A new study by scientists from Ireland, the UK and Germany has shown that the Atlantic meridional overturning circulation (AMOC), of which the Gulf Stream is a part, has never been so weak over the past 1,000-plus years, phis.org reports. Scientists have come to this conclusion by analyzing the data that made it possible to reconstruct the evolution of the AMOC: information was collected from ocean sediments, ice cores, corals, tree rings, as well as from historical evidence such as records from ship logs.
The circulation of the Atlantic Ocean works like a giant conveyor belt that carries warm surface waters north from the equator and sends cold and slightly saline deep waters back south. AMOC, thanks to which the climate in Europe is so mild, moves almost 20 million cubic meters of water per second - a flow 100 times stronger than the Amazon. Studies have shown that with the end of the Little Ice Age, which occurred around 1850, ocean currents began to weaken, but until the end of the 19th century, the system was relatively stable. In the middle of the 20th century, a second, sharper decline began.
Why is this happening? Most likely, the reason is global warming caused by greenhouse gases. The so-called deep convection that exists in the Atlantic is caused by differences in the density of ocean water: warm and salty water moves from south to north, where it cools and thus becomes denser. When the water becomes heavy enough, it sinks into the deeper layers of the ocean and flows back south. Global warming disrupts this mechanism. Increased precipitation and increased melting of the Greenland ice sheet are increasing the amount of fresh water at the ocean's surface. This reduces the salinity and therefore the density of the water. The water sinks into the depth less actively, and the flow of the AMOC slows down.
The consequences of such a slowdown could lead to unprecedented changes on both sides of the Atlantic. Sea levels on the east coast of the United States may rise. In Europe, the weakened Gulf Stream will cause frosty winters, extreme heat waves and droughts in summer, and frequent storms.
If global warming continues, then by the end of the century the Gulf Stream system will weaken even more - by 34-45%. This can lead humanity to a point where the current will finally become unstable.
The research will be published in the journal Nature Geoscience.