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Rainfall (Trends - Regional: Europe, Mediterranean) -- 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, 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 several of these studies have learned about precipitation in the Mediterranean region of Europe.

Starting at the western extreme of the continent, Rodrigo et al. (2001) used a variety of documentary data to reconstruct seasonal rainfall in Andalusia (southern Spain) from 1501 to 1997, after which they developed a relationship between seasonal rainfall and the North Atlantic Oscillation (NAO) over the period 1851-1997, which they used to reconstruct a history of the NAO from 1501 to 1997. This work revealed that the NAO influence on climate is stronger in winter than in other seasons of the year in Andalusia, explaining 40% of the total variance in precipitation; and Rodrigo et al. make a point of noting that "the recent positive temperature anomalies over western Europe and recent dry [not wet] winter conditions over southern Europe and the Mediterranean are strongly related to the persistent and exceptionally strong positive phase of the NAO index since the early 1980s," as opposed to an intensification of global warming.

Also working in the Andalusia region of southern Spain, Sousa and Garcia-Murillo (2003) studied proxy indicators of climatic change in Doñana Natural Park over a period of several hundred years, comparing their results with those of other such studies conducted in neighboring regions. This work revealed that the Little Ice Age (LIA) was by no means uniform in their region of study, as it included both wetter and drier periods. Nevertheless, they cite Rodrigo et al. (2000) as indicating that "the LIA was characterized in the southern Iberian Peninsula by increased rainfall," and they cite Grove (2001) as indicating that "climatic conditions inducing the LIA glacier advances [of Northern Europe] were also responsible for an increase in flooding frequency and sedimentation in Mediterranean Europe." Sousa and Garcia-Murillo's work complements these findings by indicating "an aridization of the climatic conditions after the last peak of the LIA (1830-1870)," which suggests that much of Europe became drier, not wetter, as the earth recovered from the global chill of the Little Ice Age.

Moving eastward into Italy, Crisci et al. (2002) analyzed rainfall data collected from 81 gauges spread throughout the Tuscany region for three different periods: (1) from the beginning of each record through 1994, (2) the shorter 1951-1994 period, and (3) the still-shorter 1970-1994 period. For each of these periods, trends were derived for extreme rainfall durations of 1, 3, 6, 12 and 24 hours. This work revealed that for the period 1970-1994, the majority of all stations exhibited no trends in extreme rainfall at any of the durations tested; while four had positive trends at all durations and none had negative trends at all durations. For the longer 1951-1994 period, the majority of all stations exhibited no trends in extreme rainfall at any of the durations tested; while none had positive trends at all durations and only one had negative trends at all durations. For the still-longer complete period of record, the majority of all stations again continued to exhibit no trends in extreme rainfall at any of the durations tested; while none had positive trends at all durations and only one had negative trends at all durations, revealing no impact of 20th-century global warming one way or the other.

Working in northern Italy, Tomozeiu et al. (2002) performed a series of statistical tests to investigate the nature and potential causes of trends in winter (Dec-Feb) mean precipitation recorded at forty stations over the period 1960-1995. This work revealed that nearly all of the stations experienced significant decreases in winter precipitation over the 35-year period of study; and by subjecting the data to a Pettitt test, they detected a significant downward shift at all stations around 1985. An Empirical Orthogonal Function analysis was also performed on the precipitation data, revealing a principal component that represented a common large-scale process that was likely responsible for the phenomenon. Strong correlation between this component and the North Atlantic Oscillation (NAO) suggested, in their words, that the changes in winter precipitation around 1985 "could be due to an intensification of the positive phase of the NAO." In this case, therefore, there was not only no increase in precipitation over the period of time when climate alarmists claim the planet warmed at a rate that was unprecedented over the past two millennia, there was an actual decrease, which not only had nothing to do with global warming but was more likely the result of a simple regime shift of the NAO.

Working in the eastern Basilicata region of southern Italy, where they concentrated on characterizing trends in extreme rainfall events, as well as resultant flood events and landslide events, Clark and Rendell (2006) analyzed 50 years of rainfall records (1951-2000). This work indicated, in their words, that "the frequency of extreme rainfall events in this area declined by more than 50% in the 1990s compared to the 1950s." In addition, they report that "impact frequency also decreased, with landslide-event frequency changing from 1.6/year in the period 1955-1962 to 0.3/year from 1985 to 2005, while flood frequency peaked at 1.0/year in the late 1970s before declining to less than 0.2/year from 1990." Hence, they concluded that if the climate-driven changes they observed over the latter part of the 20th century continue, "the landscape of southern Italy and the west-central Mediterranean will become increasingly stable," or as they say in their concluding paragraph, "increased land-surface stability will be the result."

