Between 880 and 1250 A.D., climate change allowed Europe to thrive while the Mayan civilization collapsed. In the 1400s, another climate shift led to torrential rains and crop failure in Europe, starving 1.5 million people.

Throughout history, some civilizations weathered cold and hot spells, droughts and floods, while others were devastated. A number of researchers are trying to understand why.

"Climate change goes back at least 400,000 years," said Brian Fagan, an emeritus anthropology professor from the University of California, Santa Barbara, "but until 10 years ago, nobody studied the impacts on ancient civilizations."

Tonight at 7:30, Fagan and other historians, anthropologists and archaeologists will discuss their ideas about climate change in a public lecture at the University of Pennsylvania Museum of Archaeology and Anthropology.

Climate scientists expect something more disruptive and unpredictable than a smooth warming around the world. The coming years will likely parch some regions and soak others, just as climate changes did in the past.

Fagan, author of

The Little Ice Age

and

The Great Warming

, said his research had led him to appreciate the complexities of climate changes. "People have no idea of the challenge of drought we face," he said.

During the so-called Little Ice Age, he said, the biggest problem wasn't cold but storminess. Not only did floods ruin crops and cause famines, he said, but also a storm surge in 1433 killed 100,000 Europeans in low-lying areas. Later in that cold period, storms destroyed the Spanish armada.

Climate has worked its way into the fields of archaeology and anthropology in the last 20 years as climatologists have found ways to precisely measure weather from past eras, Fagan said. Much of that information comes from ice cores taken from Greenland and Antarctica.

There, researchers have drilled more than two miles into the ice caps to reconstruct more than 110,000 years worth of climate history.

To read these natural records, climatologists measure the texture and composition of ice at different layers and sample pockets of ancient air left in tiny bubbles.

The Penn Museum's director, Richard Hodges, specializes in ancient Rome - a civilization whose course was altered by several climate convulsions triggered by volcanic eruptions. An eruption around 530 A.D., for example, left a veil of dust in the air. Crops failed and economic turmoil followed for a decade.

"That tipped some communities over the edge," Hodges said. But at the same time, the problems in Rome allowed Anglo-Saxon communities to spread south.

"One person's pain turned out to be another person's gain," Hodges said.

The Medieval Warm Period, from 880 to 1250, brought a combination of gain and pain, too, with the pain catastrophic for the Mayans in tropical Mexico. Political and economic changes made them more vulnerable to the climate shift, which nearly destroyed them, University of Cincinnati anthropologist Vernon Scarborough said.

Mayan civilization had prospered for 1,500 years in a region that's still nearly uninhabitable, he said. "They had a good run" thanks to a very different social structure from that in the West.

Because of the tropical climate, Mayan cities had just a tenth of the population density of their European counterparts. The climate made storing food and getting rid of waste hard, so people spread out and became extremely organized in moving resources around. "They had to invest in things like schedules and calendars and road systems," Scarborough said.

People spread out through the countryside, and population grew slowly.

But by around 700, Scarborough said, the Mayans started to change their ways of life, growing denser cities and adopting "steep, pitched hierarchies" in which a few people concentrated power and resources.

Severe droughts then hit them between about 740 and 900, after which the population crashed below a tenth of its peak. Fields filled with sediment, and swamps reclaimed the towns.

Advances in technological sophistication in our own time can be misleading, said Santa Barbara's Fagan. "The most fascinating thing about all of this is not that we've learned how to master climate but that we've become much more vulnerable to climate change," he said.

Farming, irrigation, sewers and modern medicine allow our cities to accommodate millions of people, "but we are infinitely more vulnerable because we cannot move."

Besides the impending climate threat, Scarborough said, "we have an economic system out of balance."

"Technology can do some marvelous things," he said, "but one more widget is not going to bail us out."

Contact staff writer Faye Flam

at 215-854-4977 or fflam@phillynews.com.