Researchers at Yale University are challenging a long-standing model of Pacific Ocean temperature variability that assumes an ancient period of "permanent" El Niño climate conditions.
Their research casts doubt on such a situation and suggests the tropics could become significantly hotter in the future, they say.
Modern El Niño phenomena create unusually warm temperatures in surface water in the eastern equatorial Pacific with often-dramatic effects on the world's weather patterns, causing extreme amounts of rainfall in some regions and drought in other places.
Many scientists have held the view that sea temperatures in the warmest region of the equatorial Pacific remained relatively constant for millions of years, acting as an ocean "thermostat" mechanism controlling temperatures.
However, the Yale researchers say a reconstruction of Pacific surface temperatures over a 12-million-year period suggests a greater variability of temperatures and the absence of any such temperature control "permanent El Niño" conditions might provide.
That's both good and bad, Yale geophysics Professor Mark Pagani says.
"The good news is that global warming does not drive the Pacific Ocean into a permanent El Niño-like condition with all the other regional climate impacts that come with that," he says. "The bad news is that the tropics will warm as we continue to add greenhouse gases to the atmosphere -- and the recent past was probably much warmer than generally assumed."
Pagani and fellow Yale researcher Yi Ge Zhang, a doctoral candidate, determined Pacific temperatures were significantly higher millions of years in the past than had been previously believed, at least 7 degrees Fahrenheit warmer.
"El Niño conditions today are characterized by very low equatorial Pacific temperature gradients," Pagani says. "It seemed from previous data that the equatorial Pacific maintained similarly low temperature gradients in the past and thus reflected a 'permanent' state characteristic of the modern El Niño."
However, he says, the new study shows the processes creating today's much stronger temperature gradients, with a western warm region and an eastern colder region, were also present in past eras.
Therefore, he says, "there is no evidence of a tropical thermostat that keeps the tropics from overheating."
Pagani, who is the director of the Yale Climate and Energy Institute, says the findings are important as humans continue to increase their emissions of carbon dioxide into the world's climate system.
"Building a better understanding of the world and clarifying the nature of a warmer Earth helps us better prepare for the inevitable impact of our behavior," he says.
