Before the end of this century, the water level at our North Sea coast will be 130 centimeters higher than it is now. Says the Dutch Delta Committee. But, isn’t the committee exaggerating just a little bit? Definitely not, swears professor Pavel Kabat. Even worse: ‘We will easily make that 1.30 meter.’
So, how about those numbers? How did the committee come up with these 130 centimeters, nearly half a meter more than the maximum level KNMI prepared us for two years ago? Wait wait, says Kabat. The difference is not that big. ‘The KNMI arrived at a rise of 85 centimeters, without taking the effect of soil subsidence into account. Inclusion of that effect adds up to a total of 95 centimeters. We found an upper value of 130 centimeters, including soil subsidence. That is a difference of merely 35 centimeters.’
Still, that is a considerable adjustment of the KNMI’s prognosis. To some degree, that is because the committee assumes that the planet may become a few degrees hotter than what the KNMI took into account. As a result, the seawater will expand a little bit more. But the effect of that is only marginal. By far the biggest contribution, according to Kabat, comes from accelerated melting of the ice shelves of Greenland and Antarctica. ‘We made use of the newest data of glaciologists and paleoclimatologists. Those data reveal that the land ice in Greenland and specifically in Antarctica is melting faster. For that melting, a simple model was made to enable extrapolation to the year 2100.’ The result is those 35 centimeters, for which the greatest contribution is made by the melting ice shelves of West Antarctica with approximately 20 centimeters.
Big question is of course whether the calculation is correct. Global climate change is still partly ill understood, and that holds more than doubly for the melting of ice shelves. It is difficult to apply climate models to that problem. Let alone carry out detailed calculations. Nevertheless, Kabat emphatically rejects the idea that guesstimation had anything to do with it. ‘How, do you think, did the IPCC (Intergovernmental Panel on Climate Change, ed.) and KNMI arrive at their predictions? It is a misconception that we have fewer data compared with the study of most other processes in the area of climate.’
Kabat underlines that the extreme rise of 1.30 meter is an upper limit. ‘A plausible upper limit. Plausible in the sense of ‘it is possible’ and ‘it cannot be ruled out’. Compare it to building a bridge. When designing it, what do you do? You take the heaviest traffic as starting point and add a safety margin. That’s what it is, a safety margin. On the basis of the state of the art in science, that is 1.30 meter.’
The past one hundred years, sea level rose by no more than twenty centimeters. Critics say that this fact clashes blatantly with the dramatic predictions of the Delta Committee, the KNMI or the IPCC. Kabat simply discards those criticisms. ‘The past one hundred years cannot be compared to the next one hundred years. The conditions in the past century were very different. You therefore cannot simply extrapolate toward the future. In the past century, temperature also only rose by half a degree or thereabouts.’
By way of illustration: the Delta Committee expects, just like the IPCC, a temperature increase of up to six degrees C. Furthermore, the oceans are an extremely sluggish system according to Kabat. Changes develop slowly and keep echoing for a long time. ‘When the temperature were to rise by for example two degrees in the next fifty years, that would have an effect on sea level for hundreds of years. The same holds for the effect of the CO2 emission on temperature.’ The past proves, according to Kabat can, that it is possible, such a large increase in sea level. Paleoclimatologists have found periods during which in conditions comparable to those of the present, sea level rose greatly as well. ‘The earth’s system therefore does allow a sea level rise of one meter in one hundred years.’
To be honest, Kabat feels that the committee is even likely erring on the side of caution with its prognosis. ‘I think we will easily make that 1.30 meter. I believe that the calculation regarding the melting of ice shelves is a prudent one.’ Kabat points out a number of phenomena that weren’t yet included in the calculations. In addition to melting ice shelves at the edges, there is also land ice that slides into the sea. Melt water in cracks and crevices functions like a sort of lubricant. ‘We do not know anything yet about that contribution’, says Kabat. Furthermore, it is still unclear how all that melt water will be distributed through the oceans.
In addition, the emission of CO2 is still increasing. Last week, the Global Carbon Project presented alarming numbers. According to this international partnership, the production of CO2 is rising faster than was foreseen in the IPCC’s unfavorable scenario. That scenario includes a temperature increase of six degrees between now and 2100. A higher temperature leads to higher sea level. Last year, the emission of CO2 from fossil fuel burning reached a new high of ten billion tons. There is more than one third CO2 more in the air than in the period preceding the Industrial Revolution. The annual increase occurs 33% faster than in the previous twenty years.
All uncertainty regarding the extremes has, according to Kabat, little effect on the measures recommended by the Delta Committee. Those are based on the less extreme KNMI scenario for 2050. ‘Making the dikes safer by a factor ten, for example, follows from the norms set in the old Delta Act. That has nothing to do with the 1.30 meter. But everything you do until 2050 has to be done in such a way that you can continue. Whatever you do in the meantime has to be robust enough to be able to proceed with following steps. And on the horizon, there is this 1.30 meter.’
Kabat predominantly points out the opportunities the rising water offers. ‘Everything we come up with with an eye to the sea level increase has a large innovative component. This is the golden-water age. It's an opportunity we must grab.’
In the view of Kabat, this specifically applies to the function of the IJssel Lake. The committee would like to allow the water level of the IJssel Lake rise by one and a half meter. Partly, that is necessary to provide our country with sufficient drinking water. The intruding sea water causes salinization of the soil. Notably in the southwestern part of the Netherlands this will become a large problem, according to Kabat. But the committee has a broader perspective. ‘We are blessed with the largest freshwater basin in Europe’, says Kabat. ‘That is gold. Water will become invaluable. Why shouldn't we change the IJssel Lake into the freshwater supply of Europe?’