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 |  Subject: What Are the Milankovitch Cycles?  Sat Oct 08, 2022 7:52 pm | |
| The Milankovitch cycles describe how relatively slight changes in Earth's movement affect the planet's climate. The cycles are named for Milutin Milankovitch, a Serbian astrophysicist who began investigating the cause of Earth's ancient ice ages in the early 1900s, according to the American Museum of Natural History (AMNH).
Earth experienced it's most recent ice ages during the Pleistocene epoch, which lasted from 2.6 million years ago to 11,700 years ago. For thousands of years at a time, even the more temperate regions of the globe were covered with glaciers and ice sheets, according to the University of California Museum of Paleontology.
To determine how Earth could experience such vast changes in climate over time, Milankovitch incorporated data about the variations of Earth's position with the timeline of the ice ages during the Pleistocene. He studied Earth's variations for the last 600,000 years and calculated the varying amounts of solar radiation due to Earth's changing orbital parameters. In doing so, he was able to link lower amounts of solar radiation in the high northern latitudes to previous European ice ages, according to AMNH.
Milankovitch's calculations and charts, which were published in the 1920s and are still used today to understand past and future climate, led him to conclude that there are three different positional cycles, each with its own cycle length, that influence the climate on Earth: the eccentricity of Earth's orbit, the planet's axial tilt and the wobble of its axis.
Eccentricity
The Earth orbits the sun in an oval shape called an ellipse, with the sun at one of the two focal points (foci). Ellipticity is a measure of the shape of the oval and is defined by the ratio of the semiminor axis (the length of the short axis of the ellipse) to the semimajor axis (the length of the long axis of the ellipse), according to Swinburne University. A perfect circle, where the two foci meet in the center, has an ellipticity of 0 (low eccentricity), and an ellipse that is being squished to almost a straight line has an eccentricity of nearly 1 (high eccentricity).
The Earth's orbit slightly changes its eccentricity over the course of 100,000 years from nearly 0 to 0.07 and back again, according to NASA's Earth Observatory. When the Earth's orbit has a higher eccentricity, the planet's surface receives 20 to 30 percent more solar radiation when it's at perihelion (the shortest distance between the Earth and sun each orbit) than when it is at aphelion (the largest distance between the Earth and sun each orbit). When the Earth's orbit has a low eccentricity, there is very little difference in the amount of solar radiation that is received between perihelion and aphelion.
Today, the eccentricity of Earth's orbit is 0.017. At perihelion, which occurs on or around Jan. 3 each year, Earth's surface receives about 6 percent more solar radiation than at aphelion, which occurs on or around July 4.
Axial tilt
The tilt of the Earth's axis relative to the plane of its orbit is the reason that we experience seasons. Slight changes in the tilt changes the amount of solar radiation falling on certain locations of Earth, according to Indiana University Bloomington. Over the course of about 41,000 years, the tilt of the Earth's axis, also known as obliquity, varies between 21.5 and 24.5 degrees.
More: .https://www.livescience.com/64813-milankovitch-cycles.html |
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