Atlantic Ocean circulation is not collapsing – but as it shifts gears, global warming will reaccelerate

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July 18, 2018

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.

In the Atlantic Ocean’s part of the global ocean circulation, warmer water travels north at the surface, then sinks in the far northern part of the North Atlantic and travels back deep below the surface.NOAA

While many aspects of the movie are unrealistic, oceanographers are concerned about the long-term stability of the 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 regular, decades-long cycle that will affect temperatures in coming decades.
The paper was published July 18 in 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 atmospheric sciences.
“Many have focused on the fact that it’s declining very rapidly, and that if the trend continues it will go past a tipping point, bringing a catastrophe such as an ice age. It turns out that none of that is going to happen in the near future. The fast response may instead be part of a natural cycle and there are signs that the decline is already ending.”
The results have implications for surface warming. The current’s speed determines how much surface heat gets transferred to the deeper ocean, and a quicker circulation would send more heat to the deep …

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