From the looks of the USHCN graph above, you would think that temperatures at Long Beach, Washington were getting a lot warmer. More than a degree warmer since 1950.
Whether or not the temperatures are getting warmer, one thing for sure, the trend we see is due to adjustments. The plot below shows USHCN final temperatures minus measured temperatures.
In the 1950s, they subtracted about 2.2 degrees from the thermometer readings. Starting in the late 1960s, they subtracted 1.2 degrees from the thermometers, and in recent years they have subtracted between 0 and 0.5 degrees from the thermometer readings.
By making the past progressively cooler, they have made the present appear to be getting warmer.
Here is their explanation for why they do it.
Here is the spreadsheet with my calculations.
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