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Due to global warming, a deep ocean current around Antarctica that has been relatively stable for thousands of years could head for “collapse” over the next few decades.
Such a sudden shift could affect the planet’s climate and marine ecosystems for centuries to come.
So says a recent study that was published in the peer-reviewed journal Nature.
The cold water that sinks near Antarctica drives the deepest flow of a network of currents that spans throughout the world’s oceans, known as the overturning circulation. The overturning carries heat, carbon, oxygen and nutrients around the globe.
This in turn influences climate, sea level and the productivity of marine ecosystems. Indeed, the loss of nutrient-rich seawater near the surface could damage fisheries, according to the study.
‘Headed towards collapse’
This deep ocean current has remained in a relatively stable state for thousands of years, but with increasing greenhouse gas emissions and the melting of Antarctic ice, Antarctic overturning is predicted to slow down significantly over the next few decades.
“Our modeling shows that if global carbon emissions continue at the current rate, then the Antarctic overturning will slow by more than 40% in the next 30 years – and on a trajectory that looks headed towards collapse,” said study lead author Matthew England of the University of New South Wales in Australia.
Speaking about the new research, paleoclimatologist Alan Mix told Reuters “that’s stunning to see that happen so quickly.” Mix, a paleoclimatologist at Oregon State University and co-author on the latest Intergovernmental Panel on Climate Change assessments, who was not involved in the study, added “It appears to be kicking into gear right now. That’s headline news.”
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Atlantic current also affected
Such a collapse would also impact a nearby Atlantic Ocean current, known as the Atlantic Meridional Overturning Circulation, or AMOC, which transports warm, salty water from the tropics northward at the ocean surface and cold water southward at the ocean bottom.
This current includes the well-known Gulf Stream, which affects weather patterns in the U.S. and Europe. “The main issue for the AMOC at the moment is meltwater from Greenland, which slows that current,” England told USA TODAY.
Other studies in recent years about the AMOC drew comparisons to the scientifically inaccurate 2004 disaster movie “The Day After Tomorrow,” which used such an ocean current shutdown as the premise of the film. In a 2018 study, authors said a collapse was at least decades away but would be a catastrophe.
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Cause of the current slowdown
What’s causing the currents to slow down and potentially collapse? “Climate change is to blame,” England wrote for the Conversation. “As Antarctica melts, more freshwater flows into the oceans. This disrupts the sinking of cold, salty, oxygen-rich water to the bottom of the ocean”.
Specifically, more than 250 trillion tons of that cold, salty, oxygen-rich water sinks near Antarctica each year. This water then spreads northward and carries oxygen into the deep Indian, Pacific and Atlantic Oceans.
“If the oceans had lungs, this would be one of them,” England said.
“Simply put, a slowing or collapse of the overturning circulation would change our climate and marine environment in profound and potentially irreversible ways.” he wrote.
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How would it impact the US?
England told USA TODAY that the main impact for North America would be sea-level rise along the East Coast.
In addition, another impact of the collapse of the AMOC would be a transition to a more La Nina-like-state in the Pacific Ocean, England said. La Niña, a natural cooling of sea water in the tropical Pacific Ocean, affects weather and climate in the U.S. and around the world.
It tends to lead to worsening droughts and wildfires in the Southwest U.S., and more hurricanes in the Atlantic Ocean.
What can be done?
“Our study shows continuing ice melt will not only raise sea levels, but also change the massive overturning circulation currents which can drive further ice melt and hence more sea-level rise, and damage climate and ecosystems worldwide,” England wrote in the Conversation. “It’s yet another reason to address the climate crisis – and fast.”
Contributing: The Associated Press
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