A publication of the Archaeological Institute of America
Rising sea levels are eating away at coastal sites, increased rainfall is eroding mud-brick ruins, creeping desert sands are blasting the traces of ancient civilizations, and the melting of ice is causing millennia-old organic remains to rot. "With climate change, we're feeling a sense of urgency," says University of Northern Colorado anthropologist Michael Kimball, who organized a panel discussion on climate change and archaeology at the World Archaeology Congress in Dublin last year. "It definitely focuses the mind."
For countless communities, archaeology can be a source of local identity, pride, and even income. "It may be intangible, but when a community loses its connection to history it loses something pretty important," says Kimball.
The International Panel on Climate Change (IPCC), a group of more than 1,000 experts on climate science convened by the United Nations, estimates that the world's temperature has risen about two degrees in the past century, thanks in part to an increase in carbon dioxide that traps heat in the earth's atmosphere. The consequences have already been dramatic. The world's oceans have risen four inches in that time. Weather patterns have also gotten less predictable and more extreme.
Over the next hundred years, the IPCC predicts that sea levels will rise at least another four inches. The worst-case scenario is truly frightening: a 10-degree rise in global temperatures, causing ice caps to melt and sea levels around the world to rise more than three feet.
Archaeologists can't stop global warming, but they can make dealing with it a priority. That may mean documenting sites before they disappear; in some places, simple steps like putting roofs over melting or rain-threatened areas are ways to preserve them. Action, however, must be taken soon. "Our job is not so much to talk about how to get climate change to stop," says Giovanni Boccardi, the chief of UNESCO's Asia and Pacific Unit. "While climate change is global, lots of solutions are local--and within our reach." What follows is a look at some of the threats facing archaeological sites around the world.
University of Bern archaeologists document artifacts exposed by melting alpine ice sheets. (Courtesy University of Bern)
Retreating Swiss Glaciers
The summer of 2003 was a scorcher in Europe, setting record temperatures across the continent and contributing to the deaths of more than 30,000 people. High in the Swiss Alps, the heat wave melted glaciers and snow, causing severe floods in the valleys below.
On September 17, a hiker named Ursula Leuenberger was crossing an iced-over pass near the Schnidejoch glacier when something odd caught her eye--a leather quiver that had been left high in the Alps by a Neolithic hunter around 2800 B.C.
The following summer, University of Bern archaeologist Albert Hafner organized a team of glaciologists and archaeologists to follow Leuenberger back up the mountain. There they found a five-foot-thick ice patch 260 feet long and 100 feet wide. In just one sunny week, the edges of the ice patch shrank 20 feet. Over the course of two summers, archaeologists found in it everything from prehistoric leather pants and shoes to nails from Roman sandals.
The finds revealed that people have climbed high in the Alps for millennia, despite its harsh conditions. (At Schnidejoch's altitude, the ground is covered in snow nine months out of the year.) "This was just the quickest way from one valley to another," says Hafner. His work also showed that 1,000-year gaps in the ages of the artifacts corresponded with cold periods when glacial ice would have blocked the pass. The fact that fragile organic materials were preserved near Schnidejoch for more than 5,000 years means the ice cover hasn't been this small since the Stone Age. "I think in the next years if there is a hot summer, the ice will disappear completely," says Hafner. "It's obviously related to climate change."
For archaeologists, the melting ice is both a crisis and an opportunity: the artifacts at Schnidejoch never would have been found without climate change, but as more and more alpine ice fields thaw and vanish, countless more artifacts may rot away and disappear forever, along with the icy glaciers and snowfields that define the Alps. Hafner says he has his eye on other sites that are on the verge of thawing. "I'm very happy to find the objects because they will give us new inputs, but I am not happy about the climate change," he says. "I'm an archaeologist, but I'm also an alpinist."
The civilizations that rose and fell in the bone-dry deserts of coastal Peru knew the signs well. When Spanish conquistadors arrived, they noticed its effects around Christmas, and named the phenomenon El Nino, or little boy, after the Christ child. Every seven to ten years, currents in the Pacific Ocean shift, changing weather patterns from Australia to California. In Peru, El Nino means warmer water, and heavy rainfall along the coast.
The difference between a normal and a bad El Nino year can be tremendous. Peru's deserts typically get just over an inch of rain per year. In 1998, the last severe El Nino season, the region was doused with 120 inches, which caused serious flooding. Water takes a heavy toll on exposed archaeological sites, many of which are located along rivers or on easily eroded slopes.
