Sea level rise and the Dutch Deltacommission


(Nederlanse versie hier)


The Dutch Deltacommittee released their report on how to protect the Netherlands against the rising waters. The advice goes quite far, from the inevitable heightening of dikes to increasing the waterlevel of the major lake by 1.5 meters.


Starting point

The starting point is an estimate of sealevel rise of 0.55 to 1.1 metres by 2100 and of 2 to 4 metres by 2200. To their credit, the prognosis doesn’t stop in 2100, and neither does sealevel rise. In a business as usual scenario the sealevel will continue to rise (long) after 2200. The report mentions that they use a “plausible upper bound” of sealevel rise. A comparable range (0.5 to 1.4 metres by 2100) is found by extrapolating the observed correlation between temperature and sealevel rise.


The consequences of ice dynamics (e.g. mechanical instability of large ice sheets due to  more meltwater, associated with large uncertainties) is included in their estimate. That is the main reason that they are higher than the KNMI and IPCC estimates for 2100 (40 to 85 cm and 25 to 76 cm for 2100, respectively). A new article in the journal Science gives 80 cm as the most likely sealevel rise for 2100, and 2 metres as the upper bound (including uncertainties related to ice dynamics). Besides uncertainties regarding ice melt, the future greenhouse gas emissions are of course an important variable, and one that we can influence (for better or for worse).  Realclimate has a discussion of sealevel rise here and a thorough review of the IPCC estimates here.



Can the Netherlands adapt to such high sealevels? The Deltacommitte is very positive about that, at least up to a 4 metre (!) sealevel rise. I think that at some point the possibilities for adaptation become limited. For example, can the Netherlands continue to exist amidst a sealevel that is 6 metres higher than now? That’s what sealevels were 125,000 years ago, when the global average temperature was “only” 1 to 2 degrees higher than now. Such a massive change in sealevel probably takes centuries, if not millennia, to achieve, but it makes sense to me that we’d try to avoid it from happening nevertheless. Therefore we cannot afford to keep the earth very long or very high above the 1-2 degrees higher temperature. For how long or how high can we, before the big icesheets (Greenland and the Antarctic) start melting irreversibly? Nobody knows. But it’s not worth an experiment, I’d say.



The emphasis in the committee’s report is strongly on adaptation to rising sealevels, although emission reduction (mitigation) is of course also necessary. Otherwise it’s like mopping while the tap is running, as we say in Dutch. Is it perhaps better to relocate certain economic activities to safer grounds instead of pumping large sums of money into keeping them in the current low lying and vulnerable area? One comment I heard is from a member of parliament, who wondered whether our (grand)children would be happy  to pay for the measures we’d be taking now (because part of the money would be borrowed is the plan). I think that if anything, they will complain that we did too little for the problems facing us than too much.


To what extent should we anticipate (and thus adapt to and trying to prevent) future problems, that haven’t manifested themselves to their full extent? That’s a debate that’s worth having. Science doesn’t tell us which risks are worth taking and which are not; that’s very much an individual choice. Science does have an important role in informing us about the chances of a certain outcome; in other words, about the risk. The difficulty is that an individual’s choice in this matter has consequences for the risks of others, but their own risk is only marginally affected: the “tragedy of the commons”. Governments also have to make choices regarding the safety of their citizens. The same tragedy plays there too: The risk we run is strongly dependent on what other countries do. But let’s not use that as an excuse to then not do anything ourselves. And let’s not use scientific uncertainty as an excuse either. It does not decrease the risk; to the contrary.


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