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Julia Karow Scientific American
About
50,000 years ago, a pile of volcanic rubble buried a conifer
forest in the southern Lake District of Chile. Only an earthquake
in 1960 brought the almost fossilized trees back into the
light. Now, some 40 years later, researchers have studied
the rings of the ancient trunks and have read from them
details about Earth's climate during the Late Pleistocene
when the trees were alive.
In fact,
the trees belong to the species Fitzroya cupressoides, which
are good climate indicators: their annual rings respond
to variations in summer temperature. The scientists from
Chile and other countries measured the rings of 47 cross
sections from 28 trees and constructed a timescale spanning
1,229 years—the oldest tree-ring chronology to date.
Their analysis of ring width, published in today's Nature,
revealed a number of long- and short-term climate cycles
with different periods. Some of the longer cycles are probably
a result of varying solar activity. It remains unclear,
however, whether the shorter ones—on a timescale of
two to seven years—are a result of the El Nino Southern
Oscillation, which largely determines short-term climate
variability today.
When
the researchers compared the data from the ancient trees
with measurements from modern, 1,000-year-old ones, they
found very similar growth cycles. Thus, factors shaping
the climate during the relatively warm period of the Late
Pleistocene are probably doing much the same today.
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