Most people hardly think about the future. Neither do I. I know it would be wise to look into my pension matters – after all, it only lasts 25 years – but there are always other things that are more important.
A popular solution of right-wing politicians to future problems is to pretend that the future does not come. Then you can have all kinds of problems parking there. For a long time, it was no problem for right-wing parties to park climate agreements somewhere in 2030. But now 2030 is almost six years away and you notice in the Netherlands but also in Europe that it is all getting very close. “The year 2030 is not sacred to us,” said Wopke Hoekstra during his time as CDA party leader. The EU's new climate goals for 2040 are also “a dialogue, not a goal.” That's a nice description of the long track. Because if we can postpone the problems for a few more years, it will no longer exist for a while.
A very interesting one too bold research on the future of the climate appeared last week, by Utrecht oceanographers. A future that is closer if you do nothing about the climate problem. It is about the cessation of the supply of warm ocean water to Europe, a scenario that was caricatured as central to the apocalyptic disaster film The Day After Tomorrow from 2004.
Thanks to the warm Gulf Stream, or better the Atlantic Meridional Overturning Circulation (AMOC), the Netherlands is the warmest country in the world at our latitude. The AMOC carries tropical heat from the Gulf of Mexico to Western Europe. The AMOC is the result of density differences in seawater. Salt water is heavier than fresh water. A lot of water evaporates on the way from Mexico to Europe, causing the water left behind to become increasingly salty and heavier. In the northern Atlantic Ocean, that heavy water sinks and flows back south over the ocean floor. This conveyor belt of water transports heat to Europe as far as Spitsbergen.
Ever fresher ocean water
It has been speculated for decades that the AMOC may weaken as the water in the northern Atlantic Ocean becomes increasingly fresh. This may be due to an increase in meltwater from the Greenland ice sheet, but also due to more rain. Both are happening right now, and coincidence or not, the AMOC has indeed slowed down over the past few decades. This may be why there is hardly any warming around Iceland. For the Netherlands, the consequences are not yet noticeable in terms of temperature. We are actually warming up quite quickly.
Previous research already showed that it is in principle possible for the AMOC to come to a standstill. This happens as a self-reinforcing tilt. If the sinking of salt water decreases, the AMOC flows less quickly, which means even less salt water is supplied, and so on. Until now, simulating this in an ocean model required an unrealistically large splash of fresh water. The new research is ingenious in that regard, and uses an extremely long simulation with a climate model. In this, the freshwater flux in the northern ocean is increased very slowly, to see whether the climate system itself responds very abruptly at a certain point. And that indeed appears to be happening. This research appears to show that the shutdown of the AMOC is a realistic abrupt tipping point within the current climate system.
The climate of Northern Sweden
The consequences of a stagnant AMOC are enormous, especially for Europe. Our continent is at the receiving end of the AMOC and our climate depends on it. Stopping leads to an end of the heat supply. In the Netherlands, the shutdown of the AMOC would reduce the annual temperature by about 7 or 8 degrees. That is the climate of Northern Sweden.
The consequences are greatest in Scandinavia: there the temperature can drop by 15 degrees. This is because if the AMOC comes to a standstill, the sea ice will extend to the southern coast of Norway. This entire climate change could happen within a century. On a global average, the AMOC's shutdown makes no difference. After all, the ocean does nothing other than redistribute heat. A cooling of Europe will be compensated by more warming elsewhere.
On top of that comes something we call dynamic sea level rise. The current folding of sea level on Earth is the result of differences in gravity and the location of ocean currents. Fast-flowing bodies of water have lower sea levels than stagnant ones. The shutdown of the AMOC will lead to about 80 centimeters of dynamic sea level rise off the Dutch coast. Quite a challenge.
Any limitations to this study? There is no specific date for when the tipping point will be reached. According to measurements, we are “on our way there”. We can reduce the risk of such a disruptive tilt by stopping the freshwater supply to Greenland. Read: quitting fossil fuels. Maybe we should work on that. So that we can postpone a regional ice age in the Netherlands for a while. To a distant future.
Peter Kuipers Munneke is a glaciologist at Utrecht University and weatherman at NOS.
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