The strange death of the thermometers

Here is something really odd. The number of thermometers being used to calculate the global temperature seems to be declining and declining rapidly. In fact a huge proportion of the long term and intact temperature stations (the gold nuggets of temperature history) have been deleted from the global temperature record in recent years with no official comment as to why.

Given the current enormous interest in temperature trends you would think that the number of measurement points would be increasing rather than rapidly declining.

Are the stations still collecting data? Is someone choosing not to include them in the global calculation? Nobody seems to know.

This graph shows the astonishingly sharp recent decline of the number of thermometer stations included in the global average.

In the last 25 years there has been an accelerating reduction in thermometer counts globally with the pace of deletion rising rapidly in recent years. Over 6000 stations were active in the mid-1990s. Just over 1000 are in use today.

The stations that dropped out were mainly rural and at higher latitudes and altitudes — all cooler stations.

China had 100 stations in 1950, over 400 in 1960, then only 25 by 1990. Here is a chart with Chinese thermometer numbers used in the global calculations shown by year (the pink line).

As you can see there have been two drops in thermometer numbers. Earlier, we can see the drop in numbers coinciding with World War 2, but then the numbers rapidly rise back to a normal trend. In 1958, the numbers stabilise at about 400. This holds with astounding stability up until 1989 – 91; when if falls off a cliff to less than 40.

In the USA the number has dropped from 1850 thermometers at peak (in the year 1968) to 136 now thermometers (in the year 2009).

In Japan there now no thermometer records above 300 meters (Japan has no mountains now in the temperature record).

For California, where there were thermometers in the mountain snow and in the far north near Oregon there are now just 4 surviving thermometers all near near the beach and in the warm south (Mount Shasta with it’s glaciers and the snows and ice of Yosemite winters no longer feature in the USA’s temperature record).

All very odd.

One has to assume that the thermometers are still there collecting data but those compiling the global temperature estimates are just choosing to use far fewer stations in their calculations for some reason.

Needless to say there are plenty of conspiracy theories about this but I am not a big one for such theories. Nevertheless for such a huge change to occur in a dataset as crucial and high profile as the global temperature record with no explanation is very, very strange.