SEA level is measured in two ways: from tidal gauges and by satellite altimeter. According to the University of Colorado, Bolder, since August 1992 the satellite altimeters have been measuring sea level on a global basis with unprecedented accuracy and since 2005 the steady upward trend has stumbled.
The recent dip could not qualify as a trend, but it is interesting – particularly given that atmospheric levels of carbon dioxide continue to rise.
Of course even a drop in the global sea level may not save Tuvalu because the great majority of oceanic islands, including Tuvalu, were formed by volcanic activity. While the volcanoes are active, the islands rise relative to the global averaged sea-level. When volcanic activity stops, the islands will cool and eventually start to sink. So there are islands rising and sinking all the time – and Tuvalu should be sinking.
[Hat tip to Jack Moevich for the link to the latest data on global sea levels.]