Sea level

Land meets ocean at Kapp Linne, Isfjorden, Svalbard.
Photo: Stein Ø. Nilsen / Norwegian Polar Institute

Should a single quantity need to be applied to describe the climate on the Earth, it would probably have to be the global sea level. The global sea level reflects both short- and long-term changes in the climate of the atmosphere, the cryosphere, the land areas, and the oceans. In Svalbard, the sea level is monitored in Barentsburg. For comparison, sea level measurements for Tromsø and Vardø are also presented.

What is being monitored?

Sea level

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The figure shows the annual average sea level in Barentsburg. The strong decline in the observed level is thought to reflect a weakening of the West Spitsbergen Current. Other factors may also have contributed. For instance, land uplift after the last Ice Age is greater in the Arctic than in other areas and this helps to give less sea-level rise in the Arctic than elsewhere in the world.

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The figure shows the annual average sea level in Tromsø. The sea level declined faster in 1952–1985 than in 1985–2016.

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The figure shows the annual average sea level in Vardø. Whereas a decline is observed in the first part of the monitoring period, the sea level has generally risen in the last two  decades.

Status and trend

Sea level measurements from Tromsø, Vardø and Barentsburg all have the same properties, and high correlation between the annual mean change in sea level at these stations implies that long-term variability in these regions is shaped under the influence of the same driving forces.

All three time series show negative trends throughout the period. Barentsburg has the maximum negative trend in annual sea level variability in 1949–2016 (-2.75 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. The trends in Tromsø and Vardø are nearly identical and not equally substantial. Tromsø has a very insignificant negative trend of -0.02 mm/yr and Vardø* a negative trend of -0.26 mm/yr throughout the measurement periods.

Tromsø and Vardø show a different variability in the period prior to than after 1985. Before 1985, there is a stable, significant negative trend (-1.91 mm/yr for Tromsø and -2.35 mm/yr for Vardø). The maximum negative values in the trend in this period were achieved in October and November. The linear trend in the interannual variation for the period after 1985 is weakly negative in Tromsø (-0.18 mm/yr) and positive (0.65 mm/yr) in Vardø. In Tromsø, the trends for all the months except January and February are negative, but there are particularly high positive values for those two  months.

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.

The most significant contribution to the rate of global sea level rise has so far been increasing sea temperatures, decreasing salinity and a reduction in pressure at sea level. Rising temperatures and reduced salinity affect the density in the water, thus raising the sea level without there being more water in the seas for that reason.

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, melting of glaciers also affects the land uplift, because the land rises more when the weight of the glaciers is reduced when they melt.

Consequences

A 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.

Whereas melting of ice and expansion of water result in a rise in sea level in the longer term, variations in ocean currents, winds and changes in pressure give sea-level changes that can be observed over shorter time periods. Sea-level changes in time and space, together with other climate parameters, may therefore help to explain how climate changes occur in the sea.

Places and areas

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring