Atlantic Ocean circulation shows “exceptional” slowdown

Ars Technica : Ocean water varies in salinity and temperature due to many processes, including evaporation, precipitation, freshwater inflow from rivers, and sea-ice melting. Warmer, saltier water mixes with cooler, less salty water because of currents induced by waves, wind, and tides. One such major current, the Atlantic meridional overturning circulation (AMOC), appears to have slowed down markedly in the latter part of the 20th century, according to a recent study published in Nature Climate Change. Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research and colleagues studied the instrumental temperature record from the past 100 years and temperature reconstructions for the past 1000 years. They say that over the 20th century, the AMOC showed a marked slowdown of about 14%, with a particularly low point lasting from the 1970s to the mid 1990s, perhaps because of the melting Greenland ice sheet. Because climate models have not indicated any weakening of the AMOC in the 20th century, it’s possible they are underestimating climate change developments, according to the researchers.