Short answers, pulled from the story.
The Atlantic meridional overturning circulation moves warm, saline water northward in the upper layers of the ocean and returns cold, less salty deep water southward. This system comprises half of the global thermohaline circulation with the other half being the Southern Ocean overturning circulation.
Willi Dansgaard and Hans Oeschger discovered these events analyzing Greenland ice cores in the 1980s. Twenty-five abrupt temperature oscillations occurred during the Late Pleistocene between 126,000 and 11,700 years ago.
Henry Stommel conducted research into the AMOC during the 1960s using what became known as the Stommel Box model. His work introduced the idea that the AMOC could exist either in a strong state or effectively collapse to a much weaker state without recovery unless conditions changed back.
A November 2024 study published in Nature Geoscience found a slowdown of 0.46 sverdrups per decade since 1950 after matching observations with Earth system and eddy-permitting coupled ocean-sea-ice models. Direct observations of AMOC strength have been available since 2004 from RAPID an in situ mooring array at 26°N in the Atlantic Ocean.
An extensive assessment identified sixteen plausible climate tipping points including AMOC collapse triggered by global warming levels between one and two degrees Celsius. A February 2025 study published in Nature concluded AMOC is resilient to extreme greenhouse gas and North Atlantic freshwater forcings across thirty-four climate models suggesting unlikely collapse in twenty-first century.