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Ancient Tree Rings Tell of Climate Changes

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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