Multidecadal Variability of Global Ocean and its Relationship to Recent Global Warming Slowdown

When the global-mean surface temperature did not warm as expected in the presence of ever increasing atmospheric concentration of greenhouse gases that enhance the long-wave radiation to space, there can be only two possible reasons, both involving the energy budget of the earth: (1) the radiative heating was not appreciably reaching the surface--most of it presumably was reflected back to space by, for example, increasing aerosols from volcanoes and anthropogenic pollution, or (2) that the heating was reaching the surface and below, but was sequestered in the oceans. From an energy perspective, while more heat was moved into deeper oceans in the 21st century, surface warming slowed. The main sites of ocean heat uptake below 300m are found in the Atlantic and the Southern Oceans, and not in the Pacific. The longer record of intermediate layer ocean measurements in the North Atlantic suggests that the interval between ocean regime shifts is about three decades, is density/salinity initiated, and involves a negative feedback that produces the acceleration and deceleration regimes of the Atlantic Meridional Overturning Circulation on the multidecadal time scales.