Key ocean current weaker than previously thought, could collapse in 30 years
The AMOC is driven, by differences in water temperatures and salinity, but climate change could disrupt that balance.
The Atlantic Meridional Overturning Circulation (AMOC) regulates the large-scale circulation of the Atlantic Ocean and influences the global climate, but a recent report from researchers at Utrecht University argues the current is more unstable than previously thought, and could begin collapsing in as little as 30 years.
This challenges the assumption made in a 2021 report by the Intergovernmental Panel on Climate Change (IPCC), which said the risk of an AMOC collapse this century is low.
The AMOC is part of the global conveyor belt, a complex system of global ocean currents that circulate cool subsurface water and warm surface water across the planet, the National Oceanic and Atmospheric Administration (NOAA) explains.
The AMOC is driven, by differences in water temperatures and salinity, but climate change could disrupt that balance.
“As rainfall increases and the Greenland ice sheet continues to melt, the water in the North Atlantic becomes less salty, and therefore less dense,” reads a statement from Utrecht University.
“Under normal conditions, cold, salty water near Greenland sinks into the deep ocean, driving the AMOC. But as the water becomes lighter due to freshening, this sinking process weakens, disrupting the entire system. This weakening is being driven by climate change.”
Topographic map of the Nordic Seas and subpolar basins with surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures. (Caption and image: Wikipedia/R. Curry, Woods Hole Oceanographic Institution/Science/USGCRP - CC BY 3.0)
For their study, researchers used several climate models to examine several scenarios of AMOC weakening, with varying levels of freshwater pouring into the North Atlantic, to determine how the European climate would be influenced.
In one moderate climate change scenario, researchers found that Europe could experience regional cooling due to a weakened circulation system, with Arctic sea ice potentially reaching parts of Northwestern Europe, including Britain, Scandinavia, and the Netherlands.
“Since sea ice reflects much more sunlight than the darker ocean surface, this expansion amplifies the cooling. As a result, winter temperatures in those regions could plummet,” Michiel Baatsen, the co-author of the study, says in a statement.
Researchers found the is AMOC more likely to collapse in a high-emission scenario, but warmer ocean temperatures limit southward sea-ice expansion which could make extreme cold in Northwestern Europe less severe.
In other words, impacts on future winter weather depend on the scenario, the study’s authors say.
A weakened AMOC could also result in less precipitation, which would decrease European agricultural yields by about 30 per cent, Sybren Drijfhout, a professor of physical oceanography at the University of Southampton in the U.K. and Utrecht University in the Netherlands, told Live Science.
A collapsing AMOC could also result in faster sea-level rise in the Atlantic Ocean, increasing the risk of storm surge and floods in coastal regions — but the effects won’t be immediately felt. Experts estimate it could take more than 100 years for a weakening AMOC to start influencing weather patterns.
While a high emissions scenario is unlikely, a “middle road” future is a real possibility. In that event, emissions would remain similar to today (2.7°C above pre-industrial levels), and that would cause the AMOC to begin collapsing in 2063.
"An AMOC collapse scenario can possibly be prevented when following a low emission scenario," René van Westen, lead author of the study, told Live Science, “but this would require reaching net-zero carbon emissions around 2050.”
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Header image: Visualization of global ocean current (Wikipedia/NASA/Goddard Space Flight Center Scientific Visualization Studio) Public domain.