Ancient tree rings give climate clues

Giant South American trees live for up to 3,600 years

By BBC News Online's Ivan Noble

Ancient tree stumps uncovered in a South American earthquake have provided the most detailed picture yet of the world's climate before the last ice age.

It is a bit like a lottery win

Dr Keith Briffa, University of East Anglia

An international team looked at the seasonal growth rings in 28 examples of Fitzroya cupressoides, a conifer from the region.

They found what seems to be early evidence of El Niño, the largest single source of modern weather variation, which is caused by a cyclical movement of warm waters in the Pacific.

The researchers say the trees, from Pelluco in southern Chile, provide an unprecedented weather record from 50,000 years ago.

"What it has done is give us a first glimpse of year-by-year records," explained Dr Keith Briffa of the University of East Anglia, UK.

'Lottery win'

The scientists were able to study the trees as a result of two natural disasters.

The first covered up and preserved the trees around 500 centuries ago. The second, in 1960, began to bring the trees back to the surface.

"It is a bit like a lottery win," Dr Briffa told BBC News Online. "There was a bit of tectonic movement in 1960 which allowed erosion to expose the remains."

Dr Briffa is co-author of a study of the trees, which is published in the journal Nature.

He helped analyse the data collected from the ancient specimens, and put together information from separate trees to make one single 1,229-year climate record.

Bigger picture

"It is probably the oldest ever, continuous, annually resolved chronology," he said.

By studying the annual growth spurts, dendrochronologists can get an idea of the seasonal conditions that existed year on year through a tree's life - how warm it might have been, the amount of moisture that might have been in the soil, etc.

Well-preserved or subfossil trees have been found before in Tasmania and Siberia, but they were around 10,000 years old - much younger than the Chilean samples.

The data will be more significant once they can be linked to other evidence of ancient climate variation - what scientists refer to as proxy data.

"At present, most of our information is from oxygen isotopes in ice cores in Greenland and studies have been done tying this in with ocean sediments," Dr Briffa added.

These data allow researchers to build a picture of what the Earth's climate was like before humans were around to make written records.