A good number of official climate stations of record in the USHCN network used for climate studies are at airports. All have been converted to the automated ASOS systems, and the placement of these is often chosen to be away from the airport tarmac so that temperature and dewpoint readings aren’t biased.
While climate monitoring is a secondary consideration of these stations. keeping these readings accurate is vital to aviation safety, particularly in calculating density altitude, which is used to determine the maximum takeoff weight for an aircraft and what runway takeoff length would be needed for a given weight.
But what happens to the accuracy when your “out of the way” station suddenly sits just a few feet from a building and parking lot being constructed?
Alert volunteer Janet Elias helped me locate the USHCN station in Lafayette, LA. The Microsoft Live Earth map showed quite a surprise in the making:
Click for a larger interactive image
Of course it didn’t always used to be this way, the Google Earth image, which is a bit older, shows the area before the construction started:
Click for a larger interactive image
Here is the NASA GISS plot of temperature for this station. A call to the LFT airport authority at this contact from their website told me that the contract for the new fire station facility was awarded in July of 2005 and that construction started shortly after that. The new fire station, show being constructed in the top photo is now complete.
So that calls into question the last two data points on this graph, for 2005 (21.11°C) and 2006 (21.19°C), which happen to be the two highest annual average temperatures since the 21.56°C recorded in 1973. For some reason, the 2007 data is not complete yet you can view it here.
Are 2005 and 2006 the real measure of air temperature or a result of bias from the new fire station being constructed within a few feet of the LFT ASOS temperature sensor?
How would NOAA or NASA or Hadley know if they don’t check out the station environment and examine for such issues?
Click for full sized original data plot
Previously I’ve touched on the problems with airports and the ASOS system, including the warm bias that the acres of asphalt runways, tarmac, and buildings can impart into the climate record from USHCN stations placed at airports. Plus we have the maintenance and accuracy issues of the HO83 thermometers used in the ASOS stations initially, which has been shown to be very serious.
The primary mission of the ASOS was for aviation, and remains that today.
So the question arises: why is NOAA, GISS, and HadCRUT still using data from these airport stations as part of the climate record? You can’t correct what you don’t know about or don’t evaluate, and it seems clear that such site level encroachment biases are not being examined in detail by climate researchers.
UPDATE- Reader Davis Smith writes:
Fifteen miles north of the Lafayette airport is another temperature site named Grand Coteau. It seems reasonable to expect the two to have similar trends (using GISS adjusted data) due to their proximity. A comparison of the two for recent years is here :
Click for larger image
Looks like a divergence circa 2004.
I also plotted the 106-year difference between the two sites:
http://davidsmith1.files.wordpress.com/2008/04/0417082.jpg
Both sites are flat land with the Grand Coteau MMTS located on a campus in a small town while the Lafayette airport is being encroached by the urban parts of Lafayette. My suspicion is that the trend difference reflects urbanization.
REPLY: Thanks David, UHI due to encroachment is certainly a factor, but so is local site bias. I suspect the two are additive in this case.
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Perhaps someone could explain why station pairs are used.
To be able to see signs of global warming linked to CO2 you need two things (1) accurate CO2 data and (2) accurate temperature data. There is I believe accurate instrumental CO2 data but only since 1958 at Mauna Loa, as for temperature, well there are thousands of high quality rural weather stations throughout the world and especially in the US and the northern hemisphere that have long histories and NO UHI bias. These stations are totally uncontaminated and provide temperature data from a totally natural environment like Mauna Loa supposedly does for CO2.
What do warmers such as Hanson/Giss do, well, they compare data from a highly UHI contaminated urban city weather station with CLEAN data from a neighbouring RURAL station. They then Use some secret algorithm put all the data through a computer which then gives them the result in degrees C. The odd thing is that the result always appears to show a steep rising temperature trend when the neighbouring RURAL CLEAN data shows only a flat or a slightly rising temperature trend.
Would it not have been more logical to have discarded the contaminated data from the Urban stations and used only the clean data from the Rural sites.
Surely data from fewer clean stations is preferable.