Joe,

Interesting. However, as you know, "proxy data" is never data, at all. A better term is
"educated guess".

However, even Greenpeace postulates that the hockey stick may well be right:

THE "MEDIEVAL WARM PERIOD"

Evidence from a variety of sources, such as tree rings, ice cores, historical documents,
glaciers, geology, and borehole temperatures, suggests that there may have been a
period of climatic warming between the ninth and fourteenth centuries, when
temperatures were higher than at the start of the 20th century, at least in some parts of
the globe. These include Scandinavia, China, the Sierra Nevada in California, the
Canadian Rockies and Tasmania. Evidence from other regions, such as the south
eastern United States, Mediterranean Europe, and parts of South America, shows that
during the same period temperatures were little different from later times. This
postulated period has been called the Medieval Warm Period, and is widely believed to
have been followed by the Little Ice Age.

Climate reconstructions from tree rings show little evidence for a sustained warm period
during the last 1000 years, except in the Sierra Nevada, the Great Basin, and the Polar
Urals. However, consistent features are a cooling tendency in the early and mid- 17th
century, and a warm period between the mid-12th and early 14th centuries. Ice core
evidence is being treated with caution, although it suggests warming during the early
centuries of the second millennium. Historical evidence is largely based on records of
crop planting in more northern latitudes than the present, and on archaeological
evidence from settlements in Iceland and Greenland. Glacial evidence appears
stronger, with glacial retreats in Europe and elsewhere before AD 900 and after 1250,
but not between these dates. Borehole temperature records are too coarse at present
to give accurate indications, but it appears that sometime between late in the first
millennium and the middle of the second, there was a period of undetermined length
with above average temperatures.

The evidence is not conclusive. Warmer conditions may have prevailed in some
seasons in some regions during the period of interest. Much of the data that had been
formerly used to present a more conclusive picture of the Medieval Warm Period, and
of the Little Ice Age, have now been superseded or discarded. What the current data
does show is that variability in climate on a decadal scale is apparent over the last 1000
years, but because the data is so incomplete, it is very difficult to use it to predict future
climate trends. (M.K. Hughes and H.F. Diaz, "Was there a 'Medieval Warm Period?",
Climatic Change, v.26, p.109-142, March 1994).

GREENPEACE Climate Impacts Database

In addition, I have heard (have no reference at hand) that, during this same period, the
tropics were cooler. If so, the global average may not have budged much.

In any case, isn't this rather academic when we are faced with vast increases of
atmospheric CO2 and correlated increased global average temperatures over more
than a century, as shown by the business end of the hockey stick?

Best regards,

Brian



On 17 Dec 2003 at 12:15, Joe Fjelstad wrote:

> http://www.technologyreview.com/articles/wo_muller121703.asp
>