Hockey stick controversy

The hockey stick graph is based on a scientific study published in 1999 by Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes to global warming. It was known by the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC ). By representing the temperature profile of the earth during the past thousand years, it served to illustrate the measures taken in this interim report. Its name is due to its resemblance to the shape of a hockey stick.

The diagram was often used in press reports about the Third Assessment Report and on issues of global warming for illustration. After 2003, a controversy about the statistical basis of the diagram and the conclusions to be drawn from it developed. An assessment of the conclusion of the chart as well as the controversy is mentioned in the Fourth Assessment Report. An expert panel of the National Research Council ( NRC) in 2006 came to the conclusion that the conclusion is plausible that the last decades of the 20th century have been the warmest period in the last millennium in the Northern Hemisphere.

Climate data

For the creation of the chart, a large number of available climate data from the last few centuries has been summarized, including data from weather stations, but also some indirect climate data (called proxies) from sediments, core studies of polar ice or data from the bristle pine chronology ( tree ring data). The result was a chart that showed a relatively uniform temperature profile over a long time and from the 20th century documented a significant increase in temperature. The similarity of this curve with the shape of an ice - hockey stick or lawn quickly led to its catchy name.

The chart hit on a wide media interest and was significant in that it seemed to represent the increase in the global average temperature obvious. Thus, it supports the theory of man-made global warming within the last centuries, the cause of which is seen especially in the combustion of fossil fuels and thereby increasing proportion of greenhouse gases in the atmosphere.

In the Fourth Assessment Report of the IPCC in 2007 is written to the temperature rise shown in the diagram:

"The TAR pointed to the ' exceptional warmth of the late 20th century, relative to the past 1,000 years'. Subsequent evidence Has Strengthened this conclusion. It is very likely did average Northern Hemisphere temperatures applications falling on the second half of the 20th century were higher than for any other 50 -year period in the load 500 years. It is therefore likely thatthis 50 -year period which the warmest Northern Hemisphere period in the load of 1.3 kyr, and thatthis warmth what more wide spread than falling on any other 50 -year period in the load of 1.3 kyr. "

Translation:

" The TAR ( = third Sachstandsbereicht, editor translator ) pointed to the exceptional warmth in the late 20th century compared to the last 1,000 years. Subsequent evidence has strengthened this finding. It is very likely that the average temperature of the Northern Hemisphere were during the second half of the 20th century, higher than any other 50 -year period in the last 500 years. It is also likely that this 50 -year period was the warmest of the last 1300 years and that this warming was considerably more extensive than any other 50 -year period of the last 1300 years. "

Controversy

Since its release, the methods and therefore the results of the hockey stick graph was a highly publicized debated topic. It has therefore been checked by different scientists. Especially Steven McIntyre and Ross McKitrick, an economist at the University of Guelph, analyzed the statistical procedure for obtaining the hockey stick graph and criticized it fundamentally.

Thus, errors identified in the computer-based analysis of the basic data on which was based the characteristic diagram. In particular, the use averaging routines from libraries should be able to provide correct results 1902 implementation due until the year. Also, experiments on the review of the program by the Monte Carlo method with multiple input data sets that these mutant under certain circumstances to the already well-known hockey stick shape. Added to this, there would software errors that contributed to the falsification of the results.

According to McIntyre and McKitrick from hence it is a statistical artefact. According to paleoclimatologists Eugene choice and Caspar Ammann, however this view is refuted.

While it has been held by some, the position, the chart would be refuted, on the other hand, some of the critics hasty and immature approach was maintained. The main reason that discussions on the methodological questions of detail looked after so intense because of accusations of impropriety of the graphics, especially within public debates, as alleged evidence against the thesis that man is the main cause of global warming, was used.

In contrast, several since then carried out reconstructions of the climate of the past 1000 years have the hockey stick graph similar picture supplied. These new graphs are specified by the original hockey stick graph and its error limits the scope of the development temperature has not exceeded.

Checks

The hockey stick chart was reviewed by various sides several times for errors. The results of Mann et al. were thus confirmed several times.

