ONAccording to a new study, the oceanic “conveyor belt” that pulls warm water from tropical regions to the North Atlantic and cold water back south is the weakest in more than 1,000 years. The work, published yesterday (February 25th) in Natural geosciencesConsistent with previous predictions and insights into the effects of climate change on what is known as the Atlantic Meridional Overturning Circulation (AMOC), but uses proxy measures to go back in time and confirm the unprecedented nature of these recent changes.
“I think that only makes this conclusion much stronger,” says Stefan Rahmstorf, oceanographer at the Potsdam Institute for Climate Impact Research in Germany and co-author of the study The Washington Post.
Rahmstorf and his colleagues compared the results of 11 indicators for the strength of the AMOC circulation, which have only been measured directly since 2004. These indicators included reconstructions of sea temperature patterns and data on deep-sea sediments dating back to about AD 400. The patterns in nine of the indicators were consistent, co-author Niamh Cahill from Maynooth University in Ireland tells us Inside Climate Newsand together they show a “consistent picture” of unprecedented weakening of the circulatory system.
The study found an initial weakening in the AMOC in the mid-19th century, corresponding to the end of a relatively cool period known as the Little Ice Age, and a more pronounced decline from the mid-20th century onwards, when human effects on climate changed accelerated. A press release said previous studies found AMOC strength to decrease by about 15 percent since the mid-20th century. Researchers have predicted that this slowdown could affect fisheries and lead to sea level rise and more frequent hurricanes on the US east coast, as well as more extreme weather events in Europe.
An explanation of how the “ocean conveyor” works
YOUTUBE / AN OCEAN
Philip Duffy, director of the Woodwell Climate Research Center in Massachusetts, relates Inside Climate News that models of man-made climate change predicted the study’s impact on the AMOC. “If this continues, the social consequences will be quite significant,” he quotes the cooling of the Atlantic near Greenland. “Another consequence is the accelerated sea level rise along the US east coast that we are already seeing.” Duffy, who was not involved in the study, adds that the complete breakdown of the circulatory system is a “low probability, high consequence” event.
“The AMOC has a profound impact on the global climate, particularly in North America and Europe. Therefore, this evidence of persistent slowdown in circulation is critical new evidence for interpreting future projections of regional and global climate,” said Andrew Meijers, MP Polar Ocean Science Guide to the British Antarctic Survey, tells The guard. “The AMOC is often modeled in such a way that it has a tipping point below a certain circulation strength, at which the relatively stable overturning cycle becomes unstable or even collapses. The ongoing weakening of the tip-off means we risk finding this point, which would have profound and likely irreversible effects on the climate. “Meijers was also not involved in the study.
“If we continue to drive global warming, the Gulf Stream system will weaken by 34 to 45 percent by 2100 according to the latest generation of climate models,” says Rahmstorf in the press release. “This could bring us dangerously close to the turning point where the flow becomes unstable.”