Geological evidences of Cyclical Climatic-Environmental Changes in the Mediterranean Area (2500 BP-Present Day)
(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 -
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 (
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
Figure 5 -
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
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-
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
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
Figure 6 - Correlation between geoarchaeological
stratigraphy and solar activity
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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