As Atlantic Ocean circulation shifts gears, global warming will reaccelerate

Waves crashing on a beach — In coming years, Atlantic Ocean circulation will no longer send more of the excess heat trapped by greenhouse gases deep into the North Atlantic.

A huge circulation pattern in the Atlantic Ocean took a starring role in the 2004 movie, “The Day After Tomorrow.” In that fictional tale, the global oceanic current suddenly stops and New York City freezes over.

While many aspects of the movie are unrealistic, oceanographers are concerned about the long-term stability of Atlantic Ocean circulation, and previous studies show that it has slowed dramatically in the past decade. New research from the University of Washington and the Ocean University of China finds the slowdown is not caused by global warming but is part of a regular, decades-long cycle that will affect temperatures in coming decades. The paper was published July 18 in the journal Nature.

“Climate scientists have expected the Atlantic overturning circulation to decline long-term under global warming, but we only have direct measurements of its strength since April 2004. And the decline measured since then is 10 times larger than expected,” said corresponding author Ka-Kit Tung, a UW professor of applied mathematics with an adjunct appointment in the Department of Atmospheric Sciences.