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Is collapse of the Atlantic Ocean circulation really imminent? Icebergs’ history reveals some clues

Yuxin Zhou, University of California, Santa Barbara and Jerry McManus, Columbia University, The Conversation on

Published in Science & Technology News

When people think about the risks of climate change, the idea of abrupt changes is pretty scary. Movies like “The Day After Tomorrow” feed that fear, with visions of unimaginable storms and populations fleeing to escape rapidly changing temperatures.

While Hollywood clearly takes liberties with the speed and magnitude of disasters, several recent studies have raised real-world alarms that a crucial ocean current that circulates heat to northern countries might shut down this century, with potentially disastrous consequences.

That scenario has happened in the past, most recently more than 16,000 years ago. However, it relies on Greenland shedding a lot of ice into the ocean.

Our new research, published in the journal Science, suggests that while Greenland is indeed losing huge and worrisome volumes of ice right now, that might not continue for long enough to shut down the current on its own. A closer look at evidence from the past shows why.

The Atlantic current system distributes heat and nutrients on a global scale, much like the human circulatory system distributes heat and nutrients around the body.

Warm water from the tropics circulates northward along the U.S. Atlantic coast before crossing the Atlantic. As some of the warm water evaporates and the surface water cools, it becomes saltier and denser. Denser water sinks, and this colder, denser water circulates back south at depth. The variations in heat and salinity fuel the pumping heart of the system.

 

If the Atlantic circulation system weakened, it could lead to a world of climate chaos.

Ice sheets are made of fresh water, so the rapid release of icebergs into the Atlantic Ocean can lower the ocean’s salinity and slow the pumping heart. If the surface water is no longer able to sink deep and the circulation collapses, dramatic cooling would likely occur across Europe and North America. Both the Amazon rain forest and Africa’s Sahel region would become dryer, and Antarctica’s warming and melting would accelerate, all in a matter of years to decades.

Today, the Greenland ice sheet is melting rapidly, and some scientists worry that the Atlantic current system may be headed for a climate tipping point this century. But is that worry warranted?

To answer that, we need to look back in time.

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