This probably isn't the place for such a discussion. PJ is probably going to
lower the lid on us shortly. However until she does ...
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.
It was Mann who did the flawed PCA.
M&M merely exposed the flaws. You deliberately misconstrue M&M as an
attempt to build a valid proxy reconstruction. They were not attempting to do
this and made no claims to have done so. They simply showed that what Mann had
done was not a valid reconstruction.
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.
How can you say Mann's work passed validation. Quite apart
from the fact that validation is meaningless when using a broken methodology (he
didn't properly center his data) - his reconstruction has an R value of zero!
Once again, M&M were not attempting to build their own reconstruction and so
the rest of your comment simply builds and destroys a straw man (straw
Mann?).
Regarding the Medieval Warm period: er, who denies it
was warmer then, than during the Little Ice Age that followed?
Mann came pretty close to denying this.
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)
And yet
Greenland today isn't green and grapes don't grow well in Britain. Funny that.
There are many reconstructions that show a MWP just as warm if not warmer
than today. No doubt those are the ones you have cherry picked away by accusing
them of cherry picking. (recursive cherries?)
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.
Temperature reconstruction in the MWP
is at best uncertain. This uncertainty (which is often uncertainty as to date)
smooths the temperature graph when different reconstructions are averaged
lowering estimates of rate of change. Comparing rate estimates in the MWP to
rate estimates today is therefore comparing apples and pears.
Rather than
look at the MWP why not look more recently where we have much better data.
Temperatures rose in the period 1920-1940 at almost exactly the same rate as
they rose in the period 1970-1990. Note that the earlier rise occurred too early
to be significantly effected by burning of fossil fuel.
How can you say
there is no sign of slowing? Temperatures have been essentially flat since the
peak in 1998 and are tracking at well below the IPCCs most optimistic
temperature scenario based on zero emissions despite the world having singularly
failed to halt the rise in CO2. Yes this could be merely a temporary plateau in
an overall upward trend. But 14 years is really starting to stretch my
definition of temporary.
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 here.
This is indeed the claim
often made - that coincidentally the warming only occurred in the one place
where people were actually measuring the temperature and it was actually really
cold everywhere else. But actually the MWP does show up in other places wherever
one can overcome the difficulties of accurately reconstructing temperatures.[ Reply to This | Parent | # ]
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