Researchers have published results of a study of the Atlantic Meridional Overturning Circulation (AMOC), more commonly referred to as the Gulf Stream. The AMOC is one of the planet’s most important ocean circulation systems, bringing warm water from the Gulf of Mexico to northern Europe and returning colder water to the tropics. It is responsible for the relatively warmer winters in Europe and operates on the differences in salt and density of fresh and cold water interacting with salty and warm water. The significance of the AMOC cannot be overstated:
“The Gulf Stream (also known as the Atlantic Meridional Overturning Circulation, or AMOC) is essentially a “giant conveyor belt” along the East coast of the United States, study co-author Stefan Rahmstorf, a researcher at the Potsdam Institute for Climate Impact Research (PIK) in Germany, said in a statement.
The current begins near the Florida Peninsula, carrying warm surface water north toward Newfoundland before meandering east across the Atlantic. By the time it reaches the North Atlantic, that warm surface water becomes cooler, saltier and denser, sinking into the deep sea before being driven south again, where the cycle repeats. According to Rahmstorf, the current moves more than 5.2 billion gallons (20 million cubic meters) of water per second, or ‘almost 100 times the Amazon [River] flow.'”
But climate change seems to have affected the strength of the AMOC. Melting ice from Greenland has increased the amount of fresh water flowing into the North Atlantic, creating what some have called the “Cold Blob” just south of Greenland. That reservoir of cold, fresh water seems to be slowing the AMOC down to a considerable extent. The researchers point out that
“The AMOC is a sensitive nonlinear system dependent on subtle thermohaline density differences in the ocean, and major AMOC transitions have been implicated, for example, in millennial climate events during the last glacial period1. There is evidence that the AMOC is slowing down in response to anthropogenic global warming—as predicted by climate models—and that the AMOC is presently in its weakest state for more than 1,000 years.”
Benjamin Franklin was one of the first to identify the Gulf Stream and he published a map of the Gulf Stream in 1768. The New York Times has published a fascinating interactive article on the AMOC. But scientists have only been able to study rigorously the AMOC for less than two decades, so the research is based on a number of climate proxies such as tree rings and sedimentation. This approach makes the study problematic since it does not rely on direct evidence. But the proxy evidence is troubling. If the research proves to be accurate then we can expect significant changes by the end of this century:
“The team concluded that, at the current rate of climate change, the Gulf Stream’s flow could weaken by an additional 45% by the year 2100, plunging the current close to a critical tipping point. If the flow continues to weaken (or collapse entirely), the effects could be severe.
“‘Several studies have shown that a slowdown of the [AMOC] exacerbates sea-level rise on the US coast for cities like New York and Boston,’ Caesar [Levke Caesar, a climatologist at Maynooth University in Ireland] said. Other studies have linked severe heat waves and storm patterns in northern Europe and the eastern United States to the weakened current.
The precise impacts could be ‘even more severe,’ Caesar said, though scientists won’t know for sure until we cross that bridge. Hopefully, by limiting global warming as much as possible in the coming decades, we’ll never have to find out.”
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