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| Seeing Green: Where have all the glaciers gone? |
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By Will Stahl  In 1989 during my first trip to Alaska, my lifelong friend Sam and I drove through a gap called “Redrock Canyon” by his friends. Though the rock was red, this was not a canyon cut by a stream, at least not in our geologic time, but simply a narrow slot between two rock formations that soon widened out into a vast open gravelly expanse. We made camp in a flat place by the truck and I began to look around. In the golden late-day light of a June Alaska evening, it was a beautifully strange place surrounded by snow-spotted mountains. This was the valley of the Cantwell Glacier, and we were camped on its outwash and the random piles of till it had left behind. Our immediate surroundings had clumps of willow and fireweed and other pioneer vegetation that can put roots down anywhere, but up the valley the land was raw and bare. I suddenly realized I had seen land shaped like this in Wisconsin and northern Illinois, only there it was covered with grass and trees. The house I grew up in is built on such land; dig and you find a few inches of soil and then nothing but gravel and rocks. Where was the glacier? From the newness of the vegetation, it was clear it had been here not long ago, but it was nowhere in sight, receded miles up the valley in just a few short years. The braided stream of melt that ran gleaming in the long sunset was the only evidence it was still up there somewhere. This scene is repeating itself all over the world, wherever mountain glaciers flow down their valleys. Glaciers are complex and interesting phenomena. In places where more snow falls in winter than can melt in summer, it accumulates year after year until its weight presses the lower layers into ice. If the weight becomes enough, it begins to flow; the enormous weight causing the lower layers of ice to become plastic, something like toothpaste, and on this the glacier slides downhill. As long as more snow falls than melts, the glacier will continue to flow downhill until it reaches a lower elevation where it is warm enough that, on average, it is melting as fast as it flows. At that point, the glacier is said to be in equilibrium. Its snout will remain at about the same place. If it reaches the ocean, it may advance as an ice shelf, or if it is in equilibrium at that point, it will calve off icebergs. If any part of the equation changes, the place where the glacier reaches equilibrium will also change. More snow and/or a colder climate and the point of equilibrium will be farther downhill. Less snow and/or a warmer climate and the glacier will recede or melt back to a place of equilibrium farther up in the mountains, though the ice will continue to flow downhill. If that place would be higher than the glacier’s source or the amount of snow is decreased enough, the glacier will eventually disappear. The Cantwell Glacier was obviously in retreat, and if it were the only one or one of a few, it would be of no great significance. If glaciers were retreating in a few areas of the world, it might be unimportant. But all over the world, in every mountain range high enough to spawn them, glaciers are in retreat: over most of Alaska, the Rockies of the US and Canada, the Andes, the Alps, the Himalayas, the sub-Arctic islands such as Iceland and South Georgia, and the very highest mountains of Africa. Many of you have read that the glaciers of Glacier National Park will soon be a memory and the snows of Kilimanjaro a literary artifact, but these are only famous examples of a worldwide event. This is not simply a recent occurrence; glaciers have been receding in many places since before the turn of the last century. Between 1950 and 1980, they briefly paused or even advanced as temperatures cooled slightly, but after that they began to retreat again at an ever accelerating rate. Given their global distribution and their close association with recorded CO2 and temperature increases, mountain glaciers present a data set that should be difficult to ignore. Some global warming deniers will point to the indisputable fact that a few glaciers in a few places are advancing. Probably they are responding to some local increases in precipitation. In any case these few have advanced only short distances compared to the many that have receded much farther. The Earth’s climate is so complex it would be more than amazing if everything happened the same way everywhere. Compared to the icecaps of Greenland and Antarctica, mountain glaciers don’t hold that much water. If they all melted completely, it wouldn’t raise sea level more than a few inches. To us in eastern North America, who have no current nearby glaciers, they are chiefly alarm bells. If we are willing to listen, they are one more signal telling us something is changing in the Earth’s climate. To many others on this planet, they are much more immediately important. Some of those others are our fellow Americans who rely on the water stored in the Rockies and Sierras for drinking and irrigation. Parts of the West were settled with the unquestioning trust that these waters would always continue to accumulate in the winter and make themselves available in the summer. That plan seems to have been only hope. Flows in the Colorado and other river systems are diminishing and Plan B is a work in progress. Far more extreme could be the effects on our fellow earthlings in Asia. The headwaters of seven major river systems flow from the Himalayas: the Indus, Ganges, Brahmaputra, the Salween, Mekong, Yangtze and Yellow, the water sources for more than two billion people. Scientists didn’t think Himalayan glaciers were shrinking all that quickly until they climbed into their highest reaches and found that they were shrinking from the top as well as the bottom. Those mountains are so high and cold that their glaciers cannot disappear in any foreseeable future, but any decrease of their discharge would be bad news for those in the lower lands of China, Vietnam, Laos, Cambodia, Thailand, Burma, India, and Pakistan. Mountain glaciers are far more than a red dashboard light for many millions of south and east Asians. Scientists study mountain glaciers in part because they are relatively easy to study. They are limited in size and their sources are obvious. Often the local people have tracked their historical advances and retreats for decades or even centuries. Despite their importance to some populations, mountain glaciers contain only about one percent of the freshwater ice on Earth. The other 99% percent is in the icecaps of Greenland and Antarctica. These contain unthinkable amounts of water. If all the ice on these two landmasses were to melt, it