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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.

[doc_id=1212]

[English]

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.

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The paper has been discussed in weblogs and forums.

Weblogs and forums that discussed this article during July-September 2012

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  7. Proof that Global Warming is man-made (Daily Pundit)
  8. New Paper Blames About Half Of Global Warming On Weather Station Data Homogenization (3) (Wopular)
  9. Homogenisation is the root of all evil (Bishop Hill blog)
  10. Station Homogenization as a Statistical Procedure (Climate Audit)
  11. Google Alert - "global warming" (Event Earth)
  12. New paper blames about half of global warming on weather station data homgenization | Watts Up With That? (TOM NELSON)
  13. New paper blames about half of global warming on weather station data homogenization (4) (freak-search)
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  38. Recent findings: Smaller 20th Century Warming: Hotter Medieval Warm Period (GREENIE WATCH)
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  42. Blog discussions, conference presentations and peer review (De staat van het klimaat)
  43. More on Koutsoyiannis and the homogenization of temperature data – plus some comments on blog review (Watts Up With That?)
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Other works that reference this work:

1. #Stockwell, D. R.B., Is temperature or the temperature record rising?, Australian Environment Foundation Conference, Sydney, Australia, 2012.
2. Fleming, S. W., A non-uniqueness problem in the identification of power-law spectral scaling for hydroclimatic time series, Hydrological Sciences Journal, 59 (1), 73–84, 2014.

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