Drought triggered Mayan demise

By Helen Sewell
BBC News Online science staff

Climate change was largely to blame for the collapse of the Mayan civilisation in Central America more than 1,000 years ago, research suggests.
By the middle of the 8th Century there were up to 13 million people in the Mayan population but within 200 years their cities lay abandoned.

The Mayans built complex systems of canals and reservoirs to collect rainwater for drinking in the hot, dry summers.

Despite this there has long been speculation that the whole population was wiped out by drought, but there has not been enough evidence to support this theory.

Now research published in the journal Science suggests that climate change was indeed a major factor.

Coloured bands

To investigate the Mayan decline, scientists studied the ancient build-up of sediment on the sea floor just off the northern coast of Venezuela.

They discovered layers of deposits in bands of alternating dark and light colours each about a millimetre deep. The light bands consisted of algae and tiny fossils, while the dark bands were due to sediments of the metal titanium.

The scientists say titanium was washed into the sea by rivers during the rainy seasons. Shallower dark bands, which indicate lower levels of the metal, show the rivers were flowing more weakly. The researchers say this was because there was less rain.

They have worked out that in the 9th and 10th Centuries, probably just before the Mayan civilisation collapsed, there was a long period of dry weather and three intense droughts.

Modern implications

Archaeological evidence suggests that one reason for the Mayans’ initial success over other societies was that they controlled the artificial reservoirs.

If this is true, the scientists say the drought could easily have pushed the whole civilisation to the verge of collapse.

The German scientist who led the research, Gerald Haug, said this had serious implications for climate change today.

“A three-to-nine-year drought, which could be a failure of the monsoon systems in Africa or in India, and in particular the change in the background state of climate… is a very severe threat to modern humanity,” he told BBC News Online.

Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/2848977.stm

Published: 2003/03/14 04:20:31 GMT

Roman rise and fall ‘recorded in trees’

14 January 2011 Last updated at 12:19 ET

By Mark Kinver

The study offers a link between changes to the climate and the rise and fall of human societies

An extensive study of tree growth rings says there could be a link between the rise and fall of past civilisations and sudden shifts in Europe’s climate.

A team of researchers based their findings on data from 9,000 wooden artifacts from the past 2,500 years.

They found that periods of warm, wet summers coincided with prosperity, while political turmoil occurred during times of climate instability.

The findings have been published online by the journal Science.

“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.

Ring record

The team capitalised on a system used to date material unearthed during excavations.

“Distinct drying in the 3rd Century paralleled a period of serious crisis in the western Roman empire” – Ulf Buntgen

“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 artefacts, historical buildings, antique artwork and furniture,” they wrote.

“Chronologies of living and relict oaks may reflect distinct patterns of summer precipitation and drought.”

The team looked at how weather over the past couple of centuries affected living trees’ growth rings.

During good growing seasons, when water and nutrients are in plentiful supply, trees form broad rings, with their boundaries relatively far apart.

But in unfavourable conditions, such as drought, the rings grow in much tighter formation.

The researchers then used this data to reconstruct annual weather patterns from the growth rings preserved in the artefacts.

Once they had developed a chronology stretching back over the past 2,500 years, they identified a link 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,” the team reported.

“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.”

Dr Buntgen explained: “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.

“If you have enough wood, the dating is secure. You just need a lot of material and a lot of rings.”