would raise sea level about 230 feet. The Mississippi River would empty into the Gulf of Mexico somewhere around St. Louis. Don’t worry about your old college friends in Baton Rouge or Memphis; if you are alive while I’m writing this, you won’t live to see anything like that happen. I don’t think. Greenland and Antarctica can be thought of as large shallow bowls that fill up with snow that turns to ice as it is buried deeper and deeper by successive winters. Not much snow has to fall because these places have been so cold, very little ever melts. Antarctica is one of the driest places on the planet, hence the t-shirt, “Ski Antarctica: two inches powder, ten thousand-foot base.” That’s right, a two-inch annual snowfall has accumulated to a nearly two-mile thick icecap. The ice in these places is subject to the same dynamics as mountain ice, so when it becomes deep enough, glaciers are squeezed out through the mountains toward the ocean. In Greenland, they have typically calved off the icebergs that have long been a hazard for North Atlantic shipping. Around colder Antarctica the glaciers have fed ice shelves that covered huge bays and extended out to sea. In recent years Greenland glaciers have been accelerating, moving faster downhill and yet retreating, losing some 53 cubic miles of ice per year. The acceleration seems to be caused by meltwater under the ice lubricating its downhill flow. Antarctica had seemed to be more stable, but in recent years its ice shelves have been breaking up, in some cases calving county-sized pieces off into the southern ocean. Without the ice shelves to slow them, the glaciers draining out of the continent have accelerated. What is alarming some scientists is that they predicted these phenomena would occur, but not nearly so soon. Along with the summer melting of the Arctic sea ice, they are foreseeing changes they believed would take until mid-century or beyond occurring in the next few years. They are uneasy because they can’t be sure what kind of feedback loops could arise out of such sudden thawing of lands and seas long under ice. Always this is the problem about making the global warming case to the public; scientists hate to speak in certainties, especially about a system as complex as our atmosphere. It flows and whirls like a bankless river of air, picking up heat from sea and sun and giving it back to ice and land. We know it is subject to long-term major change as evidenced by the Ice Age that left its mark upon Wisconsin. About 70,000 years ago that cold and resulting snow buried much of the continent under ice more than a mile thick in a complex pattern of advances and recessions; then somehow, about 10,000 years ago, it receded “permanently.” Three such periods had preceded this last one, the “Wisconsin Glaciation,” named for its farthest advance. This has all been long known, deciphered from the geologic evidence on the land. In one of Sam’s many careers, he had worked on a project that contributed another kind of knowledge for solving the puzzle of climate. The University of Alaska-Fairbanks had the contract to do the ice core drilling in the center of the Greenland ice sheet. Starting as a carpenter, Sam worked his way to being in charge of logistics for this camp of scientists and technicians, deciding what to bring when on the big cargo planes that landed on the ice. It was a strange, flat, blindingly white world whose inhabitants were there only for the purpose of drilling down into the ice and bringing up long thick cylinders of it that contained in trapped air bubbles the history of the Earth’s atmosphere. Each year appears as a distinct layer and when they reached the earliest years of the “AD” era, they would hold a “Christ-ice” party, dropping into drinks bits of the cores containing air bubbles from when Jesus walked the Earth. By the time the drills reached solid rock, scientists had a good record of the atmosphere’s composition back 650,000 years. Over all those years, covering two or three ice ages and the warming between them, carbon dioxide has never been as high in the atmosphere as now. Following the end of the Wisconsin Glaciation, the temperature warmed for several thousand years, then began to slowly cool. The cooling was interrupted by the Medieval Warm Period, which allowed the settlement by the Norse of Iceland and Greenland. Then abruptly, in the 14th century, the climate dipped into the famous “Little Ice Age,” which lasted until the middle of the 19th century. Those Currier and Ives prints which show hardy New Englanders driving oxen-pulled sledges or horse-drawn sleighs through a world of deep snow and endless cold are depicting the last of the Little Ice Age. Global warming deniers like to point to the Little Ice Age as demonstrating that climate has natural variations unconnected with human activity. Not so fast. As reported in last November’s Harper’s magazine, a Virginia scientist named William Ruddiman has developed an alternative hypothesis. He noticed that the beginning of the Little Ice Age coincided with the world-wide pandemic of the Black Death, the bubonic plague that killed somewhere between a quarter and a half of the populations of Europe and Asia. Suddenly, many fewer people were burning fuel and farming. Cultivated land grew up in forest. As shown in the ice core records, carbon dioxide dropped a small but significant amount. As the population began to recover, CO2 slowly increased, only to drop again in the early 16th century at the time the Spanish were beginning to explore the New World and the diseases they introduced killed millions of its inhabitants, who had been burning the forests and burning off the prairies. The climate cooled again and didn’t reach its previous warmth until the late 19th century when the Industrial Revolution was up and rolling. Carbon dioxide and other greenhouse gas levels (and temperatures) have been increasing ever since, pausing a bit between the early 1940s and the late 1970s and then accelerating ever faster. We have no evidence they were ever higher. Recorded temperatures have been going up in parallel. Though our written weather records don’t go back past 1880, it is clear that the 10 years between 2000 and 2009 have been the warmest decade since then. 2005 was the warmest year ever. 2009 is tied for second. What? It wasn’t at all warm here; winter was cold and summer was cool. Yes, but parts of the world were cooking: Australia, some of Africa, Arctic North America, many other places. Wisconsin’s weather was cooler, but the overall Earth had heated up. Heat and drought or floods and snow are changing people’s lives over much of the globe. Glaciers are melting on every landmass that has them. What else would you need to see?
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