Natural, Rapid and Cyclical Climatic-Environmental Change in the Mediterranean Area and Human Responses During the Last 3000 Years
by
Franco Ortolani
Dipartimento di Pianificazione e Scienza del Territorio, Università di Napoli "Federico II"
Coauthors: Silvana Pagliuca, CNR-ISPAIM

The Mediterranean Area acts as a boundary zone between humid and desert zones and is highly sensitive to variations in climate and environment. Indeed, shifts in the climate bands towards north or south by only a few degrees of latitude may result in dramatic changes in soil surface conditions. This may cause, for example, desertification in areas that previously had a humid climate or vice versa.

Multidisciplinary geoenvironmental research was carried out to shed light on the climatic significance of different sediment types that have accumulated over the last 2500 years, located at various latitudes and in geographical areas with different morphoclimatic conditions (Ortolani et al., 1991; Ortolani and Pagliuca, 1993, 1994, 2001). The sediments, which cover many archaeological sites, were not affected by human impact between the Archaic Period and the Middle Ages.

In the Mediterranean area, the presence of wind-borne sand in coastal dunes is the most significant geoenvironmental indicator linked to warm-arid climatic conditions. Under conditions of heightened aridity (rainfall lower than 200 mm/yr, typical of desert areas), windborne coastal sand may even invade areas a considerable distance from the sea, forming windborne accumulations that cause the vegetation cover to disappear. This has been widely shown in the literature and verified by direct research (Ortolani and Pagliuca, 2001).

The most typical sediment characterising wetlands consists of soil that allows the development of vegetation and which differs ac-cording to latitude, local climatic and morphological conditions, and substrate lithology (Ortolani and Pagliuca, 2001). The vegetation occurs both on the surface of coastal sand dunes, which are thus stabilised, and on the alluvial sediments of the plains and altered substrate of the rocks of hill and mountain slopes.

The most significant sediments found in Mediterranean coastal dune zones in which severe climatic and environmental changes have occurred in the past consist of buried soils within layers of wind-borne sand. The presence of buried soils indicates that precipitation increased appreciably for a sufficiently long period of time to allow soil formation. Hence, there was a change in climatic conditions from desert to humid. Sediments indicating considerable climatic changes in currently humid areas include windborne sand and alluvial deposits of considerable thickness that cover areas where human impact has occurred. The presence of wind-borne sand indicates that rainfall decreased sharply until desertification (rainfall below 200 mm/yr) resulted (Ortolani and Pagliuca, 2001).

During the peak of warm-arid climatic changes, "increased greenhouse effect" environmental conditions similar to those expected in the near future were established. During the transition periods from humid to warm-arid and at the beginning of cold-humid climatic variations, other significant geoenvironmental variations (hydrologic and geomorphological instability) occurred concurrently with the marked increase in rainfall that took place after warm periods. During periods in which the temperature increased by 1-2 ^°C, coastal zones were affected by desertification up to about latitude 42^° N. During temperature decreases, the areas of alluvial plains subject to human impact and settlements were affected by an accumulation of huge volumes of sediments. This resulted in aggradation and progradation of the coastlines in the northern part of the Mediterranean, while soil formation occurred on the surface of the coastal dunes in the southern and northern parts.

The climatic zones shifting in the circummediterranean area strongly influenced human migration, at local and continental scale, during the Holocene and the historical period. We recognised a general migration at the beginning of the Holocene warm period (about 8000 years BP) from Central to Northern Europe and from Southern Mediterranean Area to Southern Iraq. Another general human migration is evident at the end of the Holocene warm period, about 4200-3800 years BP, from Northern Europe and from Southern Iraq towards the Mediterranean Area. During the historical period there are evidences of repeated migrations from Eastern and Northern Europe towards Italy and from the Apenninic mountain belt towards the coastal areas during the Little Ices Periods. During the warm periods there was a migration from the coastal areas towards the apenninic mountain belt.

The main result achieved through geoarchaeological research is the identification of cyclicity (period of about 1000 years) of the major climate and environmental changes that have resulted in 100 to 200 year environmental crises. Paleoenvironmental, paleoclimatic and geoarchaeological data show that the Mediterranean area was chiefly affected by environmental conditions similar to those of the present day (Ortolani and Pagliuca, 2001).

There is clearly a close correlation between climatic and environmental changes and solar activity. Prolonged solar activity maxima coincide with warm "increased greenhouse effect" periods and repeated solar activity minima coincide with cold periods ("reduced greenhouse effect"), such as the Little Ice Ages. The history of mankind and the environment in the last few millennia highlights progressive, cyclical climatic and environmental changes that consistently occur in multicentennial periods.

