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Milankovitch Oscillation and Climate Change


Cycles have a significant impact on the Earth's short- and long-term weather and climate. A century ago, Serbian scientist Milutin Milankovitch postulated that the long-term, cumulative impacts of changes in the Earth's orbit around the Sun are a significant driver of the Earth's long-term climate and are responsible for initiating and ending glacial periods (Ice Ages).

The Milankovitch cycles include:

The shape of Earth’s orbit, known as eccentricity

The Earth's yearly orbit around the Sun isn't precisely round, but it comes near. The gravitational force of our solar system's two greatest gas giant planets, Jupiter and Saturn, causes the shape of Earth's orbit to shift from nearly circular to somewhat elliptical over time. Eccentricity is a measure of how much the Earth's orbit deviates from a perfect circle. These differences have an impact on the distance between the Earth and the Sun. The eccentricity cycle has a relatively minor effect on global yearly insolation. Because fluctuations in Earth's eccentricity are so slight, they have only a modest role in yearly seasonal climatic variations.

The angle at Earth’s axis is tilted concerning Earth’s orbital plane, known as obliquity;

Obliquity is the angle at which the Earth's axis of rotation is slanted as it goes around the Sun. Seasons on Earth are caused by obliquity. It has changed between 22.1 and 24.5 degrees with regard to Earth's orbital plane during the past million years. The higher the axial tilt angle of the Earth, the more intense our seasons are, since each hemisphere gets more solar energy during summer, when it is slanted toward the Sun, and less during winter, when it is tilted away from the Sun. Larger tilt angles promote deglaciation periods (the melting and retreat of glaciers and ice sheets). These impacts are not consistent across the globe; higher latitudes see a greater shift in total solar energy than places closer to the equator.

The Earth's axis is now inclined 23.4 degrees, or almost halfway between its extremes, and this angle is progressively decreasing in a cycle that spans about 41,000-year cycle.

As obliquity diminishes, it progressively helps to make our seasons milder, resulting in increasingly warmer winters and colder summers that, over time, enable snow and ice to pile up into enormous ice sheets at high latitudes. As ice cover rises, more of the Sun's radiation is reflected back into space, causing even greater cooling.

The direction Earth’s axis of rotation is pointed, known as precession.

As the Earth revolves, its axis wobbles slightly, similar to a slightly off-center spinning toy top. This wobble is generated by tidal forces induced by the Sun's and Moon's gravitational effects, which cause the Earth to bulge near the equator, influencing its rotation. Axial precession reflects the changes in the direction of this wobble in relation to the fixed locations of stars. Today Earth’s North Stars are Polaris and Polaris Australis, but a couple of thousand years ago, they were Kochab and Pherkad.The axial precession cycle lasts about 25,771.5 years.

As the Earth completes a precession cycle, the orientation of the planet is altered with respect to perihelion and aphelion. If a hemisphere is pointed toward the sun during perihelion (shortest distance between Earth and sun), it will be pointed away during aphelion (largest distance between Earth and sun), and the opposite is true for the other hemisphere. The hemisphere that's pointed toward the sun during perihelion and away during aphelion experiences more extreme seasonal contrasts than the other hemisphere.

Currently, the southern hemisphere's summer occurs near perihelion and winter near aphelion, which means the southern hemisphere experiences more extreme seasons than the northern hemisphere. Seasonal contrasts become more acute in one hemisphere and less extreme in the other due to axial precession.

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