"John Hall" wrote in message
...

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?

..... I've kept a log of crude difference from the 61-90 climatology
using the 'Weather Log' charts for some years now. Looking at the 10
years 1995 to 2004, the overwhelming majority of months (no seasonal
bias as far as I can detect) had +ve anomalies (wrt 61-90).

Averaged over these 10 years, the difference (nearest half dam only ..
the size/scale+ of the charts don't justify anything more accurate) was
+1.5dam, representing an increase in the mean temperature through the
layer ( 1000 mbar to 500 mbar ) of between 0.5 and 1.0C.
Two of those years had consistent and dramatic excess over the LTA: 1997
and 2004 with anomalies of +3 dam (or roughly 1.5C increase in layer
mean T). Only one year (1996) had a negative anomaly, though 2001 was
close to zero.

Whether all this is due to GW, or circulation change I'm not competent
to say. However, I suggest that the size of the anomalies over a period
of 10yr can't be put down just to 'random' variation, particularly when
coupled to other studies which show an increase in lower tropospheric
warmth, both by classic observation and proxy series.

Martin.

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