In article ,
Martin Rowley writes:
snip
I have now ploughed through the data available on the NOAA-CIRES Climate
Diagnostics Centre site
(http://www.cdc.noaa.gov/) :
I'm not quite clear what averaging period was used though the
implication is that it runs from:- 1968 to 1996, though elsewhere on the
site, different periods are used.

Thanks, Martin. I've noticed in the monthly charts of thickness
anomalies covering most of the Northern Hemisphere that are published in
weather log, that the areas of positive anomaly almost always seem to be
much larger and more intense than those of negative anomaly, at least in
the winter months. Those take 1961-90 as their reference. So I suspect
that if one could compile a "running average" it would now be noticeably
higher than either 1961-90 or 1968-96. Another effect of GW?
--
John Hall
Johnson: "Well, we had a good talk."
Boswell: "Yes, Sir, you tossed and gored several persons."
Dr Samuel Johnson (1709-84); James Boswell (1740-95)