Sea level

Last updated 23 September 2022

The sea level reflects both short and long-term changes in the climate of the atmosphere, the cryosphere, the land areas, and the oceans. The global average sea level rises with about 3.5 mm per year due to supply of ice and melt water from land ice (mainly from glaciers and Greenland) and thermal expansion of seawater that has become warmer. In Svalbard, however, the sea level is dominated by uplift of the land since the last ice age (>10 000 years ago), the Little Ice Age (>100 years ago), and increased glacier melting since the 2000s. The sea level in Svalbard is monitored at Barentsburg (since 1948) and in Ny-Ålesund (since 1973). The long-term sea level at Barentsburg is shown here and compared to that of Tromsø and Vardø in mainland Norway.

Status and trend

There is a certain correlation between the annual measurements from Tromsø, Vardø and Barentsburg which implies that sea level variability in these regions is shaped under the influence of the same driving forces.

All three time-series (Barentsburg, Tromsø and Vardø) show negative trends throughout the periods. Barentsburg in 1949-2018 (no update since 2018) has the maximum negative trend in annual sea level variability of -2.7 mm/yr. This trend is negative for all months, and maximum values for the trend are in June and October. The winter months contribute least to the trend. Tromsø and Vardø have a negative trend of -0.49 mm/yr and -0.26 mm/yr throughout the measurement periods correspondingly, but over the most recent decades the trends have become slightly positive. This is in contrast to Barentsburg, where the trend has become more negative, probably due to land uplift as a response to the increased melting of glaciers in Svalbard over recent decades.

Causal factors

The global sea level will rise due to climate change. This takes place because large masses of ice on land melt and water expands when it is heated. In addition, the sea level is influenced by large-scale variations in ocean currents and dominant wind and pressure conditions.

As the land in Svalbard and North Norway is still rising after the last Ice Age, a global rise in sea level does not have the same effect on measurements of the relative sea level. In Svalbard, the melting of glaciers also affects the land uplift, because the land rises more as the weight of the glaciers is reduced when they melt.

Consequences

A potential rise in sea level may threaten infrastructure and cultural heritage remains in the shore zone in Svalbard. Increased erosion affects the coastline, and there are many cultural heritage remains on the coast.

About the monitoring

The global sea level has risen by about 120 metres since the last Ice Age, some 20,000 years ago, mostly due to melting of the huge Ice Age ice caps.

Despite this large rise in the global sea level, most of the Norwegian coast has experienced a drop in sea level. This is because Norway and the rest of Scandinavia have undergone substantial land uplift due to the vast Scandinavian ice sheet having melted away, its weight thereby disappearing. In Svalbard, this appears in several places as elevated shorelines in the terrain.

Whereas melting of land ice and expansion of water result in a rise in global sea level in the longer term, variations in ocean currents, winds and changes in atmospheric pressure give regional sea-level changes that can be observed over shorter time periods. Season variations in the landmass from snow and glacier melting also affect the rate of land uplift and hence the relative sea level. For better to separate the effects from ocean and land, it is desired to combine sea level measurements with geodetic measuring techniques for land uplift, like GNSS and VLBI. Absolute sea-level changes in time and space (when land rise is taken into account), together with other climate parameters, may therefore help to explain how climate changes occur in the sea.