How Not to Measure Temperature USHCN and GHCN

24 Jan 2010

I was going to place this on the Climate Humour thread but really it's too serious! It deserves a thread of its own.

How Not to Measure Temperature



This picture, taken by www.surfacestations.org volunteer Don Kostuch is the Detroit Lakes, MN USHCN climate station of record. The Stevenson Screen is sinking into the swamp and the MMTS sensor is kept at a comfortable temperature thanks to the nearby A/C units.




From NASA’s GISS graph below, the plot makes it pretty easy to see there was no discernible multi-decadal temperature trend until the A/C units were installed. And it’s not hard to figure out when that was.





That curious jump in the GISS record .. coincided with the placement of the a/c heat exchangers (I checked with the chief engineer of the radio station and he pulled the invoices to check). Steve McIntyre

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See

http://www.surfacestations.org/


for more of this hilarious stuff!

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GHCN = Global Historical Climatology Network i.e the surface stations use to measure land surface temperatures worldwide. You might ask why has it been reduced to this extent? I couldn't possibly say.






Half of global warming happened since 1990 yet less than half of the temperature stations are available since 1990?

Hmmm.

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Biker has called me a “ liar” and “stupid” repeatedly for suggesting that GISS and CRU global mean temp calculations are based on the GHCN stations which over time have been reduced to only about 1000 surface stations worldwide CURRENTLY being used to input TODAY’S temps into the database.

I have done my best to check out the figures. The situation is, indeed, as I have stated, as far as I understand it. However I decided I had to check it out AGAIN since Biker was so vehement in his denunciation.

So I emailed Chiefio and his assessment is this:

“It's all a matter of "what year". GHCN has about 7000 all told, butonly about 1200 of them are 'alive' now. By the time GIStemp drops some more about 900 contribute to the actual "warmth" of "now". So yes, 6k to 7k go in, but most of them have data only in the 1950 to1980 time interval. “

I also emailed Russell Vose, who devised the GHC Network, about Chiefio’s estimate. I wrote:

“One has heard alarming stories that, for example, less than one thousand GHCN stations are common to both the 1951-1980 baseline data and the current period. Is this correct, please? ‘

Russell said:

“I don't think this is correct. And we've done research that suggests the real-time network is more than adequate for monitoring long-term trends... But I'm pretty sure there are well over 1000...NCDC is working on a new version of GHCN for beta release later this spring.”

So, Russell Vose claims that the “real-time” (which I take to mean currently contributing to the database) number of stations is “more than adequate” and that he is “pretty sure” there are more than 1000.

I was unable to pin him down to a more precise statement. I don’t wish to put words into Vose’s mouth but what he says doesn’t exactly contradict Chiefio’s ballpark estimate, does it?

I think Biker should write to Hansen and get confirmation from the horse’s mouth that there are 6,300 surface station CURRENTLY in use in “real-time” in the GLOBAL data set used to calculate the gmt because my interpretation of his statement in para 3.1http://data.giss.nasa.gov/gistemp/paper/gistemp2010_draft0319.pdf is that this is the TOTAL stations used over the whole 1880-2009 period, NOT those currently “alive” to use Chiefio’s term.

Hansen said


Quote:

The source of monthly mean station measurements for our current analysis is the Global Historical Climatology Network (GHCN) version 2 of Peterson and Vose [1997], which is available monthly from NCDC. GHCN includes data from about 7000 stations. We use only those stations that have a period of overlap with neighboring stations (within 1200 km) of at least 20 years (see Figure 2 of Hansen et al., 1999), which reduces the number of stations used in our analysis to about 6300. We use the unadjusted version of GHCN. However, note that a subset of GHCN, the United States Historical Climatology Network (USHCN), has been adjusted via a homogenization intended to remove urban warming and other artifacts [Karl et al., 1990; Peterson and Vose, 1997]. Also bad data in GHCN were minimized at NCDC [Peterson and Vose, 1997; Peterson et al., 1998b] via checks of all monthly mean outliers that differed from their climatology by more than 2.5 standard deviations. About 15 percent of these outliers were eliminated for being incompatible with neighboring stations, with the remaining 85 percent being retained.

It looks as though Hansen is including in his 6,300 GHCN figure the extant 1,221 USHCN surface stations (which Anthony Watts is surveying mentioned in my OP) because he does refer to US trends in the article as well as the global mean temperature. The USHCN is part of the GHCN but, again, only a small percentage of these US stations CURRENTLY go into the GHCN for the purpose of measuring the “real-time” gmt , as I understand it. (All of them may be used, of course, in the course of US domestic climatic research.)


Knowing which stations go into which datasets is tricky, but essential. One thing you can ignore when speaking of the gmt is all the countless thousands of stations worldwide in the National Met Bureaux’s own archives of their local stations. Whilst these national archives DO include the handful that are sent to NOAA/NCDC for inclusion in the GHCN set, they are, otherwise, quite distinct and do not contribute to the gmt calculations. When you find, for example, the Russian’s claiming that GHCN (i.e GISS and/or CRU) have cherry-picked warm stations they are doing it on the basis of comparison with their own COMPLETE national datasets.

I believe the figure of 6,300 GHCN surface stations given by Hansen is designed to obfuscate rather than enlighten. It may be “true” but it is not the whole “truth”. It is a half-truth. Just as the claim from NCDC that the last 50 years saw a rapid rise in US temperature is only a half-truth, in that similar temperatures were previously experienced in the 1920s and 1930s.

Half-true statements like these make me doubt the Hansen/GISS/CRU/IPCC narrative of the “unprecedented” temperature rise in the late 20th century.

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