From: steve (steve365@btinternet.com)
Date: Tue Feb 05 2002 - 10:15:45 MST
----- Original Message -----
From: "Damien Raphael" <phoenix@ugcs.caltech.edu>
To: <extropians@extropy.org>
Sent: Monday, February 04, 2002 8:01 PM
Subject: Re: CLIMATE: Cooling, not warming...
> Note the cycles, being astrophysically constant, explain only why the
> individual ice ages come and go. They don't do anything to explain why
> we suddenly started having ice ages a few million years ago, or why the
> overall trend for the last few tens of millions of years had been a
> cooling trend.
I think the best explanation for this (the most parsimonious one) is plate
tectonics. For the bulk of the period you mention the Antarctic continent
has been parked over the South Pole. As well as acting like a giant
refrigerator this has locked up masses of fresh water and made the whole
planet both colder and drier. At the same time tectonic movement around the
Arctic has effectively isolated that ocean from the rest of the world's
oceans (there are only two deep water passages into the Arctic, both very
narrow). The result is it's very cold and instead of warming the circumpolar
region keeps it in the "arctic" climate we know today. That is why an ice
age is the default climate setting at this (geological) moment. It only
takes a few years of unusually heavy winters and cold summers, given the
conditions in the holarctic, to raise the planet's albedo substantially and
lower the average temperature by enough to start an ice age. After that it
doesn't take long at all for the fully fledged ice age conditions to appear.
When an interglacial arrives it takes longer for all that ice to melt. Steve
Davies
> The best explanation for _that_ which I've seen is the Himalaya
> hypothesis: the continuous and large supply of uplifted fresh rock
> has been scrubbing CO2 out of the atmosphere. (CO2 and rain react with
> rock in the natural weathering process.)
>
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