01
Sep
09

Global Warming: Nature vs. Nurture

Is global warming the result of man’s activities, or natural occurrences? It’s possible, that powerful force that’s melting the glaciers and driving polar bears to extinction is simply an example of ‘what goes around, comes around’. The average life span of a mammalian species is two million years. Maybe, like the dinosaur (who lasted longer than 150 million years), polar bears are just running out of time.

Scientists have hypothesized since the early 1900’s that one of the causes of the ice ages is the changing tilt of the Earth and its elliptical path around the Sun. This was originally called Croll’s theory, fine-tuned by Milankovich, and can be summarized as:

Disturbances of the Earth as a planet by the Moon and the Sun cause a periodic shift in the position of perihelion. The shift has a precessional period of about 21,000 years. The shift affects the distribution of solar heat received by the Earth. The result will be that any given point at a high latitude in the northern hemisphere will be affected accordingly.

Precessing_Kepler_orbit_280frames_e0.6_smaller

180px-Earth_obliquity_range.svg

When the Earth’s orbit and tilt change, Ice Ages happen. Milankovich drew an involved relationship that is accepted (with some discussion) even today:

primer1-fig2

The following article suggests it might be a chicken-or-egg problem: Are the Ice Ages caused by changes in the elliptical orbit, or does the orbit change because the Earth is cooling? Ice melts, fills the oceans (the article suggests that Earth’s increasing temperature results in warmer oceans, despite the cooling effect of ice cubes in the ocean… A discussion for another day), earth tilts.

See what you think.

Warming Oceans May Cause the Earth to Tilt

Global warming and expanding oceans may even cause the earth’s axis to shift

Human activity has widely affected our planet, reshaping surfaces, moving or extinguishing species, and warming the air and water. Now scientists say our reach has been extended even further — warming oceans may even start to shift the Earth’s axis of rotation.

Previously, the effect of warmer water temperatures was thought to be negligible and not strong enough to tilt the earth. But in a new study in Geophysical Research Letters, researchers have found that global warming and the resultant expansion of the oceans could actually shift our rotational axis significantly.

Warming causes our axis to shift because warmer water takes up more space than cooler water, and actually expanding upward and outward as it warms. Increased water volume pushes up onto shallow continental shelves, redistributing weight on the planet and causing the Earth to tilt. According to the report, the north pole of our rotational axis will travel around 1.5 centimeters a year in the direction of Alaska.

That’s not much, in the context of other forces and movement. (The earth wobbles around as much if not more under other influences, including seasonal changes, melting glaciers, and retreating ice sheets.) But it is significant enough that the effect of warming should be taken into account when monitoring the way our axis moves in the future, the researchers report. Moreover, it represents just how strong the effects of human caused global warming can be — even moving the planet itself.

[via New Scientist and Discovery News]


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5 Responses to “Global Warming: Nature vs. Nurture”


  1. September 2, 2009 at 9:02 am

    And therefore the same must be true of cooling. La plus la change, la plus la meme chose. Get used to it.

  2. September 2, 2009 at 6:19 pm

    Et c’est la vie, non? Merci, cher.


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