Sea levels and climate change
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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.

 

Figure 1 shows how the global sea level has increased since the first measurements were carried out, and how the rate of increase has been higher than the average in recent years.

 

The global average sea level has been observed by satellites since 1993. The sea level rose by 7 centimetres from 1993 to 2012.

 

Towards the end of this century (1981-2100), the sea level is likely to rise by 0.1-0.6 metres along the Danish coast, according to the most optimistic scenario (RCP2.6), and 0.3-0.9 metres according to the highest scenario (RCP8.5).

 

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.

 

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Figure 1: The absolute mean sea level around Denmark in metres 1900-2100, relative to mean sea level in the reference period 1986-2005. The grey-shaded area for the years 1900-2012 shows the observed, annual mean sea level measured by Danish water gauges, adjusted for isostatic uplift. The thin blue curve for the years 2012-2100 shows the IPCC's best estimate of mean sea level in the North Sea for the RCP4.5 scenario, and the shaded area indicates the uncertainty for this scenario. The dotted line shows the Danish Meteorological Institute's estimate of an upper limit for sea level rise for use in uncertainty calculations. The mean value and uncertainties are shown on the right in the figure for the four IPCC scenarios. Source: Danish Meteorological Institute. 

 

 

Future sea level and storm surges
The sea level will increase ever more rapidly towards the end of this century. 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. Storm surges are expected to increase by as much as the mean sea level. Thus the water level will be higher for both the frequent events with raised water levels as well as for the more rare, high storm surges. What today is a 20-year storm surge, could occur every year or every other year in the future.

The mean sea level around Denmark has increased by approximately 2 millimetres annually since 1900. Both globally and in Denmark, this sea level rise will continue up to and beyond the year 2100.

The change between 1981-2010 and the future period 2071-2100 in mean sea level (cm) in the RCP8.5 scenario is shown in Figure 2 per coastal stretch.

 

 

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Figure 2: The change between 1981-2010 and the future period 2071-2100 in mean sea level (cm) in the RCP8.5 scenario. Source: Climate Atlas

In order to illustrate the differences across Danish waters, three coastal stretches area shown: ‘Northern Wadden Sea coast', 'Fehmarnbelt', 'North Zealand coast'. Data for the remaining coastal stretches can be seen at Climate Atlas.

 

Wadden Sea coast:
Sea level
The change in mean sea level (cm) for ‘Northern Wadden Sea coast' between 1981 and 2010 and the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The expected change at the end of the century is 58cm for RCP8.5 (14cm to 103cm).

 

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Figure 3: Change in mean sea level (cm). Source: Climate Atlas 

 

 

Storm surges
20-year storm surge (cm) for ‘Northern Wadden Sea coast' in the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The grey line shows the reference value for the present (1981-2010). The expected change at the end of the century is 430cm for RCP8.5 (380cm to 510cm).

 

100-year storm surge (cm) for ‘Northern Wadden Sea coast' in the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The grey line shows the reference value for the present (1981-2010). The expected change at the end of the century is 460cm for RCP8.5 (400cm to 550cm).

 

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Figure 4: 20-year storm surge (cm) and 100-year storm surge (cm). Source: Climate Atlas 

 

Fehmarnbelt
Sea level
The change in mean sea level (cm) for 'Fehmarnbelt' between 1981 and 2010 and the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The expected change at the end of the century is 57cm for RCP8.5 (13cm to 101cm).

 

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Figure 5: Change in mean sea level (cm). Source: Climate Atlas

 

 

Storm surges
20-year storm surge (cm) for 'Fehmarnbelt' in the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The grey line shows the reference value for the present (1981-2010). The expected change at the end of the century is 212cm for RCP8.5 (160cm to 257cm).

 

100-year storm surge (cm) for 'Fehmarnbelt' in the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The grey line shows the reference value for the present (1981-2010). The expected change at the end of the century is 240cm for RCP8.5 (180cm to 300cm).

 

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Figure 6: 20-year storm surge (cm) and 100-year storm surge (cm). Source: Climate Atlas

 

North Zealand coast:
Sea level
The change in mean sea level (cm) for the 'North Zealand coast' between 1981 and 2010 and the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The expected change at the end of the century is 48cm for RCP8.5 (4cm to 93cm).

 

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Figure 7: Change in mean sea level (cm). Source: Climate Atlas

 

Storm surges
20-year storm surge (cm) for the 'North Zealand coast' in the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The grey line shows the reference value for the present (1981-2010). The expected change at the end of the century is 207cm for RCP8.5 (163cm to 253cm).


100-year storm surge (cm) for the 'North Zealand coast' in the future periods 2041-2070 and 2071-2100 in the RCP4.5 and RCP8.5 scenarios. The grey line shows the reference value for the present (1981-2010). The expected change at the end of the century is 230cm for RCP8.5 (180cm to 290cm).

 

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Figure 8: 20-year storm surge (cm) and 100-year storm surge (cm). Source: Climate Atlas

 

Read more and explore the data on Klimaatlas.dk

Senest redigeret: 19-04-2021