Air Date: Week of December 5, 1997
Abrupt and dramatic climate change destroyed some ancient civilizations. And scientists warn that history could repeat itself. Reports about global warming often talk about temperatures rising gradually during the next century. The idea of slow change leads many people and politicians to assume there will be time to adapt to warmer and wilder weather, changes in farming and shoreline erosion. But, what if that assumption is false. What if climate change happens quickly? And unpredictably? That's what some scientists worry about. A recent collaboration between climatologists and archeologists shows that rapid climate change brought down earlier civilizations. And as Living On Earth contributor Bob Carty reports, those scientists wonder if today's global warming might do the same to us.
KNOY: Reports about global warming often talk about temperatures rising gradually during the next century. The idea of slow change leads many people and politicians to assume there'll be time to adapt to warmer and wilder weather, changes in farming, and shoreline erosion. But what if that assumption is false? What if climate change happens quickly, and unpredictably? That's what some scientists worry about. A recent collaboration between climatologists and archeologists shows that rapid climate change brought down earlier civilizations. And, as Living on Earth contributor Bob Carty reports, those scientists wonder if today's global warming might do the same to us.
CARTY: If you want to look into the past, to predict the climate of the future, one of the best places to start is right here. In a parking lot.
[Car wheels to a stop]
CARTY: A parking lot at the University of New Hampshire, in the town of Durham. Here, beside the Earth Sciences Building, you can find a big white refrigerated van.
MAYEWSKI: It's a 12-by-40 freezer that contains about 600 meters of ice from different parts of the world--Antarctica, the Arctic, Asia. Some of the ice in here is 250,000 years old, and some of it goes right up to the present.
CARTY: His students call him "Dr. Ice." He prefers, Paul Mayewski, director of the Climate Change Research Center, at the University of New Hampshire. The van in the parking lot contains just a small sample of the ice Professor Mayewski has collected from around the world. It is his "Archive of the Earth's Past," and perhaps, its future.
MAYEWSKI: We're going to, just put on heavy winter gear, polar boots, and coveralls, and if we pull out one of the ice cores, we would need to put on plastic gloves and masks over our faces to keep from contaminating the cores.
[Zipping up coveralls]
CARTY: Inside the freezer, there are wooden racks, loaded with hundreds of silver tubes. The tubes contain ice cores that have been drilled out of glaciers and ice sheets. It's like drilling for oil. The ice comes out in long cylinders, 4 inches thick, like thin lamp poles. And then they're cut into manageable yard- long sections, wrapped in plastic, and stored in these silver tubes. Some of the ice here comes from Greenland, where Paul Mayewski's team drilled a core almost 2 miles deep, and a quarter of a million years back in time.
MAYEWSKI: An ice core is about as close as we think you can come, to a time machine. The snow does this because it actually captures the gases, and the dissolved chemistry, and the particles that are in the atmosphere. That snow layer gradually gets compressed under more snow layers, and the whole record is a series of pages, one plastered right on top of the other.
CARTY: And Paul Mayewski wants to turn a few pages for me. He first pulls out some "baby ice," ice formed in just the last few decades.
[Plastic gloves being put on]
CARTY: It looks like a tube of tightly packed snow. Conductor Mayewski points to the middle.
MAYEWSKI: Right about here we'd find the evidence of the Chernobyl nuclear accident. We've also found evidence of that same accident all the way down to the South Pole, demonstrating that what we put into the atmosphere can travel long, long distances. Further back down, we find a lot of the bomb layers, from the atomic bomb testing, from the 1950's.
[More crinkle of plastic ice-protecting gloves]
CARTY: The next piece of ice we look at comes from the South Pole. It's from a depth of 20 yards, and under a century of pressure, it has turned into a tube of hard, white, hockey rink ice. In this sample, Paul Mayewski and his colleagues found a layer of dust, from an event of natural origin.
