What is the situation regarding the rising sea level?

According to the climate scenarios worked out by the Royal Netherlands Meteorological Institute KNMI in 2014, the sea level rise may increase to 100 cm by 2100. Up until now, the Intergovernmental Panel on Climate Change (IPCC) has been reckoning with a sea level rise of 80 cm by 2100. However, recent studies (conducted by KNMI and Utrecht University, among other bodies) indicate that the processes affecting the melting of the ice caps in Greenland and Antarctica are developing at a much faster rate than was previously assumed. Consequently, we cannot preclude an even more rapid rise in sea level.

In the Delta Programme, we anticipate future climate change; we focus on 2050, looking ahead to 2100, and base our plans on the KNMI climate scenarios. Adaptive strategies and flexible measures enable us to factor in new knowledge and insights. In anticipation of the first interim evaluation of the Delta Programme in 2020, the Delta Programme 2018 maps out the first insights into the potential impact of a more rapidly rising sea level for the Netherlands.

Sea level rise is caused by a combination of ocean warming (warmer water expands and takes up more room) and melting land ice. The accelerated rise over the past few decades has mainly been triggered by expanding water, the more rapidly melting land ice (on Antarctica and Greenland), and melting mountain glaciers. (It is not affected by the melting North Pole ice shelf: being sea ice, this does not add water.) At the regional level, wind patterns and the gravitational force of large ice masses on water (“gravitation effect”) could also play a role.

Gravity discharge of excess water into the sea is increasingly hampered by the rising sea level and continued soil subsidence, necessitating the use of pumps. In addition, the sea is encroaching more and more on the coast, through salt intrusion in ground and surface water, but also through increasing coastal erosion and rising storm surge levels. Furthermore, the sand shoals, mud flats, and salt marshes in, e.g., the Wadden Sea, Westerschelde, and Oosterschelde are at risk of “drowning” because they cannot keep up with the rising sea level. Sand replenishment will enable us to keep our coastline in place for years on end, even if the sea level continues to rise. In the future, we may have to look for other measures.

The effect of sea level rise may even be enhanced (or mitigated) by the subsidence (or rise) of the adjoining land. Geological movements and compaction of clay and peat cause the Dutch soil in the Northwestern part of the country to subside by an average of 10 cm per century, whereas Scandinavia, on the other hand, is rising as a result of the disappearance of ice caps from the past.