KNMI has been measuring the wrong temperature for years
WUWT reader Mike writes with this little bombshell on one of the world’s leading meteorological agencies. It seems they can’t get their thermometer siting correct which resulted in a bias to the record. Hmmm. Where have we heard this before? The newspaper “AD” in the Netherlands has picked up the issue with two separate stories.Mike writes:
Dear Anthony,
I left this on the “tips” thread on WUWT, but since it is also relevant to surface stations, I felt you should hear of it directly. It probably deserves a whole story on WUWT.
As you probably already know, KNMI De Bilt is the only station in the Netherlands used for GISTEMP. The nearest long-term station is in a suburb of Brussels, hence is undoubtably UHI-polluted. De Bilt is the only long record stn in NL & within 150km in any direction would be a useful correction.
Two stories caught my eye in the Dutch papers today about a 0.5-degree error in the De Bilt record which was miraculously corrected this summer with a station move of 200 m without anyone being told of it. Here are the links to and my translations of the articles.
Mike’s translations of the newspaper stories are below, I’ve added relevant graphics. – Anthony
The instrument stood too close to a line of trees, due to which on average half a degree (Celsius) too high was measured.
After discovery of the fault the thermometer was moved to an open spot on the measurement field before last summer, the KNMI has confirmed. Due to the change the average measured temperature fell half a degree. This measurement should be reliable.
The mistake resulted in that the KNMI has announced more “official” summery and tropical days than there were in reality. According to the Institute, the defect has not or hardly influenced the scientific discussion on climate change, because researchers use the data from a large number of weather stations. SUZANNE DOCHTER
Above: GISS Temperature plot for De Bilt KNMI – notice the step function. Click for source data.
Here’s a picture and metadata for De Bilt, direct from KNMI. While I can’t be certain, this photo appears to be after the move:
Checking some nearby stations in GISS, click for source data:
The GISS plot for Maastricht Airport:
One whole data point? Why does GISS keep a station in the database with only one data point?
UPDATE: Well if GISS can’t find the data for Maastricht Airport, everybody else can, and damn quick:
See Weather Underground for current conditions.
And this website, tutiempo.net , has the complete climatic data set back to 1949.
http://www.tutiempo.net/en/Climate/Maastricht_Airport_Zuid_Limburg/63800.htm
Call out to GISS: Hey Gavin, as an American Taxpayer that funds your work, I request you take a moment from moderating realclimate.org and put some work into updating this record.
Here’s the next closest station, Essen, according to GISS a city of 7.5 million – doesn’t look much like the KNMI record:
2nd story —
KNMI has been deaf to criticism for years
WAGENINGEN – weather Institute KNMI has been deaf to years of criticism from competitor Meteo Consult of its temperature measurements in De Bilt
Weather specialists from the Wageningen-based Meteo Consult have been expressing their distrust for years, because the KNMI figures in De Bilt were always a bit warmer than in Cabau, 16 km away, where there is also a KNMI thermometer. The position of both places could, according to Meteo Consult, not explain the temperature difference of on average half a degree (Celsius). It was also not taken into account that De Bilt is located in a more built-up, and probably therefore warmer, surroundings than Cabau, near IJsselstein.
The meteorologists from Wageningen discovered this summer to their amazement that the temperature difference between both places in the KNMI figures had more or less disappeared. On enquiring of the De Bilt employees, it appeared that the thermometer had been moved. Since the intervention, the measurements from De Bilt show not 1/2°, but on average just 2 hundredths of a degree warmer than Cabauw, according to the spokesman of Meteo Consult.
This summer it appeared that the temperature difference was suddenly resolved. Again discussions blazed between the weather specialists and it was decided to closely compare the measurements between Bilt and Cabauw. “It was thus discovered that last summer in De Bilt was still 1/2 degree warmer and this year there was just a difference of 0.02 degree Celsius”, explained a spokesman of Meteo Consult.
The organisation decided to call the KNMI and heard that the “weather cabin” [translation: Stevenson Screen], in which the thermometer is located, had been moved. According to the KNMI the measuring instrument stood too close to a row of trees. Because the trees continued to get taller, the wind began to influence the temperature measurements too much. Now the “weather cabin” has been moved 200 m away, to a more open spot on the measurement field of De Bilt. KNMI employee Cees Molenaars cannot say how much influence the old placement of the thermometer has had on weather reports. “We must investigate that. We only regret is that we did not keep Meteo Consult and other parties informed of the movement.”
