news.bbc.co.uk 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.

news.independent.co.uk By Steve Connor Science Editor 14 March 2003

The Maya disappeared more than 1,000 years ago, leaving pyramids, a unique form of writing and a network of lost cities in the deserts and jungles of Central and South America.

For two centuries archaeologists have speculated why their civilisation collapsed, with theories ranging from civil war to overpopulation and environmental degradation.

Today, an international team of scientists publishes powerful evidence pointing to a series of devastating droughts over a period of 150 years, which played a pivotal role in ending one of the most intriguing cultures in human history.

Cores drilled into the muddy sediments of the Cariaco Basin of the southern Caribbean Sea have identified three intense droughts around AD810, AD860 and AD910, which correspond to the periods where the Maya are thought to have abandoned some of their cities.

The scientists, led by Gerald Haug, professor of geology at the GeoForschungSzentrum institute in Potsdam, Germany, conclude in the journal Science that a change in the climate pushed the Maya civilisation into terminal decline. "These data suggest that a century-scale decline in rainfall put a general strain on resources in the region, which was then exacerbated by the abrupt drought events," they say.

The Mayan civilisation, which existed for about 2,000 years, disappeared around AD900. The Mayans mastered a system of counting, were able to chart the movements of the stars and planets and established a rich commercial trade and ritual tradition based on bloodletting and human sacrifice.

Their disappearance went unnoticed until the early 19th century when an American explorer, John Lloyd Stephens, discovered the lost Maya city of Copan deep in the South American jungle.

The civilisation stretched across much of what is now southern Mexico, Belize and Guatemala. Its history extends over a period of two millenniums, with the culture blossoming and the population growing to between 3 million and 13 million people in the "classic" period between about AD250 and AD750.

But Professor Haug said the civilisation experienced a "demographic disaster" between AD750 and AD950. Many of the densely populated cities were suddenly emptied. Eventually the civilisation collapsed, with only a fraction of the Maya population surviving.

Some archaeologists suggested that the demise was caused by civil war between competing Maya groups. Others suggested migration, disease, over-farming, or a combination of these factors.

The sediments from the Cariaco Basin off the coast of Venezuela contained seasonal layers of titanium deposited into the basin by local rivers – making the amount of the titanium an accurate indicator of regional rainfall.

Previously, archaeologists estimated the years when Maya cities were abandoned by analysing the last dates carved into the local monuments. Professor Haug found a remarkable match between this archaeological evidence and the dates of the worst periods of drought estimated from the lowest levels of titanium in the Carioca Basin.

Water was an important natural resource for the Mayan people– they went to great effort to collect rainwater in cisterns and to build an extensive network of canals and irrigation channels.

For small villages, a relatively short drought of even a few years would not perhaps have caused mass deaths but for a large urban centre with a dense population such droughts could easily prove terminal, Professor Haug said.

Decline and fall - end of great empires

Lost civilisations and abandoned cities are the stuff of historical fiction but there are many true-life examples. The monument of Great Zimbabwe, right, is the most famous stone building in southern Africa. It is thought to have been built over a period beginning in 1200 and ending around 1450 but not everybody agrees on who was responsible. The most likely are the Karanga people.

For hundreds of years the lost city of Angkor Wat, left, in present-day Cambodia, was legendary. Peasants told French colonists of "temples built by gods or by giants". Stories told of a lost civilisation but archaeologists realised the city was the centre of a Cambodian civilisation, built more than 2,000 years ago but abandoned after invasion by the Thais.

The mystery of the huge statues on the Easter Islands, right (now called Rapa Nui), can also be explained by the rise and fall of a "lost" civilisation. When people first arrived on Rapa Nui, they quickly exploited the palm forests and planted banana trees and taro root. The population flourished until the 17th century but the depletion of natural resources led to a severe fall in numbers, raising questions over who was responsible for the statues and how they were moved to these remote islands.   14 March 2003 23:09

story.news.yahoo.com Thu Mar 13, 5:27 PM ET Add Science - AP to My Yahoo! By PAUL RECER, AP Science Writer

WASHINGTON - A study of southern Caribbean sediments suggests that a centurylong dry trend may have been the killing blow in the demise of the Mayan civilization that once built pyramids and elaborate cities in Mexico.

Konrad A. Hughen, a geochemist at the Woods Hole Oceanographic Institution, said sediments from the Cariaco Basin in northern Venezuela clearly record a long dry siege that struck the entire Caribbean starting in about the seventh century and lasting more than 100 years.

Within this dry period, said Hughen, there were years of virtually no rainfall. It was in those periods of extra dryness, he said, that the Mayan civilization went through a series of collapses before its final demise. Hughen is co-author of a study appearing Friday in the journal Science.

