Mystery Collapse of Ancient Tibetan Civilization Solved

Scientists have solved the mystery of the collapse of an ancient civilization living on the fringes of the Tibetan Plateau around 2,000 BC, and it seems that climate change is to blame.

That's at least according to a new study published in the journal Proceedings of the National Academy of Sciences, which details how cooling global temperatures at the end of the Holocene Climatic Optimum - a 4,000 year period of warm weather - would have made it impossible for these ancient people to cultivate millet, their primary food source.

Until now, scientists were left wondering why this Tibetan society died out, and also why the area's original inhabitants either left so abruptly or changed their lifestyles. This study may have finally given them the answer.

The results also help explain the success of farmers who practiced wheat and barley agriculture in the region 300 years later.

Unlike millet, wheat and barley don't require a lot of heat to survive and are highly tolerant to frost. This makes them ideal crops for the harsh environment of eastern Tibet, which is located at a high altitude and thus experiences frigid weather. These crops were introduced to the region around 1700 BC, after which time they may have become important sources of sustenance.

"Wheat and barley came in at the opportune moment, right when millets were losing their ability to be grown on the Tibetan Plateau," lead author Jade D'Alpoim Guedes, from Washington State University, said in a press release. "It was a really exciting pattern to notice. The introduction of wheat and barley really enabled Tibetan culture to take the form it has today, and their unique growth patterns may have played a crucial rule in the spread of these crops as staples across the vast region of East Asia." (Scroll to read on...)

Researchers had previously believed that the Tibetan Plateau's climate around 2,000 BC was actually favorable to millet, due to its shorter growing season compared to wheat or barley. So they were surprised to find lots of ancient wheat and barley seeds at the study sites, hinting that the crops rapidly replaced millet as the staple food source.

To get to the bottom of the mystery, Guedes' team used a new study model that was able to determine whether crops can grow in cold, high altitude environments like the Tibetan Plateau. They included total growing degree days or the accumulated amount of heat plants need over their lifetime rather than the length of a growing season.

"It revealed that global cooling would have made it impossible to grow millet in the Eastern Tibetan Highlands at this time but would have been amenable to growing wheat and barley. Our work turned over previous assumptions and explained why millet is no longer a staple crop in the area after 2000 BCE," Guedes concluded.

Ironically, while the Tibetan Plateau may have been too cool for millet way back when, current climate conditions may be just right for it to make a comeback in the region.

Today, the region is one of the areas experiencing the most rapid climate warming on the planet. There are some areas in the southeastern plateau where temperatures are 6 degrees Celsius higher than they were 200 years ago.

"Right now, these millets have almost become forgotten crops," Guedes said. "But due to their heat tolerance and high nutritional value, they may be once again be useful resources for a warmer future."

So now that researchers have solved the mystery of the collapse of this ancient Tibetan civilization, it may come in handy for those people living there today. Currently, the region's inhabitants are having a tough time growing cold weather crops and raising and breeding yaks, which are also a staple food resource in the central Asian highlands. Their survival is once again endangered, but thanks to this study and the possible return of millet, they just may make it through this time.

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