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Drought (Europe) - Summary

Climate alarmists typically contend that as the world warms it should experience more frequent and severe droughts.  A good reality check on this claim would be to see what happened over the 20th century, when climate alarmists claim that the world warmed at a rate and to a level that were both unprecedented over the past two millennia.  Hence, we here investigate this subject as it pertains to Europe.

We begin with a study from Central Scandinavia that provides a multi-century perspective on the issue.  In it, Linderholm and Chen (2005) derived a 500-year history of winter (September-April) precipitation from tree-ring data obtained within the Northern Boreal zone of the region.  This chronology indicated that below average precipitation was observed during the periods 1504-1520, 1562-1625, 1648-1669, 1696-1731, 1852-1871 and 1893-1958, with the lowest values occurring at the beginning of the record and at the beginning of the 17th century.  These results demonstrate that for this portion of the European continent, 20th-century global warming did not result in more frequent or more severe droughts.

Another five-century perspective on the issue was provided by Wilson et al. (2005), who used a regional curve standardization technique to develop a summer (March-August) precipitation chronology from living and historical ring-widths of trees in the Bavarian Forest region of southeast Germany for the period 1456-2001.  This technique captured low frequency variations that indicated the region was substantially drier than the long-term average during the periods 1500-1560, 1610-1730 and 1810-1870, all of which intervals were much colder than the bulk of the 20th century.  Hence, these results too fly in the face of climate-alarmist predictions.

A third study of interest concerns the Danube River in western Europe, where several researchers had studied the precipitation histories of adjacent regions and suggested that an anthropogenic signal was present in the latter decades of the 20th century, and that it was responsible for that period's supposedly drier conditions.  Determined to investigate further, Ducic (2005) examined these claims by analyzing observed and reconstructed discharge rates of the river near Orsova, Serbia over the period 1731-1990.  This work revealed that the lowest 5-year discharge value in the pre-instrumental era (1831-1835) was practically equal to the lowest 5-year discharge value in the instrumental era (1946-1950), and that the driest decade of the entire 260-year period was 1831-1840.  What is more, the discharge rate for the last decade of the record (1981-1990), which prior researchers had claimed was anthropogenically-influenced, was found to be "completely inside the limits of the whole series," in Ducic's words, and only 0.7% less than the 260-year mean, leading to the conclusion that "modern discharge fluctuations do not point to dominant anthropogenic influence."  In fact, Ducic's correlative analysis suggests that the detected cyclicity in the record could "point to the domination of the influence of solar activity."

In much the same vein and noting that "the media often reflect the view that recent severe drought events are signs that the climate has in fact already changed owing to human impacts," Hisdal et al. (2001) examined pertinent data from many places in Europe.  Specifically, they performed a series of statistical analyses on more than 600 daily stremflow records from the European Water Archive to examine trends in the severity, duration and frequency of drought over the following four time periods: 1962-1990, 1962-1995, 1930-1995, and 1911-1995.  This work revealed, in their words, that "despite several reports on recent droughts in Europe, there is no clear indication that streamflow drought conditions in Europe have generally become more severe or frequent in the time periods studied."  To the contrary, they report that "overall, the number of negative significant trends pointing towards decreasing drought deficit volumes or fewer drought events exceeded the number of positive significant trends (increasing drought deficit volumes or more drought events)."

In conclusion, it is clear from these several reports that the media's portrayal of increasing 20th-century warming-induced drought in Europe is not supported by real-world data, just as it is not supported by data from other continents.

References
Ducic, V.  2005.  Reconstruction of the Danube discharge on hydrological station Orsova in pre-instrumental period: Possible causes of fluctuations.  Edition Physical Geography of Serbia 2: 79-100.

Hisdal, H., Stahl, K., Tallaksen, L.M. and Demuth, S.  2001.  Have streamflow droughts in Europe become more severe or frequent?  International Journal of Climatology 21: 317-333.

Linderholm, H.W. and Chen, D.  2005.  Central Scandinavian winter precipitation variability during the past five centuries reconstructed from Pinus sylvestris tree rings.  Boreas 34: 44-52.

Wilson, R. J., Luckman, B. H. and Esper, J.  2005.  A 500 year dendroclimatic reconstruction of spring-summer precipitation from the lower Bavarian Forest region, Germany.  International Journal of Climatology 25: 611-630.

A Pair of Two-Millennia-Long Climatic Records
Reference
Cini Castagnoli, G., Taricco, C. and Alessio, S.  2005.  Isotopic record in a marine shallow-water core: Imprint of solar centennial cycles in the past 2 millennia.  Advances in Space Research 35: 504-508.

What was done
A δ13C profile of Globigerinoides rubber was extracted from a shallow-water core in the Gulf of Taranto (3945'53"N, 1753'33"E) to produce a high-precision record of climate variability over the past two millennia.  This high-precision record was then statistically analyzed, together with a second two-millennia-long tree-ring record obtained from Japanese cedars (Kitagawa and Matsumoto, 1995), for evidence of recurring cycles using Singular Spectrum Analysis and Wavelet Transform, after which both records were compared with a 300-year record of sunspots.

What was learned
Plots of the two two-thousand-year series reveal the existence of the Dark Ages Cold Period (~400-800 AD), Medieval Warm Period (~800-1200 AD), Little Ice Age (~1500-1800 AD), and Current Warm Period, the roots of which can be traced to an upswing in temperature that began in the depths of the Little Ice Age "about 1700 AD."  Results of the statistical analyses showed a common 11-year oscillation in phase with the Schwabe cycle of solar activity, plus a second multi-decadal oscillation (of about 93 years for the shallow-water G. rubber series and 87 years for the tree-ring series) in phase with the amplitude modulation of the sunspot number series over the last 300 years.

What it means
According to the authors, the overall phase agreement between the two climate reconstructions and the variations in the sunspot number series "favors the hypothesis that the [multi-decadal] oscillation revealed in δ13C from the two different environments is connected to the solar activity," which further suggests that a solar forcing was at work in both terrestrial and oceanic domains over the past two millennia.  Thus, and once again, we have additional evidence for solar forcing of climate at decadal and multi-decadal time scales, as well as for the millennial-scale oscillation of climate that likely has been responsible for the 20th-century warming of the globe that led to the demise of the Little Ice Age and ushered in the Current Warm Period.

Reference
Kitagawa, H. and Matsumoto, E.  1995.  Climatic implications of δ13C variations in a Japanese cedar (Cryptomeria japonica) during the last two millennia.  Geophysical Research Letters 22: 2155-2158.

Reviewed 11 January 2006


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