Today Earths North Stars are Polaris and Polaris Australis, but a couple of thousand years ago, they were Kochab and Pherkad.Milankovitch (Orbital) Cycles and Their Role in Earths Climate.There are hundreds of different types of cycles in our world and in the universe.Some are natural, such as the change of the seasons, annual animal migrations or the circadian rhythms that govern our sleep patterns.
Fundamental Cycle Driver Of EarthsA century ago, Serbian scientist Milutin Milankovitch hypothesized the long-term, collective effects of changes in Earths position relative to the Sun are a strong driver of Earths long-term climate, and are responsible for triggering the beginning and end of glaciation periods (Ice Ages). These cyclical orbital movements, which became known as the Milankovitch cycles, cause variations of up to 25 percent in the amount of incoming insolation at Earths mid-latitudes (the areas of our planet located between about 30 and 60 degrees north and south of the equator). Over time, the pull of gravity from our solar systems two largest gas giant planets, Jupiter and Saturn, causes the shape of Earths orbit to vary from nearly circular to slightly elliptical. Eccentricity measures how much the shape of Earths orbit departs from a perfect circle. These variations affect the distance between Earth and the Sun. As eccentricity decreases, the length of our seasons gradually evens out. Currently, Earths eccentricity is near its least elliptic (most circular) and is very slowly decreasing, in a cycle that spans about 100,000 years. Over the last million years, it has varied between 22.1 and 24.5 degrees perpendicular to Earths orbital plane. The greater Earths axial tilt angle, the more extreme our seasons are, as each hemisphere receives more solar radiation during its summer, when the hemisphere is tilted toward the Sun, and less during winter, when it is tilted away. Larger tilt angles favor periods of deglaciation (the melting and retreat of glaciers and ice sheets). These effects arent uniform globally -- higher latitudes receive a larger change in total solar radiation than areas closer to the equator. It was last at its maximum tilt about 10,700 years ago and will reach its minimum tilt about 9,800 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. As ice cover increases, it reflects more of the Suns energy back into space, promoting even further cooling. 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. 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 13,000 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.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |