Cause of global warming "hiatus" found deep in the Atlantic Ocean

Not a hiatus, but an apparent slowing in the speed of increase in warming.

This is yet another of several regular climate cycles that are in a phase normally associated with cooling temps, including low sun activity, but we have not been cooling. There has just been a slowdown of the rise in temps. When these cycles start to shift to their warming phase, it is scary to think what will happen. However, they will not all shift at once, because some of them have different periods of time.

http://www.eurekalert.org/pub_releases/2014-08/uow-cog081514.php

PUBLIC RELEASE DATE: 21-Aug-2014

Contact: Hannah Hickey
University of Washington
Cause of global warming hiatus found deep in the Atlantic Ocean

Following rapid warming in the late 20th century, this century has so far seen surprisingly little increase in the average temperature at the Earth's surface. At first this was a blip, then a trend, then a puzzle for the climate science community.

More than a dozen theories have now been proposed for the so-called global warming hiatus, ranging from air pollution to volcanoes to sunspots. New research from the University of Washington shows that the heat absent from the surface is plunging deep in the north and south Atlantic Ocean, and is part of a naturally occurring cycle. The study is published Aug. 22 in Science.

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The results show that a slow-moving current in the Atlantic, which carries heat between the two poles, sped up earlier this century to draw heat down almost a mile (1,500 meters). Most of the previous studies focused on shorter-term variability or particles that could block incoming sunlight, but they could not explain the massive amount of heat missing for more than a decade.

"The finding is a surprise, since the current theories had pointed to the Pacific Ocean as the culprit for hiding heat," Tung said. "But the data are quite convincing and they show otherwise."

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Rapid warming in the last three decades of the 20th century, they found, was roughly half due to global warming and half to the natural Atlantic Ocean cycle that kept more heat near the surface. When observations show the ocean cycle flipped, around the year 2000, the current began to draw heat deeper into the ocean, working to counteract human-driven warming.

[Maybe explains why global warming had been occurring faster than computer models predicted.]

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The authors dug up historical data to show that the cooling in the three decades between 1945 to 1975 – which caused people to worry about the start of an Ice Age – was during a cooling phase. (It was thought to be caused by air pollution.) Earlier records in Central England show the 40- to 70-year cycle goes back centuries, and other records show it has existed for millennia.

Changes in Atlantic Ocean circulation historically meant roughly 30 warmer years followed by 30 cooler years. Now that it is happening on top of global warming, however, the trend looks more like a staircase.

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This explanation implies that the current slowdown in global warming could last for another decade, or longer, and then rapid warming will return. But Tung emphasizes it's hard to predict what will happen next.

A pool of freshwater from melting ice, now sitting in the Arctic Ocean, could overflow into the North Atlantic to upset the cycle.

"We are not talking about a normal situation because there are so many other things happening due to climate change," Tung said.