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Pat Frank Says:
January 18th, 2011 at 5:18 am
#13, Graeme, most 20th century readings were made using specialized mercury-style thermometers inside a shelter — typically a Stevenson screen (aka Cotton Regional Shelter). Over the last twenty years or so, these have been systematically replaced in North America and Europe with precision resistance thermometers inside gilled chambers, often aspirated. There’s a good run-down here of the various types of thermometers and shelters in use.
In the laboratory, the best thermometers can be calibrated to (+/-)0.1 C, although the older mercury thermometers varied in precision and may not have markings every 0.1 C. However, the real question is precision and accuracy in the field, rather than in the lab.
The screens and shelters help prevent sun and wind (among other factors) from distorting the temperature readings. But they’re not perfect, and there is systematic error in the temperature measurements.
It’s pretty clear that climate scientists have just assumed that all the measurement errors just average away. But they’ve never surveyed the thermometers and sensors in the field to test this assumption and demonstrate its validity. After my own look at published material, the evidence is that this assumption doesn’t hold at all. But in any case, such negligence is hardly the way to do experimental science, and certainly no way to justify forcing huge economic dislocations.
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Graeme Inkster Says:
January 18th, 2011 at 10:40 am
#15 Pat Frank – thanks. Were the thermometers in use in, say, 1910 as precise as those in 1980? Were they ever re-calibrated? I know it was done with one set of data from the 1700’s (I think Yale Uni) with the original thermometer(s?) and the temperature records were modified because of the big difference between the original and modern thermometer. [sorry, I've lost reference; I think H. Lamb].
Unless the instruments are/were calibrated regularly then any instrumental errors are “locked into the record”. I don’t disagree at all with your statement about the possible error range. It is more than likely that with human error it could be larger e.g. the policeman who checked the temperature at the same time every morning at 9 a.m. It turned out in practice to be after breakfast, which varied in time with the seasons. Equally, other readings were dependent on him not being busy at that time, even to the extent of records for 3 days when his dairy showed him a hundred miles away from the station house. See also the russian note in my original.
We do know that the temperature (at least in Northern Europe) went up between 1880 and 1940 because the Icelanders were able to resume growing oats/barley in the 1920’s after a hiatus of 400 years or more. But to claim that the “temperature of the Earth” (whatever that is) can be measured to hundreds of a degree as is now claimed is ludicrous. They are making the old error of “4 decimal places must be more accurate than 1 place” when they should (as you say) be wondering how accurate are the original readings.