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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