January 17, 2011

Tree Rings Provides Clues To Ancient Climate Shifts

A team of researchers conducting an extensive study of growth rings in trees say there could be a link between the rise and fall of ancient civilizations and sudden shifts in Europe's climate.

They based their findings on data from more than 9,000 wooden artifacts that have come from civilizations from over the past 2,500 years, BBC News reports.

In the study, published online in the journal Science, the researchers found that periods of warm, wet summers coincided with prosperity, while political turmoil occurred during times of unstable climates.

"Looking back on 2,500 years, there are examples where climate change impacted human history," co-author Ulf Buntgen, a paleoclimatologist at the Swiss Federal Research Institute for Forest, Snow and Landscape, told the Science website.

"Archaeologists have developed oak ring width chronologies from Central Europe that cover nearly the entire Holocene and have used them for the purpose of dating artifacts, historical buildings, antique artwork and furniture," the researchers wrote.

"Chronologies of living and relict oaks may reflect distinct patterns of summer precipitation and drought," they added.

The team studied how weather patterns over the past couple hundred years affected the growth rings in living trees.

During seasons of good growth, when water and nutrients are in plentiful supply, trees form broader rings, with their boundaries further apart. Unfavorable conditions, however, such as droughts, the rings grow in much tighter formation.

The team then used this data to reconstruct annual weather patterns from the growth rings preserved in the artifacts collected.

Once they had a chronology of events reaching over the past 2,500 years, they identified an association with prosperity levels in past societies, such as the Roman Empire.

"Wet and warm summers occurred during periods of Roman and medieval prosperity. Increased climate variability from 250-600 AD coincided with the demise of the Western Roman Empire and the turmoil of the migration period," reported the team.

"Distinct drying in the 3rd Century paralleled a period of serious crisis in the western Roman empire marked by barbarian invasion, political turmoil and economic dislocation in several provinces of Gaul."

"We were aware of these super-big data sets, and we brought them together and analyzed them in a new way to get the climate signal," explained Dr. Buntgen. "If you have enough wood, the dating is secure. You just need a lot of material and a lot of rings."


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