New paper finds global warming over past century was only about half of IPCC claims

A recent paper presented at the European Geosciences Union meeting finds global warming over the past century was only about one-half [0.42°C] of that claimed by the IPCC [0.7-0.8°C]. The paper finds that in 2/3 (67%) of the weather stations examined, questionable adjustments were made to raw data that resulted in "increased positive trends, decreased negative trends, or changed negative trends to positive," whereas "the expected proportions would be 1/2 (50%)." According to the authors,

"homogenation practices [adjustments to raw data] used until today are mainly statistical, not well justified by experiments, and are rarely supported by metadata. It can be argued that they often lead to false results: natural features of hydroclimatic times series are regarded as errors and are adjusted." 

"While homogenation is expected to increase or decrease the existing multiyear trends in equal proportions, the fact is that in 2/3 of the cases the trends increased after homogenation" 

"The above results cast some doubts in the use of homogenation procedures and tend to indicate that the global temperature increase during the last century is smaller than 0.7-0.8°C"

selected slides below, full presentation available here 

 

 

 

Investigation of methods for hydroclimatic data homogenization

Steirou, E., and D. Koutsoyiannis, Investigation of methods for hydroclimatic data homogenization, European Geosciences Union General Assembly 2012, Geophysical Research Abstracts, Vol. 14, Vienna, 956-1, European Geosciences Union, 2012.

We investigate the methods used for the adjustment of inhomogeneities of temperature time series covering the last 100 years. Based on a systematic study of scientific literature, we classify and evaluate the observed inhomogeneities in historical and modern time series, as well as their adjustment methods. It turns out that these methods are mainly statistical, not well justified by experiments and are rarely supported by metadata. In many of the cases studied the proposed corrections are not even statistically significant.
From the global database GHCN-Monthly Version 2, we examine all stations containing both raw and adjusted data that satisfy certain criteria of continuity and distribution over the globe. In the United States of America, because of the large number of available stations, stations were chosen after a suitable sampling. In total we analyzed 181 stations globally. For these stations we calculated the differences between the adjusted and non-adjusted linear 100-year trends. It was found that in the two thirds of the cases, the homogenization procedure increased the positive or decreased the negative temperature trends.
One of the most common homogenization methods, ‘SNHT for single shifts’, was applied to synthetic time series with selected statistical characteristics, occasionally with offsets. The method was satisfactory when applied to independent data normally distributed, but not in data with long-term persistence.
The above results cast some doubts in the use of homogenization procedures and tend to indicate that the global temperature increase during the last century is between 0.4°C and 0.7°C, where these two values are the estimates derived from raw and adjusted data, respectively.

 Full text:

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