[jstanley]

I don't know if average temperatures in December in Miami are particularly representative of anything, but I went to the trouble of plotting a graph of average December temperatures from the Miami link you gave, from 1990 to 2020, and I would say there does appear to be a slight upwards trend over time: https://img.incoherency.co.uk/3145

Picking 2 dates at random is not a good way to expose long-term trends, as evidenced by your observation that there can be several degrees of variation from one year to the next.