If climate change is left unmitigated, the authors of new research claim that the construction of a 637km long Northern European Enclosure Dam (NEED) might be “the most viable solution to protect Northern Europe against sea level rise”.

According to Sjoerd Groeskamp from the Royal Netherlands Institute for Sea Research, and Joakim Kjellsson from the Centre for Ocean Research in Germany, it is virtually certain that sea level rise (SLR) will continue beyond 2100. A baseline of 2.3m global mean SLR per oC temperature rise is predicted, suggesting an unavoidable 5-11m increase over the next centuries to millennia.

“It might be impossible to truly fathom the magnitude of the threat that global mean sea level rise poses,” the authors say, adding that their solution to this extraordinary global threat could protect over 25 million people and important economical regions in Northern Europe.

Groeskamp and Kjellsson propose the construction of NEED that stretches between France, the UK and Norway. They acknowledge that it “may seem an overwhelming and unrealistic solution at first” but state that their “preliminary study suggests that NEED is potentially favourable financially, but also in scale, impacts and challenges compared to that of alternative solutions, such as (managed) migrations and that of country-by-country protection efforts”.

As the authors warn: “NEED showcases the extent of protection efforts that are required if mitigation efforts fail to limit sea level rise.”

Two components

In their research which was published in the Bulletin of the American Meteorological Society, Groeskamp and Kjellsson say that the Northern European Enclosure Dam will disconnect the North and Baltic Seas from the Atlantic Ocean to protect 15 Northern European countries from global-mean SLR. This can be achieved by constructing two enclosure dams which have a total length of 637km:

The southern part of NEED connects France (near Brest) to the south-west coast of England and measures 161km in length with an average depth of about 85m and a maximum depth of 102m. 

The Northern part extends from the north-east tip of Scotland, via the Orkney and Shetland Islands to Bergen in Norway. The northern part has a total length of 476km and average depth of 127m with a maximum of 321m in the Norwegian Trench. 

The two components together would protect coastal communities that under current population density consist of about 25 million people below 2m SLR, while 55 million live below 15m SLR. 

“If constructed,” the authors say, “NEED would be one of the largest civil engineering challenges ever faced.”

When looking at the technical considerations for constructing NEED there is “substantial” expertise available. The authors name the largest constructed enclosure dams to date as being the Afsluitdijkn in the Netherlands which is 32km long, about 11m in height and 90m wide; while the Saemangeum Seawall in South Korea is 33km long, an average of 36m high (maximum of 54m) and 290m wide. 

“These dimensions are not far off those required for the construction of NEED-south and NEED-north near the Orkney and Shetland islands. However, we expect a substantial but surmountable technological challenge for the part of NEED-north that crosses the Norwegian Trench with depths over 300m,” Groeskamp and Kjellsson state. They go on to mention that fixed oil rigs are feasible in depths over 500m, while moored oil rigs operate in waters over 2000m depths, indicating that having fixed constructions over 300m depths is possible. 

“Although dams have different requirements than oil rigs,” they acknowledge, “this is encouraging for the possibility of constructing NEED.”

The two-component Northern European Enclosure Dam will disconnect the North and Baltic Seas from the Atlantic Ocean to protect 15 Northern European countries from global-mean sea level rise.

Technical Considerations

Other considerations include the fact that enclosing the North and Baltic Seas will yield a net freshwater discharge of 40,000m3 s −1 into the basin which would lead to a SLR of 0.9 m year−1 within the enclosure, and must therefore be pumped out into the Atlantic Ocean.

“The discharge will also lead to freshening of the basin and reduce the salinity by a factor 10 in about 100 years. The freshening is expected to affect ecosystems, biodiversity and the fishing industry,” the authors admit.

In addition, the maritime industry would be significantly impacted by the construction of NEED. As the authors state: “The busiest trading ports in Europe (Rotterdam, Antwerp, Hamburg, Bremerhaven) lie within the enclosure. Without a proper solution to reduce the impact of NEED on the maritime industry, NEED would be a less viable solution for protection against SLR. Solutions are available, as NEED could for example incorporate sluice gates to allow for a continuation of ongoing shipping traffic. Sluice gates allowing for some of the largest ships in the world are already operational in the Netherlands and Belgium. Alternatively, harbours could be built on the ocean-side of NEED from where goods could be transferred to trains or to vessels operating within the enclosure. 

