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Rainfall (Trends - Regional: Europe, Central) -- 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 enhanced variability. As a result, many scientists are examining historical and proxy precipitation records in an effort to determine how temperature changes of the past millennium or more may have impacted these aspects of earth's hydrologic cycle. In this summary we review what three such studies learned about rainfall across Central Europe.

Koning and Franses (2005) conducted a detailed analysis of a century of daily precipitation data that had been acquired at the de Bilt meteorological station in the Netherlands. Using what they call "robust nonparametric techniques," they found that the cumulative distribution function of annual maximum precipitation levels remained constant throughout the period 1906-2002, leading them to conclude that "precipitation levels are not getting higher." In addition, they report that similar analyses they performed for the Netherlands' five other meteorological stations "did not find qualitatively different results."

Moving eastward, and extending the temporal domain of study from one century to five, Wilson et al. (2005) developed two versions of a March-August precipitation chronology based on living and historical tree-ring widths obtained from the Bavarian Forest of southeast Germany for the period 1456-2001. The first version, standardized with a fixed 80-year spline function (SPL), was designed to retain decadal and higher frequency variations, while the second version used regional curve standardization (RCS) to retain lower frequency variations. Their efforts revealed significant yearly and decadal variability in the SPL chronology; but there did not appear to be any trend toward either wetter or drier conditions over the 500-year period. The RCS reconstruction, on the other hand, better captured lower frequency variation, suggesting that March-August precipitation was substantially greater than the long-term average during the periods 1730-1810 and 1870-2000 and drier than the long-term average during the periods 1500-1560, 1610-1730 and 1810-1870. Once again, however, there was little evidence of a long-term trend.

Moving still further east in Central Europe, and covering a full millennium and a half, Solomina et al. (2005) derived the first tree-ring reconstruction of spring (April-July) precipitation for the Crimean peninsula, located on the northern coast of the Black Sea in the Ukraine, for the period 1620-2002, after which they utilized this chronology to correctly date and correlate with an earlier precipitation reconstruction derived from a sediment core taken in 1931 from nearby Saki Lake, thus ending up with a proxy precipitation record for the region that stretched all the way back to AD 500. In describing their findings, Solomina et al. say that no trend in precipitation was evident over the period 1896-1988 in an instrumental record obtained at a location adjacent to the tree-sampling site. Also, the reconstructed precipitation values from the tree-ring series revealed year-to-year and decadal variability, but remained "near-average with relatively few extreme values" from about the middle 1700s to the early 1800s and again since about 1920. The most notable anomaly of the 1500-year reconstruction was an "extremely wet" period that occurred between AD 1050 and 1250, which Solomina et al. describe as broadly coinciding with the Medieval Warm Epoch, when humidity was higher than during the instrumental era.

The results of these several analysis demonstrate that over the period of 20th-century global warming -- which climate alarmists claim was unprecedented over the past two millennia or more -- the climate-model-based expectation of enhanced precipitation was not observed in Central Europe. Of course, Central Europe represents but a small portion of the entire planet. Nevertheless, for a warming that was supposedly so extreme, one would have expected to have seen something along the lines of what climate alarmists have claimed would be the case ... if they were correct. But we don't! And perhaps the reason why we don't see what they predict is that earth's climate is likely not yet as warm as it was during the Medieval Warm Period, when the data of Solomina et al. suggest that the region they studied was distinctly wetter than it was both before and after that time, and when, of course, the air's CO2 concentration was fully 100 ppm less than it is today.

References
Koning, A.J. and Franses, P.H. 2005. Are precipitation levels getting higher? Statistical evidence for the Netherlands. Journal of Climate 18: 4701-4714.

Solomina, O., Davi, N., D'Arrigo, R. and Jacoby, G. 2005. Tree-ring reconstruction of Crimean drought and lake chronology correction. Geophysical Research Letters 32: 10.1029/2005GL023335.

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.

Last updated 23 January 2008