Ancient trees give clues to climate change

By Juan Bustamante

PUERTO BLEST, Argentina (Reuters) - On the shores of lake Nahuel Huapi, in the wild mountains of Argentina's Patagonia, live some of the world's most ancient trees.

Known in Spanish as the alerce, the Patagonian cypress grows extremely slowly, but can reach heights over 50 meters (165 feet) and live for 2,000 years or more, putting some of them among the oldest living things on earth.

For scientists who come from around the world to study them, the alerces give an exciting snapshot of years past.

Argentine geoscientist Ricardo Villalba, a contributor to the Nobel Prize-winning United Nations report on climate change last year, studies what the ancient trees say about changing weather patterns.

Like other trees, alerces form a new layer of wood under their bark every year. So samples taken straight through the trunk can help gauge what the weather was like in each year of the tree's life.

"This has allowed us to see that in some sectors of Patagonia, the year 1998 was the hottest in the last 400 years," Villalba said during a recent expedition.

"The marked tendencies that have occurred over the last few decades have no precedent in the last 400 or 500 years, which is as far as the registers in Patagonia have permitted us to analyze up until now."

The tree rings show that temperatures in the 20th Century were "anomalously warm" across the southern Andes. At their worst, mean temperatures over the last century went up 0.86 degree Celsius (1.5 degrees Fahrenheit) when compared to temperatures in the previous 260 years.