Milankovitch Cycles Part 1: Orbital Cycles and Earth’s Ice Ages

Milankovitch Cycles Part 1: Orbital Cycles and Earth’s Ice Ages

This is the story of the imprint of Earth’s orbital cycles on the climate of our planet. Scientists now believe that certain features of Earth’s orbital motions act as a trigger for Earth’s long-term climate cycles, including the cyclical planet-wide glacier cover, popularly called the “Ice Ages” — and termed by science glacial epochs. Scientists first discovered the glacial cycles in the middle of the 19th Century. But the theory linking the glacial epochs to variations in solar radiation caused by cyclical changes in certain of Earth’s orbital motions, had to wait until the first years of the 20th Century.

This is first in a series by RCA Member David Horne.

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Milankovitch Cycles Part 2: Agassiz’s Boulders and Earth’s Orbital Cycles

Milankovitch Cycles Part 2: Agassiz’s Boulders and Earth’s Orbital Cycles

For hundreds of years, people in northern and central Europe had been noticing large, out-of-place boulders that seemed to have been dropped in a field, or popped up from underground. “Erratics”, they came to be called. Legends attributed the boulders to giants, trolls, and the Devil. By the early 1820s many natural history philosophers, scientists, came to focus on ‘ice’ as the likely mechanism of transport. But the source of all the ice was a mystery.

This is second in a series by RCA Member David Horne.

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Milankovitch Cycles Part 4: Adhemar, Le Verrier, and Croll

Milankovitch Cycles Part 4: Adhemar, Le Verrier, and Croll

By the mid-1800s a few scientists were beginning to explore a possible relationship between Earth’s orbital cycles and Earth’s Glacial Epochs and Ice Ages. Their first step was to develop a working model linking Earth’s cyclical orbital changes to corresponding changes in the amount of solar radiation received by earth. Among scientists to begin the exploration before Milutin Milankovitch, three are of special importance for this article: Joseph Adhemar, Urbain Le Verrier and James Croll. In fact, the Milankovitch cycles are sometimes referred to as the Croll-Milankovitch cycles.

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Milankovitch Cycles Part 5

Milankovitch Cycles Part 5

By 1920, Milankovtich completed the book he began writing during the World War: Mathematical Theory of Heat Phenomena Produced by Solar Radiation. In this work, Milankovtich set out the mathematical tools he developed by which he calculated and described the amount of solar radiation received planet wide on Mars, Earth and Venus. As mentioned in the introduction to this series of articles, his calculations for Mars and Earth proved accurate. But, because he was unaware of Venus’ dense atmosphere his calculations of Venus’ were not even close — spacecraft probes have measured surface temperatures over 850 degrees Fahrenheit and pressures equal to the pressure 3000 feet underwater. The book received more attention from the public for his Mars’ results than it did from geologists interested in Earth’s Ice Ages because in the first decades of the 20th Century, the popular press was filled with stories about Martians and canals on Mars.

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Milankovitch Cycles Part 6: Impressions

Milankovitch Cycles Part 6: Impressions

The Milankovitch theory identified three aspects of Earth’s orbital motion as causes of the Ice Age glacial periods and the cyclical long term climate change: (1) the changing shape of Earth’s orbit from more circular to more elliptical; (2) cyclical changes in the “tilt” of Earth’s axis of rotation (axial tilt and precession) which affect the amount of solar radiation received by each hemisphere; and (3) the first two aspects acting together to determine where along Earth’s orbit maximum and minimum levels of solar radiation are received. These orbital cycles have always affected Earth’s climate by controlling the amount of solar radiation reaching Earth.

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