May 12-18, 2000
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El Nino was active during last ice age

By Fariss Samarrai

El Nino-like climate patterns occurred in the New England region during the last ice age, 17,500 to 13,500 years ago, according to a new study. This is the first time scientists have been able to document evidence of El Nino activity during that time period.

"Our evidence suggests that the El Niņo phenomenon is more robust than we previously imagined," says Michael Mann, assistant professor of environmental sciences, and one of the study's authors. The findings appear in the May 12 issue of the journal Science.

"By looking back to a time before human impact on the environment, we can compare previous climate conditions to what we are seeing today," Mann adds. "This may help us to understand subtle ways in which global warming could be influencing the behavior of the climate.

"We have found evidence of a strong three- to seven-year cycle of El Niņo activity during the later part of the last ice age, which is much like the present three- to seven-year cycle of El Nino events."

Mann and his colleagues analyzed sediment cores from the bottom of a sequence of glacial lakes in New England. The lakes formed in an area where an ice sheet covering a large part of the North American continent left yearly sediment deposits when it retreated northward through the Connecticut Valley as the climate began warming. The layers of sediment offered Mann and his team a detailed record of climate variability. During the periodic El Nino events, the glacier melted more quickly, leaving thicker annual layers of sediment.

El Nino, a warming of sea surface temperatures in the equatorial Pacific, causes a disruption in the earth's ocean-atmosphere system. This has large consequences for global weather patterns and possibly plays a role in long-term global climate change. Climatologists are trying to understand how persistent the phenomenon is -- how long it has existed, and for how long it may continue.

Recent studies suggest that El Nino activity has moderated in recent decades, and weather patterns have been influenced by its opposite phenomenon, La Nina, which makes the sea cooler when El Niņo's affects wear off.

"Our findings provide a new perspective on the changes observed in El Nino activity in recent decades, and their possible relationship with global climate change," Mann says. "We are trying to understand what drives El Nino. We have found that this is not only a warm-climate phenomenon -- it can happen under many types of climate conditions, even when large parts of the earth are covered with ice.

The other authors of the paper are geoscientist Julie Brigham-Grette of the University of Massachusetts and graduate student Tammy Rittenour at the University of Nebraska.


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