Page 11 - climate-change2013

The changing

Mediterranean climate

The changes briefly described above are not homo-
geneous around the world. Global changes should be
understood as those which affect the whole planet,
but not necessarily in the same way everywhere. Nor
should mean changes averaged for the world’s oceans
be confused with specific changes operating on smaller Scandola MPA, Corsica. Photo: J. Garrabou
spatial scales, such as those observed or expected in
regions such as the Mediterranean. Salinity changes The waters filling the deepest basins of the Mediterra-
are an example. The alteration of the earth’s hydrologi- nean are renewed and ventilated almost every year by
cal cycle and the melting of glaciers and ice sheets are means of a process called deep-water formation. In this
affecting the salinity of the oceans on a global scale, process, which has been reported to occur in the Gulf
but, while salinity is expected to decrease at high lati- of Lion, the northern Adriatic Sea and the Aegean Sea,
tudes, it will increase at lower latitudes with the reduc- surface and intermediate waters with high salinity due
tion in precipitation and increase in evaporation. to high evaporation rates are cooled in winter, thereby
increasing in density and sinking to the deepest levels
The Mediterranean Sea is a good example of a re- of the sea to mix and become part of the new deep-
gion where particular and specific responses to global water masses.
changes have been observed. Its relatively small size,
high biodiversity, temperate climate and semi-enclosed The ongoing changes in temperature and salinity may
nature make it a place where the effects of climate reduce the formation of deep-water masses by affect-
change will be most exacerbated. Its semi-enclosed ing the duration, frequency and intensity of this process.
nature prevents rapid water exchange and therefore As a result of local climate change, this may eventually
makes it more sensitive to temperature and pH varia- have an impact on biodiversity (Pusceddu et al., 2010).
tions. Together with the high human pressure exerted
by densely populated coastal areas, this makes the Sea-level rise
Mediterranean Sea an especially vulnerable place.
The rise in sea level in the Mediterranean —which was
The region has also been recognized by the oceano- lower than in the rest of the world in the late 20th centu-
graphic community as a natural laboratory for the study ry (from the mid-1960s to the mid-1990s) due to anoma-
and analysis of climate change, as some of the main lous atmospheric pressures— has regained pace since
processes controlling ocean circulation at a global then and seems to be accelerating at a similar rate to
scale are reproduced on a much more restricted scale that observed throughout the world’s oceans.
in the Mediterranean Sea.
Sea warming Global sea-level rise
Metres
During the 20th and early 21st centuries, the surface 1.2
seawater temperature of the Mediterranean has in- historical observations projections
creased in a similar way to air temperature (Vargas- 1.0 records
Yáñez et al., 2010; Lionello, 2012): the sea’s shallow New
waters have already warmed by almost 1°C since the 0.8 estimate
1980s. The temperature of intermediate waters, that is,
those extending below the upper layer from depths of 0.6
200 m down to 600 m, has also risen.
0.4
Salinity and sea circulation changes 0.2

The salinity of intermediate and deep waters has also 0
increased, apparently due to a combination of factors: IPCC 2007
decreasing precipitation, increasing evaporation and -0.2
the damming of the main rivers draining into the Medi- 1800 1850 1900 1950 2000 2050 2100
terranean Sea. Source: Cazenave and Llovel, 2009.

According to the 2007 IPCC report, global aver-
age sea-level rise will vary from 18 cm to 59 cm by
Surface seawater temperature: 2100. The IPCC models did not account for the ac-
Water temperature between celerated melting of ice sheets in Greenland and
1 millimetre and first metres Antarctica. Some of the latest research, however,
below the sea surface. estimates a global sea level rise of between 0.6 and
1.2 metres by 2100. By Riccardo Pravettoni, UNEP/
GRID-Arendal

MEDITERRANEAN MARINE PROTECTED AREAS AND CLIMATE CHANGE: A GUIDE TO REGIONAL MONITORING AND ADAPTATION OPPORTUNITIES 9