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The stick was not just broken...
The central "evidence" for global warming presented by the IPCC in their Third Report (Houghton et al. 2001) is the "hockey stick" graph which supposedly proves that current globally averaged surface temperatures are "unprecedented" for the past 1000 years.
The original graph was published in two papers by Mann, Bradley and Hughes (1998, 1999). It purports to show globally averaged temperature anomalies for the Northern Hemisphere for the years 1000 to 1998. Since widespread thermometer measurements are only available since 1860, most of the graph consists of averaged "proxy" measurements, based on tree rings, sediments, corals, ice cores and other indicators of past temperature change. The supposed 95% accuracy is shown in the graph, so that one can deduce that the temperature in 1998 was above previous levels, to that level of probability.
This graph contradicted the opinions expressed in the first IPCC report (Houghton et al. 1990) which claimed that there were higher global temperatures than those shown today during the "medieval warm period" from about 1100 to 1250 AD and that there was a "little ice age" from about 1550 to 1700 AD. The opinion was expressed that the temperature rise shown from 1870 to 1940 may have been a delayed recovery from this Little Ice Age.
Soon and Baliunas (2003a, 2003b) gathered together many "proxies" and listed them. They concluded, firstly, that the coverage of data, even for the Northern Hemisphere, was not sufficiently representative to justify the deriving of an "average" which could be considered reliable. Their second conclusion was that both the medieval warm period and the little ice age were sufficiently frequent in the observations that they must have existed. Also, there was evidence that temperatures during the medieval warm period were frequently higher than those found today.
Von Storch (2004) questioned the assumptions of "variability" used for proxy measurements in the hockey stick. He showed that the low accuracy of the proxy measurements implies a much larger amount of "noise" which meant much higher figures for inaccuracy.
The most devastating attack on the "hockey stick" comes from papers by McIntyre and McKitrick (2003, 2005). They set out to see whether they could recalculate the Mann/Bradley data and were initially surprised to find that the data were not available and had not even been supplied to the journals publishing the work -- the papers had been published, and believed, without any check on their validity.
After a long period of wrangling they managed to get hold of most of the original data. When they carried out the calculations, however, they found serious errors which, when corrected, changed the whole conclusion that had been attributed to them. They found that they got a higher temperature in the year 1400 than is claimed for today. They found that the shape of the curve had been automatically predetermined. The small amount of actual data before 1550 led to the excessive use, including extrapolation, of several measurements that are not considered reliable by others. Holland (2007) has documented the IPCC's determined resistance to accepting these facts.
Loehle (2007) questioned the reliability of tree-ring measurements, which apply only to summer and are influenced by precipitation. Increased temperature lowers soil moisture and the rings get thinner rather than thicker. When he used all the proxies except tree rings he got a modified record which restored both the medieval warm period, the little ice age, and the lack of "unprecedented" character of recent temperatures.
The recent IPCC Report (Solomon et al. 2007) has abandoned the "Hockey Stick" graph, but they still will not accept any criticism of it.On 'The hockey stick is broken'--Well, no ... but who's playing hockey anyway? posted 1 year, 6 months ago 6 Responses