By Jon J. Ray
I would like to thank Jon for allowing me to publish his work. He publishes a number of blogs from Australia. This was from GREENIE WATCH. RK
A study just out in "Science" has already been ingested by media outlets all over the world and then pooped out in considerably altered form. Why it has been taken so seriously is a bit of a mystery as it is in fact pretty run of the mill stuff.
It has been taken as "proving" human-caused warming but in fact it didn't address human influence at all!
What the article does is a type of meta-analysis: It tries to combine ALL the information on the subject to produce a more reliable conclusion than any single study could do. Such studies are often relied on in the medical literature due to the deluge of conflicting claims there.
As it happens, I know a little bit about meta-analyses and know how important goodwill is to their usefulness. To put it bluntly, you can prove just about anything you like in a meta-anaysis by what you select to include. Selecting the date from which you begin to assemble data is a classic dodge -- and one that seems to have been used in the present study -- but it gets as crude as ignoring hundreds of articles and datasets that you simply dislike.
So a good, sincere and unbiased attitude in the researcher is vital. If you start off with (say) a Warmist bias you will usually produce Warmist results.
As it happens, the bias readily apparent in the present study is mild. It seems to show only in the chosen starting point for the analysis. Why 1992 and not (say) the beginning of satellite measurements in 1979? 1992 must just have produced the best results.
But, even so, the results are not spectacular. As one summary put it: They’re saying that only E Ant is gaining mass, and that at a low rate, so overall Ant is losing, and Greenland is losing even more. Still – that adds up to 0.6 mm/yr. So it will have to grow if its to become interesting by 2100. And undoubtedly it will, but that means predicting it remains interesting, since (linear) extrapolation is obviously pointless.
In case that's still not clear, the sea-level rise they assert is tiny and even if it continued in a steady way (most unlikely given past known variations in polar ice) it would take 100 years or more to become noticeable.
So the only way in which the study is notable is its claim to produce pooled wisdom -- and how influential that claim is depends very much on how much we believe in the objectivity of the researchers. As they would not be in their jobs if they were global warming skeptics, believing in their objectivity would be quite heroic. It's just another dodgy appeal to authority.
I append the journal abstract.
A Reconciled Estimate of Ice-Sheet Mass Balance
By Andrew Shepherd et al.
Abstract
We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth’s polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year−1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year−1 to the rate of global sea-level rise.
Science 30 November 2012, Vol. 338 no. 6111 pp. 1183-1189
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