During that same period, US minimum temperatures have increased about a quarter of a degree
The next graph shows that the difference between maximum and minimum temperatures has dropped precipitously.
Strongly elevated nighttime temperatures are the primary symptom of the Urban Heat Island effect, which appears in cities and towns of all sizes.
USHCN makes a token political adjustment of 0.1 degrees for UHI, but the actual effect is more like fifteen times larger.
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