Impact of a Northern European Enclosure Dam on North Atlantic Climate

As the climate changes the rising temperatures will not be the only change our society has to cope with now and in the future. Currently the global mean temperature is about 1°C above pre-industrial levels and the global mean sea level has risen over 21 cm since 1880. If climate change is left unmitigated, alternative protection measures will be needed. In their design fiction, Groeskamp and Kjellsson propose the construction of the Northern European Enclosure Dam (NEED) to protect Northern Europe against the future sea level rise. It would stretch between France, the United Kingdom and Norway and protect 15 countries lying at the North or Baltic Seas. The construction of NEED might be the most viable solution but it would also have various impacts on the society, the oceans and the climate. This work focuses on the changes NEED might cause in the North and Baltic Seas and the North Atlantic. Therefore we look at two 60 year long simulation runs, a control run and a run with NEED of the model Flexible Ocean and Climate Infrastructure (FOCI) coupled with the atmosphere model OpenIFS, a version of the Integrated Forecast System (IFS) model. As NEED would enclose the North Sea major changes are expected here. The model shows that the North Sea gets colder and fresher in the run with the dam as no exchange with the warm and saline water from the Atlantic is possible. After 100 years in the model the salinity has decreased from 34 PSU to 13,6 PSU. This freshening would change the hole ecosystem of the North Sea. In the Baltic Sea the model struggles to reproduce the observed stratification as we find colder and less saline waters in the bottom layers than in the upper layers instead of a salinity gradient from top to bottom, with most of the saltwater remaining at depth. In the North Atlantic as well as in the Pacific the data show a widespread warming at the surface. This warming is mainly the result of different variability between the two runs. The time period of 60 years is not long enough for the model to reach a steady climate state nor to average over several cycles of multi-decadal variability in the ocean and atmosphere. The strong warming seen along the Norwegian coast is an effect of NEED as it cuts off the circulation through the North Sea and thereby blocks the cooling and freshening effect of the exchange between the North Atlantic and North Sea waters. Most anomalies in the circulation in the Nordic Sea do not extend to the Labrador Sea. Yet more or longer data are needed to prove if building NEED has an impact on the global circulation of the oceans.

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