McArdle's citing Willis Eschenbach's "research" has attracted a flock of global warming deniers. Drum has seen this song and dance before:
[V]ia Tim Lambert, here's an excerpt from the original NOAA paper that explains how the homogenization was done:
A great deal of effort went into the homogeneity adjustments. Yet the effects of the homogeneity adjustments on global average temperature trends are minor (Easterling and Peterson 1995b). However, on scales of half a continent or smaller, the homogeneity adjustments can have an impact. On an individual time series, the effects of the adjustments can be enormous. [Italics mine.]
So, if you're a climate denier, what would you do? You'd look for local effects and you'd look for an individual time series. Look hard enough and you're bound to find some with large changes due to the homogenization. And then you'd cry foul. The books are being cooked!