In 2000, NOAA changed some of its reporting for the US Historical Climate Network Data. In 2007, Steve McIntyre discovered an inconsistency about how GISSTEMP processed the information. Obviously this error could only affect post 2000 data, but mysteriously many reports claimed that this had forced GISS to re-rank 1934 as the warmest US year instead of 1998 and the change had arisen from the correction found (Eli will resist the temptation to snark) by Blogger McIntyre (sounds Canadian, eh?). Even Gavin Schmidt on Real Climate appears to have gotten this wrong on 10 August 2007, which was very early days in the controversy
Frankly Eli paid it no never mind at the time, because the difference between 1934 and 1998 was not even fractional either way (0.01 C or so). There was a significant effect on the post 2000 years which affected their rankings for the US data. Still there were lots of such reports
We find the solution in an Email from Makiko Sato to James Hanen 24 Aug 2007:
"Of course Reto thinks the ranking that shows which year was warmer by 0.01 deg is stupid. But as long as I give the table of US mean temperature on our web site, people can make rankings themselves. What Reto wanted to tell you was from Jan 7 - Aug 7, 2007 we had 1998 warmer than 1934 by 0.01 deg in the table I showed on our web page. (The reason was those numbers keep changing by such a small amount by adding station data, as probably as Reto pointed out, we processed data in January before a lot of data came in. These recent data can change numbers in old time by small amounts.) From next time I will update the US mean table every month. I was doing it only once a year because I didn't think people would make such a mess out of 0.01 deg difference in US. 0.01 deg is negligible globally but even 2% of that for the US."Reto Ruedy lays out the details of the thing on 23 August 2007
The US temperature graph in our 1999 paper, based on GHCN data, shows 1934 0.5 C warmer than 1998; 1998 was in 5th place behind 1921, 1931, 1938, 1953.Remember this is for the US, something a lot of people disremembered sort of on purpose
In the corresponding graph in our 2001 paper, now based on the carefully corrected USHCN data, 1934 and 1998 are in first, 1921 in third place (NOAA who provided the USHCN data had 1998 slightly ahead of 1934).The final summary on GISSTEMP for 2007 states
The US table we had posted during all of 2006 showed 1998 and 1934 even at 1.24 C (I got a copy from a journalist in Brazil, we don't save these data).
As far as I know, the US table on our site from Jan to Aug 2007 was the first and only one with 1998 ahead of 1934, some US stations must have still been missing in the GHCN file we downloaded on January 8, 2007. (Each month GHCN regererates the whole file over a period of a few days; In previous years we had to wait til mid January for the US stations to be added in again.)
Finally, we note that a minor data processing error found in the GISS temperature analysis in early 2007 does not affect the present analysis. The data processing flaw was failure to apply NOAA adjustments to United States Historical Climatology Network stations in 2000-2006, as the records for those years were taken from a different data base (Global Historical Climatology Network). This flaw affected only 1.6% of the Earth's surface (contiguous 48 states) and only the several years in the 21st century. As shown in Figure 4 and discussed elsewhere, the effect of this flaw was immeasurable globally (~0.003°C) and small even in its limited area. Contrary to reports in certain portions of the media, the data processing flaw did not alter the ordering of the warmest years on record. Obviously the global ranks were unaffected. In the contiguous 48 states the statistical tie among 1934, 1998 and 2005 as the warmest year(s) was unchanged. In the current analysis, in the flawed analysis, and in the published GISS analysis (Hansen et al. 2001), 1934 is the warmest year in the contiguous states (not globally) but by an amount (magnitude of the order of 0.01°C) that is an order of magnitude smaller than the uncertainty.Never mind although Eli assumes some will proceed to have the vapors.