MAYEWSKI: The Tambora volcanic eruption of 1815. In areas like eastern North America, there was no summer in 1815, because there was so much sulfuric acid in the atmosphere that it actually shielded incoming radiation. Interestingly enough, that's also the summer that Mary Shelley wrote "Frankenstein," and a lot of people believe that it was such a depressing summer in Europe when she was spending that summer with Keats and Byron, that she was prompted to write this terrifying novel.
CARTY: One of the discoveries from all of this ice, may itself be a bit terrifying. Until recently, scientists believed that the Earth's climate has been relatively stable since the last Ice Age, 11,000 years ago. Climate has changed, but not that often. Not too fast, and not too much. Mayewski's ice has sparked a little revolution in that thinking.
MAYEWSKI: What we now understand, is that changes in climate operate extremely fast. They may occur in less than 10 or 20 years. And these changes, once they occur, in some cases are 10 degrees centigrade, or more, shifts in temperature. If we experience something like that within 10 to 20 years, we would see major disruptions in the way we live.
CARTY: Paul Mayewski is worried about the future, because of what he sees in the past. Ice core research has led historians, and archeologists, to new insights about past civilizations. Professor Mayewski pulls out a core of beautifully clear ice from about 3,000 years ago.
CARTY: It's a piece of the puzzle of human history.
MAYEWSKI: This particular piece of ice comes from our program in central Greenland, and it happens to contain a very interesting section of history. It documents a 2200 BC collapse of the Mesopotamian Empire.
CARTY: To find out what some old, frozen water has to do with Mesopotamia, you have to shift from ice experts to archeologists.
WEISS: The world's first cities and states evolved in southern Mesopotamia, around 3,000 BC, what is today Iraq and northeastern Syria.
CARTY: Henry Weiss is a professor of Near-Eastern archeology at Yale University, and an expert on the rise and fall of what was humankind's first great civilization, the Mesopotamian Empire.
WEISS: Cities were characterized by monumental public works, such as the famous ziggurats, pyramids constructed of mud brick. As well as monumental public buildings, housing, administrators, kings, and their bureaucrats, with all sorts of craft specialists, such as scribes, potters, leather workers--this imperial realm suddenly collapsed, at 2,200 BC.
CARTY: The question for Professor Weiss is, how do you explain that? Historians usually explain the collapse of a civilization as the result of warfare, or class rebellion, religious crises, or unsustainable economies. But in the case of Mesopotamia, the truth appears to be closer to the words of the poets of the time, who wrote a lamentation called, "The Curse of Akkad ."
[Swelling Middle-Eastern music]
WEISS: "The large fields and acres produce no grain. The watered gardens produce no honey and wine. The heavy clouds do not rain. On its plains, where grew fine plants, only lamentation weeds now grew."
CARTY: Drought. The Mesopotamian Empire collapsed because of a drought, that came upon them quickly, and lasted for hundreds of years. Scientists have now found evidence of that drought not only in ice cores, but also in lake and ocean sediments. What caused the drought is not known, but its impact was sweeping.
WEISS: Agriculture, essentially, collapsed. Populations were forced to abandon the region. Societies from Greece to Pakistan all found it impossible to sustain their previous forms of social and political organization. This suggests this 2,200 BC event is not only hemispheric, but is in fact, global. Which, of course, then brings us to a rather startling observation, that in fact, there has been a series of abrupt climate events, which have had rather considerable impacts upon human civilizations.
[Whirr of an ice core saw]
CARTY: Back in the freezer in New Hampshire, Paul Mayewski is cutting through a piece of ice from a glacier on Mt. Everest, to take to his lab for further study.
MAYEWSKI: We measure, literally, every different part of this core. The ice, which we melt down to water, we measure the air content, which is largely within the bubbles. We can measure up to 50 different environmental parameters. These range from greenhouse gases, CO2 and methane, to the dissolved chemistry in the atmosphere, which tells us about volcanoes, forest fires, intensity of storms on land and over the ocean. It tells us a tremendous amount.
CARTY: One thing it can tell us it the climate report for about 1,000 years ago. It was warm enough then for vineyards in Britain, and sheep herds in Greenland. And in what is now Guatemala and Mexico, there was a protracted drought. There is growing evidence that that drought was responsible for the much- debated collapse of the Maya Empire. And in South America, one of the greatest civilizations, came to a sudden end.