The Cariaco Basin is on the southern Caribbean; the Mayan lived for about a thousand years on the Yucatan, now part of Mexico, on the northwestern edge of the Caribbean. Hughen said both areas share the same climate, with a wet season and a dry season, so the dry trend detected in the Cariaco Basin sediments is thought to reflect the same climate experienced on the Yucatan.

Hughen said the Maya flourished in what is known as the pre-classic period before 700 A.D., building cities and elaborate irrigation systems to support a population that soared above a million. The civilization collapsed and many of the sites were abandoned early in the 800s. They were later reoccupied only to collapse again, with some cities deserted in 860 and others in 910.

"Those abandonments occur synchronously with the timing of the droughts in our record (from the sediments), suggesting the droughts were causing those events," said Hughen.

The sediment records show that the gradual drying started about 1,200 years ago, but there was still enough rain for the Mayans to flourish.

"They were still getting rain, but clearly it was less than their grandparents did," said Hughen. "Then, all of a sudden, there were periods of nine, three and six years when there were very dry conditions."

He said the populations were already stressed by a trend of sparse rainfall and the "exceptionally severe" periods were enough to cause the collapses.

"A severe event didn't have to be long" to force the Mayans to abandon some sites, said Hughen. "Each one of those dry events resulted in the collapse of a certain portion of the Mayan population."

A severe dry spell in 910, he said, "was the last straw."

Mayan communities in the southern and central lowlands collapsed first, while those in the northern highlands lasted for another century before the final collapse.

"The northern areas had access to more ground water resources," said Hughen. "They were able to weather the first and second dry periods, but not the third."

T. Patrick Culbert, a professor emeritus at the University of Arizona and a noted authority on the Mayan culture, said the climate study offers a plausible explanation of what happened to the Mayans.

"They were so vulnerable that anything could have knocked them over," said Culbert. "If there were these severe droughts, it would have been a disaster for them."

Takeshi Inomata, an associate professor at the University of Arizona who studies early American civilizations, said the study by Hughen and his colleagues supports other studies linking climate to the Mayan collapse. There could have been other contributing causes, he said.

"The general climate problems may have contributed to the Mayan collapse, but that isn't all that we need to consider," Inomata said. "It may have been more complex than that."

On the Net: Science: www.sciencemag.org

news.nationalgeographic.com Stefan Lovgren for National Geographic News March 13, 2003

With their awe-inspiring architecture and sophisticated concepts of astronomy and mathematics, the Maya were undoubtedly among the great ancient civilizations of Mesoamerica. At the peak of their glory, around 800 A.D., the Maya ranged from Mexico's Yucatán peninsula to Honduras.

Then, almost in an instant, a society of some 15 million people imploded, leaving deserted cities, trade routes, and immense pyramids in ruins. The sudden demise is one of the greatest archeological mysteries of our time. What caused the collapse of the great Maya civilization?

The Castillo pyramid, built by the Maya possibly as early as A.D. 618, has four stairways totaling 365 steps, which may represent the days in a year.

The answer, say researchers, is climate change. According to a new study published in the current issue of Science, a long period of dry climate, punctuated by three intense droughts, led to the end of the Maya society. "Climate change is to blame for one of the most catastrophic collapses in human history," said Gerald Haug, a professor of geology at the University of Potsdam, Germany, and one of the study's authors.

Identifying the Culprit

The drought hypothesis is not new. Sediments taken by scientists in 2001 from a lake on the Yucatan peninsula showed that a series of extended droughts coincided with major cultural upheavals among the Maya people.

But the study of that lake also found man-made effects, such as deforestation and soil erosion, and therefore didn't reflect a "pure climate signal," according to Haug. For the new study, the scientists instead analyzed sediment core from the Cariaco Basin off northern Venezuela, where the record is cleaner.

Identifying annual titanium levels, which reflect the amount of rainfall each year, the Swiss and U.S. researchers found that the pristine sediment layers in the basin formed distinct bands that correspond to dry and wet seasons. According to the scientists, there were three large droughts occurring between 810 and 910 A.D., each lasting less than a decade.

The timing of the droughts matched periodic downturns in the Maya culture, as demonstrated by abandonment of cities or diminished stone carving and building activity.

Experts say the Maya were particularly susceptible to long droughts because about 95 percent of their population centers depended solely on lakes, ponds, and rivers containing on average an 18-month supply of water for drinking and agriculture.

Reading the Sun

The Maya were skilled astronomers who constantly followed the movements of the sun and the moon. They predicted eclipses, explained the movements of planets, and devised a sophisticated calendar of the solar year.

Scientists have found that the recurrence of the drought was remarkably cyclical, occurring every 208 years. That interval is almost identical to a known cycle in which the sun is at its most intense every 206 years. Nothing suggests the Maya knew anything about the sun's change in intensity.