Study by the National Research Council

At the request of the U.S. House of Representatives asked the National Research Council ( NRC), a twelve member expert committee together, which together contributed all the scientific evidence for temperature over the last 2000 years, and amongst other things Mann's work on the hockey stick graph examined. In June 2006, the NRC published a comprehensive 155 page report on the topic.

In the NRC report states that Michael Mann has been underpinned research since its publication by a variety of evidence. Based on this evidence it keep the experts at the NRC plausible that the last decades of the 20th century have been the warmest period in the last millennium in the Northern Hemisphere. However, the safety of statements of historical temperature profiles differed, depending on what time period you look at. Almost certainly could be said that the average global surface temperatures during the last decades of the 20th century were higher than in any comparable period during the preceding four centuries. For the period before 1600, large-scale temperature reconstructions are still connected (at the time of the report) with uncertainties are difficult to quantify, but would make an important contribution to climate research. The available climate proxies would suggest that temperatures at many, but not all, individual locations during the last 25 years were higher than in any comparable long period between the years 900 and 1600's.

A proposal in the NRC report following, repeated in 2006 man, Bradley and Hughes their climate reconstruction of the last 2000 years using a greatly increased amount of climate proxies and validated several, mutually independent methods. The 2008 published results confirmed the anomaly for at least the last 1300 years. Considered one also tree ring data, this can apply with strong restrictions for the last 1700 years. Virtually all comparable work on climate reconstruction over these periods fall partly on the same chronologies and are therefore not completely independent of each other. If one individual proxy series - such as the controversial tree rings - from the study out, the result, however, does not change significantly. All reconstructions of the climate, which are obtained from proxies are associated with some uncertainty.

In a brief correspondence in the journal Nature of 10 August 2006 Bradley, Hughes and husband confirmed that they had referred in its 1998 release publication on the major uncertainties and contradictions in the data before 1400, what concrete conclusions about the temperatures in the period before 1400 prevent. This was in response to remarks by Gerald North from the NRC panel of experts, who had complained that they had some uncertainties not optimally communicated.

Wegman Report

In July 2006, published Edward Wegman, Yasmin H. Said and David W. Scott, a report for the United States House Committee on Energy and Commerce on current studies of the publications on the hockey stick graph. In the often referred to as the " Wegman Report" report, which was commissioned by the Republican Committee Chairman Joe Barton, the publications of man were described as "somewhat obscure and incomplete" and shared the criticisms of McIntyre and McKitrick of publications. Further, a network of 43 authors described paleoclimatic studies with direct links to man (eg by co-authorship in publications), which quoted previously " independent studies " in the view of critics would make it appear in a not-too- independent light. The conclusion of these studies was that the thesis in 1998 was the warmest year, but have been the warmest decade of the last 1000 years, the 1990s, is not confirmed. Richard Kerr of Science magazine criticized criticized for his part Joe Barton's appearance at a later held before the Senate committee hearing on the subject.

Renewed controversy after the hacking incident in 2009

In connection with the hacking incident on climate research center of the University of East Anglia and thereby stolen emails a re-examination of Mann's relevant research by the Pennsylvania State University was conducted. For this purpose a commission was convened, which included five professors from other departments of the university. Having determined, after completion of the investigations unanimously to the conclusion that man had made ​​any scientific misconduct. Even before a three-member committee of the university had rejected after an initial examination of allegations that man retained data or explosive e- mails would be deleted.

In an investigation report by the Inspector General of the National Science Foundation ( NSF), the results of university examination were essentially confirmed. As regards the allegation of data manipulation led the NSF through its own investigation, in which critics have been heard of Mann's studies. Finally found the NSF, leaving no evidence of scientific misconduct by man were available.

Further studies

A study conducted by PAGES2K consortium in 2012 temperature reconstruction of the last 2000 years confirmed the correctness of the basic results of the reconstruction of man. This reconstruction is based on data obtained from ice cores, tree rings and lake sediments.

A published in the journal Science in 2013 study also supports the data of Mann et al. In this study, climate data were analyzed from 73 locations worldwide distributed.