Earth’s Strongest Ocean Current Could Slow 20 Percent by 2050 Because of Climate Change, Study Finds

Five times stronger than the Gulf Stream and more than 100 times stronger than the Amazon River, the Antarctic Circumpolar Current (ACC) is the most powerful ocean current on Earth. As it flows around Antarctica, it connects the Pacific, Atlantic and Indian oceans and distributes nutrients around the world.

In short, the ACC is a complex marine “conveyor belt” involved in everything from absorbing heat and atmospheric carbon dioxide into the oceans to guarding against invasive marine species—but because of climate change, scientists now say it might slow down by as much as 20 percent by 2050.

Researchers used a climate simulator on Australia’s fastest supercomputer to model changes in the ACC given the projected ice melting and ocean warming under different carbon emission scenarios, as detailed in a new study published Monday in the journal Environmental Research Letters. While natural phenomena also release the planet-warming gas, humans have increased atmospheric carbon dioxide by 50 percent in less than two centuries due to burning fossil fuels, according to NASA.

The simulation revealed that in a “high emissions scenario,” the ACC will slow down by as much as 20 percent by 2050, as cool and fresh water melts from Antarctic glaciers and dilutes the salty ocean. But even a lower emissions scenario could have similar consequences, if polar ice continues to melt the way previous studies have forecast it might, as climate scientist and study co-author Taimoor Sohail from the University of New South Wales explains in a statement.

“In this future projection, cold, fresh melt water from Antarctica migrates north, filling the deep ocean as it goes. This causes major changes to the density structure of the ocean,” Sohail and co-author Bishakhdatta Gayen, a fluid mechanist from the University of Melbourne, write in an article for the Conversation. “It counteracts the influence of ocean warming, leading to an overall slowdown.”

“The ocean is extremely complex and finely balanced. If this current ‘engine’ breaks down, there could be severe consequences, including more climate variability, with greater extremes in certain regions and accelerated global warming due to a reduction in the ocean’s capacity to act as a carbon sink,” Gayen says in the statement.

Additionally, the ACC’s strong current prevents certain species from other continents from reaching Antarctica. If the current slows significantly, invasive species such as types of kelp, shrimp and mollusks could access and severely disrupt the Antarctic ecosystem.

The current also keeps out warm water. So, a slower ACC might allow that water to reach the Antarctic shelf—which would speed up ice melt and further slow the ACC, triggering a “potentially vicious cycle,” Sohail tells Cosmos’ Richard Musgrove.

These results, as Gayen tells the Guardian’s Petra Stock, are “quite alarming.”

Edward Doddridge, a physical oceanographer at the University of Tasmania who did not participate in the study, was surprised by its outcome, since previous research had suggested that ocean warming was actually making parts of the ACC stronger, per the Guardian.

In theory, rising temperatures should make the current move faster, since warmer water is less dense, lighter and able to be carried more quickly, the team writes in the Conversation. But their computer simulation, they say, was able to account for additional factors such as eddies that might change how ocean currents would behave.

“Ocean models have historically been unable to adequately resolve the small-scale processes that control current strength,” Gayen explains in the statement. “This model resolves such processes and shows a mechanism through which the ACC is projected to actually slow down in the future.”

He notes, however, that further research will be needed to definitively confirm their results.

And while the consequences of a slower ACC would be “profound and far-reaching,” the researchers emphasize that “the future is not predetermined,” per the Conversation. “Concerted efforts to reduce greenhouse gas emissions could still limit melting around Antarctica.”