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Rainfall (Trends - Regional: Europe, Northern) -- Summary
Climate model predictions of CO2-induced global warming typically suggest that rising temperatures should be accompanied by increases in rainfall amounts and intensities, as well as by enhanced variability. As a result, numerous scientists are examining historical and proxy precipitation records in an effort to determine how temperature changes of the past millennium may have impacted these aspects of earth's hydrologic cycle; and in this summary we review what three such studies have learned about the subject in Northern Europe.

Out in the middle of the North Atlantic Ocean in Iceland, Hanna et al. (2004) analyzed variations in several climatic variables, including precipitation, over the past century in an effort to determine if there is "possible evidence of recent climatic changes" in that cold island nation. For the period 1923-2002, precipitation appeared to have increased slightly, although they questioned the veracity of the trend, citing several biases that may have corrupted the data base.

Back on the mainland, Linderholm and Molin (2005) analyzed two independent precipitation proxies, one derived from tree-ring data and one from a farmer's diary, to produce a 250-year record of summer (June-August) precipitation in east central Sweden. This work revealed there had been a high degree of variability in summer precipitation on inter-annual to decadal time scales throughout the record. Over the past century of supposedly unprecedented global warming, however, precipitation was found to have exhibited less variability than it did during the 150 years that preceded it.

Finally, in a study covering the longest time span of all, Linderholm and Chen (2005) derived a 500-year winter (September-April) precipitation chronology from tree-ring data obtained within the northern boreal forest zone of west-central Scandinavia in an effort to better understand historic precipitation variability within this region. The reconstructed chronology they developed showed considerable variability, with the exception of a fairly stable period of above-average precipitation between AD 1730 and 1790. Additionally, above average winter precipitation was found to have occurred in 1520-1561, 1626-1647, 1670-1695, 1732-1851, 1872-1892 and 1959 to the present, with the highest values reported in the early to mid-1500s; while below average winter precipitation was observed during 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 the beginning of the 17th century. These findings thus demonstrated that non-CO2-forced wetter and drier conditions than those of the present have occurred repeatedly within this region throughout the past five centuries, and that similar extreme conditions may therefore be expected to naturally recur in the future.

In considering these diverse observations from Northern Europe, it is clear they provide no support whatsoever for climate-alarmist claims of imminent changes in precipitation characteristics outside the bounds of historic variability.

References
Hanna, H., Jónsson, T. and Box, J.E. 2004. An analysis of Icelandic climate since the nineteenth century. International Journal of Climatology 24: 1193-1210.

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.

Linderholm, H.W. and Molin, T. 2005. Early nineteenth century drought in east central Sweden inferred from dendrochronological and historical archives. Climate Research 29: 63-72.

Last updated 20 February 2008