Global warming pause 'may last for another decade', scientists suggestHeat is being stored deep in the Atlantic and Southern Oceans but is likely to return to the surface in a decade, triggering more warming, scientists say 
A new study suggests that a natural cycle of ocean currents has caused the global warming "pause" by drawing heat from shallow waters down almost a mile into the depths of the Atlantic and Southern Oceans. Photo: Tiago Fioreze/ Wikimedia CommonsBy Emily Gosden, Energy Editor
7:00PM BST 21 Aug 2014
The “pause” in global warming may last another decade before surface temperatures start rising again, according to scientists who say heat is being stored in the depths of the Atlantic and Southern Oceans.
Global average surface temperatures rose rapidly from the 1970s but have been relatively stable since the late 1990s, in a trend that has been seized upon by climate sceptics who question the science of man-made warming.
Climate change scientists have proposed more than a dozen theories to explain the "hiatus",
which they say is a "distraction" from the widespread consensus on global warming.
A new study, published in the journal
Science, suggests that a natural cycle of ocean currents has caused the phenomenon by drawing heat from shallow waters down almost a mile into the depths of the Atlantic and Southern Oceans.
The cycle naturally produces periods of roughly 30 years in which heat is stored near the surface of the Atlantic Ocean, leading to warmer temperatures, followed by roughly 30 years in which it is stored in the depths, causing cooler surface temperatures, it suggests.
Rising surface temperatures in the last three decades of the 20th century were roughly half caused by man-made global warming and half by the ocean currents keeping more heat near the surface, it finds.
When the ocean cycle reversed around the turn of the century, drawing heat down into the depths, this served to counteract the effects of man-made global warming.
"When the internal variability that is responsible for the current hiatus switches sign, as it inevitably will, another episode of accelerated global warming should ensue," the study concludes.
Prof Ka-Kit Tung of the University of Washington, one of the report's authors, said: "Historically the cool period lasted 20 to 35 years. The current period already lasted 15 years, so roughly there [are] 10 more years to go."
But he said that other impacts of climate change could upset the cycle, which is caused by variation in the salinity of the water as denser, saltier water sinks.
Prof Tung said the study's findings were a surprise because previous studies had suggested it was the Pacific Ocean that was "the culprit for hiding heat".
"The data are quite convincing and they show otherwise," he said.
Prof Piers Forster, professor of climate change at the University of Leeds, said the paper was "another a nail in the coffin of the idea that the hiatus is evidence that our projections of long term climate change need revising down".
"Variability in the ocean will not affect long-term climate trends but may mean we have a period of accelerated warming to look forward to," he said.
Prof Richard Allan, professor of climate science at the University of Reading, said: "Although it is human nature to seek a single cause for notable events, in reality the complexity of the climate system means that there is not one simple explanation for a decade of unusual climatic conditions.
