Op-ed Peter Kuipers Munneke in NRC
The question is not if the Netherlands will disappear below sea level, but when
I recently came across an interview with the engineer who was responsible for the construction of the Oosterscheldekering, a key dam in protecting the southwestern part of the Netherlands against flooding. He said that, technically speaking, this dam could last 200 years. When it was first designed in the 1970s, it was proudly claimed that it could withstand a sea level rise of as much as 40 centimetres. If you consider how little was known about sea level rise at the time, the sheer thought of it was almost revolutionary.
Since then, more than fourty years of research have gone by. And both theory and observation have taught us that the great Greenland and Antarctic ice sheets are not ice cubes that are slowly melting off from the top. Their location, partly below sea level, makes them far more sensitive to warm ocean water than we could anticipate ten or twenty years ago. So, even with the strongest greenhouse gas reduction and if the most conservative climate scenario came to fruition, the Oosterscheldekering dam will not make it to its 200th anniversary.
But how much is sea level going to rise? A thorough review (with Utrecht input) of what the distant past teaches us about ice sheets and sea levels appeared in Nature Geoscience recently. It included a simple yet intriguing diagram of the long-term effects of global warming: the two degree increase from the Paris Agreement will eventually, in a few thousand years, lead to a sea level rise of approximately 15 meters.
This is hardly surprising, though, if you consider that twenty thousand years ago, at the last glacial maximum, Earth’s temperature was approximately five degrees Celsius lower than present, and sea level stood at hundred and twenty meters below its current level.
But how do we match such a result with scientists who patiently and repetitively explain - as I did last month at the table of Dutch talk show Jinek - that abandoning fossil fuels decreases the chance of serious sea level rise considerably?
The keyword here is time scales. On time scales from ten to a hundred years, we primarily see the processes that adapt relatively quickly to a growing CO2 concentration. Like the warming of the atmosphere, which is almost instantaneous. And that of the ocean is lagging a bit behind.
But on truly long time scales, slow and almost unstoppable processes come into play. As glacier ice warms, for instance, it deforms more easily, making the ice flow faster down into the ocean. Another process is that the surface elevation of an ice sheet drops when it melts. At lower elevation, the air is warmer, reinforcing the melt. Such processes are at play on time scales covering centuries to millenniums. Global warming stretches far into the future.
Therefore, the question is not if the Netherlands will disappear below sea level, but when. I don't mean this to be taken in the alarmist way. It's just looking at all of the lessons that physics and the geological archives are teaching us.
By the figures in the 2013 IPCC report, one can estimate that in a worst-case scenario, we will reach 2 meters of sea level rise at some point in the second half of the next century. More recent research has explored ways in which the Antarctic ice sheet will lose its ice more rapidly and does not rule out a 2-meter rise by the end of the current century.
Admittedly, this scenario requires a massive acceleration of melt: 2 meters this century implies an average of 25 mm of sea level rise per year over the next 80 years, as opposed to the current 3 mm per year. But this is science too: we cannot (as yet) rule out this scenario with certainty.
The year 2100, 2400 or 4000 AD could be a possible best before date for the Netherlands. Natural science puts an interesting, philosophical question to politicians here. For whom do we make climate policy? For whom do we raise dikes? The next three generations? The next ten? How far should our policy really stretch?
These are questions about ethics and morality that perhaps cannot be answered. But they do lead to a change in reasoning at the Dutch Directorate-General for Public Works and Water Management. From now on, let’s only build no-regret waterworks. Dams that you can raise or extend if reality or scientific insights so demand. With this philosophy, the Oosterscheldekering dam would never be built in this day and age.
Dr Peter Kuipers Munneke is a polar meteorologist at Utrecht University, and a weather presenter at NOS, the largest Dutch public broadcasting organisation. He investigates melt of the Greenland and Antarctic ice sheets.
Scientists from Utrecht University are reporting in the climate blog of the NRC on their research in the field of sustainability. They are united around the strategic theme of 'Pathways to Sustainability'.