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 Author: Citizen Runner Subject: RE: Greenland ice sheet melting faster than previously thought. PLEASE RECYCLE!

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rose colored glasses? wrote:

Thanks kindly for the paper CR.

Here is a look at the models of past temperature:

Image: http://i44.tinypic.com/15wj5i1.jpg

I think people should study that for a bit and dwell on it. I've read a little bit of the background information attached to the paper. These estimates are based on a large number of "proxy indicators" including tree ring data and numerous other bits of evidence.

The first thing I'd like to point out is that while each individual model represents its own inherent uncertainty (as a broad colour band adjacent to their best fit curve), these are CLEARLY all grossly underrepresentative of actual uncertainty, given that none of the other models, presumably each developed by competent scientists, agree with each other.

I believe you're using a different definition of uncertainty than they are. My assumption is that they are giving a measure of the statistics of the data and the way it is combined without any a priori knowledge of "truth", that is, it is a measurement of residuals from the curve fit. Data can be biased (reasons for this are discussed in the text) without being "noisy". You're looking for an assessment of how far off of "truth" is their estimate.

Now let's look a little closer at some specific aspects of the curves:

Image: http://i42.tinypic.com/344tixs.jpg

First look at the right side of the bottom graph. They are showing an overall measured temperature increase of about 1.3 degrees C since 1900. Earlier work we've looked at from the IPCC report shows about 0.5 degree increase. Is this paper using a different data source, or is there lack of agreement in the literature about actual recorded temperatures? Or am I maybe missing something? This is a VERY significant difference (more than a factor of 2), leading to potentially severe errors in interpretation.

The red line is instrument Northern Hemisphere Land-Only average temperature as discussed in the text. They include that because the reconstructions in that figure are NH. The grey line is the Global Average and is, I believe, the same as used in the IPCC report.

The second thing I'd like to emphasize from this second image is in the upper graph. Look at the huge range in modelledtemperatures around 800 AD. We have either increased global temparatures by 0.5C or 2C since 800 AD (if we are meant to believe the instrumented record, which I've just pointed out is suspect).

That's a difference of a factor of 4.

A factor of FOUR!!!!

These graphs represent the "data" against which our forward modelling are based. If our backward modelling, based on real scientific data, gives us uncertainty measured in ORDERS OF MAGNITUDE, then how culd we possibly trust models attempting to predict furture climate?

We can't in my opinion.

Several points:

a) The disconnect around 900 between the CPS and EIV results is discussed in the text, comparison of the two reconstruction approaches being the gist of the article. They note that the CPS approach seems particularly sensitive to a particular subset of the observation data. In any case they note that there are increasing uncertainties in the reconstruction that generally increase the further back one tries to look.

b) We have either increased global temperatures by 0.5C or 2C since 800 AD - Maybe this isn't what you meant, but there is nothing in AGW theory that claims "we", as in the human race, had any significant impact on global climate until the last few hundred years. Nor is there anything that denies natural variations.

c) While it's possible that the people doing climate modeling gravitate toward validation using reconstructed data points with significant uncertainty, if it were me, I'd lean toward using data from the instrumented history or more recent reconstructions where more comprehensive data is available if my interest is in estimating relative near term behaviors.

Coincidentally, I was reading Maclean's magazine today (Canada's most popular English language national news magazine), and there' a lengthy article on cimate, related to the general absence of normal winter in Canada (ad extremely severe winter in Europe and Asia). In the article, it is noted tha "before winter had begun, weather experts were warning Canadias to brace for an exceptionally cold and snowy winter," and yet we've had one of the warmest and least snow on record. The "experts" got it COMPLETELY wrong.

That's weather, not climate, but this is the first time I've seen unseasonably warm weather in some region spun as an argument against AGW. Well done.

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