From: tobis@skool.ssec.wisc.edu (Michael Tobis)
Newsgroups: sci.environment
Subject: Re: Gallup Poll on Global Warming
Date: 14 Sep 92 18:27:07 GMT
Distribution: usa
Organization: Space Science and Engineering Center, UW Madison

In article <STEINLY.92Sep12144323@topaz.ucsc.edu>, steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes:

|> Yup, the problem is that is not the question public policy asks...

Now wait just a cotton pickin minute. This thread startes with a typical
misrepresentation of the opinion of climate scientists that one sees in
certain branches of the media these days. That we did not address the
question you wanted answered is not because of evasion, but because that 
question hadn't been raised.

The thread proceeded along the usual lines:

1) a gross misrepresentation of the opinion of the climatological community,
which is best represented by the IPCC report, rather than by a few oddballs
who consort with journalists.

2) an obfuscation of the difference between a lack of statistical proof
that existing warming is caused by the greenhouse effect with the clear
results that 1) there has been a statistically significant warming 2) it
is consistent in magnitude with predictions of greenhouse warming 3) the
warming is not predicted to pass the usual statistical tests for causation
for another decade or so. This is a bit subtle for the popular press, but
that is no excuse for misrepresenting it.

3) an attack on the reliability of models, which will never be perfect
in representing a vast extent of a nearly inviscid fluid with a finite
number of data points, and a failure to acknowledge that the basis for
concern is not numerical models but purely physical and mathematical
models, to which the numerical models and past record only offer modest
confirmation.

That we responded to these criticisms in no way should be taken as 
evidence that the relevant aspects of public policy are not being addressed.
Unfortunately, in a democratic context, we have to convince the public
of the seriousness of the problem in the face of deliberate "lawyers'
science" efforts to cast doubt upon the results without a balanced
consideration of the evidence on all sides of the question.

In this regard, we are in not much different of a position than nuclear
engineers dealing with the misrepresentations and fact-twisting we have
recently seen in this newsgroup. The people we are dealing with tend to
be a disjoint set, but the methods are comparable.

That said, I will take up your two serious points.
|>    >b) Are albedo changes adequately modelled? 
|>    >A definitely niggle is illustarted by a major glacial
|>    >vs CO2 concentration chart that was in Nature last month,
|>    >showing a major glacial epoch occurred while CO2 concentrations
|>    >were O(10) time current ones. Clearly some combination of
|>    >albedo and continental shifts managed to cool the Earth despite
|>    >a much greater greenhouse effect.

Sensitivity to clouds remains the largest point of disagreement among
the numerical models and the largets point of uncertainty in the physical
question. It is importatnt to note, however, 1) that increased absolute
humididty does not necessarily imply more cloud cover: cloud cover is
a function of relative humidity, and it is precisely the presumption that
relative humidity will stay roughly constant over the oceans (according
with local boundary-later physics) that leads to the result that absolute
humidity will increase and 2) cloud albedo feedback, while a large term,
is balanced by cloud greenhouse effect feedback: many clouds are more
opaque in the infrared than in  the visible. 

Whatever the effect of greenhouse gases on the permanent ice pack, it
is clear that the seasonal snowpack is and will continue to be retreating.
This is taken as a positive (exacerbating) feedback.

It is my understanding that the surface area covered by vegetation is so small
compared to the total area of the earth  that vegetation albedo feedback
effects if any will be local. In this context, it is interesting to note
that actual leaf transpiration effects as compared to bare ground are
believed to be more significant than albedo feedback. Dickinson is a
leading researcher in this area.

In any case, unlike many of our other correspondents, you have indeed
identified a weak link in the reasoning. Nevertheless, reasonable
assumptions on all these terms leads to the range of predictions that
is usually given. It is not clear to me that taking the "best case" on
all debatable quantities is the most appropriate course for public
policy, nor that the "best case" does not lead to serious problems
in the absence of policy constraints, albeit delayed by a few decades.
 
|>    >a) what the actual CO2 load will be given known emissions
|>    > - the GCMs take an assumed change in CO2, but the CO2 balance
|>    >is clearly missing a term, there's an unknown sink, and presumably
|>    >at least one missing feedback loop - I noted that IPCC92 started
|>    >allowing for biofeedback, which I seem to remember was assumed
|>    >negligible in IPCC90? Also there's ocean sinks and anthropogenic
|>    >sinks ;-)


Since you are familiar with the IPCC reports, you should also be faimiliar
with the fact that the historical record has been a smooth inexorable rise:
indeed the excess over background CO2 has followed an almost perfectly
exponential curve. Thus, near-term extrapolation is not nearly so
difficult as you describe. The ocean sink response time constant is
on the order of a century, so the atmosphere is essentially an integrator
of excess CO2 on shorter time scales, barring biotic fertilization and
surface layer absorbtion. Indeed, best estimates of these terms fails to
aacount for about 25% of emissions. I believe that the scenarios presented
assume that absorbtion efficiency remains constant. If the missing term
is biotic, it is likely to eventually  saturate due to external causes
(nutrients?) so predictions would  have  to be adjusted, if at all, in 
a more pessimistic direction.


|> In article <dhalliwe.716273811@muskwa.ucs.ualberta.ca> userDHAL@mts.ucs.UAlberta.CA (David Halliwell) writes:
|> 
|>        Ignore climate modelling. The 4W/sq.m is based on fairly straight-
|>    forward measurements of the radiative absorption coefficient for CO2,
|>    combined with a postulated doubling of atmospheric CO2. The question
|>    being dealt with to begin with is "if we double CO2, how will this
|>    alter radiative losses to space, with NO change in other components
|>    of the atmosphere".
|> 
|> I absolutely agree that with CO2 doubling _and_ _NO_ other changes
|> there will be warming; that follows directly from the energy balance
|> and frequency dependent opacity in radiative transfer. 
|> Unfortunately this does not answer the question actually asked
|> by the public: namely how much CO2 increase will various emission
|> levels lead to, what climate change will result from this, _and_ how
|> bad will it be.

Your familiarity with the IPCC assessments leads me to wonder why you
ask in such a way. I refer you to IPCC1990 section 1.2.6 Results of
"box-diffusion" models (essentially mass conservation and mass flux between
large scale reservoirs) indicate that CO2 doubling, in the absence of change
in the rate of increase of emissions (plausible if coal resources are
exploited) occurs around 2050. An immediate restriction of emissions to
1990 levels leads to concentrations asymptoting to 420 ppmv, or 150%
of current concentrations. A decision to hold concentrations to current levels
would require an immediate reduction in emissions by 70%. Since this last
scenario is implausible, we are already committed to an increase in 
CO2 concentrations of about 50% over current levels, or about 65% above
preindustrial levels. Allowing increases to continue for another 20 years
leads to doubled CO2 by the end of the century, asymtopting (eyeballing
a graph here) to about triple preindustrial levels sometime in the 22d century.

Note that these are for CO2 alone. Other gases contribute a factor of
an additional 1.5 to 2.0 multiplier. Accordingly, we will be very fortunate
to avoid doubled equivalent CO2 warming by 2030.

Contrary to yur implication, the IPCC reports directly address these
questions. While the uncertainties are large, the trends are smooth.
Extrapolating more than 50 years is quite dubious, but the smoothness
of the rcord indicates that predictions for the next few decades are
quite robust, barring a climate catastrophe. The uncertaintied are much
larger in the direction of things getting worse than things getting better.

mt