Using instrumental data and those obtained from natural archives, we propose a climatic re-construction of the past 2500 years.

A valid frame of reference for assessing and quantifying the changes that will occur at different latitudes during the Increased Greenhouse Effect of the Third Millennium is provided by: (1) climatic and environmental data relating to the Warm Medieval Period in the Mediterranean area; (2) results achieved from research into geoenvironmental changes linked to historical climatic variations, especially those of the last few centuries, and; (3) various multidisciplinary data obtained from research conducted in various parts of the world.

Instrumental data chiefly concerning the last 150 years in the Mediterranean show a consistently close correlation between environmental variations (increase in solar activity and temperature and changes in the quality and quantity of rainfall) and the period of transition from the cold-humid climatic conditions of the Little Ice Age to those that may probably characterise the Warm Period of the Third Millennium (Increased Greenhouse Effect of the Third Millennium).

If cyclical climatic variation as occurred in the past will continue, it might result in new environmental conditions along the belts bordering the current climatic zones. In particular, a large part of the areas that are currently subtropical deserts might be transformed into humid areas. These conditions may be at times better and at times worse than those of the Little Ice Age.

This speculated shift in Mediterranean climatic conditions a few degrees to the north would cause an appreciable change (decrease) in rainfall in The Mediterranean Area and consequent climatic desertification of the coastal zones, as it happened just 1000 years ago during the Medieval Warm Period.

Central-northern Europe, also, will be severely affected by near future climatic environmental change. Since the 18th century, this area has been characterised by an almost homogeneous distribution of rainfall over the year and consequently, a constant river water regime. Mediterranean-type rainfall could probably increasingly affect this area in the near future. This seasonalisation of rainfall would result in an increased frequency of bankful flow conditions. Ongoing millennial climatic cyclicity forecasts that river valleys will be affected by repeated catastrophic flooding. Given that these valleys were urbanised on the basis of a constant river water regime, serious damage to the consolidated socio-economic organisation of central-northern Europe would therefore result.

The near future climatic change will affect severely the southern part of the present day humid belt of Asia causing the northwards shifting of the desert zone. Many million people will be forced to migrate northwards and westwards. The wars for water control ("liquid gold") will increase.

References

Ortolani F. & Pagliuca S. (2004) - The Climatic Risk: a new risk for the cities of the Circummediterranean Area. 32nd IGC Congress, Florence 19-28 August 2004.

Ortolani F. & Pagliuca S. (2004) - 2600 BP-Present Day geoenvironmental and urban evolution of Naples (Italy). 32nd IGC Congress, Florence 19-28 August 2004.

Ortolani F., Pagliuca S. & Serva L. (2004) - Geological causes of last millennium tsunamis affecting the Italian coast. 32nd IGC Congress, Florence 19-28 August 2004.

Ortolani F. & Pagliuca S. (2004) - Geoarchaeological evidences of recent climatic changes and catasthrophic events in the Neapolitan urbanised area. 32nd IGC Congress, Florence 19-28 August 2004.

Ortolani F. & Pagliuca S. (2004) - Urbanisation and man-geoenvironment relationships in Campania (Southern Italy). 32nd IGC Congress, Florence 19-28 August 2004.

Ortolani F. & Pagliuca S. (2004) - Variazi/ne climatica, diminuzione delle risorse idriche e impatto sull'agricoltura dell'Italia meridionale. Atti dei Convegni Lincei, "Giornata mondiale dell'acqua" La siccità in Italia, Roma 21 marzo 2003, Accademia Nazionale dei Lincei 2004.

Ortolani F. & Pagliuca S. (2004) - L'evoluzione del clima in Italia dalla Piccola Età Glaciale (1500-1850) al prossimo futuro (Effetto Serra del Terzo Millennio). Atti dei Convegni Lincei, "Giornata mondiale dell'acqua" La siccità in Italia, Roma 21 marzo 2003, Accademia Nazionale dei Lincei 2004.

Ortolani F. & Pagliuca S. (2004) - Il clima Mediterraneo: modificazioni cicliche degli ultimi millenni e previsioni per il prossimo futuro. Atti dei Convegni Lincei, "Giornata mondiale dell'acqua" La siccità in Italia, Roma 21 marzo 2003, Accademia Nazionale dei Lincei 2004.

Stuiver, M., Braziunas, T. F., Becker, B. and Kromer, B., 1991: Climatic, Solar, Oceanic and Geomagnetic influences on late glacial and Holocene Atmospheric 14C/12C change. Quaternary Research, 35, 1-24.

Date received: July 20, 2005

Copyright © 2005 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caqy-41.