Embargoed until 2 p.m EDT
NSF PR 02-48 - May 30, 2002
New Climate Study Challenges Thinking on Large-Scale,
Global Climate Change
A study of past climate changes in the South American
tropics has challenged traditional understanding of
the mechanisms that triggered the advance and retreat
of glaciers during the last ice age. The National
Science Foundation (NSF)-funded study was published
in the May 31 issue of Science.
A research team found that glaciers in the tropical
Andes Mountains retreated several thousand years earlier
than North American glaciers during a period of wet
climate conditions, and during a time when the sun's
warming radiation (solar insolation) was at a minimum.
The finding contradicts traditional thinking that climate
conditions in the northern latitudes generate the
advance and retreat of global glaciation, and that
glaciers retreated during dry climate conditions and
when solar insolation was at its maximum, said lead
researcher Geoffrey Seltzer of Syracuse University.
"If the tropics warmed earlier than the northern latitudes,
as our study demonstrates, that means there is something
else influencing climate change that we don't yet
David Verardo, director of the NSF's paleoclimate program,
which funded the project, said that Seltzer and his
colleagues "offer remarkable insights into the intricate
movements of a climate tango of sorts between the
low and high latitudes as one hemisphere alternately
leads or follows in influencing long-term weather.
Getting the moves of this tango down is important
for understanding climate."
Added Seltzer, "We know from our experiences with El
Nino that the tropics are the focus of energy and
water vapor that drives the global climate system.
Our research provides a hint that something important
happened in the tropics that could be an important
trigger for the last retreat of the global ice age."
The researchers compared climate data derived from
sediment cores they collected from Lake Titicaca,
located on the border of Peru and Bolivia, and Lake
Junin, located in Peru, with published data from ice
cores collected in Greenland and Antarctica. A key
component of the research was an analysis of inorganic
sediment accumulation in the lakes. The researchers
found that during periods of maximum glaciation, the
tropical lakes overflowed and the sediment that flowed
into the lakes from the surrounding region contained
a high concentration of fine-grained magnetic minerals.
During periods of glacial retreat, the sediment was
trapped behind moraines (mounds of rock and debris
left by glaciers), resulting in a lower concentration
of magnetic minerals flowing into Lakes Titicaca and
"From the analysis, it is clear that the tropical Andes
deglaciated several thousand years earlier than higher
latitude warming," the authors wrote. "In contrast,
maximum glaciation in the U.S. Sierra Nevada persisted
several thousand years after deglaciation had commenced
in the tropical Andes." If early warming occurred
throughout the tropics, this climate change could
have been transmitted both atmospherically and by
ocean circulation processes to produce deglaciation
of alpine and continental ice sheets in the Northern
Hemisphere, the scientists believe.
The study is part of a larger, ongoing research project
on climate change in the tropics that includes a $2
million expedition to Lake Titicaca, funded through
NSF's Earth System History (ESH) program.