( 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 . Special report : Sea-level rises . 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 . 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 . See also : Five cities battling flooding , heats and storms . 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 .
Global sea-levels rose by an average of about three millimeters ( mm a year over the end of the century . Most accurate data yet based on satellite data from ESA . Sea-level rises uneven around the world with Pacific islands region hit worst . Philippines one of many cities upgrading flood protection barriers .