OT: Climate Change, Isaac Asimov and the 1975 TV Guide

Things like orbital motions are technically oscillations, but there is no gain mechanism, no real control loop except for some basic Newtonian mechanics. The sunspot cycle, which seems to have a big forcing influence on our climate, is certainly a very complex control loop.

At least the orbital things are predictable.

Have you seen one of these?

I look at that historical temperature graph and see something that turns off at a low temperature and something that turns on at high temperature. The freezing and melting of the Arctic Ocean fit that description.

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ges in particular. The most recent burst of ice age to inter-glacial altern ations started about 2.58 million years ago, when the continents had drifte d into positions where you had a more or less land-locked Arctic Ocean, and a land mass under the south pole, all of which allowed big enough ice shee ts to build up to appreciably increase the average albedo of the planet - a positive feedback.

and a small regular pertubation - the Milankovitch effect

up with the data in the 1920's - though it took the Greenland and Antarcti c ice core data to really nail it down, and the first 100,000 year ice core from Greenland wasn't extracted until 1989.

ing those vertical lines in the bottom two? I see a hysteresis (bang-bang) controller like this

ut it's not driving those temperatures.

The Milankovitch effect is tiny. What drives the temperatures is the switch from high albedo ice sheets across a lot of the Northern Hemisphere, backe d up by positive feedback from the greenhouse gases CO2 and H20.

The Milankovitch effect just triggers the switch from ice age to interglaci al and back again.

There are cycles going on within an ice age - Dangaard-Oeschger events happ en every 1470 years, and roughly six them form a Bond cycle which ends with a Heinrich event, when a lot of the Laurentide ice sheet slid off into the Atlantic.

If Northern hemisphere insolation is high when this happens, the ice sheet ends up going away, rather than rebuilding, and you have an interglacial.

All horribly messy, but it does repeat every 100,000 years or so.

Only on denialist web-sites.

It's not a control loop - it's just the way the sun-spot cycle works.

They are - in fact - chaotic, though we can make predictions for next few million years

I keep reminding John Larkin about this, but the information doesn't seem to register with him.

Only on denialist web-sites.

The sun-spot cycle doesn't control the earth's climate.

In fact they are chaotic, but the few few million years are predictable.

Except that it doesn't melt during regular interglacials. Most of it seems to have melted during the most recent interglacial (about 125,000 year ago) but that was warmer than most interglacials (including the current one).

Sea level rise went further than it does now, so there was more very-low albedo ocean surface at lower latitudes (where it makes more difference).

Asimov seems to have been doing a bit of hand-waving (which was pretty much all he could do in 1975).

What is the difference between Chemical Physics and Physical Chemistry?

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ts in Review Scientific Instruments for years now, and some of those commen ts have been published there. I have made the point that Phil Hobbs isn't t hat kind of physicist (and more than Win Hill is that kind of chemist - tho ugh Win did give up on his Ph.D. in Chemical Physics when his real interest s became obvious), but there are quite a few blinkered specialists around

- Phil Hobbs, Win Hill and I aren't representative samples.

The Journal of Physics Chemistry is older than the Journal of Chemical Phys ics, and the papers in the former have more chemistry and less math.

I was never motivated to nail it down when I was a graduate student, but my feeling is that physical chemistry is using physical methods - fancy instr umentation - to nail down chemical problems, while chemical physics was phy sicists exercising their skills on chemical problems. There was a lot more statistical mechanics and partition functions in the Journal of Chemical Ph ysics.