Re: The warming trend & extinction events & ex-astra expl.

p3voices (
Tue, 16 Jul 1996 23:33:34 -0400

Timo Naruma writes:
8) Now we have three explanations for these trends, that are not exclusive: Sun's
variability, Milankowicz cycles, and asteroid or comet hits. All that we now from
the end of the ice age points as to my mind that the impact theory is the
although the other two may have had some influence.

9) There is still a fourth variable: interstellar clouds. But we know too little
about them to say anything more than that they can cause an ice age.

P3 replies:

I count that you can support four explanations for the end of the ice age and other
recent climatic changes (I could imagine a few more non-absurb explanations, but
let's leave that to a later discussion). I still suggest that you pick just one
(not two or three) as +the+ explanation. Well I agree that a meteor strike could
have caused a rapid climactic change, I have a very hard time supporting that
explanation without the supporting "smoking gun" data supporting it (a properly-
dated large-enough crater, shocked-rocks, debris fields, etc)

Personally, within the realm of speculation, I doubt the edge of interstellar gas
clouds would have a well enough defined "edge" to cause a rapid climactic change.
If the edge of the cloud were gradual, or vague, or rippled, the solar radiation
striking the earth would have been just gradually reduced, perhaps over sevral
scores of years or hundreds of years. Even given a strong climactic feedback loop,
I doubt this could have caused a sudden cessation of the ice age. I have seen zero
astronomic data suggesting that this gas cloud has an abrupt "edge". Until then,
let's discount this theory.

That leaves the Sun's variability or Milankowicz cycles as possible causes. The
latter, to me, is unappealing, as I agree with you that it probably could not have
led to a rapid enough cessation of the ice age.

As for the Sun's variability, this explanation is appealing, but suffers from the
same problem as the Niroma meteor-strike hypothesis - a dearth of data.

Ah well,....the search for the cause continues.