The Hockey Stick is Bad Science

Climate Reconstruction Using Proxies Con correctly states that proxies are widely used in the historical reconstruction of temperatures. That is because there have only been reliable widespread direct temperature measurements for about a century. Scientist would like to know what temperatures were like before that. There are quite a number of measurements that can be used to deduce temperatures. con mentioned a few, but there are more. Some are better than others. Tree rings depend upon rainfall as well as temperature, and only reflect climate during the growing season. Trees of different species or at different altitudes or in different local climates will produce different indications of climates. Some species grow more rapidly due to the carbon dioxide rise in the 20th century. Local variations affect virtually every type of proxy. Scientists must use statistical methods to attempt to derive correct temperature reconstructions. By 2003, at least 350 historical temperature reconstructions had been published, with contributions from around the world. If all the data are combined, the picture of climate for the past thousand years is not a hockey stick. Con asks why there are four of the 350 that show hockey sticks. With 350 to choose from, finding four for almost any shape is not be surprising, given the variability. However, it seems that Prof. Mann and his colleagues shared tips on processing techniques, and the methods they derived works to make a hockey stick result out of any large data set. I don't believe there is any deliberate attempt to falsify data and I'm not alleging any malfeasance. The group seized upon a bad method and believes to this day it is correct. This is not shocking. Climate scientists are not experts in statistical methods, so it took experts in mathematical statistics to unravel the errors.The graphs below are scaled versions of those in [1. http://www.john-daly.com... ] The IPCC report of 1990 (A) had an entirely different graph of climate history. That graph showed a Medieval Warm Period (MWP), warmer than the present and lasting to about 1300, followed by the Little Ice Age, a period much colder than the present lasting through the early 1800's. Both disappeared in the hockey stick. (B) [1] shows a number of climate reconstructions confirming (A) and disconfirming (B). Mann's Errors Why did major climate variations disappear in the hockey stick? Scientists, led by Ross McKitrick, a professor at the University of Guelph in Canada, spent enormous effort trying to reconstruct Mann's work to find out. Mann refused to supply his data or the computer program that he used to process the data. Under intense pressure, enough of the data was revealed and enough information about the algorithms was revealed to allow reconstructing and analyzing the methodology. The actual software had never been released.The details of the analysis are provided in full in a thirty page article by scientist Ross McKitrick, [2] "The Mann et al Northern Hemisphere 'Hockey Stick': A Tale of Due Diligence." published in the book "Shattered Consensus" edited by Patrick Michaels. A good summary by a scientist who believes in human-caused global warming is from the MIT magazine Technology Review: [3. http://www.technologyreview.com...]The basic errors in the hockey stick derivation are:1. Mann used an algorithm that normalized past data based upon the data of the last 78 years. This algorithm was tested by putting noise into the algorithm. Noise is fake data that just bounces around with no trends. When processed through the Mann algorithm, a hockey stick is produced. It makes hockey sticks out of nothing.2. Mann used a method called "component analysis" as part of his method. When the raw climate data is put into a standard off-the-shelf computer program that does component analysis, the MWP and Little Ice Age reappear as they were in the 1990 IPCC report.3. A variety of different types of data were used as inputs to Mann's analysis. The data are various proxies for temperature, like tree ring growth. Most of the data does not show a hockey stick, but one data set from the rings of trees growing at high altitudes did show a hockey stick. Mann not only included it, but weighted it 380 times more highly than other data."Almost all of the ... series selected for overweighting [by Mann] were of a single type and from a single researcher, Donald Graybill. The series were high-altitude bristlecone pine tree-ring chronologies, many of which had been studied by Graybill and Sherwood Idso as possible examples of CO2 fertilization of tree growth, following a similar study by Lamarche et al. on Sheep Mountain. The sites were selected for "cambial dieback," that is, the bark had died around the circumference of the tree. ... They related that the anomalous twentieth century growth was unrelated to the temperature from nearby weather stations." McKitrick in Michaels, [2] p 41Mann didn't hand-select the odd data to be overweighted, his computer processing did it automatically. The method selected matches to recent instrumental data and weighted them as the best proxies. Since the match was a matter of chance, earlier data from those proxies was mostly noise. Later examination of the chosen proxies showed they didn't track the next decade at all.4. There were errors in the method of filling in missing data.Expert Evaluation Mann said he didn't have the time to reveal his data or computer programs, and that no matter what critics did to reconstruct his work, Mann claimed they were not doing it right. Pressure mounted, and ultimately the National Science Foundation was asked to investigate the matter. They came back with an obfuscated report that seemed to confirm the criticisms, but at the same time didn't say the hockey stick was wrong.The matter was finally referred by Congress to a panel of statistical experts experienced in the processing of climate data. The panel featured Edward Wegman. Wegman is a statistics professor at George Mason University, and past chair of the National Research Council's Committee on Applied and Theoretical Statistics. He holds a Ph.D. in mathematical statistics and is a Fellow of the American Statistical Association. He was selected to provide the highest level of expertise on the statistical methods employed. Wegman and the panel determined unambiguously that the critics were correct, and that the hockey stick was invalid.Harvard Smithsonian Metastudy In 2003, the Harvard Smithsonian Center for Astrophysics reviewed 350 published reconstructions and concluded:"... the 20th century is neither the warmest century nor the century with the most extreme weather of the past 1000 years. The review also confirmed that the Medieval Warm Period of 800 to 1300 A.D. and the Little Ice Age of 1300 to 1900 A.D. were worldwide phenomena not limited to the European and North American" continents. [4. http://www.cfa.harvard.edu...] Aside from the data reconstructions, books have been published documenting the exceptional nature of the MWP [5. http://www.amazon.com...] and the LIA [6. http://www.amazon.com...]. the MWP had Greenland named for its greenery and grapes growing in northern Scotland. The LIA produced painting of ice skaters on the canals of Holland and a yearly festival on the ice of the Thames. Why the Hockey Stick is Bad Science The hockey stick was derived using incorrect procedures. It wrongly claimed temperatures were soaring exponentially, and because it was allegedly unprecedented, we should expect that to continue. So have they continued to soar exponentially since the late 90s? No, actually the trend was slightly downward after 1995. [7. http://www.factsandarts.com...]