Sea levels and climate change

Global warming is unequivocal according to the UN IPCC, and many of the climate changes observed since the 1950s are unprecedented. This has significance for the water levels in the world's oceans, and for the levels along the Danish coast. The most important reason for the sea level rise is increased global warming. This causes the seawater to expand and the Antarctic and Greenland ice caps and the world's glaciers to melt.

The sea level around Denmark has been rising since the first measurements were made, and the rise has been higher than average in recent years. The sea level will increase the least in northern Jutland and most in the southwestern part of Jutland. This difference is due to the isostatic uplift from the most recent Ice Age.

Figure 1: Mean water level for three representative stations in Denmark since 1890. Points correspond to annual averages. The blue line corresponds to an average over several decades. More details can be found in DMI Report 18-16 (Source: DMI). 

Future sea level and storm surges

The sea level will increase ever more rapidly towards the end of this century. Sea level is expected to rise between 30 cm and 60 cm towards the end of the century (2071–2100) compared to the present (1981–2010) under a low and a high emmission scenario, respectively.

Figure 2: Change in mean sea water level (cm) in Denmark between 1981–2010 and the future periods 2041–2070 and 2071–2100.

As the sea level rises, the water level associated with storm surges will rise by a corresponding height. The same storm surge in the future climate will therefore be able to reach further up the terrain. The change in storm surges will also mean that a certain height (e.g. where properties are at risk) is exceeded more frequently than today. A sea level that today is exceeded only once in a 20-year period will be exceeded 40 times more frequently (ie, every year to twice a year) by the end of the century under a high discharge scenario (Figure 3).

Figure 3: Change in frequency of a current 20-year event (storm surge) in Denmark (1981–2010) and the future periods 2041–2070 and 2071–2100. Note that the indicator is set to a maximum of 60 events per 20 years.