Hanksville, UT USHCN climate monitoring station with Stevenson Screen - sited over a gravestone. Photo by surfacestations.org volunteer Juan Slayton
Posted on 01/22/2011 3:39:06 PM PST by Ernest_at_the_Beach
or those that don’t notice, this is about metrology, not meteorology, though meteorology uses the final product. Metrology is the science of measurement.
Since we had this recent paper from Pat Frank that deals with the inherent uncertainty of temperature measurement, establishing a new minimum uncertainty value of ±0.46 C for the instrumental surface temperature record, I thought it valuable to review the uncertainty associated with the act of temperature measurement itself.
As many of you know, the Stevenson Screen aka Cotton Region Shelter (CRS), such as the one below, houses a Tmax and Tmin recording mercury and alcohol thermometer.
Hanksville, UT USHCN climate monitoring station with Stevenson Screen - sited over a gravestone. Photo by surfacestations.org volunteer Juan Slayton
They look like this inside the screen:
NOAA standard issue max-min recording thermometers, USHCN station in Orland, CA - Photo: A. Watts
Reading these thermometers would seem to be a simple task. However, that’s not quite the case. Adding to the statistical uncertainty derived by Pat Frank, as we see below in this guest re-post, measurement uncertainty both in the long and short term is also an issue.The following appeared on the blog “Mark’s View”, and I am reprinting it here in full with permission from the author. There are some enlightening things to learn about the simple act of reading a liquid in glass (LIG) thermometer that I didn’t know as well as some long term issues (like the hardening of the glass) that have values about as large as the climate change signal for the last 100 years ~0.7°C – Anthony
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This post is actually about the poor quality and processing of historical climatic temperature records rather than metrology.
My main points are that in climatology many important factors that are accounted for in other areas of science and engineering are completely ignored by many scientists:
Metrology is the science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology. Believe it or not, the metrology of temperature measurement is complex.
It is actually quite difficult to measure things accurately, yet most people just assume that information they are given is “spot on”. A significant number of scientists and mathematicians also do not seem to realise how the data they are working with is often not very accurate. Over the years as part of my job I have read dozens of papers based on pressure and temperature records where no reference is made to the instruments used to acquire the data, or their calibration history. The result is that many scientists frequently reach incorrect conclusions about their experiments and data because the do not take into account the accuracy and resolution of their data. (It seems this is especially true in the area of climatology.)
Do you have a thermometer stuck to your kitchen window so you can see how warm it is outside?
Let’s say you glance at this thermometer and it indicates about 31 degrees centigrade. If it is a mercury or alcohol thermometer you may have to squint to read the scale. If the scale is marked in 1c steps (which is very common), then you probably cannot extrapolate between the scale markers.
This means that this particular thermometer’s resolution is1c, which is normally stated as plus or minus 0.5c (+/- 0.5c)
This example of resolution is where observing the temperature is under perfect conditions, and you have been properly trained to read a thermometer. In reality you might glance at the thermometer or you might have to use a flash-light to look at it, or it may be covered in a dusting of snow, rain, etc. Mercury forms a pronounced meniscus in a thermometer that can exceed 1c and many observers incorrectly observe the temperature as the base of the meniscus rather than it’s peak: ( this picture shows an alcohol meniscus, a mercury meniscus bulges upward rather than down)
Another major common error in reading a thermometer is the parallax error.
Image courtesy of Surface meteorological instruments and measurement practices By G.P. Srivastava (with a mercury meniscus!) This is where refraction of light through the glass thermometer exaggerates any error caused by the eye not being level with the surface of the fluid in the thermometer.
(click on image to zoom)
If you are using data from 100′s of thermometers scattered over a wide area, with data being recorded by hand, by dozens of different people, the observational resolution should be reduced. In the oil industry it is common to accept an error margin of 2-4% when using manually acquired data for example.
As far as I am aware, historical raw multiple temperature data from weather stations has never attempted to account for observer error.
We should also consider the accuracy of the typical mercury and alcohol thermometers that have been in use for the last 120 years. Glass thermometers are calibrated by immersing them in ice/water at 0c and a steam bath at 100c. The scale is then divided equally into 100 divisions between zero and 100. However, a glass thermometer at 100c is longer than a thermometer at 0c. This means that the scale on the thermometer gives a false high reading at low temperatures (between 0 and 25c) and a false low reading at high temperatures (between 70 and 100c) This process is also followed with weather thermometers with a range of -20 to +50c
25 years ago, very accurate mercury thermometers used in labs (0.01c resolution) had a calibration chart/graph with them to convert observed temperature on the thermometer scale to actual temperature.