The thermometer of De Bilt is the official measurement used for determining heatwaves, cold waves, and summery days. To speak of a heatwave it must be at least 25°C released 5 days. Also it must be warm than 30° for 3 days. At 25° one can talk about a summery day.
With a cold wave, freezing temperatures must be measured for 5 adjoining days at De Bilt, with also 3 days with a hard frost. “The differences in minimum temperature between de Bilt and Cabauw were much smaller,” said the spokesman of Meteo Consult. “The chance that a cold wave is missed, is thus smaller.”
The thermometer in De Bilt has less influence on KNMI weather predictions. These are performed on the basis of the data of tens of measurement stations. Further, for scientific purposes, such as climate change research, the central Dutch temperature was brought to life long ago. For this, data from various stations is used [NOT TRUE — GISTEMP ONLY USES DE BILT!]. Meteo Consult are above all happy that the riddle has been solved. For fun they have also calculated what an extra half degree in De Bilt would have meant for this summer: 5 extra summery days and 2 tropical ones.
====================
Coincidentally, I’ve been conversing with Jos de Laat of KNMI, the Dutch Meteorological Institute who offered some scans of weather station siting specifications from the World Meteorological Institute (WMO)
he writes:
OK then, you can find the first part of the report here (~ 1 Mb):
http://www.knmi.nl/~laatdej/TMP/WMO488.pdf
Especially the beginning of part 3 is relevant, I guess. Because of document size considerations for now I only scanned up to paragraph 3.1.2.1.7 (after paragraph 3.1.2.1.7 the description of requirements for measuring on other locations like sea and the free troposphere starts).
Descriptions of sensor and siting requirements are also available online (see below) …
… but they are more formal and largely based on WMO report 488, which contains some interesting quotes that are not present in later reports. The online reports also refer to the report below, which unfortunately I was not able to locate either online nor in our library.
World Meteorological Organization, 1993a: Siting and Exposure of Meteorological Instruments (J. Ehinger). Instruments and Observing Methods Report No. 55, WMO/TD-No. 589, Geneva.
These specs are worth a read, because they show that quite a lot of thought and analysis went info choosing the specs.
As for the 100 feet cited by the NWS on this page: http://www.nws.noaa.gov/om/coop/standard.htm
I suspect its a round off of 30.48 m where 30 meters is the minimum distance to an artificial heat source cited for a Class 2 climate site as defined by the specs used in the Climate Reference Network (CRN) which has a French lineage, and likely traces back to WMO.
It seems that no matter where you look, meteorological agencies can’t follow siting specifications.
Steve McIntyre of Climate Audit has more on De Bilt and the adjustments that are being applied there:
http://www.climateaudit.org/?p=1650
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OT: It has been confirmed,
COLDEST SEPTEMBER TEMPERATURE ON GREENLAND: -46.0 C
http://vejret.tv2.dk/article.php/id-25292765.html
OT: Greenpeace is at it again, someone needs to shut down this terror ring.
http://www.pittsburghlive.com/x/valleynewsdispatch/s_644707.html
Urederra (09:05:17) :
The instrument stood too close to a line of trees, due to which on average half a degree (Celsius) too high was measured
Strange. My common sense would have said that if there is a line of trees shadowing the thermometer, this should read lower temperatures, not higher.
That would be a natural conclusion if the trees shade the instruments for some time during the day. If, however, the trees are on the north side of the instrument package, they could, presumably, reflect sunlight onto the instruments. The explanation put forward by AnonyMoose is also plausible and valid.
The temperature drop after moving the instruments should give one pause in claiming “global warming” at this site.
http://heliogenic.blogspot.com/2009/09/eu-ets-kaput.html
Cold greendland warm west europe. But the NAO can change in a month.
19.955M
Mark (10:35:29) :
Do these people and organizations that take care of these weather stations ever make ‘mistakes’ that end up with a negative bias?
What a great question! I’m not aware of a single documented case myself, but there might be one out there, lurking, somewhere… Anyone?
They managed to find Normandy.
