Scientists from the University of Washington have determined that some of the heat that has been recently absent from the surface has been going deep down into the Atlantic Ocean.
Recent studies indicated that this missing heat was likely going into the Pacific Ocean.
The lead researchers, Ka-Kit Tung and Xianyao Chen also found that this process was part of a naturally occurring cycle.
The authors' state that this subsurface ocean warming explains why global average temperatures have nearly flatlined since 1999 despite a steady increase in atmospheric greenhouse gas concentration.
The data showed that it is a slow-moving current in the Atlantic Ocean, which carries heat between the two poles that actually sped up earlier this century, which in turn forced more heat deep into the ocean to a depth of almost a mile.
The research team used recent observations from ARGO floats, computer reconstructions and older oceanographic measurements to form this conclusion.
They found that there was an increase in heat sinking deep into the ocean starting around 1999, which coincides with the start of this most recent period of a reduced rate of global warming.
This natural cycle began when denser, saltier water at the surface in the north Atlantic near Iceland causes the water to sink. This process alters the spread of the massive current in the Atlantic Ocean which redistributes heat throughout the globe.
Excerpt from the University of Washington News report....
The oscillations have a natural switch. During the warm period, faster currents cause more tropical water to travel to the North Atlantic, warming both the surface and the deep water. At the surface this warming melts ice. This slowly makes the surface water there less dense and after a few decades puts the brakes on the circulation, setting off a 30-year cooling phase.
There is evidence that this 40-70 year cycle may go back centuries or more.
The authors note that the current slowdown in warming could last for another decade or longer before rapid warming returns.
The study was published in the journal Science.
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