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THE tide is going out in the Mediterranean. Over the past 40 years, sea
levels have been dropping in the near-landlocked sea, while over the rest of the
globe sea levels have been steadily rising, according to a new analysis.

“The change is dramatic,” says Michael Tsimplis of the Southampton
Oceanography Centre, who has analysed the records of seven long-term tidal
gauges around the Mediterranean. Global warming makes seawater expand, and has
pushed up sea levels around the world by more than a millimetre a year over the
past 100 years. The Mediterranean followed suit until 1960, but since then its
level has been dropping by as much as 1.3 millimetres a year, returning to
levels not seen since early last century.

Tsimplis believes the drop in sea level is caused by the Mediterranean
becoming more salty, which he puts down to the weather and dam builders. Since
1960, rising air pressure over the sea has reduced rainfall, bumping up
salinity. Rivers that bring fresh water into the sea have also been dammed. As
water gets saltier it becomes more dense, and takes up less space, more than
counterbalancing any expansion due to global warming, Tsimplis says.