'They depress the temps that were actually recorded in past decades, in order to make today's temps look warmer: Below is a copy of national weather data summary for Feb. 1934. If we look at, say Arizona, for month we see that state avg. temps for that month was 52.0°F. However, if we look atcurrent NCDC temp analysis we see that for Arizona in Feb. 1934 they have a state avg of 48.9°F, not the 52.0°F that was originally published. Why do they do this?'