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Re: [Phys-l] Still More Global Warming



Jim Green wrote:

I am still trying to understand Global Warming -- and the topic just
seems not to go away -- even Gore on Oprah for Pete's sake.

Do I understand correctly? -- sort of?:

Every 23kyr or so the Earth warms up -- and some 12kyr later it
freezes.

Not according to the evidence. See, for instance, <http:// en.wikipedia.org/wiki/Global_warming>

Ocean level varies some 30m in the process.

Well, more like 100 m and mostly in the downward direction (when all the water gets piled in solid form on top of the polar regions.) See, for instance, <http://en.wikipedia.org/wiki/Sea_level_rise>.

It's interesting to note that ocean levels are very rarely as high as they are today and that we seem currently to be in a multi-thousand year period of rare stability. My own not very well fleshed out pet theory is that this rare stability may be something of a prerequisite for the rise of civilization, e.g., you need to be able to establish and depend on ports.

The people in Florida don't much like this; the people in Canada are delighted when
it gets warmer.

Depends on what "this" is!

... But why 23kyrs? Well that is the period of the Earth's precession.

Wrong question => wrong answer. See above.

But why does the precession change the Earth's average
temperature? Yes, the tilt tinkers with weather patterns, but the
cross section toward the Sun doesn't change.

A bit of tutoring would be appreciated.

Bottom line: It's really complicated and not very well understood. I think the best advice is to read up on it yourself and come to your own conclusions. There is no dearth of material available online.

John Mallinckrodt
Cal Poly Pomona