Climate indicator – Sea level

The sea level changes over time due to ongoing climate change and long-term land elevation. Since the end of the 19th century, the climate-driven sea level change along Sweden's coast has caused the sea to rise approximately 15 centimeters on average. This indicates how big the rise would have been if we had had no long-term land elevation. Seas will continue to rise for a long time due to global warming, which will have major effects on coastal areas. However, humanity can influence how fast and how much the sea level will rise by limiting climate change.

Comment on the results

The parameter "Water level in RH 2000 adjusted for land elevation" shows a climate-driven sea level change of approximately 15 centimeters since the end of the 19th century at the oldest measuring stations. The long-term local land elevation is excluded in that value. However, a general value for the entire coast of Sweden will not be completely fair because local processes that affect sea level rise differ greatly between different locations. In addition, the measurement series are of different lengths and sometimes from different periods of time. 

Common to all stations is that the annual average values ​​vary greatly from year to year. It appears though, that the sea level has risen faster in recent decades than earlier. Of the 15 centimeters rise since the end of the 19th century, almost 10 centimeters has occurred in the last 40 years.

The ongoing land elevation can be said to hide the sea level rise, as reference points on the coast are moved up at the same time as the sea level is also rising. In the places in central and northern Sweden where the land elevation is speeding, there has not been an experienced sea level rise in place as the land elevation is faster. In southern Sweden it is the opposite.

In the parameter "Water level in RH 2000" the long-term land elevation is not taken into account. Since the land elevation varies from station to station, as seen in the "Total land elevation" parameter, the slope of the line showing the moving average also varies. Where the land rise is greater than the sea level rise, the water level in RH 2000 falls, see for example Ratan, while the water level in RH 2000 rises in places where the land rise is less, see for example Klagshamn.

How is the indicator sea level defined?

The climate indicator sea level shows how sea level changes over time due to ongoing climate change. In Sweden, the sea level is not only affected by climate change, but also by land elevation which has been going on since the last ice age. In order to distinguish how much of the changes are due only to the climate, the long-term land elevation has been excluded and that is how the climate indicator is defined.

Why is this indicator important?

The rise of the sea level is an indication of how climate change develops over time. The increasing temperature in the atmosphere causes ice sheets and glaciers to melt faster than they are built, which means that more water is added to the oceans and the level rises. As the oceans warm, their volume increase due to thermal expansion. These two processes are the main contributors to sea level rise.

Raised sea levels can have effects on coastal areas through, for example, flooding with damage to buildings and other infrastructure. A rising sea can also cause coastal erosion, raised groundwater levels and saltwater intrusion.

How has the indicator been calculated?

The water level in the sea is measured at roughly 60 stations along Sweden's coast. However, not all stations have been active long enough for the climate indicator to be calculated there with certainty. Measured values ​​in RH 2000 from water level stations have been averaged per year. Only years with data coverage of 80% or more have been used. From these values, the long-term land elevation, calculated as below, has been subtracted to give the parameter "Water level in RH 2000 adjusted for land elevation". From these data, moving average values ​​over approximately 10 years have also been calculated.

Data for land elevation comes from Lantmäteriet's model NKG2016LU. The biggest contribution in the model is a long-term land elevation that is mainly due to the rise of the earth's crust after the last ice age, so-called postglacial land elevation. But land elevation is also affected by how much ice is melting on land in modern times due to global warming.

Large amounts of melting ice causes land elevation in the regional immediate area and land subsidence in areas far away from the ice. This elastic component of land elevation amounts to approximately 0.6-0.7 millimeters on average of elevation per year for Sweden today. This contribution is subtracted from the land elevation model data. This way, the climate indicator can show the relative sea level change due to global sea level rise, including the contribution of land rise caused by climate change, but without the impact of long-term land rise.

Rising sea levels in the future

Future sea level rise is strongly dependent on how climate change develops. How high the levels will be is determined by to which extent society will be able to limit the emissions of greenhouse gases.

In many places in Sweden where the land is rising rapidly, for example in the coastal region of Västerbotten, it will not seem like the sea is rising in the coming decades. If emissions continue to rise, however, sea level rise may begin to outpace land rise in these areas later in time.

Along Götaland's coasts, the sea level is getting higher and higher as the land elevation is slower than the sea level rise already today. Southern Sweden's coasts are already affected to a significant degree by the increase and will also be worst affected in the future.