The Second Version

10/09/07

Meaning of Measurement

A question I ponder sometimes is, how actually meaningful is a global average temperature? There's an awful lot of discussion raging about how this average is changing and why, but so little about the actual physical meaning of it.

In the last few years I had to do quite a lot of accurate temperature measurements - now I'm even in the business of calibrating thermometers myself - and I realized that it is by no means easy.

An accuracy better than 0.1 °C (or °K) requires quality, calibrated instruments - and the only true reference for this is the old mercury thermometer. Electronic sensors must be used with due care because of their intrinsic errors and the further distortion caused by signal processing - it is not unusual for thermocouple digital thermometers to be off by a few degrees.

I'm fairly sure that the ones used in meteorology perform better than that; however, in these days even tenths of a degree seem to be politically important - so instrumental issues become prominent.

The implicit assumption, especially among the supporters of the AGW hypothesis, is that temperature measurements are all sufficiently precise and accurate. But is that really so? Is it possible that at least part of the observed warming - which seems to be settled around 0.6 +/- 0.2 °C: a 33% uncertainty - may be due to inaccurate instruments?

Another aspect is inhomogeneity - in simpler words, the temperature of atmosphere varies greatly from one regione to the other. For that matter, temperature varies appreciably even within the volume of a laboratory oven, and the arithmetic mean of temperature I then used as an input for my equation of state was a barely satisfactory compromise. Again I wonder, does it make sense to concentrate something as huge and
complex as the atmosphere into a 2-digit number and a linear temperature trend?

Yes, average temperature can be seen as an index for total energy content, and maybe in that regard is meaningful, but one must not think that any day now is roughly 0.6 °C hotter that it was a couple of centuries ago. That's a very wrong way to take it.

Etichette: ,

1 Commenti:

  • Fabio,

    This is sort of OT for this post, but are you familiar with IEC Fusion?

    Bussard Fusion Reactor
    Easy Low Cost No Radiation Fusion

    It has been funded:

    Bussard Reactor Funded

    I have inside info that is very reliable and multiply confirmed that validates the above story. I am not at liberty to say more. Expect a public announcement from the Navy in the coming weeks.

    The above reactor can burn Deuterium which is very abundant and produces lots of neutrons or it can burn a mixture of Hydrogen and Boron 11 which does not

    The implication of it is that we will know in 6 to 9 months if the small reactors of that design are feasible.

    If they are we could have fusion plants generating electricity in 10 years or less depending on how much we want to spend to compress the time frame. A much better investment that CO2 sequestration.

    BTW Bussard is not the only thing going on in IEC. There are a few government programs at Los Alamos National Laboratory, MIT, the University of Wisconsin and at the University of Illinois at Champaign-Urbana among others.

    Di Blogger M. Simon, Alle 17/9/07 00:17  

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