Certain ocean water moves up and down the globe in a slow but important journey that brings nutrients that sustain life and regulates water temperature.
This system – the Atlantic meridional overturning circulation (AMOC) – includes the Gulf Stream, an ocean current that brings warm water from the Gulf of Mexico to the Atlantic Ocean. It could be headed towards collapse in a few short years, according to a study published this week in the Nature journal.
“In this work, we show that a transition of the AMOC is most likely to occur around 2025-2095,” it said.
A collapse of the system “would have severe impacts on the climate in the North Atlantic region,” researchers said. Already, weakening circulation has been reported in the system in recent years.
AMOC, also referred to as a “global conveyor belt” by the National Oceanic and Atmospheric Administration, has a very long total circulation cycle – around 1,000 years for any given cubic meter of water to move from one end of the belt to another. It is driven by changes in saltiness and ocean temperature that cause water to circulate north to south.
“The circulation process begins as warm water near the surface moves toward the poles (such as the Gulf Stream in the North Atlantic), where it cools and forms sea ice,” the NOAA explained. “As this ice forms, salt is left behind in the ocean water. Due to the large amount of salt in the water, it becomes denser, sinks down, and is carried southwards in the depths below. Eventually, the water gets pulled back up towards the surface and warms up in a process called upwelling, completing the cycle.”
Part of the cycle occurs in the Gulf Stream, a current that carries warm water from the Gulf of Mexico and extends all the way up the eastern coast of the U.S. and Canada. Here in the U.S., its impact can be felt in the Florida climate and other southeastern states.
“Since the Gulf Stream also extends toward Europe, it warms western European countries as well,” said the NOAA. “In fact, England is about the same distance from the equator as cold regions of Canada, yet England enjoys a much warmer climate. If it weren’t for the warm water of the Gulf Stream, England would have a much colder climate.”
Professor Peter Ditlevsen at the University of Copenhagen, an author of the recent study, told BBC News that scientists have been braced for the potential collapse of the AMOC for almost two decades.
“There’s been worries that this current is weakening for as long as we have had measurements of it - since 2004,” he explained.
However, “assessments by the Intergovernmental Panel on Climate Change (IPCC), based on the Climate Model Intercomparison Project (CMIP) model simulations suggest that a full collapse is unlikely within the 21st century,” said the study.
A full collapse might be unlikely, but that doesn’t mean we’re in the clear.
“Tipping to an undesired state in the climate is, however, a growing concern with increasing greenhouse gas concentrations,” researchers said.
“Predictions based on observations rely on detecting early-warning signals, primarily an increase in variance (loss of resilience) and increased autocorrelation (critical slowing down), which have recently been reported for the AMOC. Here we provide statistical significance and data-driven estimators for the time of tipping. We estimate a collapse of the AMOC to occur around mid-century under the current scenario of future emissions.”
It warned that “we ought not to ignore such clear indicators of an imminent collapse.”
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