In one of Steve Goddard's posts at WUWT, there was some mocking of interpolation in GISS. "Is the temperature data in Montreal valid for applying to Washington DC.? " was asked.
Well, it turns out, yes it is, using anomalies. I looked in the raw GHCN data at McGill Montreal (71627/003), which has the only long GHCN record there, vs Washington NA (WMO 72405/000), which also has a very long record. I used a 4-year tapered smoothing filter (triangle) on the monthly data. Here's how it turned out:
Anomalies are relative to each station mean over the period. Notice the slip at about 1915, where Montreal seems to go up about half a degree relative to Washington. It could well be a station move or change. This is just the sort of thing GISS type algorithms can pick up, even so far apart. But this is unadjusted data.
We might not be certain, but…..
1 hour ago