GCMs-misuse? part II

Joseph Coughlan josco at gaia.arc.nasa.gov
Fri Dec 10 20:44:19 EST 1993

In article <CHsDpq.Ky9 at murdoch.acc.Virginia.EDU> rjw9y at envsci.evsc.virginia.edu. (rjw9y) writes:

You describe a problem but what is the solution.  Do you have a better
idea about how an ecologist should obtain better forcasting of long
term climatic patterns, PPT, Temps, humidity, etc. ?

For example, I have an ecosyustem model and I am asked to determine
what the sensitivity of the ecosytem is to a climatic warming or drying
for the intermountain region of the United states.

What to I do?  What climatic pertubation should I use?  

I understand the limitations of GCM output but you cannot expect a
hydrologist or ecologist to stop experiments and forcasting until GCM's
become more accurate.  This is science not engineering.  The problem is
misunderstanding the uncertainity in the forecasting, not in conducting

It is not GCM misuse when you understand what your using. If you do
not - well most tools or measurements are misused when not understood.
Model output is not unique.

joseph coughlan

>I am the author of GCMs-misuse.  Thanks to Rick Adair for coming to my
>rescue.  I responded to Len's grammar flame by e-mail to him.  My
>feeling is that some jargon like '2xCO2' and 'eigenevctor analysis' may
>have been the problem.
>To mt;
>you responded with'
>"While I'm not one to claim that no drivel gets past peer review, the
>statement that modellers don't "want" their output compared to
>data misrepresents the situation badly."
>A peer review from the journal Science recently responded, 
>"These simulations [transient GCM 2xCO2 runs] are not intended to be
>'transient forecasts'".  .... Natural variability is certainly present,
>and the model could not replicate this because of the way it has been
>initialized.  ...  Those who work with GCMs know the problems
>associated with their models.  This paper is not an objective critique
>of those problems."
>Peer reviews from the journal Nature were not dissimilar.  One author
>tells us we have confused GCM output, designed as a sensitivity
>analysis, with climate forecasts.  If we have confused them then so
>have the myriad of published papers which use transient 2xCO2 GCM
>output to predict the future responce of a number of physical and
>ecological systems.
>It is argued that GCMs cannot be compared to observations for their
>output runs were not meant as forecasts.  Ecologists, economists, and
>others are readily supplied with GCM output to be used in this way-and
>they get published!!!  By not allowing statistical analyses of GCM
>accuracy to demonstrate that GCM output should not be used as a
>forecast, there is obvious bias in the climate change literature. 
>Since Science and Nature both publish such work and GCMers distribute
>their output freely to these authors,  both parties (or all three if
>you count both journals) are supporting this bias.
>And i dont understand how you have come to believe, as you wrote, " The
>largest observed anomalies do in fact have a spatial pattern
>consistent with that of the regions where most severe warming is
>I would like to know what measurements or papers you have read which
>have lead you to this conclusion.  The paper submitted to Science and
>Nature about which i speak clealy demonstrates that the GFDL transient
>(1%/yr) GCM run introduces error to the tune of 240% greater than the
>climate change it correctly captures when compared to 20th century
>ground-based temperatures. 
>I agree with the modellers in that GCMs are great tools which can be
>used to study the atmosphere and evaluate our ability to simulate it. 
>However these same GCMs have no buisness being used to predict climate
>change in any sort of quantitative manner.  When you use GCM output as
>data you are assuming that they correctly simulate future climate in a
>quantitative manner.  A number of studies have shown that GCMs do a
>poor job of simulating today's climate especially on scales smaller
>than regional.  The misuse of GCM output is the prime reason they have
>gotten such a bad rap.
>"People and critters" as you put it live in a world with pronounced
>natural cliamte variability exhibited in a myriad of proxy climate
>records (tree rings, Devils Hole calcite, ice cores, etc).  Since we
>dont even understand yet how clouds, the ocean, or terrestrial
>vegetation will respond to CO2 emissions how can we expect the models
>we build to accurately forcast climates of the future????
>I welcome your e-mail responce or postings.  I really think this is a
>problem which is hidden in the closet.  On the otherhand please dont
>take my writing as antagonlistic i enjoy this subject and would like to
>encourage these discussions.
>bob w
>e-mail=     rjw9y at virginia.edu         

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