Magazine article Science News

Ancient Tree Rings Reveal Past Climate

Magazine article Science News

Ancient Tree Rings Reveal Past Climate

Article excerpt

Fifty millennia ago, volcanic ash and mud buried a forest of conifers along a Pacific shoreline in what is now southern Chile. In 1960, an earthquake loosened these sediments, and erosion then exposed the long-entombed trees. Now, by examining the tree rings of the remaining stumps, an international team of scientists has reconstructed the earliest year-to-year record yet of climate variation.

The stumps of the tree species Fitzroya cupressoides are roughly 50,000 years old, says lead scientist Fidel A. Roig of the Laboratory of Dendrochronology at IANIGLA-CONICET, an earth-sciences research center in Mendoza, Argentina. Roig notes that there's a virtual forest of these stumps, which are still woody and well preserved.

Data from these trees "provides a year-by-year indication of general climate variability for a period before there was anything even approaching that sort of resolution," says research team member Keith R. Briffa of the University of East Anglia in Norwich, England.

Scientists have looked at past climate patterns--some going back hundreds of thousands of years--by studying layers in ocean sediments and ice cores. But older layers often become too compressed to reveal year-to-year differences, explains team member Hakan Grudd of Stockholm University.

However, using annual growth-ring patterns in trees, some researchers have inferred temperatures dating back about 10,000 years, or to the end of the last ice age. More ancient records have been difficult to re-create because the trees needed for such studies have either rotted away or been destroyed by glaciers, according to the researchers. …

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