What is the AMOC and how does it work?
The Atlantic overturning circulation is a huge current system that carries warm, light water from the tropics to the ocean surface and then northwards, where it cools down, sinks into the depths and flows southwards again. In total, the AMOC moves 15 million cubic metres of water per second – the equivalent of 6,000 Olympic swimming pools.
The AMOC circulation is maintained by the salinity of the water, because salty water is heavier than fresh water. Accordingly, the water in the northern Atlantic, where the warm, salty water from the subtropics cools, is therefore very salty. This brings us to the next topic, because if there is an influx of fresh water in the region – for example due to melting ice – then the water becomes less salty, i.e. less heavy, which is why it no longer sinks properly. This then leads to a slowdown in the AMOC. As a result, less salt is added to the region, which is why the AMOC slows down further – a so-called feedback loop.
To understand the consequences of this slowdown, we first need to look at how the AMOC affects our planet.
How does the Atlantic circulation influence the global climate?
The northward flow of warm water is responsible for the comparatively warmer temperatures in the northern hemisphere, as the AMOC transports up to 25% of the Atlantic’s total heat towards the northern hemisphere. Incidentally, the Atlantic Ocean is the only ocean in which heat flows northwards from the equator. The course of the AMOC is therefore one of the main reasons why Northern and Western Europe are warmer on average than Canada, even though they lie at roughly the same latitude.
However, the AMOC is not only responsible for regulating the temperature in and around the Atlantic, but also plays an important role as a carbon sink. A carbon sink is a natural reservoir that temporarily absorbs and stores more carbon from the atmosphere than it releases. The AMOC fulfils this function by drawing dissolved carbon with the cooled, heavy water as it sinks to higher latitudes. It is also important that the warm, carbon-rich water is transported to the cooler, higher latitudes, because water at higher latitudes stores carbon better. This is because low temperatures facilitate the dissolution of CO₂ in the atmosphere.
All these processes contribute to the AMOC being the largest carbon sink in the Northern Hemisphere. So what happens when the AMOC slows down?
What changes are expected in the Atlantic circulation as the AMOC slows down due to global warming?
The Intergovernmental Panel on Climate Change published a special report on this topic in 2019, in which all available literature is analysed and summarised. They conclude that a slower Atlantic circulation would lead to a higher sea level rise in the North Sea. In addition, a weaker circulation would be able to transport less heat from the (sub)tropics to the north, which is why increasing aridity and more droughts are to be expected in South Asia and the Sahel region. Reduced rainfall in these regions would have an extreme impact on grain production – this would also affect us in Germany, as it would lead to migration pressure and global supply problems.
As far as Germany is concerned, the researchers expect that we will have to deal with increasing precipitation and storms, as well as increasingly colder temperatures.
Researchers have illustrated the specific expected effects in the following graphic:
If the AMOC were to collapse completely, temperatures in north-west Europe would fall by more than one degree per decade, with temperatures in some cities dropping by 5 to 15 degrees. However, it must also be said that the researchers themselves say that a collapse is unlikely in the near future. Let’s take a look at exactly how unlikely.
How likely is a collapse of the AMOC?
Most researchers agree that a collapse by 2100 is very unlikely. Around 2300, however, the probability of collapse is already 44% if we don’t manage to reduce emissions. However, collapse or not, a weakening of the AMOC alone can have far-reaching consequences – and it has already been proven that the circulation is actually losing strength. In 2018, researchers found that the AMOC has already lost 15% of its total strength since the middle of the twentieth century and is therefore weaker than at any time in the last millennium. By 2100, this figure could be as high as 40% unless we drastically reduce CO₂ emissions. There is no doubt that the weakening of the Atlantic circulation is due to us humans, as there are clear differences compared to the pre-industrial period.
What needs to be done? Draw a conclusion.
It is clear: There is a lot to do, but what needs to be done is clear. Emissions must be reduced – drastically. We have now exceeded the 1.5-degree target of the Paris Climate Agreement, but every fraction of a degree counts. We know what the effects of both AMOC weakening and AMOC collapse would be, and that these scenarios must be prevented at all costs.
In everyday life, it is sometimes difficult for people to make a significant contribution to reducing emissions, although individual measures also have their place in the chain of action. Consumer decisions, for example, have a huge impact on corporate behaviour and branding. So, if we all work together as climate protectors to choose products that protect the climate or are even good for the environment and, if possible, products that are manufactured in our neighbourhood, we can achieve a lot.
It is also particularly important to vote for parties and politicians who are committed to the environment and climate protection. Politicians are in the best position to use legislation to put major emitters in the energy, industry and transport sectors in their place. But petitions and referendums, as instruments of direct democracy, also have the potential to influence political decisions, regardless of party programmes. You can use the following map from GermanZero to find existing groups that are campaigning against climate change at local level and are happy to receive any support.
Organisations such as DUH, NABU, Greenpeace and the Munich Environmental Institute also regularly publish petitions with great transparency and research work behind them. It’s always worth taking a look.
Otherwise, it is important to be visible and defend democratic values. Demonstrate together, inform yourself, inform others. Don’t give up. And if you want to find out more about the projects that the Daniel Schlegel Environmental Foundation is involved in, take a look at current projects here: https://danielschlegel-umweltstiftung.org/en/projects/
