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Shutdown of thermohaline circulation


A shutdown or slowdown of the thermohaline circulation is an effect of global warming on a major ocean circulation.

Data from 2010 NASA suggested that the Atlantic Meridional Overturning Circulation has not slowed down, but may have actually sped up slightly in the recent past. However, this has been superseded by a 2015 study that suggests 'that the Gulf Stream has weakened by 15-20%'

Don Chambers from the University of South Florida College of Marine Science mentioned, "The major effect of a slowing AMOC is expected to be cooler winters and summers around the North Atlantic, and small regional increases in sea level on the North American coast."James Hansen and Makiko Sato stated,

AMOC slowdown that causes cooling ~1°C and perhaps affects weather patterns is very different from an AMOC shutdown that cools the North Atlantic several degrees Celsius; the latter would have dramatic effects on storms and be irreversible on the century time scale.

Downturn of the Atlantic meridional overturning circulation, has been tied to extreme regional sea level rise.

Lohmann and Dima 2010 found a weakening of the AMOC since the late 1930s. Climate scientists Michael Mann of Penn State and Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research suggested that the observed cold pattern during years of temperature records is a sign that the Atlantic Ocean’s Meridional overturning circulation (AMOC) may be weakening. They published their findings in a study, and concluded that the AMOC circulation shows exceptional slowdown in the last century, and that Greenland melt is a possible contributor. Didier Swingedouw concluded in a 2015 study that the slowdown of AMOC since the 1970s is unprecedented over the last millennium.

A study published in 2016 found further evidence for a considerable impact from sea level rise for the U.S. East Coast. The study confirms earlier research findings which identified the region as a hotspot for rising seas, with a potential to divert 3–4 times in the rate of rise, compared to the global average. The researchers attribute the possible increase to an ocean circulation mechanism called deep water formation, which is reduced due to AMOC slow down, leading to more warmer water pockets below the surface. Additional the study noted, "Our results suggest that higher carbon emission rates also contribute to increased [sea level rise] in this region compared to the global average."


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