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Poptech · 29-04-2008, 05:56 PM

Quote:

Originally Posted by Akria

You mean the MBH?

The method of statistical analysis used to produce it was flawed, yes, but the conclusions - that the twentieth century's temperature rise is unprecedented in the past millennium at least - was ruled to be broadly accurate.

WRONG! The report said the following:

"It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries."

No kidding since this goes back to the little ice age. They made no such conclusions about the MWP.

Surface Temperature Reconstructions for the Last 2,000 Years (PDF) (National Academy of Sciences, 2006)

Quote:

Originally Posted by National Academy of Sciences

Even less confidence can be placed in the original conclusions by Mann et al. (1999) that "the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium" [...]

Prior to about 1600, ...periods of medieval warmth are seen in a number of diverse records, including historical information from Europe and Asia; cave deposits; marine and lake sediments; and ice cores from Greenland, Ellesmere Island, Tibet, and the equatorial Andes. [...]

Using proxies sensitive to hydrologic variables (including moisture-sensitive trees...) to take advantage of observed correlations with surface temperature could lead to problems [...]

For tree ring chronologies, the process of removing biological trends from ringwidth data potentially obscures information on long-term changes in climate. [...]

Large-scale surface temperature reconstructions yield a generally consistent picture of temperature trends during the preceding millennium, including relatively warm conditions centered around A.D. 1000 (identified by some as the “Medieval Warm Period”) and a relatively cold period (or “Little Ice Age”) centered around 1700. The existence and extent of a Little Ice Age from roughly 1500 to 1850 is supported by a wide variety of evidence including ice cores, tree rings, borehole temperatures, glacier length records, and historical documents. Evidence for regional warmth during medieval times can be found in a diverse ...set of records including ice cores, tree rings, marine sediments, and historical sources from Europe and Asia

Von Storch, Zorita and Gonzalez-Raucen statement on the NAS Panel Report (Climate Audit, June 22, 2006)

Quote:

We share the assessment of the NRC committee that the evidence for unprecedented warming of a single decade or even a single year in times prior to 1500, or so, is stretching the scientific evidence too far. However, this was the key claim made in the contested 1998-nature and 1999-GRL-papers by Mann et al.

With respect to methods, the committee is showing reservations concerning the methodology of Mann et al.. The committee notes explicitly on pages 91 and 111 that the method has no validation (CE) skill significantly different from zero. In the past, however, it has always been claimed that the method has a significant nonzero validation skill. Methods without a validation skill are usually considered useless. [...]

Thus, the public perception that the hockeystick as truthfully describing the temperature history was definitely false.

We find it disappointing that the method of Mann et al. was not sufficiently described in the original publication, and thus not peer-reviewed prior to publication, and that no serious efforts were made to allow independent researchers to check the performance of the methods and of the data used.

Spin can’t hide the facts concerning the hockey stick (PDF) (Stephen McIntyre, B.Sc. Mathematics, Ross McKitrick Ph.D. Economics, July 26, 2006)