Error & Accuracy in scientific studies

One thing I learned from studying Physical Chemistry in college is that you take measurements & the uncertainty & combine them together. So a reading is never just 37inches.  It is 37 inches + / - 0.1 inch.  This allows you to factor in your ability to measure the property & the accuracy of your instruments. Some of our instruments for weight had a known & posted error uncertainty. Our precision scales were somewhere near + / - .0001g. in accuracy  If you are using formulas such that you have to add some numbers then the uncertainty is additive.  If you have multiplication then the errors multiply...etc.

The NAS study doesn't show any of the raw data & formulas or accuracy readings. It does not list the exact location of all the samples. I don't believe that the NAS study did any new measurements.  I think it was all a collection of stuff that had been previously done in other studies by other groups. Therefore what you believe about the NAS study is based upon your faith in the credentials of the people who aggregated the data & their opinions of what it all means. They state pointedly that there was nothing offered in the way of suggestions about policy nor was the study even designed around making recommendations about policy.
So IMHO you would be in error taking the findings & saying we should do something about it.

If you read the parts about their methodology surrounding proxy measurements you run into this:
source: ... Although calibration against instrumental data is a necessary step to determine how well proxies reflect climate, proxy records are not perfect thermometers, that is, the true relationship between the proxy and the local surface temperature is not known exactly. Furthermore, all proxies are influenced by variables other than temperature, and it can be difficult to account for these confounding factors.
... one thing they leave out of the things like the multi-proxy consideration is the accuracy of each of the methods such as ice cores, tree rings etc. - the actual measurements, not the correlation. Instead of inches of mercury they must go to inches in the width of a tree ring. Similarly for ice cores & other data. They admit that much beyond a couple hundred years is uncertain. Some data they even got from paintings of nature areas.

The Earth's surface is approximately 197 million square miles (most of it is water!).  How accurate do you suspect that an average temperature over the whole thing can be made. What would that mean anyway?? The technology in the year 1900 was less accurate than today. How accurate do you suppose the measurements at the beginning of the last century were compared to that of today ? The pure scale of the job of measuring the surface temperature of an object the size of the Earth says you probably can't get within 5 degrees - all other considerations being equal.  You also have to take the temperature at the same places every time. The current NCAR readings are not even doing that. Some of the probes fail to send etc.  (see JunkScience.com's thermometer). You also can't just take a single snapshot. You need the whole temperature profile throught the seasons & the times of day to get what is happening. The temperature at any spot varies according to the season & the time of day & the weather at that location. You can't just do a mashup of the data that proves your hypotheses & throw out the rest.

Please take some of this into consideration the next time you find yourself worshipping at the Church of the Great Tsunami .

Tags

  1. globalwarming
  2. scientific measurements

Comments


Seth says
source: M above
one thing they leave out of the things like the multi-proxy consideration is the accuracy of each of the methods

M, i think your assertion is false.   Every section and many of the graphs in the IPCC study do include statements of the accuracy.  For example this one ...


source: Climate Change 2001: Working Group I: The Scientific Basis

solid curve and dark shading; standard area weighted anomalies and uncertainties (adapted from Jones et al., 1997b, 2001)

Mark de LA says
None of this says anything about the uncertainties of the instruments they used to measure it. As a matter of fact what you show sounds like they threw in a "jesus factor" to smoothe out their data. (My data doesn't fit the expected curve, but if I multiply by a factor of 0.7 then it fits - Halleluiah! - I don't have to collect data - I can explain the phenomena)


Mark de LA says
I was talking about the NAS study. Was the above graph part of that ?


Mark de LA says
BTW, the Statistical Background beginning at pg 79 is interesting. It goes into how they used statistics to smoothe out the curves & draw some conclusions & make clearer some of the uncertainties. I will get into the latter parts of the study if my interest survives & time permits. The aforementioned graph was not in the NAS study.

Mark de LA says
BTW,  I detect a note of adversarial temperament in your writing. Basically what I expressed was my reading of uncertainty in the study based on my limited training in physics & chemistry & a degree in mathematics & my years of reading English in technical material. And the fact that I haven't penetrated very deep yet in the NAS study.  In particular the size of the Earth & the ability to create a meaningful average temperature for it is absurd in my mind (especially to an accuracy of +/- 1 degree). This wasn't even addressed in the study. There are a lot of pretty graphs in the latter part of the study which I will get to when I get a 


Mark de LA says
seth 2006-06-28 15:05:54 3820
M 2006-06-28 15:01:52 3820
I was talking about the NAS study. Was the above graph part of that ?
I may be wrong, but i don't believe the NAS study added any new data ... rather they just analized the existing data, including the IPCC data, and reported their results to Congress. 
Yep I said that in my item. But, was this graph in the NAS report or did you pick it up somewhere else?  What in the name of the Holy Floating Iceburg is this?
source: ... uncertainties due to bias corrections in sea surface temperature
... what kind of a metric is that & later on this?  :
source: ... uncertainties due to urbanisation of the land component
...



Mark de LA says
I just pointed out the obscure uncertainties in the above graph - didn't you read them ? they are not real metrics.


Seth says
M 2006-06-28 15:12:14 3820
But, was this graph in the NAS report or did you pick it up somewhere else? 
That graph was in the IPCC study as I clearly indicated in the source line in my comment above.  I dont know for a fact whether this uncertainty analysis was used in the NAS study or not.  My point is that these scientists have not neglected to analize the uncertainty of their measurements.   I find your allagations of such completely unfounded. 

The way to make some progress here would be for you to point to a specific point in the NAS report where your feel the scientists have been neglegent in analize the uncertainty of their findings.  Then we can go there and read the documents and see if your alligation is true or not.

Mark de LA says
And another thing here is some of the variabilithy in the surface area of the Earth as reported by those who measured it. I think I want to sign up for a plot of land at the Church of the Expanding Globe.  Maybe global warming is making the Earth expand 


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