Temperature cycles in the glass bulb of a thermometer harden the glass and shrink over time, a 10 yr old -20 to +50c thermometer will give a false high reading of around 0.7c
Over time, repeated high temperature cycles cause alcohol thermometers to evaporate vapour into the vacuum at the top of the thermometer, creating false low temperature readings of up to 5c. (5.0c not 0.5 it’s not a typo…)
Electronic temperature sensors have been used more and more in the last 20 years for measuring environmental temperature. These also have their own resolution and accuracy problems. Electronic sensors suffer from drift and hysteresis and must be calibrated annually to be accurate, yet most weather station temp sensors are NEVER calibrated after they have been installed. drift is where the recorder temp increases steadily or decreases steadily, even when the real temp is static and is a fundamental characteristic of all electronic devices.
Drift, is where a recording error gradually gets larger and larger over time- this is a quantum mechanics effect in the metal parts of the temperature sensor that cannot be compensated for typical drift of a -100c to+100c electronic thermometer is about 1c per year! and the sensor must be recalibrated annually to fix this error.
Hysteresis is a common problem as well- this is where increasing temperature has a different mechanical affect on the thermometer compared to decreasing temperature, so for example if the ambient temperature increases by 1.05c, the thermometer reads an increase on 1c, but when the ambient temperature drops by 1.05c, the same thermometer records a drop of 1.1c. (this is a VERY common problem in metrology)
Here is a typical food temperature sensor behaviour compared to a calibrated thermometer without even considering sensor drift: Thermometer Calibration depending on the measured temperature in this high accuracy gauge, the offset is from -.8 to +1c
But on top of these issues, the people who make these thermometers and weather stations state clearly the accuracy of their instruments, yet scientists ignore them! a -20c to +50c mercury thermometer packaging will state the accuracy of the instrument is +/-0.75c for example, yet frequently this information is not incorporated into statistical calculations used in climatology.
Finally we get to the infamous conversion of Degrees Fahrenheit to Degrees Centigrade. Until the 1960′s almost all global temperatures were measured in Fahrenheit. Nowadays all the proper scientists use Centigrade. So, all old data is routinely converted to Centigrade. take the original temperature, minus 32 times 5 divided by 9.
C= ((F-32) x 5)/9
example- original reading from 1950 data file is 60F. This data was eyeballed by the local weatherman and written into his tallybook. 50 years later a scientist takes this figure and converts it to centigrade:
60-32 =28
28×5=140
140/9= 15.55555556
This is usually (incorrectly) rounded to two decimal places =: 15.55c without any explanation as to why this level of resolution has been selected.
The correct mathematical method of handling this issue of resolution is to look at the original resolution of the recorded data. Typically old Fahrenheit data was recorded in increments of 2 degrees F, eg 60, 62, 64, 66, 68,70. very rarely on old data sheets do you see 61, 63 etc (although 65 is slightly more common)
If the original resolution was 2 degrees F, the resolution used for the same data converted to Centigrade should be 1.1c.
Therefore mathematically :
60F=16C
61F17C
62F=17C
etc
In conclusion, when interpreting historical environmental temperature records one must account for errors of accuracy built into the thermometer and errors of resolution built into the instrument as well as errors of observation and recording of the temperature.
In a high quality glass environmental thermometer manufactured in 1960, the accuracy would be +/- 1.4F. (2% of range)
The resolution of an astute and dedicated observer would be around +/-1F.
Therefore the total error margin of all observed weather station temperatures would be a minimum of +/-2.5F, or +/-1.30c…
fyi
Actually, it would be incorrect to round to the original significant figures, as that converted number is being used in further calculations. Tha appropriate place to apply the level of precision is at the final step.
That is the question.....
Pedro’s Weather Forecast: Chili today, hot tamale!
Climate change study had 'significant error': experts (OOPSIE!)
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WASHINGTON (AFP) – A climate change study that projected a 2.4 degree Celsius increase in temperature and massive worldwide food shortages in the next decade was seriously flawed, scientists said Wednesday.
Round to whatever's desired, whenever desired, if it's Hansen, from what I can tell.
Do We Really Know Earth’s Temperature?
