Annual theoretical mean sea level values on the Finnish coast referenced to the geodetic height systems (N2000, N60, N43 and NN) are given in the tables below.
At the Finnish mareographs, sea level is measured related to a fixed reference level of each mareograph. This reference level is bound to the geodetic height systems, and its datum (zero level) lies about two meters below the estimated mean sea level of 1921. The possible movement of a mareograph related to its reference level is checked by annual levelings to a nearby benchmark. Every three years the stability of the mareograph and its benchmark is verified by levelings to other local bedrock-bound benchmarks.
There are four geodetic height systems currently in use in Finland:
The mean sea level referenced to these height systems has been decreasing over the past decades. Thus, the so called theoretical mean sea level (MW) has been adopted.
The theoretical mean sea level (or theoretical mean water, MW) is an estimate for the long-term mean value (more precisely, expectation value) of sea level, made for practical purposes. Land uplift, global sea level rise, as well as changes in the Baltic Sea water balance are taken into account. Because of these changes the theoretical mean sea level is not a constant. The rate of change of the theoretical mean sea level from year to year is not constant either, due to changing rate of the global sea level rise and changes in the Baltic Sea water balance. The Finnish Meteorological Institute confirms the height of the theoretical mean sea level annually, using the most recent knowledge on the past and future changes of the factors affecting the sea level.
The theoretical mean sea level is commonly used in Finland as a reference level when sea level information is given for instance on the internet or radio and in the newspapers.
More information on land uplift and the effects of sea level rise on the Finnish coast is available on the Climate Guide web site (see the link on the right side of this page).
In 2000, a sea level value of +15 cm, referenced to the theoretical mean sea level, was measured at Helsinki. The sea level is converted to N2000 and N60 systems, respectively, as follows:
In 2012, a sea level value of -22 cm, referenced to the theoretical mean sea level of 2012 (MW2012), was measured at Pietarsaari. The sea level in relation to the theoretical mean sea level of 2005 (MW2005) is obtained as follows, utilizing the geodetic height systems:
Using the N2000 height system:
Using the N60 height system:
How much has the land risen from the sea at Pietarsaari during 1960-2010? How much during 2000-2010?