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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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