“Do they ever make mistakes that end up with a negative bias?”
Not often.
It is easier to make an “honest mistake” that adds an upward bias. For example, urban sprawl only engulfs a sensor that was previously in the country, the reverse doesn’t happen. Green spaces get converted into black-top parking areas and highway, the reverse seldom happens. Air conditioning gets added and is seldom removed.
Secondly, and more sadly, data sanitization is dependent on the observers. People expecting an up-trend will soon find a way to fix a down-trend sensor.
The temperature record from De Bilt is one of the longest continuous records in the world and is often praised for its usability in climate studies. Sadly it appears that the data available from GISS, also used by Anthony, is faulty. There are at least two issues: both the raw and homogenized GHCN data deviates strongly from the official KNMI measurements (both uncorrected and homogenized), which have been available for decades. Second, GHCN claims to have De Bilt measurements before 1897, the year that measurements started there. Before 1897 measurements were taken in Utrecht, Haarlem and Zwanenburg (near Amsterdam). These series were combined by KNMI into one homogenized record for the central part of Netherlands, starting in 1706. The GHCN series deviates from that homogenized series as well. Notably, though the differences disappear almost entirely after 1951. This is the year that KNMI starting use a better type of radiation shield and lowered the sensor from 2.2 meters to the current 1.5 meters (WMO standard).
I have made NASA/GISS aware of the issues with the De Bilt series in the GHCN and pointed them to the proper data source for updating/replacing the record of De Bilt in the GHCN database. For those interested, I made an intercomparison of the De Bilt series from GHCN raw (blue), GHCN homogenized (red) and KNMI homogenized (green): http://benlanka.tweakdsl.nl/climate/comparison.jpg
Ben Lankamp
Meteorologist from The Netherlands
If moving a thermometer a couple hundred meters can chop a half degree off “global warming”, maybe we ought to move ’em all! 🙂
Best,
Frank
the only place with a negative bias could be a themometer in tjernobyl
for a birdseye view of the trees on the side of the observation field see:
http://www.bing.com/maps/default.aspx?v=2&FORM=LMLTCC&cp=spgv8xhdy769&style=b&lvl=1&tilt=-90&dir=0&alt=-1000&phx=0&phy=0&phscl=1&scene=11657685&encType=1
[i]Strange. My common sense would have said that if there is a line of trees shadowing the thermometer, this should read lower temperatures, not higher.[/i]
This is a common feature in Holland we call the “garden effect”: narrow gardens with 6 ft walls between them generate microclimates with significantly higher temperatures then the official readings give and gave the effect its name. This only works if the north side of the compound is sheltered from cooling northerlies. It seems that the KNMI suffered from “garden effect”, an effect that any amateur takes into account and tries to avoid (if possible) when setting up a weather station.
anybody interested in homogenised de bilt (my homogenisation!) relative to rural hohempeissenberg
http://members.casema.nl/errenwijlens/co2/europe.htm
So they have been measuring Double Dutch? Maybe they should have chopped down the offending trees and done some ring analysis to correct the past and future temperature records 🙂
Oh wait… yes this is Holland we are talking about… they don’t even cut the grass on the road verges anymore, let alone cut down trees. Silly me.
jeroen (15:53:10) :
I think it had a massive spike a while back 😉
Hans Erren: Judging from the map it looks like a very good site. Much better than nearly all the US sites.
Of course it is well known that a small site change even from one “good” location to another can result in large differences. But it is an eye-opener that a site move so small in relation to trees so distant should result in such a large step change.
It certainly makes one wonder how well documented these changes are and what the margin of error is regarding the adjustments. Homogenization doesn’t fix the problem, though, it just spreads it around and makes it harder to detect.
Murray Carpenter (11:16:12)
forgive the blunt question, but who the heck would pay any attention to the Met Office? They don’t know what on earth is happening at the present,at least if the present consists of between 2007 and 2009, but can predict exactly what will happen in 2080?
This is the same sort of Alice in Wonderland answer they reply to my questions, and its not in my nature to be vituperative about a scientific organisation’s response, so I just don’t question them anymore
To feel cooler, I often sit under a tree that adjoins my patio, but does this report mean that if I sat in the sun under an umbrella and far from some trees I would feel even cooler? (By the way, does “umbra” means shadowed or shaded? I think “ella” is a diminutive, meaning a “a little”, so does an “umbrella” provide a “little shade”?)
