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.:)
Not that Michael's above points are wrong. I don't want to debate global
climate changes anyway. My only reason for bringing up this work was to
show that life has survived through some pretty serious sh*t here on Earth,
which gives me hope it has done so elsewhere.
This still doesn't mean there are lots of sentients out there, and I fear
the Great Silence attests to their nonexistence.
Prove me wrong! Please!
Daniel Ust
http://mars.superlink.net/neptune/
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