Climate scientists Michael Mann of Penn State and Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research suggested that the observed cold pattern during years of temperature records is a sign that the Atlantic Oceans Meridional overturning circulation (AMOC) may be weakening. They published their findings, and concluded that the AMOC circulation shows exceptional slowdown in the last century, and that Greenland melt is a possible contributor.  Tom Delworth of NOAA suggested that natural variability, which includes different modes, here namely the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation through wind driven ocean temperatures are also a factor. A 2014 study by Jon Robson et al. from the University of Reading concluded about the anomaly, "...suggest that a substantial change in the AMOC is unfolding now.'" Another study by Didier Swingedouw concluded that the slowdown of AMOC in the 1970s may have been unprecedented over the last millennium.