Between 2002 and 2009, the team says, there was no trend discernible – just a lot of variability on short timescales.
The satellite record going back to 1993 did suggest a small increase in flow, although the researchers cannot be sure it is significant.
“The changes we’re seeing in overturning strength are probably part of a natural cycle,” said Josh Willis from Nasa’s Jet Propulsion Laboratory (JPL) in California.
“The slight increase in overturning since 1993 coincides with a decades-long natural pattern of Atlantic heating and cooling.”
It’s difficult to overstate just how much trouble the whole world would be in if that circulation stopped (as it has during other warming events).