KOLATA: The people of Tiwanaku, in the period from about AD 400 to 1,000 AD, really controlled huge area of the Lake Titticaca basin, down to the coasts of Peru and Chile, down south to northwest Argentina, an area that's somewhat larger than the state of California.
CARTY: Alan Kolata is a professor of anthropology at the University of Chicago, and one of the world's leading experts on the Tiwanaku Empire. The Tiwnaku lived on the high plateaus of what is now Bolivia and Peru, and some of their achievements surpassed those of the Aztecs, the Mayas, and the Incas.
KOLATA: You look at the remnants, the temples and so forth, you find extraordinary feats of labor in which some of these stones, individual stones, weigh as much as 160 tons. And again, recall that this is up at 14,000 feet.
CARTY: At 14,000 feet, the Tiwanaku developed productive irrigated agriculture. Canals for water and sewage. Their roofs were adorned with gold. Then, around 1,100 AD, they abandoned their cities, and descended to the jungles of the Amazon. Professor Kolata explains it with evidence from an ice core taken from an Andean glacier. The Tiwanaku collapse was due to a dramatic climate change.
KOLATA: Within a relatively short period of time, perhaps as short as 50 years, Lake Titticaca dropped anywhere between 15 to 18 meters. Now, this is an enormous lake, sort of almost equivalent to one of our own North American Great Lakes, so you can imagine what it would be like if 45 feet of the lake essentially drops. And that's directly related to this drought, the proportions of which are unprecedented.
CARTY: And it now appears that drought also caused the decline of the Pueblo Indians of the American Southwest, and the abandonment of the villages of the Great Plains Indians, from Iowa to Colorado. All of which leads archeologist Alan Kolata to reflect on parallels for today. Kolata notes that climate change surpassed the Tiwanaku's ability to adapt within their existing political and social structures.
KOLATA: People did adapt, they did not disappear, but they did have to change how they lived. They no longer lived in splendid cities, so there is a morality tale here, in that sense, that we can't be so presumptuous that technology, any technology that we can invent will somehow automatically save us. It's not as if this is something that happened in the past, and may never occur again. The assumption here is that it will occur again.
[Ice saw whirring, slicing more ice]
CARTY: Back at the University of New Hampshire, Paul Mayewski agrees. Based on his study of climate changes of the past, he's certain there will be abrupt and dramatic natural changes in the future. But he's also worried that greenhouse gases, produced by humans, may be the trigger for equally perilous changes. That fear is founded in what scientists understand, and don't understand, about feedback loops in climate systems: how one change can set off another, and the whole climate system snowballs.
KOLATA: At different times, different things trigger changes in climate. Is it possible that these tremendously increased rates of greenhouse gases in these very high magnitudes are a new kind of trigger to climate change? I think the answer is yes. There's a very strong possibility.
CARTY: Still, some will argue that the past is not prologue, that our technologies are far more sophisticated today, that surely, we can adapt. Maybe, but only maybe, says James McCarthy. McCarthy is the co-chair of the group studying the impact of global warming for the United Nations Intergovernmental Panel on Climate Change.
MCCARTHY: Some of the changes occurred in the past, we might be able to minimize the effects of. Although if it happens suddenly, as we saw in Chicago a couple of summers ago, vulnerable segments of society, namely the elderly, the ill, the very young, will suffer, with massive mortality. If you look at the situation in a nation like North Korea, 3 years ago they had a century-scale drought. Two years ago, a century-scale drought. This past year, a century-scale flood. Today, there is massive loss of life from famine.
[Door shuts. Man's voice: "A little nicer out here."]
CARTY: As we leave the sub-zero temperatures of the ice freezer, the relatively warmer environment outside is a relief. The possible climate changes of our future are not so comfortable. Like many societies before ours, we may soon have to modify our social and economic and political systems in the face of uncertain climate challenges. The difference this time, is that the challenge is of our own making. In Durham, New Hampshire, I'm Bob Carty, for Living on Earth.
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