The Global Warming Hiatus and Southern Ocean

Global mean surface temperature record does not indicate a monotonic increase, instead contains multi-decadal fluctuations with a warming trend since 1880. In particular, the pause or hiatus of the global warming shown in early 21^st century seems to be related to influence of ocean upwelling areas such as eastern tropical Pacific and Southern Ocean (SO), represented by negative phases of the Pacific Decadal Oscillation (PDO) or Inter-decadal Pacific Oscillation (IPO). Main mechanisms behind the multi-decadal variabilities associated with ocean upwelling areas are still not understood clearly. Recently, a high-resolution ocean model resolving eddies shows that there exist long-term oscillations of around 30-50 years penetrating up to 4km in depth in the Atlantic sector of the SO near 60-80S. Here we show that the local multi-decadal oscillation in the SO is a driver of multi-decadal variabilities of the PDO and the Atlantic Multi-decadal Oscillation. A warming (or cooling) originated from the Atlantic sector of the SO spreads over the entire SO via the Antarctic circumpolar current and then goes up to the Eastern Tropical Pacific through the Peru current. At the same time, the increase (or decrease) of ocean upwelling is strongly correlated with meridional mass transport in the Atlantic Ocean leading to warming (or cooling) of the North Atlantic Ocean. Unfortunately, most of coarse-resolution coupled GCMs are unable to generate the multi-decadal oscillation of the Atlantic SO due to the absence of detailed eddy-mean interactions. This suggests the importance of eddy-resolving high-resolution ocean models to simulate realistic multi-decadal variabilities of global climate.