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Precessing_Kepler_orbit

Natural tilts in earth’s axis cause ice ages, says Harvard geophysicist


“The idea that slight shifts in Earth’s axis might have been enough to trigger the ice ages is a century old.”

“But a Harvard earth sciences Professor Peter Huybers has finally proved it, using computer models to test competing ideas – and finding that earth’s tilting axis is the only one that works.”

In a paper published in the journal Nature, Huybers points out that the way in which the Earth’s axis of rotation spins controls our climate. The process involves two cycles, one lasting about 10,000 years, the other roughly 40,000 years.

When the two cycles align ‘correctly’, the glaciers retreat rapidly, says Huybers.  At the other extreme, glaciers advance.

‘These periods of deglaciation saw massive climate changes,’ Huybers said. ‘Sea level increased by 130 meters, temperatures rose by about 5 degrees C, and atmospheric CO2 went from 180 to 280 parts per million.’

Did you catch that? Temperatures rise, CO2 levels rise, and sea levels rise, all due to a NATURAL cycle!

‘We know with greater than 99 percent confidence that shifts in earth’s axis are among the factors that contribute to deglaciation,’ says Huybers.

Unfortunately, Huybers then veers into political correctness, saying that CO2 and increased summer radiation are “both expected to push the climate system toward less ice.”

He does concede, however, that “it could also be that orbital forcing causes a rise is atmospheric CO2.”

Make sure you catch that one, too. “It could also be that orbital forcing causes a rise is atmospheric CO2.”

Earth precessional movementThe idea that the shorter 10,000-year cycle could trigger an ice age has been around for centuries, but was refined by a young Serbian engineer by the name of Milutin Milankovitch.

Orbital forcing is the effect on climate of slow changes in the tilt of the Earth‘s axis and shape of the orbit. These orbital changes change the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes (from 400 to 500 Wm−2 at latitudes of 60 degrees). In this context, the term “forcing” signifies a physical process that affects the Earth’s climate.

This mechanism is believed to be responsible for the timing of the ice age cycles. A strict application of the Milankovitch theory does not allow the prediction of a “sudden” ice age (rapid being anything under a century or two), since the fastest orbital period is about 20,000 years. The timing of past glacial periods coincides very well with the predictions of the Milankovitch theory, and these effects can be calculated into the future.

Milankovitch developed a mathematical theory to describe the climates on Earth, Mars, and Venus, at different latitudes, at any time.

A tall order. No one had ever calculated the distribution of sun-light over the wobbling, tilting planets.

Due to the success of his calculations, the ice-age cycle, controlled by a totally natural process called equinoctial precession, is now known as the Milankovitch cycle. Every geology student in the world has probably heard of it.

Precession-of-the-Equinoxes

Precession of the Equinoxes – Copyright Robert W Felix

Our axis of rotation wobbles like a top, tracing a clockwise circle around true north. Called axial precession, it takes about 25,800 years to complete the full circle.

Precession occurs, say scientists, because the sun and moon exert a gravitational pull on the earth’s equatorial bulge. Rotating objects such as tops and gyro­scopes also precess. So does Mars.

To understand this phenomenon, picture the globe spinning around a long stick (the axis of rotation). Tilted away from true north, the top of the stick traces a circle around the North Pole, while the bottom makes an identical trip around Antarctica.

As our axis of rotation moves, it constantly points toward a different star, painting an imaginary circle on the heavens. The process of painting that circle on the celestial ceiling is called precession of the equinoxes.

Sir Isaac Newton solved yet another aspect of the riddle. The earth’s orbit around the sun also revolves, said Newton. Our orbit revolves backward, or counter-clock-wise. Precession of the equinoxes, the time it takes to paint that imaginary circle on the heavens, therefore takes about 23,000 years. It’s like waiting for someone on a merry-go-round; you’ll reach them sooner if you walk toward them.

   Today when viewed from the northern hemisphere, the stars seem to rotate around Polaris, at the end of the handle of the Little Dipper. That’s why it’s called the Pole Star, because the North Pole points toward it.

Gyroscope_precessionBut in 2,000 B.C. the North Pole pointed toward a spot halfway between the Little Dipper and the Big Dipper. In 4,000 B.C. it pointed toward the end of the handle of the Big Dipper. Twelve thousand years from now it will point toward a different star, toward Vega, and in 23,000 years it will point toward Polaris again.

Except for Huybers’ contention that we’re headed for less ice (I think we’re headed for more), it’s heartening to see confirmation of what I’ve been saying all along.

Resources:

Precession

Natural tilts in earth’s axis cause ice ages, says Harvard geophysicist

Orbital forcing

Scientist predicts earth is heading for another Ice Age

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