Deep ocean early warning signals of an Atlantic MOC collapse

/ November 25, 2014/ IMAU, Ocean Circulation and Climate

Atlantic Meridional Overturning Circulation (MOC) has been identified as one of the most dangerous tipping points in the climate system. If the Atlantic MOC collapses, the North Atlantic region may enter a new ice age, as was so vividly portrayed in the movie “The Day after Tomorrow”. However, before you consider immigrating to Africa or South America, it is important to know how much time is left for you to pack.

Unfortunately, observations of the MOC strength are only available for the last 10 years, but already these show a trend of the MOC slowing down, so an MOC collapse may not just be fiction. In this study, we used output of a big general circulation model (GCM), which clearly predicts the MOC collapse in a future warming climate.

The method we used is the Pearson Correlation Climate Network, in which the link between two nodes is determined from the Pearson correlation values of the time series. If a node has a lot of links with others, it has a high degree. When approaching the tipping point, high degree nodes emerge from the deep ocean, thereby strongly changing the pattern of degree field while there is no significant accompanying change in the strength of the MOC.

Based on these changes, we propose an indicator to provide an early warning signal more than 130 years ahead of MOC collapse. Furthermore, through quality measures of this indicator we also provide suggestions on the optimal observation locations for monitoring the MOC.

Qing Yi Feng, PhD student Oceans and Climate at IMAU

For more details, we refer to the paper recently published in Geophysical Research Letters by IMAU researchers Qing Yi Feng, Jan Viebahn and Henk Dijkstra.

Qingyi_MOC_fig

Figure: Annual mean MOC stream function patterns (left panel) and degree patterns of the PCCNs (right panel) of equilibrium simulations