Anyhow, can anyone explain to me why nearby trees that are providing a little shade near a sensor would cause temperature readings higher than normal? Pardon my ignorance, but is this because of heat generated by decaying vegetation that often is found under trees unless it has been raked up and removed? Or is there another reason?
This raises an interesting issue about slowly growing time-span biases in temperature measurements. If there are trees growing near the thermometers over a period of years, does this compound the growing bias over time caused by the heat island that also is growing near the sensor — e.g., more asphalt parking lots are paved (sparing the nearby trees), more people are moving into bigger buildings that must add more heat-generating air-conditioning condensers, wider paved roads are built for better access by more traffic to the bigger buildings, etc?
So do trees growing within the growing urban heat island create a sort of temperature bias double-whammy?
evanmjones (16:35:12)
Homogenization doesn’t fix the problem, though, it just spreads it around and makes it harder to detect.
So we fix the problems, spread it, nobody knows.
It seems that James Hansen at GISS is breaking some sort of law by tampering with temperature data.
RealClimate says this change of location is nothing? This opinion of theirs tells more about they themselves than they know.
REPLY: AFAIK they have not commented on it. That was sarcasm from an earlier commenter. – A
Espen (08:16:22) : I tried to find stations with long records in Holland, and found De Bilt (near Utrecht) which shows the same result of homogenization as the arctic cities: The temperatures from 1881 to 2009 first shows a flat trend (-0.05C/century), but after homogenization there’s suddenly a +1C/century trend! For Milano, Italy, it’s even stranger – a -0.7C/century trend is turned into a +0.7/century trend. I.e. the homogenization performs the reverse of an UHI correction, despite the fact that Linate is an airport very close to a huge city!
Notice the part about Milano here. I’m starting to believe that the GISS data for Europe (and probably other parts of the world too) is even worse than what you have discovered in the US with the surfacestations project. And the CRU data we can’t even evaluate…
This is a direct result of the processing done in the PApars.f program using “reference stations” up to 1000 km away. Many of these are in the mountains and in particular Hohenpeissenberg is the longest lived station in the area. This means it is applied first for “UHI” correction. One Small Problem: It is on the edge of the Alps and rather cold and GIStemp has what I think is a “bug” in the processing so that the first station applies a bias (rather than correcting it out). The end result is that anything within 1000 km of Hohenpeissenberg ends up with a bogus UHI correction. A second effect comes from other cold high mountain stations also making the UHI go the wrong way. GIStemp claims not to do this, but the result of running the code and reading the code says otherwise. Details at:
http://chiefio.wordpress.com/2009/08/30/gistemp-a-slice-of-pisa/
The end point conclusion is rather simple: GIStemp is fatally flawed and produces a useless temperature series.
Given that HadCRUT is the “dogs lunch”…
We’re left with not much of a foundation for the AGW fantasy.
The reports about the “on average half a degree error” are erroneous themselves.
Newspapers are not to be relied upon, at least not with regard to scientific data, because in general news-reporters are often more interested in writing juicy stories than to present objective balanced information. This certainly applies here.
It seems that the “journalists” based themselves upon an article of Meteo Consult which speculated about the alleged measurement errors of the KNMI at De Bilt. That article compared data from De Bilt with a location at Cabauw about 16 km away from De Bilt, comparing data over the period 15 May – 15 September in 2008 and 2009.
It seems that numbers were selectively taken from that article and were misinterpreted along the way. Meteo Consult found out that the average maximum temperatures in the summer of 2008 were 0.53 degree higher for De Bilt compared with Cabauw, while the difference was only 0.02 degree in 2009. So I guess this is where that “half a degree error” comes from.
But what the newspaper articles don’t report is that Meteo Consult also found out that the average minimum temperature at De Bilt was actually 0.36 degrees lower in 2008 and 0.22 degrees lower in 2009 compared with Cabauw! That finding probably wasn’t helpful for a juicy story.
So you see, the reports about the “on average half a degree error” are based upon misinterpreted selectively chosen data from speculations. However, it is true that the station at De Bilt was moved to a better location. I will lookup some real data and post it in my next message.