From: steinly@topaz.ucsc.edu (Steinn Sigurdsson)
Newsgroups: sci.environment
Subject: Re: Gallup Poll on Global Warming
Date: 14 Sep 92 12:51:44
Organization: Lick Observatory/UCO
Distribution: usa
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	<1992Sep14.182707.12523@daffy.cs.wisc.edu>
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In-reply-to: tobis@skool.ssec.wisc.edu's message of 14 Sep 92 18:27:07 GMT

In article <1992Sep14.182707.12523@daffy.cs.wisc.edu> tobis@skool.ssec.wisc.edu (Michael Tobis) writes:

Hey, wow, this is turning into a nice thread...

   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.

Eek. I'm not sure which side the miscommunication is on, probably
somewhere in the middle ;-) But, the question being asked was not
necessarily the question that was heard... plus there is the
understandable tendency of scientists to obey the drunk-by-a-lightpole
rule and answer questions that are answerable, not those that need answering...

 ...

   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.

This is far from clear! A major possible feedback mechanism
is ocean current instability, if the Gulf Stream flips to a southern
path the seasonal snowpack (and in fact permanent snow pack) in
northern Europe will advance drastically. Even in the absence of 
a major instability, snowpacks are local and may advance or retreat.

   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.

Interesting, my guess had been vegetation albedo was negligible.

   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.

Right, this is now beyond the realm of climate modelling, into
predicting what the atmospheric CO2 will be given some emission
level, I'd bet on ocean sinks saturating (or worse, desaturating
catstrophically) before biofeedback saturates - interestingly, it
seems to me now anthropogenic sinks may actually be significant,
the magnitude if I remember correctly is 9GT/year - a number I saw
recently for recycled paper is 0.1 GT/year - which suggests organic
waste may be stored by humans on GT scales per year! (This was
actually proposed as a joke in "Analog" recently - government
paperwork as salvation - the ultimate technofix ;-) It would be
interesting to compare net organic matter fixing in waste and
long term infrastructure with the size of the sink. I'd guess it's
at least a 10% effect...

   |> 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.

If I remember correctly, this is assuming no biofeedback, and
extrapolating backwards leads to an overestimate of current CO2 levels
given past emissions? 

	 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.

I never implied the IPCC did not adress the public policy questions,
merely that knowing the mean temperature response as a function of
(effective) CO2 content only was insufficient to answer the real
question being asked. That does not in any way reduce the relevance of
knowing the effect of CO2 doubling as it provides a benchmark for
reality.

   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.

you define "staying the same as better"? This is then the best of all
possible worlds???

 :-) Sorry, couldn't resist. And before anyone blows their top,
I am aware of the problems of change, especially rapid change...

*  Steinn Sigurdsson   			 Lick Observatory     	  *
* steinly@lick.ucsc.edu		       "standard disclaimer"  	  *
* But, oh, love is strange 					  *
* and you have to learn to take the crunchy with the smooth,      *
* I suppose 				              - B.B. 1983 *


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