Larger tilt angles favor periods of deglaciation the melting and retreat of glaciers and ice sheets. It was last at its maximum tilt about 10, years ago and will reach its minimum tilt about 9, years from now. As obliquity decreases, it gradually helps make our seasons milder, resulting in increasingly warmer winters, and cooler summers that gradually, over time, allow snow and ice at high latitudes to build up into large ice sheets.
Precession — As Earth rotates, it wobbles slightly upon its axis, like a slightly off-center spinning toy top. This wobble is due to tidal forces caused by the gravitational influences of the Sun and Moon that cause Earth to bulge at the equator, affecting its rotation.
The trend in the direction of this wobble relative to the fixed positions of stars is known as axial precession. The cycle of axial precession spans about 25, Axial precession makes seasonal contrasts more extreme in one hemisphere and less extreme in the other. Currently perihelion occurs during winter in the Northern Hemisphere and in summer in the Southern Hemisphere.
This makes Southern Hemisphere summers hotter and moderates Northern Hemisphere seasonal variations. But in about 13, years, axial precession will cause these conditions to flip, with the Northern Hemisphere seeing more extremes in solar radiation and the Southern Hemisphere experiencing more moderate seasonal variations. Today, the Earth is tilted Earth wobbles just slightly as it spins on its axis, similarly to when a spinning top begins to slow down.
This wobble, known as precession , is primarily caused by the gravity of the sun and moon pulling on Earth's equatorial bulges. The wobble doesn't change the tilt of Earth's axis, but the orientation changes. Over about 26, years, Earth wobbles around in a complete circle, according to Washington State University.
Now, and for the past several thousands of years, Earth's axis has been pointed north more or less toward Polaris , also known as the North Star. But Earth's gradual precessional wobble means that Polaris isn't always the North Star.
About 5, years ago the Earth was pointed more toward another star, called Thubin. And, in approximately 12, years, the axis will have traveled a bit more around its precession circle and will point toward Vega , which will become the next North Star.
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. In theory, insolation should average out every year as Earth wobbles back and forth with the seasons.
Because ice reflects back more solar radiation than land or water, this drives a feedback loop that can plunge the planet into an ice age. In the warm climate of 1 million years ago, the asymmetry in sea ice growth decreased as overall sea ice decreased, and the glacial periods more closely followed the 40,year cycle of obliquity. Further research is needed to incorporate the influences of factors like ocean circulation, glacial dynamics, or carbon cycling, but the study is the first to pinpoint how Milankovitch cycles can spark glaciation through the action of sea ice, a question fundamental to our understanding of the planet and how its climate shifts.
Strelich, L.
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