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Re: Human vs. natural influences on the environment
snark@swcp.com wrote:
>
> In article <32244d4d.176361891@nntp.st.usm.edu>,
> Harold Brashears <brshears@whale.st.usm.edu> wrote:
> >"D. Braun" <dbraun@u.washington.edu> wrote for all to see:
> [snip]
>
> >>Actually, the global warming issue isn't an issue any longer, but a
> >>reality. The recent IPCC report settled that.
>
> >You think so? I tend to disagree with you. There has been some
> >controvery concerning that report, with some of the participants
> >claiming that the body of the report changed to conform to a more
> >alarmist summary. The administrators state that the changes were made
> >only in response to the initiatives by some of the other participants,
> >but that does not change the fact that some object to portions of the
> >report.
>
> I have not seen a report that any of the participants had
> objected--rather, it was outside critics objecting. I'd be interested
> in seeing such an article.
>
I believe the history is as follows. The chapters were written by the
lead authors for each chapter after consulting many scientists, all of
whom are listed in the Report. There was time for commentary, and
eventually a meeting in Madrid. At that meeting, Chapter 8, the
one about which the controversy was raised, was criticized as not being
sufficiently clear. I have read now read Chapter 8. I think it
clearly reflects what has been said about the main author Benjamin
Samter. He seems an absoultely `straight arrow', but he is so
concerned with completeeness and bringing attention to every facet of
the subject of detection, that it is easy not to notice that the chapter
actually does draw a conclusion. Even in the modified form, this is
true. I conjecture that at Madrid, some of the other scientists
objected that the forest was lost in the trees, and suggested that the
basic conclusion be stated more emphatically at the end of the chapter.
Samter agreed to this and made the changes he was asked to make by his
peers. This then led to an accusation by some people, some of whom
were associated with a lobbying group for the fossil fuel industry, that
the end of the report was changed to deemphasize the uncertainties for
political reasons. However, to my mind, I don't think any fair minded
person who actually reads that chapter can come to that conclusion. The
uncertainties are discussed in enormous detail. Despite this, one of
the main conclusions is that the latest information and methods, for
example the use of models incorporating greenhouse warming and aerosols,
do support the contention that human activieties have affected climate.
>In any case, if I remember correctly, the report forcasts an average
> >global 0.5 C change in the next hundred or so years. I still do not
> >see that, even if all scientists agreed, as any type of emergency.
>
> "For the mid-range IPCC emission scenario, IS92a, assuming the "best
> estimate" value of climate sensitivity and including the effects of
> future increases in aerosol, models project an increase in global mean
> surface air temperature relative to 1990 of about 2 deg. C by 2100."
>
The actual range given is from 1 deg C at the low end to 3.5 deg C at
the high end by the year 2100. This is about 1/3 less than estimates
in earlier IPCC Reports. As indicated in the above quote, the main
reason is inclusion of cooling by aerosols, which are somewhat better
understood than they were earlier, but about which there is still great
uncertainty. It is important to be aware of the full plausible range
since as Michael Tobis has often pointed out, the worst case scenario
which has some reasonable degree of plausibility, could lead to much
greater economic and social disruption than the most benigh or even the
best guess. In decision theory, in its simplest form, you multiply
the expected loss by the probability for each outcome and add them up.
That is the expected loss (or gain if the loss is negative, i.e., a
gain). So ignoring the range is not a rational approach. Now I don't
think anyone can give precise probabilities for any of these
eventualities, so the best we can really do in these circumstances is to
keep these factors in mind. Just because we can't completely quantify
the decision theory at present doesn't mean that its principles don't
tell us anything. So, it still makes sense to adopt a no-regrets
policy for reducing the growth of fossil fuel emissions and waiting for
more information before taking more extreme measures. However, what
people are willing to consider a reasonable policy may depend somewhat
on what they are aware of. I suspect that if the general public were
more aware of what they might be bequeathing to their grandchildren,
they might be less inclined to buy vehicles with very low gas mileage.
They might be more willing to walk or use bicycles for short trips,
which would be good for their health anyway. Who knows? They might
even support an increase in gasoline taxes which would bring American
prices up to say half of what they are in most other countries.
> Climate Change 1995, pp. 5-6.
>
> >Regards, Harold
>
> snark
--
Leonard Evens len@math.nwu.edu 491-5537
Department of Mathematics, Norwthwestern University
Evanston Illinois
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