An international group of scientists has found that the recent weakening of the Atlantic current system can influence the climate in the future, according to two papers published in the journal Nature.
The first research, led by University College London (United Kingdom), examines the impact that this process has on a system of currents known as the Atlantic meridional overturning circulation (AMOC).
The AMOC, the experts explain, has a great influence on the climate, since it redistributes heat and affects the carbon cycle, but it was not known until now if the apparent weakening experienced in the last decades could manifest itself in natural long-term variability.
The authors of this study, with the geographer David Thornalley as the lead, have presented “paleo-oceanographic evidences” that show that the deep convection current of the AMOC and the Labrador Sea — between the Canadian peninsula of Labrador and the Danish island of Greenland– has been unusually weak since the end of the Little Ice Age, compared to the previous 1,500 years.
The Little Ice Age is the most important cold period in the northern hemisphere from the late fourteenth to the nineteenth century. Experts argue in this new study that the end of the Little Ice Age was marked by a discharge of fresh water from the Arctic and Nordic seas, which caused the alteration of AMOC.
However, it is still unclear if that transition occurred abruptly towards the end of that cold period, after 1850, or through a more gradual process during the last 150 years.
The second research, developed by the Potsdam Institute for Climate Impact Analysis (Germany), combines sets of global climate models with databases of global temperatures of the sea surface.
This methodology led them to identify a “footprint” that indicates that the AMOC experienced a deceleration of about three sverdrups — unit of measurement of volume flow per unit of time, that is, almost 15% since the middle of the twentieth century.
This footprint, which is more pronounced during winters and springs, entails a cooling of the sub-polar zone of the Atlantic Ocean, caused by a drop in heat transport and a warming in the region of the Gulf Stream, caused by a displacement the route to the north.
The anthopogenic climate change is the main suspect of this weakening that can have important effects, especially in the European climate, according to a statement from the Spanish Complutense University, one of the participants in the study.
Both studies differ in the chronology of the deceleration of AMOC, due, according to some authors, to the nuances contained in the definition of this system of currents.
In an article accompanying the two papers, Summer Praetorius, from the US Geological Survey of California, believes that, “at least from a scientific point of view”, the parties agree that the modern AMOC is in “a relatively weak state”.
On the other hand, adds the expert, facing the study of future climate change scenarios, these divergences are “perhaps less reassuring” because a “weakened AMOC could generate considerable alterations in weather patterns and rainfall throughout the Northern Hemisphere” .