NASA Study Finds Atlantic “Conveyor Belt” Not Slowing

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The latest climate models predict the overturning circulation will slow down as greenhouse gases warm the planet and melting ice adds freshwater to the ocean. “Warm, freshwater is lighter and sinks less readily than cold, salty water,” Willis explained.

For now, however, there are no signs of a slowdown in the circulation. “The changes we’re seeing in overturning strength are probably part of a natural cycle,” said Willis. “The slight increase in overturning since 1993 coincides with a decades-long natural pattern of Atlantic heating and cooling.”

If or when the overturning circulation slows, the results are unlikely to be dramatic.

No one is predicting another ice age as a result of changes in the Atlantic overturning. Even if the overturning was the Godzilla of climate 12,000 years ago, the climate was much colder then. Models of today’s warmer conditions suggest that a slowdown would have a much smaller impact now.

But the Atlantic overturning circulation is still an important player in today’s climate. Some have suggested cyclic changes in the overturning may be warming and cooling the whole North Atlantic over the course of several decades and affecting rainfall patterns across the United States and Africa, and even the number of hurricanes in the Atlantic.

—Josh Willis

(A hat-tip to Thomas!)

Resources

• Willis, J. K. (2010), Can in situ floats and satellite altimeters detect long-term changes in Atlantic Ocean overturning?, Geophys. Res. Lett., 37, L06602, doi: 10.1029/2010GL042372