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The last couple of days I posted on an 8.5 year side-by-side test conducted by German veteran meteorologist Klaus Hager, see here and here. The test compared traditional glass mercury thermometer measurement stations to the new electronic measurement system, whose implementation began at Germany’s approximately 2000 surface stations in 1985 and concluded around 2000.

Hager’s test results showed that on average the new electronic measurement system produced warmer temperature readings: a whopping mean of 0.93°C warmer. The question is: Is this detectable in Germany’s temperature dataset? Do we see a temperature jump during the time the new “warmer” system was put into operation (1985 – 2000)? The answer is: absolutely!

1900 to 1985: almost no warming

Josef Kowatsch, an independent scientist and regular contributor at EIKE, has looked at the German temperature dataset and discovers that Germany’s mean temperature indeed coincidentally jumped by a similar 0.9°C during the same period. First he sent me a chart depicting Germany’s annual mean temperature from 1900 to 1985, measured using the old glass mercury thermometers:

For 85 years the trend was pretty much consistent, hovering at about 8.2 or 8.3°C. As indicated by the bold black line, there was an increase from 1900 to 1935, followed by a slight decrease from 1935 to 1985, i.e. in a time when CO2 emissions were rising strongly worldwide.

1986 – 2000: massive warming

Next Josef sent me a second chart depicting Germany’s mean temperature trend while the country was transitioning over to the new electronic measuring system, described here, from 1986 to 2000:

Here we see the trend for the period rising strongly, from about 8.4°C to 9.3°C, i.e. precisely during the instrumentation transition period! This too happens to be a rise of 0.9°C, which coincides precisely with the results of the side-by-side temperature measurement test Hager conducted over 8.5 years comparing mercury thermometers to electronic ones. That could be a sheer coincidence, but on the other hand it is screaming to be investigated.

2000 to present: no warming

Next Kowatsch provided a chart showing Germany’s mean annual temperature for period 0f 2000 to present, i.e. the period that has been using the new electronic measurement system:

Here we see there is no longer any rising trend, but that the mean temperature is at a new, higher plateau. As a result, almost the entire mean annual temperature rise Germany has seen since 1900 occurred during the single short 1986-2000 period. Josef Kowatsch commented (by e-mail):

In these 15 years, did CO2’s greenhouse gas effect suddenly go into action? Who switched on the CO2 greenhouse gas effect for these 15 years?”

Moreover, didn’t Germany’s national DWD Weather Service check and calibrate the new electronic system to be sure it would produce results similar to the earlier used mercury thermometers and thus ensure the recording of reliable data? Hager says they never did, and it seems they were quite content to adopt the warmer readings.

The following chart is a plot of Germany’s mean annual temperature over the entire 1900 to present period:

Chart adapted from here.

To me this all appears to have all the elements of an epic instrumentation debacle that is as bad and sloppy as any could get. Again, I repeat: Hager writes that the DWD never conducted any systematic comparison tests in order to be sure the new electronic ones were producing reliable daily data.

If this is really the case, then we can be happy that the DWD is not in the business of calibrating altimetry systems for commercial jets.

Of course the 1986 – 2000 rise likely is not solely an artifact of poor instrumentation calibration, as part of the warming is surely due to the natural ocean cycles which pushed global temperatures up during the end of the 20th century. However, the results of Hager’s comparison test are difficult to ignore and raise lots of questions.