"We are not able to say for sure that climate change was definitely the reason that the Roman Empire and the Byzantine Empire declined, but rather that we now have data that correlates with the hypothesis historians have put forward," Orland said. "We're just adding data to the big pile that's already there."
Scholars have debated for centuries over the causes of those declines, and no doubt much more was at work than just climate change. But some records indicate that trade and agriculture both declined, which could have been caused by droughts. However, many historians also point to high taxes on goods and farmland as a probable cause for those declines.
If weather does turn out to be a significant player, it will not be an isolated incident. North America's Anasazi Indians created impressive "cities" throughout what is now the U.S. Southwest, including six-story apartment complexes that predate the arrival of the first Europeans, and wide roads stretching 200 miles, even though they had no vehicles and no beasts of burden.
But about 1,000 years ago, the Anasazi abandoned their homes, and historians have argued for years over why. Tree rings analyzed at the University of Arizona indicate that the four corners region where the Anasazi maintained their cultural centers, went into prolonged drought, and thus, the Indians fled south to join the Hopis and an easier life.
But that, according to a number of scholars, is probably only part of the reason. Big monuments, built by years of hard labor more than 1,000 years ago, were probably demanded by leaders who perhaps had become more worrisome than drought. The answer as to why civilizations collapse is never as simple as a single cause, although drought has been linked to other collapses in Asia and elsewhere around the world.
The Wisconsin researchers said they weren't trying to resolve that controversy. It just kind of fell into their laps.