The drought theory is still controversial among some archeologists who believe a combination of overpopulation, an internecine struggle for control among the nobles, a weak economic base, and a political system that didn't foster power-sharing led to the Maya's collapse. One hypothesis suggests the Maya people themselves were responsible for their downfall as a result of environmental degradation, including deforestation.

Defenders of the climate change theory, however, say the droughts sparked a chain of events that led to the demise of the Maya. "Sunny days, in and of themselves, don't kill people," said Richardson B. Gill, author of The Great Maya Droughts: Water, Life, and Death. "But when people run out of food and water, they die."

Living on the Edge

In their twilight days, the Maya were a society in deep trouble, according to the authors of the new study. Densely populated cities strained resources. Agricultural production became crucial in order to feed the people. "They were living on the absolute edge," said Hoag.

While the Maya had learned to live with shorter droughts, the study indicates that a more subtle, long-term drying trend was ongoing during the collapse. The three specific droughts may have been what pushed the Mayan society over the edge.

"Not only did the Maya have to face an intense climatic catastrophe, but the duration was something that they had never experienced before," said Hoag. "If they had stayed for another two years, they may have survived. But how could they know that the drought would end?"

Learning from the Past

Other human societies have succumbed to climate swings. In Mesopotamia, a canal-supported agricultural society collapsed after a severe 200-year drought about 3,400 years ago. With wetter conditions, civilizations thrived in the Mediterranean, Egypt, and West Asia. Ten years after their economic peak in 2,300 B.C., however, catastrophic droughts and cooling hurt agricultural production and caused regional collapse.

Other societies, however, have survived past climate changes by changing their behavior in response to environmental change. About 300 years after the Mayan collapse, the Chumash people on California's Channel Islands survived severe droughts by transforming themselves from hunter-gatherers into traders.

Experts say the Maya collapse could serve as a valuable lesson today to societies in Africa and elsewhere that are vulnerable to droughts. When droughts strike, they can trigger a chain reaction beginning with crop failures, leading to malnutrition, increased disease and competition for resources, and ultimately causing warfare between nations and sociopolitical upheaval.

"We can handle climate change if we're prepared for it," said Hoag. "The Maya were not prepared."

www.newscientist.com The World's No.1 Science & Technology News Service  19:00 13 March 03 NewScientist.com news service   The Mayan civilisation of Central America collapsed following a series of intense droughts, suggests the most detailed climatic study to date.

The sophisticated society of the Maya centred on large cities on the Yucatán peninsula, now part of Mexico. Their population peaked at 15 million in the 8th century, but the civilisation largely collapsed during the 9th century for reasons that have remained unclear to this day.

Now, researchers studying sediment cores drilled from the Cariaco Basin, off northern Venezuela, have identified three periods of intense drought that occurred at 810, 860 and 910AD. These dates correspond to the three phases of Mayan collapse, the scientists say.

Furthermore, the entire 9th century suffered below average rainfall, "so it was a dry period with three intense droughts", says Gerald Haug, from ETH in Zurich, Switzerland, who led the research. "The climate change must have been what pushed the Mayan society over the edge."

Experts on the Maya have greeted the new data cautiously. "Any explanation for decline is a complex one: over-population, environmental problems and economic factors all made them vulnerable," says Jeremy Sabloff, director of the Museum of Archaeology and Anthropology at the University of Pennsylvania. "But there is growing evidence that climate played a role. Perhaps it was the straw that broke the camel's back."

Wet and dry

Haug and his colleagues identified the bands in the sediment cores that correspond to the annual wet and dry seasons. They then analysed the concentration of titanium in the sediment in great detail, taking measurements at intervals of 50 micrometres.

Titanium is an indicator of rainfall, explains Haug, because higher precipitation washes more of the metal from the land into the ocean floor sediments. The difference in concentration between the wet and dry season each year is as much as 30 per cent.

"We looked in detail at the period corresponding to 9thand 10thcenturies - taking 6000 measurements per 30 centimetres of sediment - and found three extreme minima, as well as a low background level of that lasted about 100 years," Haug told New Scientist.

Latest and greatest

But archaeologist Norman Hammond, at Boston University, is unconvinced that drought caused the downfall of the Maya. He notes that the northern Yucatán city of Chichén Itzá was not abandoned until the 13th century.   "Why did the latest and greatest fluorescence of the Mayan series occur in the area that we know to be the driest," he asks.

The Maya certainly had hydraulic expertise, Jeremy Sabloff points out, building canals, viaducts and reservoirs. Moreover, they had experienced and survived droughts before.

"The Maya thrived for 1500 years before these droughts, so it's clearly not climate alone that brought down the southern cities of the Yucatán peninsular," he says.

Journal reference: Science (vol 299, p 1731)

Gaia Vince

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