“Regardless,” Groeskamp and Kjellsson continue, “the effect of NEED on the maritime industry will remain uncertain, both economically and technically. However, it is certain that without the construction of NEED, the maritime industry will also be economically affected and technically challenged as SLR will force ports to relocate, or adopt and continuously upgrade their protection measures.”

In addition, the “the availability, sourcing and transport of building material [sand] and related energy cost to build and maintain the enclosure could pose limitations on the ability to construct NEED”.

Estimates suggest that building NEED would require about 51 billion tons of sand which is equal to about one year’s worth of global sand use. Sand is also acknowledged as becoming an increasingly scarcer material.

“However,” the authors argue, “constructing new coastal defences and maintaining, upgrading and expanding the thousands of kilomeres of coastal defence that are already in place to protect Northern European coastal communities will also provide complex technological challenges that may not be easy to overcome. As such, these challenges could well exceed those that arise when constructing NEED.”

Financial feasibility

Looking at the financial feasibility of the project, the authors provide a “back-of-the-envelope” estimate of the construction costs achieved by scaling up the construction costs of several existing projects (Saemangeum Seawall in South Korea; Maasvlakte 2 – an extension of Rotterdam Harbour, plus pumps used at Afsluitdijk and New Orleans).

“Combining all the above we estimate,” the authors say, “the total costs to be roughly 250-550 billion Euro. When assuming a 20-year construction time over which to spread the costs, this gives an annual expense of 0.07 – 0.16% of the combined Gross Domestic Product of the 15 involved countries.”

In addition, the report goes on to discuss that even for SLR of a few metres, the integrated cost of individual protection of all 15 countries together “far exceeds” the costs of constructing NEED. For protection against long term SLR projection (>10m), NEED is “almost certainly” considered as being the least costly option.

Afsluitdijk, a major dam and causeway in the Netherlands, runs from Den Oever in North Holland to the village of Zurich in Friesland province, damming off the Zuiderzee, the salt water inlet of the North Sea.


When looking at the impact of social factors such as loss of places and culture, Groeskamp and Kjellsson admit that these are difficult to quantify, are often subjective but are real for those experiencing them. They add: “We hope that the mere suggestion of NEED as a solution, and associated protest, may instigate a thought process that sparks public awareness of the threat that SLR poses, possibly clearing a path for global scale action to address long-term climate change related threats.”

Without new policy however, SLR will lead to unavoidable and irreversible loss of physical places, cultural heritage and environmental and ecological systems. In addition, landlocked European countries will also suffer from global mean SLR as a result of changes in trade, migration  and social-political instabilities. 

“Therefore the question is not if we should start adaptation efforts, but which adaptation measures we should start to implement right now,” the authors stress. “We take the stand that a policy that has the least direct impact on people’s daily life, at reasonable costs, has the largest potential to be implemented with the required urgency to be effective. As NEED would be constructed mostly in the sea (reducing direct impact on people’s lives) and may have financial advantages over individual protection measures, it could become a solution with which policy makers can concur. 

“A solution such as NEED requires individuals and policy makers to think in terms of a collaborative and pro-active approach that spans across political parties, countries, and generations. That is, a European-wide endeavour that reduces financial costs, improves quality of protection measures, reduces local impacts and boosts international political and economic ties. As such, NEED represents a solution of the scale that is required to counter the threat we are facing.”

Treating the cause

The authors have also identified various other regions where mega-enclosures such as NEED could serve as a solution to protect against regional SLR. However, they all require future studies to assess if construction is worthwhile. These include the:

  • Irish Sea.
  • Japanese Sea.
  • Mediterranean Sea.
  • Baltic Sea alone (unless covered by NEED).
  • Red Sea.
  • Persian Gulf.

In conclusion the authors discuss the “extraordinary global threat of global mean SLR that we are facing”, and add that solutions such as NEED are symptomatic treatments of the effects of climate change. 

“The best solution will always be treatment of the cause: human-caused climate change. If, however, climate change is left unmitigated, only solutions as impact-full as NEED, or worse, will remain. We therefore advocate for immediate action to further intensify climate mitigation efforts,” Groeskamp and Kjellsson say, “so that global mean SLR can be limited and there will be no need for NEED.”