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 50m 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 analyse 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°C when compared to temperatures in the previous 260 years.
Reaching into the past
At the nearby Puerto Blest Biological Research Station, Villalba has been able to compare his results with those of other leading scientists.
Evidence from tree rings is what scientists call proxy data, meaning they know the data is not exact but if it corroborates other proxy data — like evidence of glacier retreat — it can be used to draw real conclusions.
The scientists have also been able to use their proxy data to test computer models used for predicting climate changes in the future.
”In this part of the world there is a decrease in precipitation in the last decade and a very marked increase in temperature, which is entirely what the computer models predict for global change,” said researcher Brian Luckman of the University of Western Ontario and the InterAmerican Research Institute. ”So we can use some of the results that we have to verify and to test some of the computer models and to see if they really give realistic pictures of what has happened in the past or what will happen in the future.”
Tree rings also provide a long-term perspective in the climate change debate, such as in the question of whether global warming is a result of human activity or is part of a natural earth cycle.
The more scientists learn about those natural cycles and about weather patterns in the past, the more they are able to answer that question.
And the alerces still have a lot more information to provide.
”The Alerce has the peculiarity of longevity and of being very resistant to wood decay,” Villalba said. ”So you can find buried material or subfossil material that can be used to extend these chronologies further back into the past.”
When these chronologies are fully compiled, they could provide a new source of data currently only available from ice core samples, ocean sediments and ancient pollen.
And that would help scientists reach further into the past, far beyond human records, which began in 1856 — when the British Meteorological Society began collecting data around the world. – Reuters