Technotranscendence wrote:
>
> On Tuesday, March 21, 2000 8:29 PM Michael S. Lorrey retroman@turbont.net
> wrote:
> > > While I agree with what Billy is saying here for the most part, Earth is
> not
> > > as tame as some might think. Even now, some climatists have proposed
> that
> > > the Earth has completely frozen over several times in its history and
> that
> > > rapid climate change followed by stable periods might be the rule. (See
> > > "Snowball Earth" by Paul F. Hoffman and Daniel P. Schrag in _Scientific
> > > American_ 2000 Jan for the former (now at
> > > http://www.sciam.com/2000/0100issue/0100hoffman.html) and "Rapid Climate
> > > Change" by Kendrick Taylor in _American Scientist_ 1999 July-August.)
> This
> > > is by no means like a highly elliptical orbiting planet scenario, say,
> of
> > > Poul Anderson's _A Circus of Hells_, or the OnOff Star scenario in
> Vernor
> > > Vinge's _A Deepness in the Sky_, but it should give one pause.
> >
> > Actually, the basis of the earth's deep freeze occilations were due to
> > the travels of the continents. With most continental areas on the
> > equator and periods of heavy vulcanism, such periods were a natural
> > consequence. During this period, antarctica was not at the south pole,
> > so it was not sequestering 3/4+ of the ice on the planet. No land locked
> > ice cap meant sea levels 200 meters higher than they are now. Higher
> > pressure at the bottom of the ocean allowed greater sequestration of
> > methane hydrates under the ocean floors, and thus less methane in the
> > atmosphere(methane is about 6x more effective as a greenhouse gas) The
> > loss of methane causes a cooldown, increases in ocean ice caps, and
> > glacial buildup, the vulcanism of the newly spreading continents kept
> > the dust levels high. The CO2 concentrations and global climate
> > temperature are linked only by a log relationship, such that CO2
> > concentrations variances at low levels have wide impact on temperature
> > fluctuations, but as concentrations increase, this effect falls off.
> > According to my geologist cousin, essentially if we dropped the
> > atmospheric CO2 levels by 50%, we'd drop global temps by 20-30 degrees,
> > while if we increase them by 50% from the current levels, global temps
> > will go up by less than 5 degrees.
> >
> > According to Drew, the antarctic ice cap (the large one, not the small
> > one on the coast) is stable over the long term, and its been that way
> > since the last major extinction/possible impact period of 22 million
> > years ago. The winds flow outward from the cap (the catabatic winds),
> > and are replenished from cold upper atmospheric air that drops down from
> > high altitudes (and the higher altitudes are cooling down while the
> > surface levels of temperate climates is warming up.) The Greenland ice
> > cap may collapse, and the arctic ice cap will most likely vanish in a
> > few decades. If the Greenland ice cap collapses, it will result in sea
> > level rises of 3-9 meters at most. If only the arctic ice cap melts
> > away, there will be little or no sea level changes, because that ice is
> > already floating in the water. Any rise will simply be due to thermal
> > expansion of the oceans.
>
> Michael's point being? I was merely trying to focus attention on some
> recent work that shows the Earth's climate is not as stable as some might
> think. The actual instabilities now being theorized are much greater than
> was once thought. E.g., the "Snowball Earth" scenario posits that the
> oceans completely froze over to a depth of about a kilometer and surface
> temperatues of about -50 degrees C. This is a much more drastic than former
> ice age scenarios. (Of course, according Hoffman and Schrag to it did not
> happen all that often either.:)
THe point being that so since such deep freezes are the apparent result
of the positions of the continents with regard to the poles. Given such
slow moving phenomena, I doubt that any intelligent species would be
wiped out by such a change, they would see it coming from a long ways
away. Given also the theories that planets need occasional catastrophes
to keep spinning the genetic slot machine in order to come up cherries
at least once (intelligence).
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