eccentricity of Earth (or Mars) are by no means fixed, but rather vary due to gravitational perturbations from other planets in the Solar System on a timescale of tens of thousands or hundreds of thousands of years. Thus, for example Earth's eccentricity of about 1% regularly fluctuates and can increase up to 6%, and at some point in the distant future the Earth will also have to deal with the calendrical implications of seasons of widely differing length and the major climate disruptions that go along with it.
  