Invisible and soundless
AMOC
In the Atlantic Ocean, invisible and soundless, one of the most powerful systems in the world is in motion. It is called AMOC, Atlantic Meridional Overturning Circulation. The name might sound unfamiliar, but AMOC has determined the climate for a large part of the world and definitely for the Netherlands for thousands of years already.
Warm, salt water flows from the tropics towards the north, along the coasts of Europe. That water gives off its warmth to the air. Because of the warmth of this water flow, the climate in Northwest Europe is much milder than you would expect based on the latitude. London is on the same latitude as the much colder Calgary in Canada, Amsterdam on the same altitude as big parts of Siberia. Thanks to AMOC, a soft westerly wind blows over our rooftops.
When the water heading to the north has given off its warmth, it cools down. Cold water is heavier than warm water and salt water is heavier than freshwater. This causes the cold water to sink deeply to the bottom of the ocean and flow back to the south at that depth. In the Southern Ocean, the water comes back up again and the circle is complete. The engine has already been running like that for millennia. Until now.
Because now, the meltwater of Greenland is messing it up. Or more specifically, freshwater. Because of global warming, the Greenland ice is melting faster than Earth has experienced in thousands of years. All that melted freshwater flows into the ocean, precisely in the spot where the salt, cold water normally sinks. Freshwater is lighter. It does not sink. And so, the engine brakes. Scientists have already been measuring that AMOC is getting weaker for decades. Not from one day to another, but steadily, measurably, precariously.
What if the engine fails?
The consequences are different than you might expect. It will not get warmer, it will get colder. And more capricious. Without the supply of warm Atlantic water, the winters in Northwest Europe will cool down substantially. Researchers, including climate scientist René van Westen from Utrecht University, talk about possible decreases in temperature of 10 degrees in the winter on average, with dips towards extreme cold. At the same time, the continent will dry up. Less precipitation, more evaporation, failed harvests. The storms will become fiercer too.
So the paradoxical thing is that a world which becomes warmer because of CO2 can become colder, more capricious and more unpredictable for the Netherlands due to AMOC failing. The result will not be a new balance. It will be chaos.
So when will that happen?
That is the question no one has the answer to. Some scientists think the tipping point can already be reached before the year 2100, others stick with later or never. But remarkably many recent studies estimate the tipping point will be reached earlier than expected. What we DO know for sure is that the engine is already running slower. And an engine which is running slower shuts down more easily. That is not climate activism. That is simple physics. Once AMOC has tipped over, recovery can take centuries.
This is one of those moments. This is now.
Not to keep you awake, but this is actually going on now. What does it mean if AMOC actually collapses? We asked René van Westen what daily life could look like about 50 years after the tipping point.
Capricious seasons
The future according to Van Westen
Unlike movies like ‘The Day After Tomorrow’, the changes cannot be felt from one day to another, Van Westen emphasises. After the tipping point, it will still take approximately one hundred years before the consequences are fully visible. The winters in the Netherlands will become a lot colder, with deep-freezing conditions and fierce winter storms. We will have shorter, chilly summers with maximum temperatures around 15 degrees more often, alternated with heat waves. In the worst-case scenario, a dry hot autumn, followed by a long cold winter and a cold and wet spring. Fierce storms and sudden changes from hot to cold or from dry to wet, sometimes from one day to another: the weather will not only become more extreme, but also more and more fickle and harder to predict. It is a sober but disturbing image.
Harvests will fail, bills will rise
Agriculture will not escape it either, Van Westen expects. Because of the capricious winters, harvests will fail and some crops will disappear from the Netherlands. This will then be immediately observable in the supermarket: empty shelves and unpredictable supply. And on the energy bills, because of higher heating costs. Sustainable energy will also become more unreliable: less sun throughout the year, but with high peaks during heat waves, and windmills which will be shut down more often due to storms.
Roads, water and living
Bigger temperature differences will affect buildings and tear open the asphalt. Roads will regularly become impassable due to ice, snow and storms, and trains will not escape this either. On the coast and along the rivers, Van Westen expects trouble with high water levels and floodings because AMOC also has an influence on the rising sea level. Roughly 50 centimetres will be added to it. And the tourism will flip along with it. The long traffic jams on the Route du Soleil to the south will disappear. Everyone will instead want to go to the north, because the south will become even hotter and dryer. Especially in the summer months, shortages in drinking water will be a recurring problem. Some areas will become uninhabitable; for instance, the inland of Spain can turn into a desert. Actually, the Sahara Desert will cross the Mediterranean Sea.
It is not a happy prospect. But Van Westen is still hopeful. If we limit global warming now, we can still prevent AMOC from shutting down. The knowledge is there. We know the task in front of us.
René van Westen (UU) is a climate scientist and an expert in the field of the AMOC. René investigates the risk of the AMOC shutting down under climate change and the accompanying shift in climate. René van Westen will tell more about AMOC on Tuesday 29 September at 4 pm, during the Utrecht Science Week.
Text: Yavanne van Tiggelen
Image: Istock