Though the climate of the last 10,000 years has been thought to be relatively stable, the researchers found that the Pacific intermediate depths have generally been cooling during that time, though with various ups and downs. From about 7,000 years ago until the start of the Medieval Warm Period in northern Europe, at about 1100, the water cooled gradually, by almost 1 degree C, or almost 2 degrees F. The rate of cooling then picked up during the so-called Little Ice Age that followed, dropping another 1 degree C, or 2 degrees F, until about 1600. The authors attribute the cooling from 7,000 years ago until the Medieval Warm Period to changes in Earth's orientation toward the sun, which affected how much sunlight fell on both poles. In 1600 or so, temperatures started gradually going back up. Then, over the last 60 years, water column temperatures, averaged from the surface to 2,200 feet, increased 0.18 degrees C, or .32 degrees F. That might seem small in the scheme of things, but it's a rate of warming 15 times faster than at any period in the last 10,000 years, said Linsley.
One explanation for the recent slowdown in global warming is that a prolonged La Niña-like cooling of eastern Pacific surface waters has helped to offset the global rise in temperatures from greenhouse gases. In a study in the journal Nature in August, climate modelers at the Scripps Institution of Oceanography showed that La Niña cooling in the Pacific seemed to suppress global average temperatures during northern hemisphere winters but allowed temperatures to rise during northern hemisphere summers, explaining last year's record U.S. heat wave and the ongoing loss of Arctic sea ice.
When the La Niña cycle switches, and the Pacific reverts to a warmer than usual El Niño phase, global temperatures may likely shoot up again, along with the rate of warming. "With global warming you don't see a gradual warming from one year to the next," said Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo., who was not involved in the research. "It's more like a staircase. You trot along with nothing much happening for 10 years and then suddenly you have a jump and things never go back to the previous level again."
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Pacific Ocean waters absorbing heat 15 times faster over past 60 years than in past 10,000