The new climate hockeystick

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The new hockeystick is http://www.pnas.org/content/early/2008/09/02/0805721105.full.pdf

the abstract:

Following the suggestions of a recent National Research Council report [NRC (National Research Council) (2006) Surface Temperature reconstructions for the Last 2,000 Years (Natl Acad Press, Washington, DC).], we reconstruct surface temperature at hemispheric and global scale for much of the last 2,000 years using a greatly expanded set of proxy data for decadal-to-centennial climate changes, recently updated instrumental data, and complementary methods that have been thoroughly tested and validated with model simulation experiments. Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats. The reconstructed amplitude of change over past centuries is greater than hitherto reported, with somewhat greater Medieval warmth in the Northern Hemisphere, albeit still not reaching recent levels.
They use two methods of reconstruction:

...Most attempts to reconstruct hemispheric temperatures have used some variant on the ‘‘composite plus scale’’ (CPS) methodology (10), in which proxy data (such as tree rings, ice cores, or corals) considered to be sensitive to past surface temperature variations are standardized and centered, potentially weighted, and then composited to form a regional or hemispheric series,...

recently, Hegerl et al. (13) use a weighted composite of proxy temperature series, but scaling is accomplished by a so-called ‘‘error-in-variables’’ (EIV) regression method (‘‘total least squares’’) to allow for errors in both predictors (i.e., proxy composite) and predictand (i.e., the instrumental hemispheric mean temperature series)....
About those methods they observe:

The skill diagnostics (Fig. 2; see also Dataset S4) for the validation experiments indicate that both the CPS reconstructions (with the screened network) and EIV reconstruction (with the full network) produce skillful NH land reconstructions back to A.D. 400. When tree-ring data are eliminated from the proxy data network, a skillful reconstruction is possible only back to A.D. 1500 by using the CPS approach but is possible considerably further back, to A.D. 1000, by using the EIV approach. We interpret this result as a limitation of the CPS method in requiring local proxy temperature information, which becomes quite sparse in earlier centuries. This situation poses less of a challenge to the EIV approach, which makes use of nonlocal statistical relationships, allowing temperature changes over distant regions to be effectively represented through their covariance with climatic changes recorded by the network.
So looking at this reconstruction we see the EIV showing a distinct medieval warm period and what also bugs a bit is the addition of the instrumental records, showing a increase of about 1.3 degrees over the last century. It should be noted that the normal temperature increase for the last century used to be about 0.6 degrees per century (for instance http://www.geog.ox.ac.uk/~mnew/teaching/Online_Articles/folland_et_al_temp_uncertainties_GRL_2001.PDF [Broken]).

What also seems to be strange is the increasing deviation between those temperature records and the reconstruction, staying clearly behind in the last part of the graph.

Now see what happens if we remove those recorded temperatures.

See that the temperature range of the reconstructions are indeed close to 0.6 degrees in the last century. So it would be interesting to see where that 1.3 range comes from. Note also that the reconstructions without those instrumental records would not support the claim:

...We find that the hemispheric-scale warmth of the past decade for the NH is likely anomalous in the context of not just the past 1,000 years, as suggested in previous work, but longer...
 
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wolram

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I wonder how the present would be interpreted from historical data, (if records were lost),
Would we be able to say: A 160sq mile section of the Wilkins ice sheet broke away, or if volcanoes on the sea floor near Fiji (Dugong and Lobster), were active, it seems we know more about the surface of Mars than we do about Earths seafloor.
I think there are to many butterflies to ever sort out an accurate reason for historical climate.
 
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mheslep

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I thought one of the more highly criticized points in the original hockey stick was the cut and paste job w/ proxy methods and modern instrument data. Yet it is still in there and as Andre shows it is still misleading to co-join the two. Is there at least some new proposed rational for trying this again, or is the methodology somehow different and I've missed it?
 
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It is not only there, it has doubled in size.

Here some ideas about the last centuries warming:

See how the inflation starts:

http://www.sciencedaily.com/releases/2001/07/010704092014.htm

On the contrary, our results suggest that the actual warming during the 20th century may have been slightly larger than the warming estimated from the incomplete observational data of -about 0.7 degrees Celsius instead of 0.6 degrees Celsius."
http://www.usgcrp.gov/usgcrp/seminars/991118FO.html

Global climate of the 20th century has warmed by 0.7-0.8?C.
http://ambio.allenpress.com/perlserv/?request=get-abstract&doi=10.1639%2F0044-7447(2001)030%5B0072%3ACCWATL%5D2.0.CO%3B2&ct=1 [Broken]

Climate warming by ca. 0.8°C between the late-19th and late-20th century,
But still not 1.3 degrees.
 
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vanesch

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Kudos for Andre! Keep up the good work ! :approve:
 
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Thanks Vanesch

Wondering how such a 100% deviation slipped through peer review, when it catches the eye of those who are not qualified to judge immediately. Makes one wonder what else may have slipped through.

