Climate change threatens nation's largest archaeological site

 

When we think about what’s at stake with climate change, we usually imagine impacts to our current way of life. But as a new report from the Union of Concerned Scientists points out, our shared human history is at risk of being wiped away as well. Colorado’s Mesa Verde National Park – the largest archaeological preserve in the U.S., with some 500,000 visitors a year – is among 30 sites profiled in the report, which puts a spotlight on the impacts of climate change on the nation’s landmarks. The park’s abundance of archaeological sites have already been pummeled by fire and erosion, which are increasingly fueled by climate change; and archaeologists fear sites will be destroyed before they can be studied, or even discovered.

Mesa Verde’s history goes back centuries, to around 600 C.E. when the once-nomadic Ancestral Puebloans settled in the southwest corner of what’s now Colorado. They built pueblos atop Mesa Verde, a limestone and sandstone plateau set among an ecosystem that varies dramatically from low elevation shrub-steppe and sagebrush, to piñon-juniper forests, to mountain shrubs, to Douglas fir and Ponderosa pine at the highest elevations. After a few hundred years, the Puebloans descended into canyons and built multistory homes of sandstone, wooden beams and mortar under the shelter of cliffs. But less than a century after constructing the cliff dwellings, they abandoned Mesa Verde and headed south to settle in what’s now Arizona and New Mexico, leaving behind nearly 5,000 well-preserved archaeological sites that represent the cultural heritage of tribes native to the region and the remains of some of North America’s most fascinating early human settlements.

At least 30 of the nation's most important landmarks are at risk from climate change, according to a new study. Image courtesy of the Union of Concerned Scientists.

Fast-forward 700 years. Summer temperatures in Mesa Verde, the report says, have gradually risen over the past 50 years, and at a faster rate than during the previous century. The story is similar across the Southwest, and it’s driving an increase in wildfire in the region, the report says: as average temperatures have risen, the number of 1,000-acre-plus wildfires in the West has increased from a yearly average of 140 between 1980 and 1989, to 250 per year between 2000 and 2012; and fires burned 300 percent more acreage from 1987 to 2003 than they did from 1970 to 1986. The upward trends are expected to continue.

The risk of climate-change-induced wildfire in Mesa Verde is compounded by a century of fire suppression that allowed the largely piñon-juniper forest to grow denser than its natural state. And increasing temperatures and declining precipitation, the report says, have dried and weakened the forests, leaving the area more vulnerable to fire.

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The map shows the acreage burned by wildfire over the years in Mesa Verde. Image courtesy of the National Park Service.

Mesa Verde has already seen its share of damaging wildfire – 12 fires larger than 30 acres have burned since 1906. Back-to-back fires in summer 2000 burned nearly half the park’s 52,000 acres, destroying trees and vegetation, staining the landscape with the red dye of fire retardant slurry, and peeling away surface sandstone layers with its intense heat, damaging petroglyphs. Wildfire has also exposed hundreds of previously undiscovered archaeological sites and artifacts, at least 676 by 2007 – like pueblos, pottery kilns, ceramics and masonry stones – leaving them vulnerable to the erosion and flash floods that can occur on fire-scarred landscapes. Of course, fires and floods have always had an effect on historical sites like these, but as the report notes, the threats are only getting worse.

If there’s a bright side, it may be that all of that fire catalyzed new preservation techniques in Mesa Verde. After the 1996 Chapin 5 Fire, archaeologists began using natural matting and silt logs to slow runoff and placing burned logs on slopes above cliff dwellings to prevent water from eroding the structures, and applying silicon to cliff faces to redirect water’s natural flow downward. These techniques have been largely successful.  In New Mexico’s Bandelier National Monument, the 2011 Las Conchas Fire, the largest in the state’s history spurred new post-fire archaeological preservation techniques as well.

These are the lessons we should continue to learn from a warming world, the report tells us: our cultural heritage must be protected before it's rubbed out by climate change.

Christi Turner is an editorial intern at High Country News. She tweets @christi_mada.