In a response to reporter Doyle Rice of USA Today, Dr. Reto Ruedy — a senior scientist at NASA — recommended the following:
Continue using NCDC’s data for the U.S. means and Phil Jones’ [HADCRU3] data for the global means. …
We are basically a modeling group and were forced into rudimentary analysis of global observed data in the 70s and early 80s. …
Now we happily combine NCDC’s and Hadley Center data to … evaluate our model results.
This response was extended later the same day by Dr. James Hansen — the head of NASA GISS:
[For] example, we extrapolate station measurements as much as 1200 km. This allows us to include results for the full Arctic. In 2005 this turned out to be important, as the Arctic had a large positive temperature anomaly. We thus found 2005 to be the warmest year in the record, while the British did not and initially NOAA also did not. …
It should be noted that the different groups have cooperated in a very friendly way to try to understand different conclusions when they arise.
Two implications of these emails: The data to which Phil Jones referred to as “independent” was not — it was being “corrected” and reused among various climate science groups, and the independence of the results was no longer assured; and the NASA GISS data was of lower quality than Jones’ embattled CRU data.
The NCDC GHCN dataset mentioned in the Ruedy email has also been called into question by Joe D’Aleo and Anthony Watts. D’Aleo and Watts showed in a January 2010 report that changes in available measurement sites and the selection criteria involved in “homogenizing” the GHCN climate data raised serious questions about the usefulness of that dataset as well.
These three datasets — from NASA GISS, NCDC GHCN, and CRU — are the basis of essentially all climate study supporting anthropogenic global warming.