More areas of the US have thermometers installed than ever before. But more importantly, thermometers now are more accurate AND more precise than ever before, measuring in tinier increments than ever before. So a 1/100th of a degree higher reading than a 50 year-old mercury reading is trumpeted as a record high temperature.
Lessee...how close to the blacktop and those air conditioners can I place this new digital temperature device?
/s
The variation of temperatures on which the warming theory relies are all within the error band and have no statistical meaning. That is why no climate science stories ever report statistical tests of significance. If they did they would blow their own cover.
Don’t forget that the thermometers that gather this important data are often surrounded by heat sinks.