Melting ice caps may not shut down ocean current, say researchers 

A portion of the Atlantic meridional overturning circulation [image credit: R. Curry, Woods Hole Oceanographic Institution @ Wikipedia]

Another supposed climate tipping point, popular with the alarm-loving media, floats away? A feature that’s “built into many models” was found not to work as advertised.
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Most simulations of our climate’s future may be overly sensitive to Arctic ice melt as a cause of abrupt changes in ocean circulation, according to new research led by scientists at the University of Wisconsin–Madison.

Climate scientists count the Atlantic Meridional Overturning Circulation (or AMOC) among the biggest tipping points on the way to a planetary climate disaster, says Phys.org.

The Atlantic Ocean current acts like a conveyor belt carrying warm tropical surface water north and cooler, heavier deeper water south.

“We’ve been taught to picture it like a conveyor belt—even in middle school and high school now, it’s taught this way—that shuts down when freshwater comes in from ice melt,” says Feng He, an associate scientist at UW–Madison’s Center for Climatic Research.

However, building upon previous work, He says researchers are revising their understanding of the relationship between AMOC and freshwater from melting polar ice.

In the past, a stalled AMOC has accompanied abrupt climate events like the Bølling-Allerød warming, a 14,500-year-old, sharp global temperature hike. He successfully reproduced that event using a climate model he conducted in 2009 while a UW–Madison graduate student.

“That was a success, reproducing the abrupt warming about 14,700 years ago that is seen in the paleoclimate record,” says He, now. “But our accuracy didn’t continue past that abrupt change period.”

Instead, while Earth’s temperatures cooled after this abrupt warming before rising again to plateau at new highs for the last 10,000 years, the 2009 model couldn’t keep pace. The simulated warming over the northern regions of the planet didn’t match the increase in temperatures seen in geological archives of climate, like ice cores.

In a study published this week in the journal Nature Climate Change, He and Oregon State University paleoclimatologist Peter Clark describe a new model simulation that matches the warmth of the last 10,000 years.

And they did it by doing away with the trigger most scientists believe stalls or shuts down the AMOC.

Continued here.

via Tallbloke’s Talkshop

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April 9, 2022 at 04:40AM

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