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This morning's chapter in Climate Connections, our series with National Geographic, takes us back hundreds of years. We're time traveling to some once thriving villages in what's now Southwestern Colorado. Scientists say that the fate of the farmers who lived in these villages shows how devastating climate change can be. What's more, the plight of these ancient farmers may have something to do to teach us today.

NPR's Elizabeth Shogren reports on the lessons we've learned and the lessons we're still learning from those who came before us.

ELIZABETH SHOGREN: Kristin Kuckelman guides me down the sandy trail. Pass sweet-smelling juniper and sagebrush. We're headed to an ancient village.

Ms. KRISTIN KUCKELMAN (Archaeologist): Okay. Why don't we come down here.

SHOGREN: Kuckelman is an archaeologist. She's been digging here at Goodman Point Pueblo for three years. The people who lived here more than 700 years ago didn't leave a written record. But Kuckelman thinks the clues they left behind may help solve a mystery that has perplexed archaeologists for more than a hundred years.

Ms. KUCKELMAN: Why did they leave? I think we're finally really making some important inroads into answering that question.

SHOGREN: For several hundred years, many thousands of people lived across the high desert plain called the Colorado Plateau that now stretches into four states. They're called the Ancient Pueblo People or Anasazi. By the late 1200s, all their villages were abandoned.

Ms. KUCKELMAN: It had to have been a pretty important reason to leave and never to come back.

SHOGREN: Kuckelman says she's getting close to figuring out the reason - by sifting through the ancient people's garbage.

(Soundbite of digging)

Ms. KUCKELMAN: In digging in this area, you can see that there is gray, this is ashing material and charcoal and so forth.

SHOGREN: Kuckelman uses the small trowel to dig outside a stonewall that surrounds one of the ancient houses. They're called kivas.

Ms. KUCKELMAN: The people who lived in this kiva periodically collected the refuse from their heart, and from their food, and broken pots and so forth -collected that and climbed up the ladder, walked across their roof and then tossed that refuse out here.

(Soundbite of digging)

Ms. KUCKELMAN: This ash and charcoal contains information about their diet.

SHOGREN: Especially what they ate in the early years of the settlement. She's also sampling ash and bones from the hearths and floors of the kivas. That will show what the ancient people ate in their last days in the pueblo. She suspects she'll find results similar to what she discovered at a nearby village that was built and then abandoned about the same time as Goodman Point.

Kuckelman spent years analyzing the remains from that other village.

Ms. KUCKELMAN: I wasn't particularly looking for anything. At some point, it just sort of jumped out of the data at me.

SHOGREN: And what jumped out was turkeys - turkey bones and lots of them, at least in the garbage from the earliest days of the pueblo.

Ms. KUCKELMAN: The percentage of turkey bones is 96 percent of the identified animal bones. Ninety-six percent, I mean, that's huge. That's huge.

SHOGREN: But only 13 percent of the bones left over from the final days of the pueblo were from turkeys. Most were from wild game. For Kuckelman, this finding is a big deal. She knew that a great drought hit this area in the 1270s. Now, her research shows what that dramatic climate change did to the people who lived here. It destroyed their ability to grow corn to feed themselves and their turkey flocks. And it made them revert to hunting and gathering.

Kuckelman thinks people from other villages were hungry, too. And sometime after 1277, the pueblo was attacked.

Ms. KUCKELMAN: At least 32 people died in that attack and no one lived in the village after the attack occurred.

SHOGREN: There is evidence of similar violence at other pueblos. She believes it's all part of one big story - climate change wiped out the Anasazi's food supply, sparked widespread violence and even cannibalism. So they packed up and left.

Ms. KUCKELMAN: There were too few options and the system fell apart. Wheels came off, they like to say.

SHOGREN: Kuckelman couldn't have come up with this theory if it weren't for the work of scientists who study the growth rings of trees to reveal important secrets about the distant past - like when those kivas where built and when the great drought hit.

