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Milankovitch Cycles and Glaciation

Milankovitch Cycles around the globe result in prominent changes in the Earth's climate and glacial regimes. At present the orbital eccentricity is nearly at the minimum of its cycle. Axial Tilt Axial tilt, the second of the three Milankovitch Cycles, is the inclination of the Earth's axis in relation to its. Mar 21, 2017 The Milankovitch cycles affect the average isolation that the Earth gets in a yearly cycle and latitudinal variations of insolation that determine the amount of ice at the poles. So which diagrams. Milankovitch cycles are classically divided into the precession, the obliquity, and the eccentricity cycles. These cycles modulate the solar insolation (i.e., the total energy the planet receives from the sun at the top of the atmosphere) or its geographic distribution.

The episodic nature of the Earth's glacial and interglacial periods within the present Ice Age (the last couple of million years) have been caused primarily by cyclical changes in the Earth's circumnavigation of the Sun. Variations in the Earth's eccentricity, axial tilt, and precession comprise the three dominant cycles, collectively known as the Milankovitch Cycles for Milutin Milankovitch, the Serbian astronomer and mathematician who is generally credited with calculating their magnitude. Taken in unison, variations in these three cycles creates alterations in the seasonality of solar radiation reaching the Earth's surface. These times of increased or decreased solar radiation directly influence the Earth's climate system, thus impacting the advance and retreat of Earth's glaciers.

It is of primary importance to explain that climate change, and subsequent periods of glaciation, resulting from the following three variables is not due to the total amount of solar energy reaching Earth. The three Milankovitch Cycles impact the seasonality and location of solar energy around the Earth, thus impacting contrasts between the seasons.

Milankovitch

The first of the three Milankovitch Cycles is the Earth's eccentricity. Eccentricity is, simply, the shape of the Earth's orbit around the Sun. This constantly fluctuating, orbital shape ranges between more and less elliptical (0 to 5% ellipticity) on a cycle of about 100,000 years. These oscillations, from more elliptic to less elliptic, are of prime importance to glaciation in that it alters the distance from the Earth to the Sun, thus changing the distance the Sun's short wave radiation must travel to reach Earth, subsequently reducing or increasing the amount of radiation received at the Earth's surface in different seasons.

Today a difference of only about 3 percent occurs between aphelion (farthest point) and perihelion (closest point). This 3 percent difference in distance means that Earth experiences a 6 percent increase in received solar energy in January than in July. This 6 percent range of variability is not always the case, however. When the Earth's orbit is most elliptical the amount of solar energy received at the perihelion would be in the range of 20 to 30 percent more than at aphelion. Most certainly these continually altering amounts of received solar energy around the globe result in prominent changes in the Earth's climate and glacial regimes. At present the orbital eccentricity is nearly at the minimum of its cycle.

Axial tilt, the second of the three Milankovitch Cycles, is the inclination of the Earth's axis in relation to its plane of orbit around the Sun. Oscillations in the degree of Earth's axial tilt occur on a periodicity of 41,000 years from 21.5 to 24.5 degrees.

Today the Earth's axial tilt is about 23.5 degrees, which largely accounts for our seasons. Because of the periodic variations of this angle the severity of the Earth's seasons changes. With less axial tilt the Sun's solar radiation is more evenly distributed between winter and summer. However, less tilt also increases the difference in radiation receipts between the equatorial and polar regions.

One hypothesis for Earth's reaction to a smaller degree of axial tilt is that it would promote the growth of ice sheets. This response would be due to a warmer winter, in which warmer air would be able to hold more moisture, and subsequently produce a greater amount of snowfall. In addition, summer temperatures would be cooler, resulting in less melting of the winter's accumulation. At present, axial tilt is in the middle of its range.

The third and final of the Milankovitch Cycles is Earth's precession. Precession is the Earth's slow wobble as it spins on axis. This wobbling of the Earth on its axis can be likened to a top running down, and beginning to wobble back and forth on its axis. The precession of Earth wobbles from pointing at Polaris (North Star) to pointing at the star Vega. When this shift to the axis pointing at Vega occurs, Vega would then be considered the North Star. This top-like wobble, or precession, has a periodicity of 23,000 years.

Due to this wobble a climatically significant alteration must take place. When the axis is tilted towards Vega the positions of the Northern Hemisphere winter and summer solstices will coincide with the aphelion and perihelion, respectively. This means that the Northern Hemisphere will experience winter when the Earth is furthest from the Sun and summer when the Earth is closest to the Sun. This coincidence will result in greater seasonal contrasts. At present, the Earth is at perihelion very close to the winter solstice.

In the eyes of Milutin Milankovitch, there’s been a noticeable trend in climate, temperature and seasons due to this cycle. And we can accredit these long-term climate changes to 3 variations in geometry between the Earth and sun:

  • ECCENTRICITY: How the Earth orbits the sun.
  • OBLIQUITY: What angle Earth faces the sun.
  • PRECESSION: How Earth’s axis of rotation changes.

Milankovitch Hypothesis

Milankovitch cycles

If you put these 3 interactions of Earth and the sun together, they form the Milankovitch Cycle. Let’s explore with more detail.

1. Orbital eccentricity

Earth revolves around the sun in a roughly circular orbit. But roughly every 100,000 years, its orbit becomes more eccentric.

Milankovitch Cycles

So it starts as a circular orbit like it is in its current state. But like a pendulum, the eccentricity will swing it back the other way with a more elliptical orbit.

Because Venus is so close to Earth, its gravitational interactions slightly pulls Earth in its orbit. Then, colossal Jupiter pulls Earth slightly outside its orbit at the opposite end. How to install anydesk for mac.

MilankovitchMilankovitch
So Earth periodically goes from a circular orbit to a more elliptical one (high eccentricity). This is due to the gravitational pull of neighboring planets. Because of its orbital eccentricity, Earth varies in distance from the sun. As a result, it receives less solar radiation causing it to cool.

2. Obliquity variation

The next piece of the puzzle is obliquity. Right now, Earth’s obliquity is 23.5°. But during the Milankovitch Cycle, it varies from 22.1° to 24.5° and takes 40,000 years to complete a full cycle.

Earth’s changing obliquity doesn’t alter the total amount of incoming solar radiation. Instead, it affects the geographic distribution of where sunlight hits the Earth.

AXIAL TILT: For example, if axial tilt increases, winters are colder in both hemispheres. And vice versa for when axial tilt decreases.

In summary, more tilt signifies more severe seasons. For instance, this can cause long periods of glaciation. And for Earth as a system, it enters positive and negative climate feedback loops.

The effects are drastic for long-term climate change. And this is all because of Earth’s change in axial tilt that gradually shifts every 40,000 years.

3. Axial precession

Axial precession is the movement of the rotational axis of Earth. According to the Milankovitch Cycle, precession has a cycle of roughly 23,000.

Precession occurs because the Earth is not a perfect sphere. It flattens out at the poles and widens at the equator. In addition, the gravitational pull from the sun and moon causes precession.

Similar to obliquity, precession doesn’t change the total amount of solar radiation that hits Earth. But precession primarily alters the perihelion and aphelion.

Axial precession is the movement of the rotational axis of Earth. Overall, this increases the seasonal differences from one hemisphere to the other.
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