Is the Pacific Ocean holding back global warming?
New research indicate that the unexpected flattening of global temperatures in recent years is linked to cooling temperatures in the tropical Pacific.
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The warm and cool phases in the Pacific Ocean studied by Xie and his colleagues appear to last much longer than the El Niño and La Niña cycles. Previously, the Earth experienced cooling in the tropical Pacific from the 1940s to the 1970s, before oscillating into a warm state from the 1970s to the 1990s.Skip to next paragraph
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Current scientific models are unable to predict when the current cooling period will end, Xie said, but when the ocean swings back into a warm phase, parts of the planet may experience warmer temperatures.
"The equatorial Pacific Ocean is associated with distinct regional patterns, like the Pacific coast of North America," Xie said. "Because of equatorial cooling, this area has not been warming as rapidly as before, but when the equatorial Pacific shifts into a warm state, those regions might expect rapid warming, on the order of 2 degrees Celsius [3.6 degrees Fahrenheit] over 15 years."
Implications for a warming planet
Scientists have known that the eastern equatorial Pacific Ocean takes in a significant amount of heat from the atmosphere, but this new study suggests this small portion of the world's oceans could have a big influence on global climate, said James Moum, a professor of physical oceanography at Oregon State University in Corvallis, Ore., who was not involved with the new study.
While the models used in the study rely on some assumptions (for instance, the researchers set the sea-surface temperature to what is observed, rather than computing the temperatures, as would be done in a numerical model), Moum called the research "a brave experiment."
"It provides a physical basis for the current global mean temperature leveling off, while at the same time, points to this equatorial cold tongue as being the major driver for that," Moum told LiveScience.
There are still many unknowns about how this warming and cooling in the Pacific Ocean interacts with man-made greenhouse gas emissions to change the Earth's climate.
"We had El Niño long before we had anthropogenic forcing — they occur independently of man-made forcing, certainly," Moum said. "Whether they're amplified by it is another question. The flip side of the story is that if this part of the ocean has an outside influence when it cools, it's going to have an outside influence when it warms. It's definitely suggested in the paper that this is a cause for concern."
The detailed findings of the study were published online today (Aug. 28) in the journal Nature.
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