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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
          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.
          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/

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