Studie: Strömmar i Atlanten nära tippningspunkt

The Atlantic meridional overturning circulation (AMOC) is a system of surface-level and deep currents in the Atlantic Ocean which are driven both by changes in the atmospheric weather and thermohaline changes in temperature and salinity. These currents collectively make up one half of the global thermohaline circulation that encompasses the flow of major ocean currents. The other half is the Southern Ocean overturning circulation, and both play highly important roles in the climate system.The AMOC is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters. These "limbs" are linked by regions of overturning in the Nordic and Labrador Seas and the Southern Ocean, although the extent of overturning in the Labrador Sea is disputed.Climate change has the potential to weaken the AMOC through increases in ocean heat content and elevated freshwater flows from the melting ice sheets. Oceanographic reconstructions generally suggest that the AMOC is already weaker than it was before the Industrial Revolution, although there is a robust debate over the role of anthropogenic climate change versus the circulation's century-scale and millennial-scale variability. Climate models consistently project that the AMOC would weaken further over the 21st century,: 19  which would affect average temperature over areas like Scandinavia and Britain that are warmed by the North Atlantic drift, as well as accelerate sea level rise around North America and reduce primary production in the North Atlantic.Severe weakening of the AMOC has the potential to cause an outright collapse of the circulation, which would not be easily reversible and thus constitute one of the tipping points in the climate system. A shutdown would have far greater impacts than a slowdown on both the marine and some terrestrial ecosystems: it would lower the average temperature and precipitation in Europe, slashing the region's agricultural output, and may have a substantial effect on extreme weather events. Earth system models used in Coupled Model Intercomparison Project indicate that shutdown is only likely after high levels of warming are sustained well after 2100, but they have been criticized by some researchers for what they saw as excessive stability, and a number of lower-complexity studies argue that a collapse can happen considerably earlier. One of those lower-complexity projections suggests that AMOC collapse could happen around 2057, but many scientists are skeptical of the claim. On the other hand, paleoceanographic research suggests that the AMOC may be even more stable than what is predicted by most models. Some research instead suggests that the traditionally overlooked Southern Ocean overturning circulation may be more prone to collapse.