for National Geographic News
During the last ice age, temperatures in the North Atlantic region rose sharply and quickly about every 1,500 years. The result: massive discharges of melted ice into the ocean which disrupted weather patterns around the world.
The trigger behind these abrupt climate cycles—called Dansgaard-Oeschger events—is the subject of a long-running debate that bears on the ability of scientists to predict climate.
Some researchers believe the climate events were triggered by changes in the North Atlantic's dominant ocean-circulation pattern, whereas other researchers believe the events are associated with the El Niño/Southern Oscillation (ENSO) phenomenon in the tropical Pacific (see sidebar for an explanation of El Niño and ENSO).
Reporting in tomorrow's issue of the science journal Nature, an international team of scientists suggests millennial-scale dry periods associated with ENSO triggered the surges of melted ice into the North Atlantic.
"We've not got conclusive evidence, but we have the strongest evidence yet that long-term changes in El Niño are driving these changes in the North Atlantic," said Chris Turney, a paleoecologist at Queen's University Belfast in the United Kingdom.
Turney and Peter Kershaw, a paleoecologist at Monash University in Victoria, Australia, were the lead authors of the study. The study is based on data collected as part of ongoing research into Australia's historical climate. The research is supported by the National Geographic Society's Committee for Research and Exploration.
Richard Alley is a geoscientist at Pennsylvania State University in University Park and expert on abrupt climate changes such as Dansgaard-Oeschger. He said that, though he disagrees with the paper's conclusion, the authors' work is to be commended.
"The paper is interesting, the data careful, the hypotheses provocative and [they] undoubtedly will stimulate much further discussion," he said.
Alley comes down on the other side of the debate, suggesting that long-term changes in the global climate are driven by changes in the dominant ocean pattern in the North Atlantic, called the thermohaline circulation (see sidebar for an explanation of the thermohaline circulation).
El Niño Record
Distinguishing whether long-term changes in the North Atlantic or the tropical Pacific drive the global climate could allow scientists to better forecast major and potentially damaging shifts in weather patterns.
"ENSO telling the thermohaline circulation what to do in the North Atlantic is very different from the North Atlantic thermohaline circulation telling the monsoon what to do and in turn influencing ENSO," Alley said.
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