Geological evidences of Cyclical Climatic-Environmental Changes in the  Mediterranean Area (2500 BP-Present Day)

Franco Ortolani (1); Silvana Pagliuca (2) Valerio Buonomo(1)

 

(1) Dipartimento di Pianificazione e Scienza del Territorio, Università di Napoli Federico II, Napoli, Italy; fortolan@unina.it

(2) ISAFOM, CNR, via Cupa Patacca, Ercolano, Napoli, Italy; pagliuca@ispaim.na.cnr.it

 

 

Key words: climate change, Mediterranean Area.

 

 

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 (figure 1).

 

Figure 1 - Climate zones in the circummediterranean Area. 1= present day limit between humid and arid zones; 2= northwards limit shift during muticentennial warm periods (enhanced Greenhouse Effect); 3= southwards limit shift during muticentennial cold periods (Little Ice Ages).

 

Figure 2 - Velia Geoarchaeological stratigraphy

 

Multidisciplinary geoenvironmental research was carried out to shed light on the climatic signifi-cance of different sediment types that have accumulated over the last 2500 years (Fig. 2, 3), 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.

 

Figure 3 -  Sibari Geoarchaeological stratigraphy

 

Figure 4 - Selinunte (SW Sicily) geoarchaeological stratigraphy

 

In  the Mediterranean area, the presence of windborne sand in coastal dunes (Fig 4) is the most significant geoenvironmental indicator linked to warm-arid climatic conditions. Under conditions of heightened aridity (rainfall lower than 200 mm, 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).

 

 

Figure 5 - Northern Egypt Geoarchaeological stratigraphy

 

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 (Figs. 4, 5). 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 wind-borne 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) resulted (Ortolani and Pagliuca, 2001).

During the peak of warm-arid climatic changes, enhanced “greenhouse effect” environmental conditions similar to those expected in the near future were established (Figs. 4 and 5). 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 (Figs. 2 and 3).

During periods in which the temperature increased by 1-2 °C, coastal zones were affected by desertification up to about latitude 42° N (Fig. 4). 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 (Figs 2 and 3), while soil formation occurred on the surface of the coastal dunes in the southern and northern parts (Figs. 4 and 5).

The main result achieved through geoarchaeological research is the identification of cyclicity (peri-od of about 1000 years) of the major climate and environmental changes that have resulted in 100 to 200 year environmental crises (Fig. 1). Paleoenvironmental, paleoclimatic and geoarchaeological data show that the Mediterranean area was chiefly affected by environmental conditions similar to those of the present day (Fig 6) (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 “greenhouse effect” periods and repeated solar activity minima coincide with cold periods, such as the Little Ice Ages (Figs. 6). 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 (Fig. 6). Variations in rainfall are expressed as percentages of current values.

A valid frame of reference for assessing and quantifying the changes that will occur at different latitudes during the enhanced 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 (enhanced 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 in rainfall in central-northern Europe.

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 (Fig. 6) 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.

 

 

Figure 6 -  Correlation between geoarchaeological stratigraphy and solar activity

 

 

REFERENCES

Allocca, F., Amato, V., Coppola, D., Giaccio, B., Ortolani F. and Pagliuca, S., 2000: Cyclical Climatic-Environmental Variations during the Holocene in Campania and Apulia: Geoarcheological and Paleoethnological Evidence. Mem. Soc. Geol. It., 55, 345-352.

Jirikovic, J. L., and Damon, P. E., 1994: The Medieval solar activity maximum. Climatic Change, 26, 309-316.

Ortolani, F. and Pagliuca, S., 2001: Le variazioni climatiche storiche e la prevedibilità delle modificazioni relative all’effetto serra. Asociazione Italiana Nucleare, marzo 2001, Roma.

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.

Ortolani F. & Pagliuca S. (2003) - Cyclical Climatic-Environmental Changes in the Mediterranean Area (2500 BP-Present Day). PAGES, Vol. 11, N. 1, April 2003, pp. 15