Gulf Stream, or an oceanic anoxic event — oxygen () below surface levels of the stagnant oceans becomes completely depleted – a probable cause of past mass extinction events. Back in 2002, a study had suggested that an AMOC shutdown may be able to trigger the type of abrupt massive temperature shifts which occurred during the last glacial period: a series of Dansgaard-Oeschger events – rapid climate fluctuations – may be attributed to freshwater forcing at high latitude interrupting the THC. 2002 model runs in which the THC is forced to shut down do show cooling – locally up to 8 °C (14 °F). A 2017 review concluded that there is strong evidence for past changes in the strength and structure of the AMOC during abrupt climate events such as the Younger Dryas and many of the Heinrich events. A 2015 study led by James Hansen found that the shutdown or substantial slowdown of the AMOC, besides possibly contributing to extreme end-Eemian events, will cause a more general increase of severe weather. Additional surface cooling from ice melt increases surface and lower tropospheric temperature gradients, and causes in model simulations a large increase of mid-latitude eddy energy throughout the midlatitude troposphere. This in turn leads to an increase of baroclinicity produced by stronger temperature gradients, which provides energy for more severe weather events. This includes winter and near-winter cyclonic storms colloquially known as "superstorms", which generate near-hurricane-force winds and often large amounts of snowfall. These results imply that strong cooling in the North Atlantic from AMOC shutdown potentially increases seasonal mean wind speed of the northeasterlies by as much as 10–20% relative to preindustrial conditions. Because wind power dissipation is proportional to the cube of wind speed, this translates into an increase of storm power dissipation by a factor ∼1.4–2,. However, the simulated changes refer to seasonal mean winds averaged over large grid-boxes, not individual storms. In 2017, a study evaluated the effects of a shutdown on El Niño–Southern Oscillation (ENSO), but found no overall impact, with divergent atmospheric processes cancelling each other out. In 2021, a study using a Community Earth System Model suggested that an AMOC slowdown could nevertheless increase the strength of El Niño–Southern Oscillation and thus amplify climate extremes, especially if another Meridional Overturning Circulation develops in the Pacific Ocean in response to AMOC slowdown. In contrast, a 2022 study showed that an AMOC collapse is