From: tobis@meteor.wisc.edu (Michael Tobis)
Newsgroups: sci.environment
Subject: Re: Gallup Poll on Global Warming
Date: 8 Sep 92 20:10:12 GMT
Distribution: usa
Organization: University of Wisconsin, Meteorology and Space Science

In article <6183@taurus.cs.nps.navy.mil> rovero@oc.nps.navy.mil (Josh Rovero) writes:

An argument somewhat speciously confusing three issues: whether there has been
sea level rise in the recent historical past, whether there has been global
temperature change in the recent historical past, and whether either of these
changes is anthropogenic in origin.

>10.  There is no absolute sea level through time.  The concept of absolute
>position appears to underlie various forecasts that sea level must rise in
>significantly in the near future.  These forecasts assume that only
>anthropogenic changes are taking place, or are about to take place, and that
>without human influence there will be no change.  A recent book (Crowley
>and North 1991) emphasizes the importance of using the record, longer than
>the instrumental record of the latest century, as a base for making 
>projections into the future.  Longer-than-instrument datasets show clearly
>that other changes have been taking place, and therefore one cannot know in
>advance how the system will react during the interval of increased
>anthropomorphic influences; some other factor may be more important.

>In his conclusions, Tanner says that since the steady rise in sea level
>since 1750 apparently was *not* caused by human activity, and since it
>is not clear that this trend is over, that any "global warming"
>demonstrated for the last 50-100 years MIGHT very well be a continuation
>of this trend.

This is a VERY long way from your previous claim that no global warming
is confirmed. This is about long term sea level trends. 

By the way, Crowley & North also say the following (chapter 14):

	"Some time in the next century the earth's climate is expected
	to undergo a major warming as a result of increasing concentrations
	of carbon dioxide and other trace gases. ... A future greenhouse
	warming therefore represents a climate change of very significant 
	levels. ... [It] represents a major climate change, which will
	occur at a rate  comparable to or exceeding any known to have occurred
	in earth history. The magnitude and duration of the event is
	significant even on geologic scales. Since there are no completely
	satisfactory analogs for the warm atmosphere-cold pole combination
	the future climate may represent a unique climate realization in
	earth history."

>He also adopts a reasonable prognosis, based on the historical record, of
>a 1-3 meter drop in sea level starting in a few centuries.

>There are several other articles and exchanges of letters in the AMS 
>Bulletin that relate to global climate change.  June and July 1991,
>plus V71 (1991), pgs 288-299 and 1291-1304.  Spirited debate, no
>consensus.  That's just the way it is.

There's spirited debate about evolution vs. creation, too. That doesn't
mean that there is no consensus among informed opinion. (This is an
extreme example to make the point. I do not wish to imply that the greenhouse
issue is as completely closed.) Citing polls indicating skepticism on detection
of the greenhouse signal in the record, ignoring similar polls indicating
agreement approaching unanimity on the expectation that the signal WILL emerge 
soon, is misleading and irresponsible.

There is plenty of room for debate on the past record, but you have agreed that
there are 4 extra watts of radiative flux to account for in the next few
decades, and I have yet to see you account for why you feel they will have
no significant effect. 

Journalists who confound 1) the debate on the past record with 2) the
consensus about a serious problem (due to rather simple radiative equilibrium
considerations) do the public a great disservice, and this was my original
point. 

I repeat: Have you read the IPCC report? (While heavy reading for the lay
public, it is light reading for a meteorologist, and I think every professional
in a climate related field should read it.) I firmly believe it represents
the consensus of opinion in the field. There is not unanimity on all points,
but there is general agreement that anticipated anthropogenic forcing is
comparable in rate and magnitude to the largest natural changes in forcing.

Thanks for the references. I will look into them.

mt