From: Mike Lorrey (mlorrey@datamann.com)
Date: Mon Feb 04 2002 - 19:49:41 MST
Damien Raphael wrote:
>
> On Mon, Feb 04, 2002 at 02:25:32PM -0500, Mike Lorrey wrote:
>
> > Astronomers and astrophysicists also contribute, with explainations like
> > the Malenkovich Cycles, which have a far greater impact on climate
>
> Milankovitch, for anyone who wanted to websearch for more information.
>
> > change than any other single factor (somewhere between 1/4 to 1/2 of all
> > influence, in fact) but you'll rarely see one of these chicken little
>
> 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.
Actually, coupling Milankovitch cycles with plate tectonic evolution of
oceanic currents, one can explain it all. 16 million years ago,
Antarctica broke away from South America, and the circumpolar current
began forming, isolating the continent from the rest of the world's
weather and operating a thermal vortex as a natural refrigeration system
whose function is to ventilate greater quantities of heat from the
southern ocean to space. This current stabilized about 14 million years
ago, and since then the southern ice cap has been stable ever since. At
this point in time, the 'ice line', which is the altitude at which ice
forms, is generally about 200 meters below the bedrock under the ice cap
around Antarctica.
Variations in the Milankovich cycles can, in fact, also explain the
cooling and warming trend that has stretched from the middle ages to the
present. The peak of the 'little ice age' was around 1300 or so, when
Norse colonies in Greenland were wiped out, and things have warmed a bit
since then, not just in the past century, entirely in keeping with
Milankovitch's predictions.
>
> 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.)
>
> Hmm, that gives me an idea... if the Greenland and Antarctic ice caps
> melted from warming, there might be a countereffect of CO2 reacting with
> all that fresh rock.
But Antarctica will require a warming of around 15 degrees at a minimum
before it melts.
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