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Bogus arguments about bogosity? | 198 comments | Create New Account
Comments belong to whoever posts them. Please notify us of inappropriate comments.
Bogus arguments about bogosity?
Authored by: Anonymous on Thursday, October 25 2012 @ 11:12 PM EDT
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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