Rising sea levels and the Wadden Sea region: no time to lean back

Tuesday 19 May 2020

Mid-2019 saw the publication of the IPCC report entitled The Ocean and Cryosphere in a Changing Climate, which was soon followed by the Sea Level Monitor, a publication by research institute Deltares. When we compared the two reports here at the PRW (Programme for a Healthy Wadden Sea Region), we were confronted with a full-scale paradox. While the IPCC report states that the average sea level rise worldwide is now measurably accelerating, the Sea Level Monitor shows that this does not apply to the North Sea and the Wadden Sea. So what is going on? And should we or should we not prepare the Wadden Sea region for a sharp rise in sea levels? Earlier this year, these questions prompted us and the Wadden Academy to invite Deltares to provide an explanation.

The Greenland effect

The report entitled Sea Level Rise at the Dutch Coast, by Bart van den Hurk (available on our website) confirms that there are no indications that the rise of the sea level in the North Sea is accelerating. The fact that the rise of sea levels is accelerating worldwide but not in the North Sea and the Wadden Sea is largely due to the high speed at which the Greenland ice cap is melting. Those meltwaters end up in the world’s oceans, and also in Dutch waters. However, the gravity of the large ice cap also pulls up the water in its vicinity – which includes the North Sea and the Wadden Sea. So when the ice cap melts, two processes occur at the same time: the meltwater causes sea levels to rise worldwide, but causes the sea level nearer to the ice cap to fall as its gravitational pull decreases. As a result, the effect of the melting Greenland ice cap is relatively modest in our region.

Provided that sand nourishment operations continue, therefore, sedimentation in the Wadden Sea will keep pace with the rising sea level – as long as the rise does not accelerate. In addition, our ports are safe for the time being and the current height of dikes in the Netherlands will remain sufficient for a long time to come.

Will climate deniers be proved right?

So can we just lean back in comfort, as climate change deniers have been arguing for years? Quite the opposite! There is another ice cap on the other side of the globe, in Antarctica, and that one is even bigger. Far bigger. It may take some more time, but eventually that ice cap is likely to melt at an increasing rate. And as for its gravitational pull, the situation is exactly the reverse compared with Greenland: because Antarctica is far away from the Netherlands, the effects when it melts will only be greater. In other words, in a couple of decades we will have to cope with rising sea levels just as any other part of the world.

To keep our feet dry, we will need to anticipate

By that time it is essential that measures are in place to keep our feet dry and protect nature in the Wadden Sea region. This requires a considerable effort. Sand nourishment volumes will have to increase dramatically (even on tidal flats), port areas will have to be adapted and new dike concepts applied, and low-lying areas behind the dikes will have to be raised. These are all large-scale interventions in nature and spatial planning. We need to start thinking now about the best approaches and timelines. The facts that emerge from the first pilots with innovative dike concepts, such as the Wide Green Dike and Double-Dike Systems, clearly confirm how urgent this is. We are quite proud of those pilots in the Wadden Sea region, and with good reason, but they required years of preparations. It is clear that the necessary roll-out across the entire region will take decades rather than years. So even though the current situation is quite manageable, if we are to deal with rising sea levels effectively, sitting back and doing nothing is not an option.

 

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