Global Warming/Cooling and Earth's Axis

[Metal Minister]

I have been pondering this for some time, and though the following is of course, anecdotal, it summarizes my question.

As a child, I remember that winter tended to begin around late October. I can still remember having snow on the ground most times when my parents would take me trick or treating. And by early March the snow would be gone. As I've gotten older I've noticed a shift. Winter doesn't seem to arrive until late November or into December, and here it is several days into March and still snowing. Again I understand this is anecdotal and not explicitly scientific, but bear with me please.

Is it at all possible, that the pattern shifts we are seeing in earth's climate (IE fears of ice ages in the 70's, fears of the planet being cooked to a cinder through the 90's, etc) be more closely linked to the planet's axis than is being studied? Is it possible, since we know the planet does not orbit perfectly and has a "wobble" which actually gives us our seasons, that this wobble has shifted, even slightly, to create these new patterns? I know while in school, we were taught that one day the wobble would become so bad that the earth would tear itself apart, or that it would even out, and the seasons would disappear. What say you?

http://en.m.wikipedia.org/wiki/Milankovitch_cycles

 

[Oafman]

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I have been pondering this for some time, and though the following is of course, anecdotal, it summarizes my question.
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[FONT=arial, sans-serif]As a child, I remember that winter tended to begin around late October. I can still remember having snow on the ground most times when my parents would take me trick or treating. And by early March the snow would be gone. As I've gotten older I've noticed a shift. Winter doesn't seem to arrive until late November or into December, and here it is several days into March and still snowing. Again I understand this is anecdotal and not explicitly scientific, but bear with me please.[/FONT]

[FONT=arial, sans-serif]Is it at all possible, that the pattern shifts we are seeing in earth's climate (IE fears of ice ages in the 70's, fears of the planet being cooked to a cinder through the 90's, etc) be more closely linked to the planet's axis than is being studied? Is it possible, since we know the planet does not orbit perfectly and has a "wobble" which actually gives us our seasons, that this wobble has shifted, even slightly, to create these new patterns? I know while in school, we were taught that one day the wobble would become so bad that the earth would tear itself apart, or that it would even out, and the seasons would disappear. What say you?[/FONT]

Milankovitch cycles - Wikipedia, the free encyclopedia

[FONT=arial, sans-serif]Axial precession (the wobble over 26,000 years) has a huge impact on the Earth's climate, as does the changing eccentricity of the Earth's orbit, and a bunch of other hugely complicated things which determine Earth's exact position relative to the Sun. [/FONT]

[FONT=arial, sans-serif]But rest assured, climate scientists have always taken all of these things into account. Actually, this is part of the reason that climate science is so technical, and so difficult for us laymen to get our heads around. [/FONT]

[FONT=arial, sans-serif]There are a couple of things you wrote which aren't quite accurate: [/FONT]

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since we know the planet does not orbit perfectly and has a "wobble" which actually gives us our seasons

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[FONT=arial, sans-serif]Nothing in nature is on a 'perfect' orbit (ie completely circular and equatorial); every orbiting body is at least slightly off perfection, some more than others. But to be clear, it's not axial precession (the wobble) that causes seasons; they are simply the result of the fact that the Earth is tilted on its axis. This tilt means that for half of the year the northern hemisphere is exposed to more sunlight, and for the other half the southern hemisphere gets more. [/FONT]

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I know while in school, we were taught that one day the wobble would become so bad that the earth would tear itself apart, or that it would even out, and the seasons would disappear.

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[FONT=arial, sans-serif]Well, I have never heard the idea of the Earth tearing itself apart, and I can't see any way in which that could happen, whatever the degree of axial precession. I *think* (don't quote me on this) that axial precession is a direct product of our axial tilt, so on that basis I don't really think it's changing, certainly not by much anyway. Hopefully one of our resident physicists will pop in and confirm this.[/FONT]

 

[essentialsaltes]

Is it at all possible, that the pattern shifts we are seeing in earth's climate be more closely linked to the planet's axis than is being studied?

No.

Is it possible, since we know the planet does not orbit perfectly and has a "wobble" which actually gives us our seasons, that this wobble has shifted, even slightly, to create these new patterns?

The tilt of the axis is what creates seasons. It has not changed appreciably.

The 'wobble' [i.e. precession] of the axis also has an effect on climate. This is the Milankovitch Cycle you referenced. The changes from precession are very slow, happening over timescales of thousands of years. It exists, but it cannot be a signficant source of current climate change.

I know while in school, we were taught that one day the wobble would become so bad that the earth would tear itself apart, or that it would even out, and the seasons would disappear. What say you?

Neither. The earth is more or less a free body spinning in space, so the situation is fairly stable. The effect of tides and the moon do cause a slight change in the precession, but it is over timescales of millions and billions of years:

"According to Ward, when, in about 1,500 million years, the distance of the Moon, which is continuously increasing from tidal effects, has increased from the current 60.3 to approximately 66.5 Earth radii, resonances from planetary effects will push precession to 49,000 years at first, and then, when the Moon reaches 68 Earth radii in about 2,000 million years, to 69,000 years. This will be associated with wild swings in the obliquity of the ecliptic as well. Ward, however, used the abnormally large modern value for tidal dissipation. Using the 620-million year average provided by tidal rhythmites of about half the modern value, these resonances will not be reached until about 3,000 and 4,000 million years, respectively. However, due to the gradually increasing luminosity of the Sun, the oceans of the Earth will have vaporized long before that time (about 2,100 million years from now)."

 

[Oafman]

ES, is it the case that precession is caused by our axial tilt? I think I once saw some demonstration with a gyroscope to show this, but I could easily be wrong. Or is it the product of gravity from other bodies, or some other cause? If our axis was north-south, would we still wobble?

 

[essentialsaltes]

ES, is it the case that precession is caused by our axial tilt? I think I once saw some demonstration with a gyroscope to show this, but I could easily be wrong. Or is it the product of gravity from other bodies, or some other cause? If our axis was north-south, would we still wobble?

It's not due to the tilt per se, but it's involved. Since the earth spins, it's fatter around the equator. Because of the tilt, the sun and moon pull in an off-center way on the earth's equatorial bulge. That twisting torque is the main cause of the precession. If the moon and all the other planets were all in the ecliptic plane, and the earth's axis was perpendicular to that plane, then precession would be much reduced. Remaining effects would come from tides or earthquakes that change the earth's moment of inertia, or other gravitational tugs from out of the ecliptic from asteroids or distant stars or something. Probably very small effects.

(the analogy with the gyroscope is valid, but subtle. A gyroscope that stands 'straight up and down' doesn't precess. If it's at an angle, gravity acts on the center of mass to make it want to fall over, exerting a torque that causes the precession. So in this case, it's very much the tilt (with respect to a uniform gravity field) that causes the precession. But there's no 'straight up and down' in space. It's that bulge that creates some tidal torque on the earth to make it precess. If the earth were a perfect, uniform sphere, it wouldn't precess. It would just spin in free space.)

 

[Oafman]

Thanks ES, it was the equatorial bulge aspect that I was missing