โ Scribed by Garth W. Paltridge
No coin nor oath required. For personal study only.
This paper was originally submitted as a background essay to an early meeting concerned with the development of the GARP Climate Dynamics Sub-Programme. It was an attempt to put the scientific problems into a context which, for the benefit of administrators, leads to a fairly natural structuring of relevant research activity. In its specific references to GARP, the essay has been somewhat overtaken by events -but the concepts are still relevant at this time when it remains unclear as to how the "climate problem" is to be solved.*
The Problem
Not being concerned with human affairs, a Martian scientist could adopt a somewhat detached attitude to the description of the earth and its physical processes. He would recognize that he was dealing with an interesting thermodynamic system which was fairly close to some form of steady state since the average planetary temperature did not change much over the years. He would observe on the other hand that the instantaneous solar energy input and infrared energy output varied considerably with time. He would postulate the presence of feedback mechanisms which continually restored the balance between input and output to its long-term mean.
His obvious first experiment would be to perform a time series and lag-correlation analysis of the total net solar input and the total net infrared output in order to establish (a) the amplitudes and frequencies of the variations about the mean and (b) some measure of the strength of the feedback processes. The experiment could extend to an examination of the geographical distribution of the variance of input and output in order to get some idea of the dominant scale of whatever physical processes might be pertinent to the feed-back. If he were a typical physicist limited by measurement difficulties and budgets, our Martian would study those periodicities in space and time which were measureable to reasonable accuracy -probably no better than 5% and certainly no better than 1%. The spatial resolution of his observations might be such as to divide the earth into no more than about 100 grid squares. He would examine only those periodicities in time whose amplitudes were above the 'noise' at the 1% level. In fact he might find in his power spectra a significant component of white noise in the system itself. This would conveniently restrict his investigation to those periodicities above the white noise level, / since he would know that variations of lesser magnitude are inherently unpredictable.
Armed with this information he could postulate various feedback processes involving cloud, rainfall, temperature and the thermodynamic character of the surface. At his level *See 'Terminology' at the end of this article for definitions of specialized terms.
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