North Atlantic climate variability in a coupled climate model : Multidecadal cold events and climate state transitions

The main focus of this study is to investigate the climate variability in the North Atlantic region on timescales ranging from centuries to millennia to better understand the origin and dynamics of these fluctuations. A focus is set on analyzing multidecadal cold events and climate transitions from one climate state to another. These climate events and shifts can have severe consequences ranging from temperature anomalies, an expansion of sea-ice cover, and social and economical impacts. Although many studies deal with climate state transitions, the trigger of these transitions often remains unclear. Important factors are the stability of the background climate, external forcings, or internal forcings either by a natural source or due to anthropogenic impact. All these factors could lead the climate system to a lower stability and further to switch to another climate state. In the North Atlantic region, where deep-water is formed, a climate transition can lead to a shutdown of the Atlantic Meridional Overturning Circulation, which transports warm and relatively salty water northwards to the polar regions and relatively cold and fresh water southwards.