Knowledge is power. . . .
Ice ages, tropical periods & the always changing climate...
A study on variations of tilt of earth's axis, variations of the eccentricity of earths orbit and the precession, or 'wobble' of the earths axis
Sources
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www.universetoday.com/47176/earths-axis/and
sciencing.com/can-earths-rotation-tilt-affect-global-climate-23082.htmland
earthobservatory.nasa.gov/features/Milankovitch/milankovitch_2.php-----------------------------------------------------------------------------------
The three variables Eccentricity ...deviations in the Earth’s elliptical (elongated) orbit from a symmetrical, circular orbit.
Obliquity ...The angle of the Earth’s axis is referred to as its obliquity. If the obliquity of the Earth equaled zero (no tilt at all), the Earth would have no seasons because no variation in temperature would occur. During the winter, the Northern Hemisphere (where most of the Earth's landmass is) is tilted away from the sun, receiving solar radiation at more of an angle. This results in colder temperatures and more extreme temperature changes. During the summer, the landmass is tilted toward the sun, resulting in warmer temperatures and less extreme changes. The cycles of obliquity last 40,000 years and the tilt itself varies from 22 to 24.5 degrees.
PrecessionPrecession describes the slight wobble in the Earth's axis caused by the moon and other planets in the solar system. Precession cycles change the times of perihelion and aphelion, causing increases and decreases in seasonal contrast. When a hemisphere is oriented toward the sun at perihelion, extreme differences in seasons result, and this pattern is reversed in the opposite hemisphere. The Earth’s axis wobbles in cycles that last 26,000 years.
Within the past few centuries, improvements in both scientific instruments and more comprehensive observations of the heavens have also helped astronomers to determine (with extreme accuracy) what the nature of Earth’s orbit is.
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Information from above sources (
my comments bracketed);
Changes in orbital eccentricity affect the Earth-sun distance.
Eccentricity measures deviations in the Earth’s elliptical (elongated) orbit from a symmetrical, circular orbit.
When the orbit is highly elliptical, the amount of insolation received at perihelion would be on the order of 20 to 30 percent greater than at aphelion, resulting in a substantially different climate from what we experience today.
If eccentricity is zero, an orbit is circular.
As an orbit becomes more elliptical, its eccentricity gets closer to one.
The two most important distances between the Earth and sun are described as perihelion, or the point in Earth's orbit when it's closest to the sun, and aphelion, or when its the farthest away.
The difference between these distances is called eccentricity. The Earth’s eccentricity varies from 0.0005 to 0.06, and the larger this number, the more solar radiation reaches the surface of the Earth.
Eccentricity cycles last between 90,000 to 100,000 years.
Currently, a difference of only 3 percent (5 million kilometers) exists between closest approach (perihelion), which occurs on or about January 3, and furthest departure (aphelion), which occurs on or about July 4.
This difference in distance amounts to about a 6 percent increase in incoming solar radiation (insolation) from July to January.
Earth is 5 million kilometers (3 million miles) farther away from the sun at aphelion than it is at perihelion.
Currently, summer in the Northern Hemisphere occurs near aphelion, so differences in temperature are less extreme and the climate is mild.
Sixteen thousand years ago, winter occurred in the Northern Hemisphere at aphelion, and there were extreme differences in temperature.
The shape of the Earth’s orbit changes from being elliptical (high eccentricity) to being nearly circular (low eccentricity) in a cycle that takes between 90,000 and 100,000 years.
[ This extremely long eccentricity cycle affects the earths climate. There's nothing we can do to change this. ]
As the axial tilt increases, the seasonal contrast increases so that winters are colder and summers are warmer in both hemispheres.
Today, the Earth's axis is tilted 23.5 degrees from the plane of its orbit around the sun.
But this tilt changes. During a cycle that averages about 40,000 years, the tilt of the axis varies between 22.1 and 24.5 degrees.
Because this tilt changes, the seasons as we know them can become exaggerated.
More tilt means more severe seasons—warmer summers and colder winters; less tilt means less severe seasons—cooler summers and milder winters.
It's the cool summers that are thought to allow snow and ice to last from year-to-year in high latitudes, eventually building up into massive ice sheets.
There are positive feedbacks in the climate system as well, because an Earth covered with more snow reflects more of the sun's energy into space, causing additional cooling.
[ Another very long cycle that we can't change ]
Precession
Changes in axial precession alter the dates of perihelion and aphelion, and therefore increase the seasonal contrast in one hemisphere and decrease the seasonal contrast in the other hemisphere.
[ Then we have axial precession. Another variable that affects our climate over long periods.
Consider how all three of these orbital and rotational variants may affect earths climate when they interact together in ways that may create extremes... like a completely tropical planet or a completely ice covered planet etc. ]
The combined effects of the cycles of eccentricity, obliquity and precession cause changes in weather patterns on Earth.
Scientists believe that these differences may account for the movement of glaciers as they repeatedly advance and retreat across the continents, affecting the Earth’s long-term climate cycles.
Milankovic Cycles are slow variations in the Earth's rotation and tilt.
These cycles include changes in the shape of the Earth's orbit, as well as the angle and direction of the axis on which the Earth rotates.
These variations occur slowly and regularly, causing cycles of change in the amount of solar radiation (heat) that reaches the Earth.
Scientists believe these cycles may affect long-term weather patterns, or climate.
Needless to say, Earth’s rotation and orbit around the Sun are not as simple we once thought.
It’s only been with time that the true nature of our planet’s inclination and movements have come to be understood. And what we know is that they lead to some serious variations over time – both in the short run (i.e. seasonal change), and in the long-run.