Ironically, archaeologists have made the problem worse. "If we don't mess with the sites, water runs off without doing too much damage," says University of Maine archaeologist Dan Sandweiss. "But if you excavate, that's the end of them, basically." Holes made by looters also channel and trap moisture, doing more damage.
Take Chan Chan, an elaborately planned city eight miles square that dates back 1,000 years. Made of unfired mud brick, Chan Chan's pyramids and palaces were put on UNESCO's list of World Heritage Sites in Danger in 1986 because they were threatened by erosion. Over the past two decades, the site has deteriorated steadily. Researchers are investigating whether global warming could make El Nino occur more frequently. "There's the potential for greater destruction if the pace of El Nino events increases," says Sandweiss.
So far, climatologists can't say for sure what climate change will do to the powerful weather phenomenon. "The models are all over the place," says National Oceanic and Atmospheric Administration climatologist David Enfield. "We're up against a huge uncertainty at present." As climate experts work to refine their predictions, archaeologists anxiously await the arrival of the next El Nino.
Violent wave action is destroying 2,000-year-old sites once occupied by the Thule culture, the ancestors of modern Inuits. (Courtesy Bjarne Gronnow)
Greenland's Melting Sea Ice
In a normal summer, Greenland's northern and eastern coasts should be ringed by an ice belt 30 to 40 miles wide. The drifting ice acts like a shock absorber, dampening the strength of the North Atlantic. "It takes a lot of wave energy to move the ice, and normally water along the coast is very calm," says Danish archaeologist Bjarne Gronnow, of the National Museum in Copenhagen.
But in the past five years, the sea ice has all but disappeared. Without its floating frozen shield, Greenland's coast is being pummeled by storm surges originating hundreds of miles away. When Gronnow visited the region last summer, his team was barely able to land their Zodiac rafts on the beaches because of waves almost 10 feet high.
The effect on the island's heritage has been catastrophic. Hardest hit have been sites associated with the Thule culture, people closely related to the Inuit of northern Canada who first migrated to Greenland around 2,000 years ago. The Thule were formidable hunters and whalers, and their villages were built close to the shore. Today, Thule houses--made of stone and turf with whale-bone rafters--are disappearing quickly, along with buried tools and artifacts. "A meter per season will be tumbled down to the beach and washed away," Gronnow says. "It's not a slow process."
Older sites along the coast are also in danger. As the Arctic warms up, archaeologists fear the frozen turf that covers Qeqertasussuk, a 4,500-year-old settlement where evidence for the earliest settlement of Greenland was found, may be melting. Gronnow--who excavated the remote site for the first time in the 1980s--is headed back this summer, and he is not optimistic. "I've been working in Greenland for 30 years now," he says. "I can see with my own eyes how it has changed."
Andrew Curry is a contributing editor at ARCHAEOLOGY.
Thawing Scythian Tombs
Three thousand years ago, Scythian nomads ruled the Eurasian steppes from the edges of the Black Sea in the west to China in the east. The Greek historian Herodotus reported their exploits as warriors and their drug-fueled religious rituals. The Scythians buried their dead in huge grave mounds that have been rich resources for archaeologists studying how this nomadic culture spread, thrived, and ultimately faded away around 200 B.C.
Though the burial mounds--called kurgans--are found everywhere from Ukraine to Kazakhstan, few are as spectacularly preserved as those in the Altai Mountains on the edge of the vast Siberian permafrost region. Many of these graves have been on ice for millennia, sandwiched between a frozen layer of earth and the insulating grave mound above.
Beginning with Soviet excavations in the 1940s and '50s, archaeologists have found amazingly well-preserved mummies in the tombs, often with their clothing, burial goods, horses, and even stomach contents intact. "Instead of archaeology, the material culture is so well preserved it's almost a kind of ethnography," says Hermann Parzinger, who discovered the tomb of a mummified Scythian warrior in Mongolia in 2006 and now directs the Prussian Cultural Heritage Foundation in Berlin.
But scientists say the Altai Mountains aren't as cold as they used to be. The glaciers that covered the slopes of the Altai are receding and even disappearing. And for the first time since their occupants were buried 3,000 years ago, the Scythian tombs are in danger of thawing out and rotting away. "These tombs are all in an area where the permafrost is just at an equilibrium," says Jean Bourgeois, an archaeologist at Ghent University who works on sites in Russia and Kazakhstan. "Just a degree or two can be enough to [destroy] frozen contents."
Mapping and listing all the region's kurgans using old spy satellite photos and old-fashioned ground surveys is the first phase of an international effort to save the frozen tombs. Bourgeois says the first priority is identifying kurgans that may still have permafrost underneath.