(Soundbite of chainsaw cutting)

SHOGREN: I drove five hours northeast to meet up with one of those scientists high in the Rocky Mountains. Connie Woodhouse is a professor from the University of Arizona.

(Soundbite of chainsaw cutting)

SHOGREN: Her team uses a chainsaw to cut slices of old dead trees. They'll take these back to the lab to study them. They also sample rings of live trees. They use a manual tool to do that called a tree borer.

Professor CONNIE WOODHOUSE (Climate Science, University of Arizona): Just look for a place to start and just, sort of, position your increment borer, and then you lean into it a bit so that that borer bites into the bark. And the treads grip it and then once it's in, you just can turn it like that.

SHOGREN: She uses both arms to screw the bit into the tree and then inserts a long, skinny scoop into the borer.

Prof. WOODHOUSE: And then pull out. There's the bark. And there's the rest of the core. You can see the rings. So that's what the core looks like.

SHOGREN: It's the size and shape of a drinking straw. You can make out distinct sections, each holds information about the past.

Ms. WOODHOUSE: The wide rings are wet years and the narrow rings are dry years. And when you put together the information from the tree rings into what we called the tree-ring chronology, it sort of gives us a picture of the variations in moisture in that area where we collected it.

SHOGREN: Woodhouse and her colleagues recently presented an alarming picture of the ancient history of the Colorado River. They sampled the oldest trees they could find — dead and alive — and they used them to estimate stream flows all the way back to the year 762. Their results show that the droughts over the last hundred years weren't as severe or as long as earlier droughts. And in fact, the first part of the 20th century was unusually wet.

Ms. WOODHOUSE: Not only was it wet in the context of 100 years, but there was not a wet period like that for at least 400 years.

SHOGREN: That has major ramifications for people who use the river today because the laws used to divvy up the Colorado River assume that extremely wet period was normal. Woodhouse says the lesson from the tree rings is that longer dry spells, like the one that chased the pueblo farmers from their kivas, could return. Some experts believe they already have.

(Soundbite of running river)

Mr. ERIC KUHN (General Manager, Colorado River District): We're right at the confluence of the Colorado and the Roaring Fork Rivers in Glenwood Springs.

SHOGREN: Eric Kuhn is the water manager for Western Colorado. He brought me right to the point where the two rivers merge. The Roaring Fork is a fast, clear river, but it slows down as it joins the muddier Colorado. Kuhn says the rivers might look big here, but they're flowing at only 70 percent of their normal rate. Other tributaries of the Colorado are flowing at only 40 percent. It's the seventh dry year the rivers had in the past eight years.

Mr. KUHN: The water community now is all hoping that this is a drought. Drought implies things will return to normal someday.

SHOGREN: But Kuhn doesn't think they will. He thinks that the lower river levels over the last several years represent a new, drier normal. And he believes climate change will make the river even drier. With that in mind, Kuhn thinks of the tens of millions of people who rely on the Colorado River - to irrigate fields, wash dishes and shower - should take the experiences of the ancient pueblo farmers seriously.

Mr. KUHN: They obviously didn't have our technology. They didn't have Hoover Dam and Glen Canyon Dam. And then when there was a change in the climate, they could not adapt to it.

SHOGREN: Modern society has lots of technology. But Kuhn says, it also has a thirst for the Colorado that's greater than its supply.

Mr. KUHN: So, I think what the ancients showed us was a microcosm of perhaps what we are in today. But the same thing is going to happen if we're used to a certain amount of water and if that changes only a little bit, it's going to cause some big disruptions in how we deal with life here in the southwest.

SHOGREN: Kuhn says homeowners will get used to cactus gardens instead of lawns. Cities will buy water rights from farmers, and irrigated agriculture — a way of life in the southwest for a century — may disappear, just like the pueblo farmers' turkey flocks.

Elizabeth Shogren, NPR News.

(Soundbite of music)

ROBERTS: You can hear all of our Climate Connections coverage at npr.org/climate.

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