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Once Again, It's Measurements Versus Models
Volume 2, Number 13: 1 July 1999

There's the real world, and there's the virtual world - the world in which we live and move and have our being and the world of models, which draws its life from a wonderful mix of the minds of men and the wizardry of computers.  Time was when we only had the former; and projections about the future were based on experiences of the past.  But no more.  Now, with the click of a mouse, one can call up a program that contains everything we think we know about the innermost workings of earth's climate system and ask it "what will be?"  And just as quickly, we see the future spread before us.

In many cases, these two worlds are very similar; and we can explore them both to our advantage.  But sometimes they do not quite resonate; and when they make discordant music, danger lurks in putting too much faith in the output of our creations.

A case in point: the greenhouse world of global warming that comes to us compliments of one of the most exciting fields of research around today.  Is it real, or is it illusory?  The question is more than academic; for those who put their faith in the strength of microchips and silicon wafers would bet a big chunk or our gross national product on their favorite pastime.  And that's our gross national product, not just their part.

So, you feeling lucky, taxpayer?  If not, perhaps we should require a little more than enthusiasm for the field as evidence of its strengths.  Maybe we should expect the climate modeling enterprise to faithfully recreate the past before we gamble our future on it.  Maybe, in fact, we should check the models against some actual measurements.

In beginning this exercise, we proffer the recent paper of Timmermann et al. (1999) as a starting point.  Spurred on by "the strong El Niņos of 1982/1983 and 1997/1998, along with the more frequent occurrences of El Niņos during the past few decades," they developed a global climate model that, for the first time, according to them, operates with sufficient resolution to address the issue "of whether human-induced 'greenhouse' warming affects, or will affect, ENSO."

Not surprisingly, in view of the fact that they apparently thought they knew what their result should be in order to be correct, Timmermann et al. found that "when the model is forced by a realistic future scenario of increasing greenhouse-gas concentrations, more frequent El-Niņo-like conditions and stronger cold events in the tropical Pacific Ocean result."  However, this is not what observational data reveal to be the case.  The more frequent strong El Niņo activity of the recent past is in actuality no different from a number of other such episodes of prior centuries, when the CO2 content of the air was considerably lower than it is today.

As proof of the truth of this statement, we point to the recent paper of Allan and D'Arrigo (1999).  They too were aware of the strong and protracted El Niņo activity of recent decades and wondered if it could "be taken as a possible manifestation of enhanced greenhouse conditions."  But instead of conducting a modeling exercise to explore the question, they turned their attention from the virtual world to the real world: they consulted actual data.

So what did they find?  Based on the instrumental temperature record for the period 1876 to 1996, Allan and D'Arrigo found four persistent El Niņo sequences similar to that of the 1990s.  What is more, based on tree-ring proxy data covering the period 1706 to 1977, they found several other ENSO events of prolonged duration.  In fact, there were four or five persistent El Niņo sequences in each of the eighteenth and nineteenth centuries.  Hence, they were forced to conclude -- for real-world data truly constrain one's options -- that there is "no evidence for an enhanced greenhouse influence on the frequency or duration of 'persistent' ENSO event sequences."

So let's go over this again.  The most sophisticated climate model ever developed to deal with this very phenomenon predicts that increasing greenhouse gas concentrations produce more frequent El-Niņo-like conditions; but real-world observations demonstrate that El-Niņo-like conditions did not increase over a nearly 300-year period of time when the CO2 concentration of the atmosphere rose from approximately 275 ppm to 365 ppm, or by approximately 33%.  Can you spell   m-o-d-e-l   f-a-i-l-u-r-e   ?  It certainly looks to us like this is a classic case of model inability to perform as promised, i.e., to mimic reality.  But whenever models compete against measurements, it would be odd to expect anything different.

And no, we don't feel lucky.  Do you?

Dr. Craig D. Idso
Dr. Keith E. Idso
Vice President

Allan, R.J. and D'Arrigo, R.D.  1999.  "Persistent" ENSO sequences: How unusual was the 1990-1995 El Niņo?  The Holocene 9: 101-118.

Timmermann, A., Oberhuber, J., Bacher, A., Esch, M., Latif, M. and Roeckner, E.  1999.  Increased El Niņo frequency in a climate model forced by future greenhouse warming.  Nature 398: 694-696.