Deep in the Atlantic Ocean, the Atlantic Meridional Overturning Circulation (AMOC) is a massive system of currents that span the entire ocean from south to north in a vertical loop. It brings warmer waters northwards along the surface (this section of it is known as the Gulf Stream) and transports colder waters at greater depths to more southern latitudes. It doesn’t just transport water; it also carries heat and nutrients — like carbon, for example. Expansive and influential, the AMOC is a fundamental behind-the-scenes part of Earth’s climate control system, regulating winters, hurricanes, rainfall, and other weather patterns globally. Its consistency is part of the reason why we have had foreseeable seasonal weather patterns.
Recently, however, researchers at the University of Miami have concluded that the AMOC has been steadily slowing down for two decades, based on compiled data from a long-term, large-scale study. Based on pressure sensors placed on the ocean bottom at various stations along the western North Atlantic, they found signs that the current may be steadily losing strength. The researchers write that activity at the western boundary of the AMOC is like a canary in a coal mine for what is happening along the entire AMOC system; this is how they can extrapolate a guess as to how the eastern boundary and other parts of the system may be behaving based on measurements at the western boundary. They do also mention, though, that continued monitoring along the eastern boundary is important to further understand how the current is moving and changing.
This study accounted for data from as far back as 2000; since the effects were observed at different times and across different locations, they seem to be persistent enough to describe a broad change, not just minor regional variations. This also means that the changes are far-reaching, affecting all the areas regulated by the current. European winters and Caribbean hurricane patterns are only the beginning of the story; sea levels and coastlines may also be affected.
One thing caused by the weakening of the AMOC, for instance, is the spread of cold and dry conditions towards the equator — a disruption to the humidity and warm conditions usually present in the tropics. Another predictable future effect is a drop in overall temperatures in Northern Europe, accompanied by a drying that would negatively affect agriculture in the region. Further consequences include the rise of sea levels along the coastline of the American continent, increasing the risk of flooding.
In this situation, more research is imperative to understand exactly how the AMOC is changing in direction, strength, and volume of water transported. It is also crucial to do research and adapt infrastructure to mitigate the effects of the disruption to patterns that have previously been regulated by the AMOC for thousands of years.
