Russ Steele
Here is the science. As study on Recent California climate variability: spatial and
temporal patterns in temperature trends by Steve LaDochy, Richard Medina1, and William Patzert.
This is the chart under investigation. Look at the blob in Western Nevada County
Click graphic for a larger image.
Here is the problem. The graphic shows that the minimum temperature, hence forth Tmin, was rising faster than Tmax, the maximum temperature.
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Here is the analysis. I have been tracking Grass Valley temperatures and have not seen an increase in Tmin over Tmax. In fact I have seen Tmin, Tmax and the mean, Tmean decline. So I plotted the Grass Valley Tmin/Tmax/Tmean from 1950 to 2000 with a regression line. As you can see no increase across the board, in fact the regression line shows cooling. Hummmm....
Next I downloaded the Nevada City data from Western Region Climate Center in Reno. The same data set used by LaDochy and his fellow scientist. Below is the plot of the data with a regression line in a contrasting color.
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Look at the growth in Tmin from about 1976 to 2000. Why? That is the subject of our investigation.
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Here is a picture of the sensor site, near the water processing plant, close to a black top road. Can the extra humidity produced by the water plant influence the Tmin.
According to Anthony Watts, that is one possible reason. When you look at the graphic, the increases in Tmin, starts about the middle of 1970, which is when the site was moved to this location. The Water Plant operator has the written history on file from about 1951 to the present and is willing to allow access. He and I will be going over this record in the coming weeks looking for clues for the increase. In the mean time, I will be studying the impact humidity has on Tmin. Anthony has suggested I start with works by Hubbard.
Right now it does not look like it was global warming that caused the blob in Western Nevada County, but sighting of the sensor. More on this as we dig in to the record. Why did the change start with relocation? Also why was Tmax not influenced by the move? Stay tuned.