Clive Best has come up with an early version of GHCN V1, which he says is from around 1990; GHCN V1 was released in 1992, and I think this must be from a late stage of preparation. Anyway, he has kindly made it available. I have been contending that GHCN unadjusted is essentially unchanged , except by addition, since the inception, despite constant loud claims that NOAA is constantly altering history.
I thought I would compare with the latest GHCN V3 unadjusted, which has data up to March 2015. This turns out to be not so simple, as the numbering schemes for stations have changed slightly, as have the recorded station names. Stations have a WMO number, but several can share the same number in both sets. They have a modification number, but these don't match.
So for this post, I settled on just one country, Iceland. GHCN is supposed to have done terrible things to this record. A few weeks ago, we had Chris Booker in the Telegraph:
"When future generations look back on the global-warming scare of the past 30 years, nothing will shock them more than the extent to which the official temperature records - on which the entire panic ultimately rested - were systematically "adjusted" to show the Earth as having warmed much more than the actual data justified.
Again, in nearly every case, the same one-way adjustments have been made, to show warming up to 1 degree C or more higher than was indicated by the data that was actually recorded. This has surprised no one more than Traust Jonsson, who was long in charge of climate research for the Iceland met office (and with whom Homewood has been in touch). Jonsson was amazed to see how the new version completely "disappears" Iceland's "sea ice years" around 1970, when a period of extreme cooling almost devastated his country's economy."
This was reported by NewsMax under the headline:
"Temperature Data Being Faked to Show Global Warming"
The source, of course, was Paul Homewood. Euan Mearns chimed in with:
"In this post I examine the records of eight climate stations on Iceland and find the following:
There is wholesale over writing and adjustment of raw temperature records, especially pre-1970 with an overwhelming tendency to cool the past that makes the present appear to be anomalously warm."
So what did I find? Nothing that could be considered 'systematically "adjusted"'. There were differences, mainly with a clear reason. I'll list the eight stations below the jump.
Clive's V1 is accessible here. V3 in CSV format is here (10Mb zipfile). I have put the extracts relevant to Iceland on a small zipfile here.
A point of comparison is with the IMO records here. These, however, are not entirely unadjusted. They can be useful for resolving differences.
These two of the eight are very simple. Exactly the same in V1 and V3.
This is a long record, 1620 months to 1990. Of these nine have been changed. Eight are sign changes, one is a minor change. In all cases, V3 and the IMO record agree. Clearly V3 corrects errors in the V1 draft.
This is also a long record. There are a lot of apparent changes. However, the real situation is revealed by a table of their magnitudes, in the top row, vs number of occurrences in the bottom:
Size 0 0.1 >0.1 Number 864 211 3
Almost all changes (211) are by ±0.1. That is, a rounding difference, presumably from monthly averaging.
- HOFN I HORNAFIRDI and AKUREYRI
Again, a fair number of rounding differences, but at most four larger (>0.1) month changes in a long record
This actually had quite a lot of small changes - 159 in a 461 month record. But I found what is happening by looking in ver 2, which records duplicates. These are different records for the same location, but may be different equipment or measuring points. The V3 version and V1 version are both recorded as duplicates in V2. In V3, they chose whichever seemed best.
At this stage, I have run out of investigative zeal. Here's the frequency table
0 0.1 0.2 0.3 0.4 >0.4 1050 37 28 20 11 4
There are 100 discrepancies in 1150 months, small, but several bigger than rounding. No obvious reason.
It is clear that there is no "wholesale over writing and adjustment" in the GHCN V3 unadjusted file for Iceland.