Archaeologists are scrambling to figure out the next step: how to keep the grave mounds cool. Instead of emergency excavations, Bourgeois hopes to work with engineers to find low-cost solutions to preserve the kurgans intact for future researchers. Proposals range from reflecting sunlight away from the kurgans by painting them white to stabilizing the underground temperature by installing "thermo-pumps." But after seeing the region's climate change with his own eyes over the past decade, Bourgeois has come to realize that even in a best-case scenario, archaeologists cannot preserve all of them. "They will have to choose."
Rising sea levels damage shell middens and other remains at sites that are more than 10,000 years old. (Blake Edgar)
Channel Islands Erosion
The Channel Islands off the coast of California are a critical link in the study of how humans settled the Americas. For decades, the consensus has been simple: America's first immigrants crossed the Bering Strait on foot and made their way south, over land through what is now Canada. Many researchers now believe, however, that the first people came to America by boat, island-hopping from Siberia all the way down to the California coast.
Some of the best evidence for this comes from the Channel Islands. "We have in excess of 10,000 years of human occupation," says Channel Islands National Park Archaeologist Kelly Minas (see "Going Coastal" May/June 2007). Evidence from shell middens, rock shelters, and other settlement sites supports the idea that early Americans were good sailors who reached the islands more than 13,000 years ago, hunting pygmy mammoths, elephant seals, and sea lions. Human bones found on Santa Rosa Island in 1959 have been radiocarbon-dated to 13,000 years ago, making them the oldest human bones found in the Americas.
Back then, the world was much colder, and the oceans much lower--low enough that four of the Channel Islands were connected by dry land. Now, rising sea levels are threatening some of the last coastal rock shelters left on the islands. "Erosion is a problem on the islands," Minas says. Coastal winds, waves, storm surges, and even seals hauling out of the water can damage or destroy coastal sites on the islands.
Rising seas now threaten to wipe out clues to how early humans made their way into the Americas just as researchers are beginning to look into the possibility of coastal migration. At Daisy Cave, a sea-side site on San Miguel Island, University of Oregon archaeologist Jon Erlandson has spent a decade excavating a 65-foot-wide midden that the island's prehistoric residents built up over thousands of years. Excavators have found the remains of tools, beads, and even baskets.
But, their work is becoming a race against time. Erlandson says the midden has shrunk by about three feet in the past decade. "If we've lost a meter in 10 years, how much will we lose in 50 or 100?" Erlandson asks. "If this keeps up, we're going to lose an incredible amount of archaeological sites."
Encroaching desert sands threaten the artwork at the 2,000-year-old site of Musawwarat es-Sufra. (Courtesy Seminar of Northeast African Archaeology and Cultural Studies, Humboldt University Berlin)
Local nomads call the ruins Musawwarat es-Sufra, or "Yellow Pictures." More than 2,000 years ago, the kings of the Meroites--a desert kingdom closely linked to ancient Egypt--built a temple complex 20 miles east of the Nile Valley, in what is today Sudan. Built of soft yellow sandstone, the walls and columns of the complex were decorated with hieroglyphs and elaborate reliefs, covered in mortar and colorfully painted. "It was probably the most important pilgrimage site of the Meroitic kingdom," says Claudia Naeser, an archaeologist at Humboldt University in Berlin who is excavating the site's reservoirs and temples.
Musawwarat's centerpiece was the 50-foot-long Temple of the Lion God, carved inside and out with reliefs dedicated to the Meroitic god of fertility, Apedemak. The lion god's temple was once in the middle of a grassland. But warming temperatures and overuse have killed off the area's vegetation, and the Sahara's sands are creeping ever closer. In the 1960s, an earlier Humboldt University mission uncovered and reconstructed the temple's collapsed walls--in retrospect, a mistake. "The reliefs suffer heavily from wind erosion," Naeser says. "The sandstone is relatively soft, and it just abrades."
Musawwarat is far from alone. Desertification is an often-overlooked problem because shifting dunes and blowing sand cover archaeological remains--leading to a misperception that the ruins are being shielded from further damage. "There's this belief that sand is protective. It's not," says Henri-Paul Francfort, a director of research at the French National Center for Scientific Research. "Sand can quickly destroy remains, both because of the weight of dunes and because of terrible winds that erase everything."
The scale of the problem is overwhelming, and solutions--from hardening stone with special chemicals to erecting protective walls or planting trees as windbreaks--are either prohibitively expensive or impossible because of a lack of water. UNESCO is now considering an application to have Musawwarat listed as a World Heritage Site. Soon, however, there may be no more "yellow pictures" to be seen.