I presume the "mathematical flaw" you refer to is the
principle component
analysis done by McIntyre & McKitrick,
which has been demonstrated to be
serious flawed, to the
point where it doesn't actually tell you anything about
the
hockey stick graph.
This page
has some detail (read Myth
#4):
Unlike the original Mann et al (1998)
reconstruction, the
so-called ‘correction’ by McIntyre and
McKitrick fails statistical verification
exercises,
rendering it statistically meaningless and unworthy of
discussion
in the legitimate scientific literature.
Regarding the
Medieval Warm period: er, who denies it was
warmer then, than during the Little
Ice Age that followed?
The most salient point is that every global climate
reconstruction made (that wasn't full of basic errors or
cherry-picked data)
clearly shows that temperatures over the
last couple of decades are
significantly warmer than the
warmest possible temperatures during the MWP.
(see e.g. t
his graph)
A more important point - look at the rate of change of
temperature around the MWP, and compare it with today. For
the MWP, it took
~300 years for global temperatures to rise
about 0.4 deg C. Global temps have
risen 0.8 deg C in the
past century, about 6 times the rate of rise during the
MWP,
and there's no sign they're going to slow down, either.
A further
complication is the regional distribution of
temperatures. The MWP was notably
warmer in the North
Atlantic, including in the eastern US, southern Greenland
&
Iceland, and Europe. Most of the rest of the world was
cooler than
normal. Compare that with today, where
temperatures are higher than the
peak of the MWP,
all over the planet. Great visual presentation he
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