The city of Venice is investing billions in a new flood defence system to protect against sea level rises
(CNN) -- Sea-levels are rising unevenly around the world, with Pacific countries in particular suffering significant increases over the past two decades, according to accurate new satellite data.
On average, global
sea-levels have been rising at about three millimeters (mm) a year,
however, this masks large differences between regions of the world.
While some regions have seen sea-level rises of 12 mm a year, others have actually seen decreases of about 12 mm a year.
The results are based on radar readings from the European Space Agency (ESA) over an 18-year period from October 1992 to March 2010.
ESA used its satellites
to send radar pulses to the sea surface below, recording the time delay
in its return and creating a precise measurement of their height above
the surface.
Scientists say sea-level
rises are the result of the expansion of water due to rising
temperatures, melting of glaciers and the melting of polar ice sheets.
Annual mean global sea-level changes 1992-2010 (ESA)
The worst hit regions
over the past two decades, according to the ESA data, have been the
Pacific countries of Indonesia, Papua New Guinea, Philippines and
vulnerable Pacific islands like the Solomon Islands.
The Philippines for one is already frequently subjected to flooding and landslides caused by heavy rain, with seasonal monsoon rains in August killing at least 11 people.
Scientists suggest
regions that have seen high sea level rises over the past 20 years will
not necessarily continue to see higher than average sea-level rises in
the future.
"We suspect that the
bigger the differences get, the more they will tend to level out in the
future," says Robert Meisner, a spokesperson for ESA.
However, a recent study
of coastal cities still predicted the Philippines' capital Manila would
see its vulnerability to flooding double by the end of the century, due
to sea-level rises.
In some regions of the
world, the increasingly accurate sea level data is being used by
planners to mitigate against the risk of flooding.
In Venice, where the
sea-level data was released, engineers are constructing a new set of
tidal barriers to protect the historic city.
The city, which attracts millions of tourists every year, is seeing sea-level rises of around 2 mm per year, together with slow, mostly natural, subsidence of about another 2 mm every year.
The new $7.9
billion-barrier system will see giant barriers placed on the sea floor
around Venice. When the water levels rise, air will be pumped into the
barriers raising them up to block the tidal flow and protect the city
from flooding.
The system is due to be completed in 2014 and is expected to be able to protect the city for the next 20 years.
http://edition.cnn.com/2012/10/02/tech/satellites-sea-level-rise/index.html
3/10/12
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