02 Nov 2011
The Permanent Service for Mean Sea Level (PSMSL) today launched the latest of its interactive maps that allow users to explore changes to sea level as observed by tide gauges. The anomalies map demonstrates how sea level varies from year to year when compared the long-term average at that site, calculated over the period from 1960 to 1990. Moving the slider along the time line shows how sea level can vary by over 20 cm from year to year at some locations.
When you first load the page showing the sea level anomalies, the background trend at each tide gauge is not removed. Thus, a majority of the early years are dominated by blue colours showing negative anomalies and the later years by red colours showing positive anomalies as the average global sea level rises. There are notable exceptions to this pattern, however. For example, the land surrounding the Gulf of Bothnia is uplifting as the earth continues to recover from the collapse of the large ice sheets that covered the region during the last ice age. This causes sea level measured by tide gauges to decrease. Thus, the anomalies in that region go from red to blue over the time span of the data. To remove this background trend at each site, use the tick box below the map.