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Errors in IPCC climate science at warwickhughes.com ^ | January 14th, 2011 | Warwick Hughes
Guest article by Pat Frank
We’ve all read the diagnosis, for example here, that the global climate has suffered “unprecedented warming,” since about 1900. The accepted increase across the 20th century is 0.7 (+/-)0.2 C. As an experimental chemist, I always wondered at that “(+/-)0.2 C.” In my experience, it seemed an awfully narrow uncertainty, given the exigencies of instruments and outdoor measurements.
When I read the literature, going right back to such basics as Phil Jones’ early papers [1, 2], I found no mention of instrumental uncertainty in their discussions of sources of error.
The same is true in Jim Hansen’s papers, e.g. [3]. It was as though the instrumental readings themselves were canonical, and the only uncertainties were in inhomogeneities arising from such things as station moves, instrumental changes, change in time of observation, and so on.
Once Hansen and his cronies realized that the guys manning the weather stations in Congo had been killed and eaten by rebel forces, they gave up on Africa as a source of temperature information!
If you use a rectal thermometer, you insert it in Washington DC to take the temperature of the US. Not really sure where you stick it to take the temp of the entire planet.
LOL!
From the comments:
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Ceri Reid says:
Very interesting post, thanks.
As an engineer, most of the ideas here were pretty familiar to me. I find it almost unbelievable that the climate records aren’t being processed in a way which reflects the uncertainty of the data, as is stated in the article. What evidence is there that this is the case (I think I mean: is the processing applied by GISS or CRU clearly described, and is there any kind of audit trail? Have the academics who processed the data published the processing method?).
I think the F to C conversion issue is tricky. I think the conversion method you favour (using significant figures in C to reflect uncertainty) would lead to a bias which varies with temperature. What is actually needed is proper propagation of the known uncertainty through the calculation, rather than using the implied accuracy of the number of significant figures. So the best conversion from 60F to C would be 15.55+/-1.1C (in your example above). But obviously, promulgating 15.55 is fraught with the danger of the known 1.1C uncertainty being forgotten, and the implied 0.005C certainty used instead. Which would be bad.
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Mike Haseler says:
I once designed a precision temperature “oven” which had a display showing the temperature to 0.01C. In practice the controller for device was only accurate to 0.1C at best and with a typical lab thermometer there was at least another 0.1C error. Then the was the fact you were not measuring the temperature at the centre of the oven and drift and even mains supply variation had a significant effect!
All in all the error of this device which might appear to be accurate to 0.01C could have been as bad as the total so called “global warming signal”.
I’ve also set up commercial weather stations using good commercial equipment which I believe is also used by many meteorological stations and the total error is above +/-1C even on this “good” equipment.
As for your bulk standard thermometer from a DIY shop. Go to one and take a reading from them all and see how much they vary … it’s normally as much as 2C or even 3C from highest to lowest.
Basically, the kind of temperature error being quoted by the climategate team is only possible in a lab with regularly calibrated equipment.
Good Stuff at the link:
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boballab says:
I actually ran a spreadsheet back in December showing how just 3 instrument changes, with each instrument having better resolution, over a long term historical record changes the trend of the data (over 1° F in change to the USCHN data)
http://boballab.wordpress.com/2010/12/06/do-we-really-know-what-the-temperature-is/
Ernest...I think you are missing something here.
What are you measuring? You have to measure something with mass. What is it? Air right?
To have a true average you must correct for the different masses associated with what you are measuring. So you must know wet bulb and dry bulb tempertures and a barometric pressure. For every station. If you don’t have this then you are just averaging readings from a thermometer.
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Ziiex Zeburz says:
As the earths surface area is +- 196,935,000 square miles and the geological parameters are as diverse as it is possible to imagine, we have intelligent people declaring that the world is heating by as much as 2.0c per 100 years, with official recorded temp. covering perhaps 1% of the total area of the earth. I fully agree with the above article, we as humans are all idiots, some of us think we understand what we are trying to do, but even reading a temp. looks beyond the scope of those who’s job it is.
Italy is a prime example of human intelligence, knowledge, and understanding, it is in that country for all to see, and Italians have in the past produced some of the worlds most outstanding thinkers, BUT !!!! if you put 100 Italians into a room and ask them to form a political party, at the end of a month you would find that they have formed 100 plus political parties, and thousands of political ideologies non of which address the problems facing the country.
And Italy is one of the worlds better countries, it had inside baths and running hot water when the English were still learning to make fire. but here we are 3000 years later and 99.9% of the world population still cannot read a thermometer, like i said above we are all idiots.
They didn’t. That is the problem.
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