Continuing westward to Bulgaria, Alexandrov et al. (2004) analyzed a number of 20th-century data sets from throughout the country, finding "a decreasing trend in annual and especially summer precipitation from the end of the 1970s" and that "variations of annual precipitation in Bulgaria showed an overall decrease." In addition, they report that the region stretching from the Mediterranean into European Russia and the Ukraine "has experienced decreases in precipitation by as much as 20% in some areas."

Last of all, based on analyses of tree-ring width data and their connection to large-scale atmospheric circulation, Touchan et al. (2005) developed summer (May-August) precipitation reconstructions for several parts of the eastern Mediterranean region, including Turkey, Syria, Lebanon, Cyprus and Greece, which extend back in time as much as 600 years. Over this period, they found that May-August precipitation varied on multi-annual and decadal timescales, but that on the whole there were no long-term trends. The longest dry period occurred in the late 16th century (1591-1595), while there were two extreme wet periods: 1601-1605 and 1751-1755. In addition, both extreme wet and dry precipitation events were found to be more variable over the intervals 1520-1590, 1650-1670 and 1850-1930, indicating that as the globe experienced the supposedly unprecedented warming of the last decades of the 20th century, May-August precipitation in the eastern Mediterranean region actually become less variable than it had been in the earlier part of the century.

In conclusion, the story told by these several studies of precipitation characteristics of Mediterranean Europe is vastly different from that which is routinely claimed for the planet as a whole by the world's climate alarmists.

Alexandrov, V., Schneider, M., Koleva, E. and Moisselin, J.-M. 2004. Climate variability and change in Bulgaria during the 20th century. Theoretical and Applied Climatology 79: 133-149.

Clarke, M.L. and Rendell, H.M. 2006. Hindcasting extreme events: The occurrence and expression of damaging floods and landslides in southern Italy. Land Degradation & Development 17: 365-380.

Crisci, A., Gozzini, B., Meneguzzo, F., Pagliara, S. and Maracchi, G. 2002. Extreme rainfall in a changing climate: regional analysis and hydrological implications in Tuscany. Hydrological Processes 16: 1261-1274.

Garcia Barron, L. 2000. Analisis de series termopluviometricas para la elaboracion de modelos climaticos en el suroeste de España. Thesis. Department of Fisica Aplicada II, University of Sevilla, Sevilla.

Grove, A.T. 2001. The "Little Ice Age" and its geomorphological consequences in Mediterranean Europe. Climatic Change 48: 121-136.

Lampre, F. 1994. La Linea de equilibrio glacial y los suelos helados en el macizo de La Maladeta (Pirineo Aragones): Evolucion desde la Pequeña Edad del Hielo y situacion actual. In: Marti Bono, C. and Garcia-Ruiz, J.M. (Eds.) El glaciarismo surpirenaico: nuevas aportaciones. Geoforma Ediciones, Logroño, pp. 125-142.

Rodrigo, F.A., Esteban-Parra, M.J., Pozo-Vazquez, D. and Castro-Diez, Y. 2000. Rainfall variability in southern Spain on decadal to centennial time scales. International Journal of Climatology 20: 721-732.

Rodrigo, F.S., Pozo-Vazquez, D., Esteban-Parra, M.J. and Castro-Diez, Y. 2001. A reconstruction of the winter North Atlantic Oscillation index back to A.D. 1501 using documentary data in southern Spain. Journal of Geophysical Research 106: 14,805-14,818.

Sousa, A. and Garcia-Murillo, P. 2003. Changes in the wetlands of Andalusia (Doñana Natural Park, SW Spain) at the end of the Little Ice Age. Climatic Change 58: 193-217.

Tomozeiu, R., Lazzeri, M. and Cacciamani, C. 2002. Precipitation fluctuations during the winter season from 1960 to 1995 over Emilia-Romagna, Italy. Theoretical and Applied Climatology 72: 221-229.

Touchan, R., Xoplaki, E., Funkhouser, G., Luterbacher, J., Hughes, M.K., Erkan, N., Akkemik, U. and Stephan, J. 2005. Reconstructions of spring/summer precipitation for the Eastern Mediterranean from tree-ring widths and its connection to large-scale atmospheric circulation. Climate Dynamics 25: 75-98.

Last updated 6 February 2008