[NatureNS] Global warming -- debate heats up

Date: Mon, 27 Nov 2006 03:12:33 -0400
From: Stephen Shaw <srshaw@dal.ca>
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may soon be confronted with... a runaway glaciation
Hi Dave,
I've deleted the front end of your message since I think we may have 
flogged it
to death by now. No, I didn't suspect that you were an agent of the tobacco
lobby.
On the rest, I think you turned up a very interesting site that you reference
below (aip, American Inst of Physics). I've read the link you provided, and in
turn a couple of its links, to equally useful related topics, see below.

>    The Smithsonian, for a magazine that covers the field from 
> aardvark to zymosis, does a surprisingly good job of informed and 
> unbiased reporting. Their take of the day, variable and possibly 
> cooling, is quite restrained compared to comments attributed to a 
> prominent climatologist at about this time; copied and pasted from 
> text at
> http://www.aip.org/history/climate/cycles.htm#M_52_
> these comments, shown within quotation marks, being--
> Since the Milankovitch cycles could be computed directly from 
> celestial mechanics, one could project them forward in time, as 
> Emiliani had done in 1966. In 1972, presenting more Caribbean cores, 
> he again advised that "the present episode of amiable climate is 
> coming to an end." Thus "we may soon be confronted with... a runaway 
> glaciation." However, he added, greenhouse effect warming caused by 
> human emissions might overwhelm the orbital shifts, so we might 
> instead face "a runaway deglaciation."(25)      These passages 
> enclosed in quotation marks were apparently published in Science i.e. 
> Emiliani, Cesare (1972). "Quaternary Paleotemperatures and the 
> Duration of High-Temperature Intervals." Science 178: 398-401.
>    These statements also give some insight into the uncertainty that 
> may bracket climatic predictions. There is a lot of ground between 
> confidence limits that are described as runaway glaciation and 
> runaway deglaciation.
> Yours truly, Dave Webster, Kentville

The fact that Emiliani was a persistent and worthy advocate of the 
importance of
Milankovitch cycles (Milankovitch's bulldog?) at the time you mention, when
others thought the effects of these cycles were small or negligible is
confirmed in the post.  He was important historically in keeping the ideas
alive.  Science was a major journal in the 1970s, as now, and spreading your
bets on both horses back then may have been a respectable pitch.  But is it so
in the 2000s?  If you read the AIP links from your own quoted URL, the answer
would be "no".  All bets now seem to be on the second horse "a runaway
deglaciation" or at least on a future hot saddle.

A related read is given on the links in the right margin of the article, to
<GCMs> or General Climate Models, written from the same .aip. outfit you quote
(American Institute of Physics, AIP). This takes you through a 
fascinating even
longer historical account on the development of computer models of the
atmospheric circulation and climate, then coupled atmosphere-ocean models.
This recounts how climate models started simple in the 60s-70s, and progressed
up until now to ever greater complexity on faster computers. These models made
a mixture of realistic and unrealistic predictions, on the way to 
achieving the
current state of the art which is still troubled by the difficulty of 
modelling
the effects of clouds.  At the end, though, the conclusion for the early 2000s
is that all of the various models of the global climate concur that an 
increase
in average temperature is likely in the relatively short term, in the range of
a few degrees above current levels.  The general benchmark that they use to
predict this is a doubling of CO2 from the historical average (current values
are much higher already than anything in the last million years or so, which
takes in many cycles of glaciation-deglaciation where the CO2 concentration
cyclically doubled, but still didn't reach current levels).  Cooling 
might have
been an intellectually respectable possibility in the 1970s/Science, but no
serious modellers (apparently) are predicting global cooling in the 
2000s, only
various levels of warming, maybe 5 degrees being the upper limit, 1 degree the
lower.  The gradual oscillating increase in CO2 to the current historically
high levels in the atmosphere over ~20 years in Hawaii is spectacularly clear,
and documented in another AIP link.
http://www.aip.org/history/climate/co2.htm
for a shorter comment by the writer/editor of these screeds, AIP director
Spencer Weart, see
http://www.aip.org/history/climate/SWnote.htm
and for the shortest read, click on his link <my page for the American 
Physical
Society> at the end of the last post above, which downloads a 1-page PDF file,
strong on carbon advocacy. He's a good writer.

Re. Bruce Stevens' related contribution which both Patrick Kelly and I
politely queried, none of these AIP documents mention the hockey stick model,
pro or con, so Bruce may be right about that -- not clear from these readings.
Following Patrick, I too would be interested in recent articles or links that
say this bent stick model is flawed.  Secondly, if Bruce meant to imply the
corollary that I thought he might be making, but didn't state (that the
publicized current and near-term predicted global warming is a matter that is
so far unresolved), that corollary is emphatically denied by all the above
stuff that Dave found: simplifying, it's hotter now overall, and going to get
hotter in the near term, on the various models summarized by Weart, that
apparently incorporate real earth data.  On a third question of whether the
ClimateReal** site that I mentioned is a dependable one, about which Bruce was
negative, Weart gives a link to it, endorsing it. (**I think that was the name
but can't easily check on this clumsy webmail pgm I'm using at home).

Thanks Dave, the AIP site and the links from it were very informative and
readable.  Re. your earlier post, the history of modelling (the AIP 
link) should
tell you why it is not useful to try to predict causal interactions between
temperature and CO2 on the basis of simple thought experiments after reading a
graph -- there are many other variables involved plus climate history, 
and even
the two variables you consider may interact in a complex way anyway.  So it is
impenetrable to unravel unless you model all this stuff to see the two CO2
states,
and how one develops into the other (running it on a supercomputer for a
year in one of the cases quoted by Weart).
Steve


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