Email 1409, Sept 2009: Tim Osborn asks Phil Jones why New Zealand pre-1930 temperatures are "now very different, being much cooler (by > 0.5 degC for a 25-year low-pass mean)"

Email 1409

For my update I've used CRUTEM3v, expecting them to be rather similar but with a few more years on the end.

But the pre-1930 temperatures are now very different, being much cooler (by > 0.5 degC for a 25-year low-pass mean) in CRUTEM3v than CRUTEM2v. Previously they had been, on average, near or even above the 1961-1990 mean, now they're at -0.5 degC.

Is this a result of some homogenization work on New Zealand summer temp data? Or just some random artefact of minor changes somewhere?