Perhaps it has to do with standards?

http://muller.lbl.gov/TRessays/23-Medievalglobalwarming.html [Broken]

When a conclusion is attractive, I am tempted to lower my standards, to do shoddy work. But that is not the way to truth. When the conclusions are attractive, we must be extra cautious.
 
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Andre has initiated a very important discussion with his citation of a PNAS report by a group of meteorologist-environmentalists. The earlier hockey stick data was strongly influenced by urban values while the new treatment uses other sources in its analysis. It also recognizes the regional nature of the problem and introduces this concept in its approach, an important improvement. But any inclusion of urban data must be challenged. Cities have become the major users of human-produced energy as well as growing concentrations of heat-generating human beings. Their size is incredibly larger than in any past age. As shown in the appendix of Michael Crichton’s 2004 book, State of Fear, cities of growing size characteristically show rising temperatures. Direct and indirect temperature readings must systematically exclude urban sources to be considered reliable. Failure to exclude their data will characteristically lead to a hockey-stick result. I have elsewhere cited the rapidly rising energy production catalogued by EIA-DOE https://www.physicsforums.com/showthread.php?t=247597 This is expended heavily in cities and has contributed as much as 20% to the temperature rise seen since 1978.
 
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The earlier hockey stick data was strongly influenced by urban values
.

Not really, the previous hockey stick from the third IPCC assessment report was a game of principle components, strongly enlarging the effect of a http://www.eman-rese.ca/eman/reports/publications/Forest/images/page16.gif [Broken] which showed abnormal growth likely related to the damage. The debunking was endorsed by the http://www.climateaudit.org/pdf/others/07142006_Wegman_Report.pdf [Broken] which seems to have vanished mysteriously from the governmental pages.

Anyway, Mann et al 2008 implicitely accept that there were some issues using tree rings:

Interestingly, although the elimination of all tree-ring data from the proxy dataset yields a substantially smaller divergence bias, it does not eliminate the problem altogether (Fig. 2B). This latter finding suggests that the divergence problem is not limited purely to tree-ring data, but instead may extend to other proxy records.
What this seem to mean is that the interpretation of records as indirect indicators for climate records suffers from the affirming the consequent fallacy (A then B, B hence A), which seems to be worst with tree rings. As a token thereof, Turbo can tell about how the bad cool and wet summer produced an extreme load of peaches, breaking the branches. Growth of trees is primarily a function of moisture and only secondary temperature.

It's this logical fallacy that ultimately determines climate policies.

Hint use the search feature of PF with key word "wegman".
 
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Andre added a new dimension to the hockey-stick problem for me by calling attention to the Wegman report, specifically critical of this group and its data handling practices. I had been focused on the CRU East Anglia and HAD Hadley data used in the report to show the hockey-stick effect in figure 3. I was previously familiar with the use of tree ring data in support of the Maunder minimum sunspot near absence model. http://en.wikipedia.org/wiki/Maunder_minimum http://www.stsci.edu/stsci/meetings/lisa3/beckmanj.html (note the astrophysical extension of magnetic behavior and “global warming” comments)
Here the main distinction is the support by rising 14C levels to the tree ring narrowing. http://books.google.com/books?id=mKLv68WBu5kC&pg=RA2-PA708&lpg=RA2-PA708&dq=Maunder+minimum+tree+rings&source=web&ots=co0WmeuPbw&sig=wYMfTI8njGt4v2tYENBEcqaVF5I&hl=en&sa=X&oi=book_result&resnum=9&ct=result
The 14C rise has never entered the more commonly discussed Little Ice Age model and has, of course, been falling since the last atmospheric atomic tests. 14C production-dilution fluctuation complicates its use in the past event time dating process.

Wegman asserts the use of a very small number of bristlecone pines from a small area as the data source of a prior report. My knowledge of bristlecone pine growth habits and habitat terrain indicates they are a poor choice for thermal surrogates. I am unable to assign species, sites and numbers to this report at this time (see their figure 1) but will look further and add commentary if I am successful. If you can help me, please do.

In the meantime, if I am correct about the East Anglia and Hadley data. I hope that you will join me in pointing out the prejudice toward hockey-stick patterns that their inclusion generates. Another kind of Mann et al. artifact seems to be the main point of the red noise studies cited in the Wegman report.
 
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Skyhunter

RE: the Wegmon report, when all was said and done the effect was a mere ~0.05C in the final reconstruction and did not alter the overall conclusions.
Wondering how such a 100% deviation slipped through peer review, when it catches the eye of those who are not qualified to judge immediately. Makes one wonder what else may have slipped through.
If you have a problem with the data here is contact information.
Tel: +44-1603-592722
Fax: +44-1603-507784
E-mail: cru@uea.ac.uk
http://www.cru.uea.ac.uk/cru/data/temperature/nhshgl.gif [Broken]

Their reconstruction is consistent with the CRU data used. And it is very similar what we see in http://en.wikipedia.org/wiki/File:Hockey_stick_chart_ipcc_large.jpg" [Broken]
 
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